Rhythmic, intermittent propagation of a fluid through a BLOOD VESSEL or piping system, in contrast to constant, smooth propagation, which produces laminar flow.
A value equal to the total volume flow divided by the cross-sectional area of the vascular bed.
Theoretical representations that simulate the behavior or activity of the cardiovascular system, processes, or phenomena; includes the use of mathematical equations, computers and other electronic equipment.
Methods of preparing tissue specimens for visualization using an electron microscope, usually a scanning electron microscope. The methods involve the creation of exact copies of the specimens by making a mold or cast (i.e., replica) of the specimen.
The flow of BLOOD through or around an organ or region of the body.
The study of the deformation and flow of matter, usually liquids or fluids, and of the plastic flow of solids. The concept covers consistency, dilatancy, liquefaction, resistance to flow, shearing, thixotrophy, and VISCOSITY.
The deformation and flow behavior of BLOOD and its elements i.e., PLASMA; ERYTHROCYTES; WHITE BLOOD CELLS; and BLOOD PLATELETS.
A purely physical condition which exists within any material because of strain or deformation by external forces or by non-uniform thermal expansion; expressed quantitatively in units of force per unit area.
Three-dimensional representation to show anatomic structures. Models may be used in place of intact animals or organisms for teaching, practice, and study.
The internal resistance of a material to moving some parts of it parallel to a fixed plane, in contrast to stretching (TENSILE STRENGTH) or compression (COMPRESSIVE STRENGTH). Ionic crystals are brittle because, when subjected to shear, ions of the same charge are brought next to each other, which causes repulsion.
Unique slender cells with multiple processes extending along the capillary vessel axis and encircling the vascular wall, also called mural cells. Pericytes are imbedded in the BASEMENT MEMBRANE shared with the ENDOTHELIAL CELLS of the vessel. Pericytes are important in maintaining vessel integrity, angiogenesis, and vascular remodeling.
Methods of creating machines and devices.
Ultrasonography applying the Doppler effect, with the superposition of flow information as colors on a gray scale in a real-time image. This type of ultrasonography is well-suited to identifying the location of high-velocity flow (such as in a stenosis) or of mapping the extent of flow in a certain region.
Technique using an instrument system for making, processing, and displaying one or more measurements on individual cells obtained from a cell suspension. Cells are usually stained with one or more fluorescent dyes specific to cell components of interest, e.g., DNA, and fluorescence of each cell is measured as it rapidly transverses the excitation beam (laser or mercury arc lamp). Fluorescence provides a quantitative measure of various biochemical and biophysical properties of the cell, as well as a basis for cell sorting. Other measurable optical parameters include light absorption and light scattering, the latter being applicable to the measurement of cell size, shape, density, granularity, and stain uptake.
The vessels carrying blood away from the capillary beds.
Devices or objects in various imaging techniques used to visualize or enhance visualization by simulating conditions encountered in the procedure. Phantoms are used very often in procedures employing or measuring x-irradiation or radioactive material to evaluate performance. Phantoms often have properties similar to human tissue. Water demonstrates absorbing properties similar to normal tissue, hence water-filled phantoms are used to map radiation levels. Phantoms are used also as teaching aids to simulate real conditions with x-ray or ultrasonic machines. (From Iturralde, Dictionary and Handbook of Nuclear Medicine and Clinical Imaging, 1990)
Small pumps, often implantable, designed for temporarily assisting the heart, usually the LEFT VENTRICLE, to pump blood. They consist of a pumping chamber and a power source, which may be partially or totally external to the body and activated by electromagnetic motors.
The circulation of the BLOOD through the LUNGS.
Echocardiography applying the Doppler effect, with the superposition of flow information as colors on a gray scale in a real-time image.
The circulation of blood through the CORONARY VESSELS of the HEART.
PRESSURE of the BLOOD on the ARTERIES and other BLOOD VESSELS.
The movement and the forces involved in the movement of the blood through the CARDIOVASCULAR SYSTEM.
A type of stress exerted uniformly in all directions. Its measure is the force exerted per unit area. (McGraw-Hill Dictionary of Scientific and Technical Terms, 6th ed)
Device constructed of either synthetic or biological material that is used for the repair of injured or diseased blood vessels.
Any of the tubular vessels conveying the blood (arteries, arterioles, capillaries, venules, and veins).
The main artery of the thigh, a continuation of the external iliac artery.
Either of the two principal arteries on both sides of the neck that supply blood to the head and neck; each divides into two branches, the internal carotid artery and the external carotid artery.
A device that substitutes for a heart valve. It may be composed of biological material (BIOPROSTHESIS) and/or synthetic material.
Treatment process involving the injection of fluid into an organ or tissue.
Abnormal outpouching in the wall of intracranial blood vessels. Most common are the saccular (berry) aneurysms located at branch points in CIRCLE OF WILLIS at the base of the brain. Vessel rupture results in SUBARACHNOID HEMORRHAGE or INTRACRANIAL HEMORRHAGES. Giant aneurysms (>2.5 cm in diameter) may compress adjacent structures, including the OCULOMOTOR NERVE. (From Adams et al., Principles of Neurology, 6th ed, p841)
The vessels carrying blood away from the heart.
The testing of materials and devices, especially those used for PROSTHESES AND IMPLANTS; SUTURES; TISSUE ADHESIVES; etc., for hardness, strength, durability, safety, efficacy, and biocompatibility.
Single pavement layer of cells which line the luminal surface of the entire vascular system and regulate the transport of macromolecules and blood components.
Computer-based representation of physical systems and phenomena such as chemical processes.
The plan and delineation of prostheses in general or a specific prosthesis.
A CALCIUM-dependent, constitutively-expressed form of nitric oxide synthase found primarily in ENDOTHELIAL CELLS.
Elements of limited time intervals, contributing to particular results or situations.
The veins and arteries of the HEART.
The main trunk of the systemic arteries.
The properties, processes, and behavior of biological systems under the action of mechanical forces.
The statistical reproducibility of measurements (often in a clinical context), including the testing of instrumentation or techniques to obtain reproducible results. The concept includes reproducibility of physiological measurements, which may be used to develop rules to assess probability or prognosis, or response to a stimulus; reproducibility of occurrence of a condition; and reproducibility of experimental results.
Any of various animals that constitute the family Suidae and comprise stout-bodied, short-legged omnivorous mammals with thick skin, usually covered with coarse bristles, a rather long mobile snout, and small tail. Included are the genera Babyrousa, Phacochoerus (wart hogs), and Sus, the latter containing the domestic pig (see SUS SCROFA).
The domestic dog, Canis familiaris, comprising about 400 breeds, of the carnivore family CANIDAE. They are worldwide in distribution and live in association with people. (Walker's Mammals of the World, 5th ed, p1065)
The change in gene frequency in a population due to migration of gametes or individuals (ANIMAL MIGRATION) across population barriers. In contrast, in GENETIC DRIFT the cause of gene frequency changes are not a result of population or gamete movement.
Theoretical representations that simulate the behavior or activity of biological processes or diseases. For disease models in living animals, DISEASE MODELS, ANIMAL is available. Biological models include the use of mathematical equations, computers, and other electronic equipment.
Domesticated bovine animals of the genus Bos, usually kept on a farm or ranch and used for the production of meat or dairy products or for heavy labor.
Cells propagated in vitro in special media conducive to their growth. Cultured cells are used to study developmental, morphologic, metabolic, physiologic, and genetic processes, among others.

Pulsatile shear stress leads to DNA fragmentation in human SH-SY5Y neuroblastoma cell line. (1/1458)

1. Using an in vitro model of shear stress-induced cell injury we demonstrate that application of shear to differentiated human SH-SY5Y cells leads to cell death characterized by DNA fragmentation. Controlled shear stress was applied to cells via a modified cone and plate viscometer. 2. We show that pulsatile shear stress leads to DNA fragmentation, as determined via flow cytometry of fluorescein-12-dUTP nick-end labelled cells, in 45 +/- 4 % of cells. No lactate dehydrogenase (LDH) release was observed immediately after injury; however, 24 h after injury significant LDH release was observed. 3. Nitric oxide production by cells subjected to pulsatile shear increased two- to threefold over that in unsheared control cells. 4. Inhibition of protein synthesis, nitric oxide production, Ca2+ entry into cells, and pertussis toxin-sensitive G protein activation attenuated the shear stress-induced cell injury. 5. Our results show for the first time that application of pulsatile shear stress to a neuron-like cell in vitro leads to nitric oxide-dependent cell death.  (+info)

Independent prognostic information provided by sphygmomanometrically determined pulse pressure and mean arterial pressure in patients with left ventricular dysfunction. (2/1458)

OBJECTIVES: The purpose of this study was to evaluate the relationship of baseline pulse pressure and mean arterial pressure to mortality in patients with left ventricular dysfunction. BACKGROUND: Increased conduit vessel stiffness increases pulse pressure and pulsatile load, potentially contributing to adverse outcomes in patients with left ventricular dysfunction. METHODS: Pulse and mean arterial pressure were analyzed for their effect on mortality, adjusting for other modifiers of risk, using Cox proportional hazards regression analysis of data collected from 6,781 patients randomized into the Studies of Left Ventricular Dysfunction trials. RESULTS: Pulse and mean arterial pressure were related positively to each other, age, ejection fraction and prevalence of diabetes and hypertension and inversely to prior myocardial infarction and beta-adrenergic blocking agent use. Higher pulse pressure was associated with increased prevalence of female gender, greater calcium channel blocking agent, digoxin and diuretic use, lower heart rate and a higher rate of reported smoking history. Higher mean arterial pressure was associated with higher heart rate, lower calcium channel blocker and digoxin use and lower New York Heart Association functional class. Over a 61-month follow-up 1,582 deaths (1,397 cardiovascular) occurred. In a multivariate analysis adjusting for the above covariates and treatment assignment, higher pulse pressure remained an independent predictor of total and cardiovascular mortality (total mortality relative risk, 1.05 per 10 mm Hg increment; 95% confidence interval, 1.01 to 1.10; p = 0.02). Mean arterial pressure was inversely related to total and cardiovascular mortality (total mortality relative risk, 0.89; 95% confidence interval, 0.85 to 0.94; p <0.0001). CONCLUSIONS: One noninvasive blood pressure measurement provides two independent prognostic factors for survival. Increased conduit vessel stiffness, as assessed by pulse pressure, may contribute to increased mortality in patients with left ventricular dysfunction, independent of mean arterial pressure.  (+info)

In vitro and in vivo comparison of three MR measurement methods for calculating vascular shear stress in the internal carotid artery. (3/1458)

BACKGROUND AND PURPOSE: Vascular abnormalities, such as atherosclerosis and the growth and rupture of cerebral aneurysms, result from a derangement in tissue metabolism and injury that are, in part, regulated by hemodynamic stress. The purpose of this study was to establish the feasibility and accuracy of determining wall shear rate in the internal carotid artery from phase-contrast MR data. METHODS: Three algorithms were used to generate shear rate estimates from both ungated and cardiac-gated 2D phase-contrast data. These algorithms were linear extrapolation (LE), linear estimation with correction for wall position (LE*), and quadratic extrapolation (QE). In vitro experiments were conducted by using a phantom under conditions of both nonpulsatile and pulsatile flow. The findings from five healthy volunteers were also studied. MR imaging-derived shear rates were compared with values calculated by solving the fluid flow equations. RESULTS: Findings of in vitro constant-flow experiments indicated that at one or two excitations, QE has the advantage of good accuracy and low variance. Results of in vitro pulsatile flow experiments showed that neither LE* nor QE differed significantly from the predicted value of wall shear stress, despite errors of 17% and 22%, respectively. In vivo data showed that QE did not differ significantly from the predicted value, whereas LE and LE* did. The percentages of errors for QE, LE, and LE* in vivo measurements were 98.5%, 28.5%, and 36.1%, respectively. The average residual of QE was low because the residuals were both above and below baseline whereas, on average, LE* tended to be a more biased overestimator of the shear rate in volunteers. The average and peak wall shear force in five volunteers was approximately 8.10 dyne/cm2 and 13.2 dyne/cm2, respectively. CONCLUSION: Our findings show that LE consistently underestimates the shear rate. Although LE* and QE may be used to estimate shear rate, errors of up to 36% should be expected because of variance above and below the true value for individual measurements.  (+info)

The pattern of changes in ovarian stromal and uterine artery blood flow velocities during in vitro fertilization treatment and its relationship with outcome of the cycle. (4/1458)

OBJECTIVES: To assess the effect of short-term (2-3 weeks) pituitary suppression and controlled ovarian stimulation on ovarian and uterine artery Doppler measurements during the in vitro fertilization (IVF) treatment cycle and to compare the pattern of these changes between conception and non-conception cycles as well as between patients with normal and those with polycystic ovaries. DESIGN: Prospective observational study of women undergoing IVF treatment. SUBJECTS: Women using the long-treatment buserelin protocol who did not have uterine fibroids, ovarian cysts or endometrioma. METHODS: Serial transvaginal color and pulsed Doppler measurements of ovarian stromal and uterine artery blood flow velocity were carried out in the early follicular phase of the menstrual cycle, on the day of pituitary suppression and on the day of administration of human chorionic gonadotropin (hCG). The main outcome measures were the ovarian stromal and uterine artery blood flow peak systolic velocity (PSV) and pulsatility index (PI). RESULTS: A total of 105 patients were recruited but six patients were excluded from the analysis because they had only one stage of the measurements performed. There was a significant decline in mean ovarian stromal artery PSV after 2-3 weeks of gonadotropin releasing hormone (GnRH) agonist therapy but no effect on ovarian stromal artery PI. The mean uterine artery PSV or PI did not change significantly after 2-3 weeks of GnRH agonist therapy. There was a significantly higher mean ovarian stromal artery PSV in conception cycles compared to non-conception cycles in the early follicular phase and on the day of pituitary suppression, but not on the day of hCG administration. There were no differences between conception and non-conception cycles in the mean uterine artery PSV or PI. Women with polycystic ovaries had a higher mean ovarian artery PSV on all the three occasions of measurement. CONCLUSION: These data suggest that assessment of ovarian blood flow before commencement of gonadotropin stimulation may play a role in assessing cycles likely to result in pregnancy.  (+info)

Characteristics of blood flow in intrauterine growth-restricted fetuses with hypercoiled cord. (5/1458)

OBJECTIVE: To clarify the characteristics of fetoplacental blood flow of growth-restricted fetuses with hypercoiled umbilical cord. SUBJECTS: Eight growth-restricted fetuses with hypercoiled cord. METHODS: Flow velocity waveforms of the umbilical cord artery and vein, fetal abdominal aorta and fetal inferior vena cava were analyzed. RESULTS: The resistance index in the umbilical artery in the hypercoiled cases was lower than that in normal fetuses. Early-diastolic reversed flow was observed in the abdominal aorta in some cases. In all cases, umbilical venous pulsation was observed in the entire cord until delivery. In one case, fetal heart failure occurred, resulting in pre-mature delivery. An atrophic type of single umbilical artery was observed in four cases. CONCLUSION: Fetal blood flow disturbance caused by a hypercoiled umbilical cord may be a cause of growth restriction.  (+info)

Pulmonary and caval flow dynamics after total cavopulmonary connection. (6/1458)

OBJECTIVE: To assess flow dynamics after total cavopulmonary connection (TCPC). DESIGN: Cross-sectional study. SETTING: Aarhus University Hospital. PATIENTS: Seven patients (mean age 9 (4-18) years) who had previously undergone a lateral tunnel TCPC mean 2 (0. 3-5) years earlier. INTERVENTIONS: Pressure recordings (cardiac catheterisation), flow volume, and temporal changes of flow in the lateral tunnel, superior vena cava, and right and left pulmonary arteries (magnetic resonance velocity mapping). RESULTS: Superior vena cava flow was similar to lateral tunnel flow (1.7 (0.6-1.9) v 1. 3 (0.9-2.4) l/min*m2) (NS), and right pulmonary artery flow was higher than left pulmonary artery flow (1.7 (0.6-4.3) v 1.1 (0.8-2. 5) l/min*m2, p < 0.05). The flow pulsatility index was highest in the lateral tunnel (2.0 (1.1-8.5)), lowest in the superior vena cava (0.8 (0.5-2.4)), and intermediate in the left and right pulmonary arteries (1.6 (0.9-2.0) and 1.2 (0.4-1.9), respectively). Flow and pressure waveforms were biphasic with maxima in atrial systole and late ventricular systole. CONCLUSIONS: Following a standard lateral tunnel TCPC, flow returning via the superior vena cava is not lower than flow returning via the inferior vena cava as otherwise seen in healthy subjects; flow distribution to the pulmonary arteries is optimal; and some pulsatility is preserved primarily in the lateral tunnel and the corresponding pulmonary artery. This study provides in vivo data for future in vitro and computer model studies.  (+info)

The effect of cold stress on uterine artery blood flow velocity waveforms in late pregnant women with and without preeclampsia. (7/1458)

Cold stimulus, immersing the hand into ice water, was given to pregnant women with and without preeclampsia. The uterine artery blood flow was observed before, during and after the stimulus by Doppler ultrasound. The pulsatility index in the uterine artery blood flow was significantly increased by the cold exposure in preeclampsia from 1.14 to 1.52, whereas it increased in normal control from 0.95 to 1.25. In two of 11 cases of preeclampsia with fetal growth restriction, cold stimulus to the mother elicited a decrease of variability on fetal heart rate monitoring. Cold stimulus induces the constriction of the uterine artery, leading to a decrease of placental blood flow.  (+info)

Transcranial color-coded duplex sonography of intracranial veins and sinuses in adults. Reference data from 130 volunteers. (8/1458)

BACKGROUND AND PURPOSE: Transcranial color-coded duplex sonography (TCCS) of intracranial veins and sinuses in adults is a new, emerging application of ultrasonographic imaging. This study reports a standardized examination protocol for venous TCCS and provides reference data for clinical application. METHODS: In 130 healthy volunteers (mean age, 45.9+/-16.9 years; range, 14 to 77 years) the intracranial venous system was examined using frequency-based transtemporal TCCS. Identification rate, blood flow velocity, resistance index, and systolic/diastolic ratio were recorded for each examined venous vessel. RESULTS: Intracranial veins and sinuses show a low pulsatile forward flow with maximal systolic blood flow velocity up to 20 cm/s. Significant side differences of blood flow velocity in the paired venous structures could not be detected. Venous flow velocities decreased with age, whereas resistance indices and systolic/diastolic ratios increased. Women showed higher flow velocities than men. Mean identification rates for all age groups ranged from 70% to 90% for the deep middle cerebral vein, the basal cerebral vein, and the great cerebral vein of Galen. The straight sinus, the transverse sinus, and the rostral part of the superior sagittal sinus could be detected in 55% to 70% of cases. Detection rates were dependent on age and decreased as age increased. CONCLUSIONS: Venous TCCS can reliably image a significant part of the cerebral venous system. This method can provide information on venous hemodynamics in normal subjects and pathological cases.  (+info)

Pulsatile flow is a type of fluid flow that occurs in a rhythmic, wave-like pattern, typically seen in the cardiovascular system. It refers to the periodic variation in the volume or velocity of a fluid (such as blood) that is caused by the regular beating of the heart. In pulsatile flow, there are periods of high flow followed by periods of low or no flow, which creates a distinct pattern on a graph or tracing. This type of flow is important for maintaining proper function and health in organs and tissues throughout the body.

Blood flow velocity is the speed at which blood travels through a specific part of the vascular system. It is typically measured in units of distance per time, such as centimeters per second (cm/s) or meters per second (m/s). Blood flow velocity can be affected by various factors, including cardiac output, vessel diameter, and viscosity of the blood. Measuring blood flow velocity is important in diagnosing and monitoring various medical conditions, such as heart disease, stroke, and peripheral vascular disease.

Cardiovascular models are simplified representations or simulations of the human cardiovascular system used in medical research, education, and training. These models can be physical, computational, or mathematical and are designed to replicate various aspects of the heart, blood vessels, and blood flow. They can help researchers study the structure and function of the cardiovascular system, test new treatments and interventions, and train healthcare professionals in diagnostic and therapeutic techniques.

Physical cardiovascular models may include artificial hearts, blood vessels, or circulation systems made from materials such as plastic, rubber, or silicone. These models can be used to study the mechanics of heart valves, the effects of different surgical procedures, or the impact of various medical devices on blood flow.

Computational and mathematical cardiovascular models use algorithms and equations to simulate the behavior of the cardiovascular system. These models may range from simple representations of a single heart chamber to complex simulations of the entire circulatory system. They can be used to study the electrical activity of the heart, the biomechanics of blood flow, or the distribution of drugs in the body.

Overall, cardiovascular models play an essential role in advancing our understanding of the human body and improving patient care.

I'm sorry for any confusion, but "replica techniques" is not a standard term in medical terminology. It may be used in various scientific or clinical contexts to refer to the creation of reproductions or replicas of biological samples, tissues, or organs, often for research, teaching, or therapeutic purposes. However, without more specific context, it's difficult to provide a precise medical definition.

In general, "replica" refers to a copy or reproduction of something, especially one that is very close in appearance or character to the original. In science and medicine, replicas may be used for various purposes such as:

* Creating backup copies of important research samples or data
* Developing teaching tools or educational materials
* Testing medical devices, drugs, or other treatments before they are used on humans
* Conducting experiments that would be difficult or unethical to perform on living organisms.

If you could provide more context or clarify what specific field of medicine or science you are interested in, I may be able to give a more accurate definition or explanation.

Regional blood flow (RBF) refers to the rate at which blood flows through a specific region or organ in the body, typically expressed in milliliters per minute per 100 grams of tissue (ml/min/100g). It is an essential physiological parameter that reflects the delivery of oxygen and nutrients to tissues while removing waste products. RBF can be affected by various factors such as metabolic demands, neural regulation, hormonal influences, and changes in blood pressure or vascular resistance. Measuring RBF is crucial for understanding organ function, diagnosing diseases, and evaluating the effectiveness of treatments.

Rheology is not a term that is specific to medicine, but rather it is a term used in the field of physics to describe the flow and deformation of matter. It specifically refers to the study of how materials flow or deform under various stresses or strains. This concept can be applied to various medical fields such as studying the flow properties of blood (hematology), understanding the movement of tissues and organs during surgical procedures, or analyzing the mechanical behavior of biological materials like bones and cartilages.

Hemorheology is the study of the flow properties of blood and its components, including red blood cells, white blood cells, platelets, and plasma. Specifically, it examines how these components interact with each other and with the walls of blood vessels to affect the flow characteristics of blood under different conditions. Hemorheological factors can influence blood viscosity, which is a major determinant of peripheral vascular resistance and cardiac workload. Abnormalities in hemorheology have been implicated in various diseases such as atherosclerosis, hypertension, diabetes, and sickle cell disease.

Mechanical stress, in the context of physiology and medicine, refers to any type of force that is applied to body tissues or organs, which can cause deformation or displacement of those structures. Mechanical stress can be either external, such as forces exerted on the body during physical activity or trauma, or internal, such as the pressure changes that occur within blood vessels or other hollow organs.

Mechanical stress can have a variety of effects on the body, depending on the type, duration, and magnitude of the force applied. For example, prolonged exposure to mechanical stress can lead to tissue damage, inflammation, and chronic pain. Additionally, abnormal or excessive mechanical stress can contribute to the development of various musculoskeletal disorders, such as tendinitis, osteoarthritis, and herniated discs.

In order to mitigate the negative effects of mechanical stress, the body has a number of adaptive responses that help to distribute forces more evenly across tissues and maintain structural integrity. These responses include changes in muscle tone, joint positioning, and connective tissue stiffness, as well as the remodeling of bone and other tissues over time. However, when these adaptive mechanisms are overwhelmed or impaired, mechanical stress can become a significant factor in the development of various pathological conditions.

Anatomic models are three-dimensional representations of body structures used for educational, training, or demonstration purposes. They can be made from various materials such as plastic, wax, or rubber and may depict the entire body or specific regions, organs, or systems. These models can be used to provide a visual aid for understanding anatomy, physiology, and pathology, and can be particularly useful in situations where actual human specimens are not available or practical to use. They may also be used for surgical planning and rehearsal, as well as in medical research and product development.

Shear strength is a property of a material that describes its ability to withstand forces that cause internal friction and sliding of one portion of the material relative to another. In the context of human tissues, shear strength is an important factor in understanding how tissues respond to various stresses and strains, such as those experienced during physical activities or injuries.

For example, in the case of bones, shear strength is a critical factor in determining their ability to resist fractures under different types of loading conditions. Similarly, in soft tissues like ligaments and tendons, shear strength plays a crucial role in maintaining the integrity of these structures during movement and preventing excessive deformation or injury.

It's worth noting that measuring the shear strength of human tissues can be challenging due to their complex structure and anisotropic properties. As such, researchers often use specialized techniques and equipment to quantify these properties under controlled conditions in the lab.

Pericytes are specialized cells that surround the endothelial cells which line the blood capillaries. They play an important role in the regulation of capillary diameter, blood flow, and the formation of new blood vessels (angiogenesis). Pericytes also contribute to the maintenance of the blood-brain barrier, immune surveillance, and the clearance of waste products from the brain. They are often referred to as "mural cells" or "rouleaux cells" and can be found in various tissues throughout the body.

Equipment design, in the medical context, refers to the process of creating and developing medical equipment and devices, such as surgical instruments, diagnostic machines, or assistive technologies. This process involves several stages, including:

1. Identifying user needs and requirements
2. Concept development and brainstorming
3. Prototyping and testing
4. Design for manufacturing and assembly
5. Safety and regulatory compliance
6. Verification and validation
7. Training and support

The goal of equipment design is to create safe, effective, and efficient medical devices that meet the needs of healthcare providers and patients while complying with relevant regulations and standards. The design process typically involves a multidisciplinary team of engineers, clinicians, designers, and researchers who work together to develop innovative solutions that improve patient care and outcomes.

Ultrasonography, Doppler, color is a type of diagnostic ultrasound technique that uses the Doppler effect to produce visual images of blood flow in vessels and the heart. The Doppler effect is the change in frequency or wavelength of a wave in relation to an observer who is moving relative to the source of the wave. In this context, it refers to the change in frequency of the ultrasound waves as they reflect off moving red blood cells.

In color Doppler ultrasonography, different colors are used to represent the direction and speed of blood flow. Red typically represents blood flowing toward the transducer (the device that sends and receives sound waves), while blue represents blood flowing away from the transducer. The intensity or brightness of the color is proportional to the velocity of blood flow.

Color Doppler ultrasonography is often used in conjunction with grayscale ultrasound imaging, which provides information about the structure and composition of tissues. Together, these techniques can help diagnose a wide range of conditions, including heart disease, blood clots, and abnormalities in blood flow.

Flow cytometry is a medical and research technique used to measure physical and chemical characteristics of cells or particles, one cell at a time, as they flow in a fluid stream through a beam of light. The properties measured include:

* Cell size (light scatter)
* Cell internal complexity (granularity, also light scatter)
* Presence or absence of specific proteins or other molecules on the cell surface or inside the cell (using fluorescent antibodies or other fluorescent probes)

The technique is widely used in cell counting, cell sorting, protein engineering, biomarker discovery and monitoring disease progression, particularly in hematology, immunology, and cancer research.

Veins are blood vessels that carry deoxygenated blood from the tissues back to the heart. They have a lower pressure than arteries and contain valves to prevent the backflow of blood. Veins have a thin, flexible wall with a larger lumen compared to arteries, allowing them to accommodate more blood volume. The color of veins is often blue or green due to the absorption characteristics of light and the reduced oxygen content in the blood they carry.

In the field of medical imaging, "phantoms" refer to physical objects that are specially designed and used for calibration, quality control, and evaluation of imaging systems. These phantoms contain materials with known properties, such as attenuation coefficients or spatial resolution, which allow for standardized measurement and comparison of imaging parameters across different machines and settings.

Imaging phantoms can take various forms depending on the modality of imaging. For example, in computed tomography (CT), a common type of phantom is the "water-equivalent phantom," which contains materials with similar X-ray attenuation properties as water. This allows for consistent measurement of CT dose and image quality. In magnetic resonance imaging (MRI), phantoms may contain materials with specific relaxation times or magnetic susceptibilities, enabling assessment of signal-to-noise ratio, spatial resolution, and other imaging parameters.

By using these standardized objects, healthcare professionals can ensure the accuracy, consistency, and reliability of medical images, ultimately contributing to improved patient care and safety.

Heart-assist devices, also known as mechanical circulatory support devices, are medical equipment designed to help the heart function more efficiently. These devices can be used in patients with advanced heart failure who are not responding to medication or other treatments. They work by taking over some or all of the heart's pumping functions, reducing the workload on the heart and improving blood flow to the rest of the body.

There are several types of heart-assist devices, including:

1. Intra-aortic balloon pumps (IABPs): These devices are inserted into the aorta, the large artery that carries blood from the heart to the rest of the body. The IABP inflates and deflates in time with the heartbeat, helping to improve blood flow to the coronary arteries and reduce the workload on the heart.
2. Ventricular assist devices (VADs): These devices are more invasive than IABPs and are used to support the function of one or both ventricles, the lower chambers of the heart. VADs can be used to support the heart temporarily while a patient recovers from surgery or heart failure, or they can be used as a long-term solution for patients who are not candidates for a heart transplant.
3. Total artificial hearts (TAHs): These devices replace both ventricles and all four valves of the heart. TAHs are used in patients who are not candidates for a heart transplant and have severe biventricular failure, meaning that both ventricles are no longer functioning properly.

Heart-assist devices can be life-saving for some patients with advanced heart failure, but they also carry risks, such as infection, bleeding, and device malfunction. As with any medical treatment, the benefits and risks of using a heart-assist device must be carefully weighed for each individual patient.

Pulmonary circulation refers to the process of blood flow through the lungs, where blood picks up oxygen and releases carbon dioxide. This is a vital part of the overall circulatory system, which delivers nutrients and oxygen to the body's cells while removing waste products like carbon dioxide.

In pulmonary circulation, deoxygenated blood from the systemic circulation returns to the right atrium of the heart via the superior and inferior vena cava. The blood then moves into the right ventricle through the tricuspid valve and gets pumped into the pulmonary artery when the right ventricle contracts.

The pulmonary artery divides into smaller vessels called arterioles, which further branch into a vast network of tiny capillaries in the lungs. Here, oxygen from the alveoli diffuses into the blood, binding to hemoglobin in red blood cells, while carbon dioxide leaves the blood and is exhaled through the nose or mouth.

The now oxygenated blood collects in venules, which merge to form pulmonary veins. These veins transport the oxygen-rich blood back to the left atrium of the heart, where it enters the systemic circulation once again. This continuous cycle enables the body's cells to receive the necessary oxygen and nutrients for proper functioning while disposing of waste products.

Echocardiography, Doppler, color is a type of ultrasound test that uses sound waves to create detailed moving images of the heart and its blood vessels. In this technique, color Doppler is used to visualize the direction and speed of blood flow through the heart and great vessels. The movement of the red blood cells causes a change in frequency of the reflected sound waves (Doppler shift), which can be used to calculate the velocity and direction of the blood flow. By adding color to the Doppler image, it becomes easier for the interpreting physician to understand the complex three-dimensional motion of blood through the heart. This test is often used to diagnose and monitor various heart conditions, including valve disorders, congenital heart defects, and cardiac muscle diseases.

Coronary circulation refers to the circulation of blood in the coronary vessels, which supply oxygenated blood to the heart muscle (myocardium) and drain deoxygenated blood from it. The coronary circulation system includes two main coronary arteries - the left main coronary artery and the right coronary artery - that branch off from the aorta just above the aortic valve. These arteries further divide into smaller branches, which supply blood to different regions of the heart muscle.

The left main coronary artery divides into two branches: the left anterior descending (LAD) artery and the left circumflex (LCx) artery. The LAD supplies blood to the front and sides of the heart, while the LCx supplies blood to the back and sides of the heart. The right coronary artery supplies blood to the lower part of the heart, including the right ventricle and the bottom portion of the left ventricle.

The veins that drain the heart muscle include the great cardiac vein, the middle cardiac vein, and the small cardiac vein, which merge to form the coronary sinus. The coronary sinus empties into the right atrium, allowing deoxygenated blood to enter the right side of the heart and be pumped to the lungs for oxygenation.

Coronary circulation is essential for maintaining the health and function of the heart muscle, as it provides the necessary oxygen and nutrients required for proper contraction and relaxation of the myocardium. Any disruption or blockage in the coronary circulation system can lead to serious consequences, such as angina, heart attack, or even death.

Blood pressure is the force exerted by circulating blood on the walls of the blood vessels. It is measured in millimeters of mercury (mmHg) and is given as two figures:

1. Systolic pressure: This is the pressure when the heart pushes blood out into the arteries.
2. Diastolic pressure: This is the pressure when the heart rests between beats, allowing it to fill with blood.

Normal blood pressure for adults is typically around 120/80 mmHg, although this can vary slightly depending on age, sex, and other factors. High blood pressure (hypertension) is generally considered to be a reading of 130/80 mmHg or higher, while low blood pressure (hypotension) is usually defined as a reading below 90/60 mmHg. It's important to note that blood pressure can fluctuate throughout the day and may be affected by factors such as stress, physical activity, and medication use.

Hemodynamics is the study of how blood flows through the cardiovascular system, including the heart and the vascular network. It examines various factors that affect blood flow, such as blood volume, viscosity, vessel length and diameter, and pressure differences between different parts of the circulatory system. Hemodynamics also considers the impact of various physiological and pathological conditions on these variables, and how they in turn influence the function of vital organs and systems in the body. It is a critical area of study in fields such as cardiology, anesthesiology, and critical care medicine.

In medical terms, pressure is defined as the force applied per unit area on an object or body surface. It is often measured in millimeters of mercury (mmHg) in clinical settings. For example, blood pressure is the force exerted by circulating blood on the walls of the arteries and is recorded as two numbers: systolic pressure (when the heart beats and pushes blood out) and diastolic pressure (when the heart rests between beats).

Pressure can also refer to the pressure exerted on a wound or incision to help control bleeding, or the pressure inside the skull or spinal canal. High or low pressure in different body systems can indicate various medical conditions and require appropriate treatment.

A blood vessel prosthesis is a medical device that is used as a substitute for a damaged or diseased natural blood vessel. It is typically made of synthetic materials such as polyester, Dacron, or ePTFE (expanded polytetrafluoroethylene) and is designed to mimic the function of a native blood vessel by allowing the flow of blood through it.

Blood vessel prostheses are used in various surgical procedures, including coronary artery bypass grafting, peripheral arterial reconstruction, and the creation of arteriovenous fistulas for dialysis access. The choice of material and size of the prosthesis depends on several factors, such as the location and diameter of the vessel being replaced, the patient's age and overall health status, and the surgeon's preference.

It is important to note that while blood vessel prostheses can be effective in restoring blood flow, they may also carry risks such as infection, thrombosis (blood clot formation), and graft failure over time. Therefore, careful patient selection, surgical technique, and postoperative management are crucial for the success of these procedures.

Blood vessels are the part of the circulatory system that transport blood throughout the body. They form a network of tubes that carry blood to and from the heart, lungs, and other organs. The main types of blood vessels are arteries, veins, and capillaries. Arteries carry oxygenated blood away from the heart to the rest of the body, while veins return deoxygenated blood back to the heart. Capillaries connect arteries and veins and facilitate the exchange of oxygen, nutrients, and waste materials between the blood and the body's tissues.

The femoral artery is the major blood vessel that supplies oxygenated blood to the lower extremity of the human body. It is a continuation of the external iliac artery and becomes the popliteal artery as it passes through the adductor hiatus in the adductor magnus muscle of the thigh.

The femoral artery is located in the femoral triangle, which is bound by the sartorius muscle anteriorly, the adductor longus muscle medially, and the biceps femoris muscle posteriorly. It can be easily palpated in the groin region, making it a common site for taking blood samples, measuring blood pressure, and performing surgical procedures such as femoral artery catheterization and bypass grafting.

The femoral artery gives off several branches that supply blood to the lower limb, including the deep femoral artery, the superficial femoral artery, and the profunda femoris artery. These branches provide blood to the muscles, bones, skin, and other tissues of the leg, ankle, and foot.

The carotid arteries are a pair of vital blood vessels in the human body that supply oxygenated blood to the head and neck. Each person has two common carotid arteries, one on each side of the neck, which branch off from the aorta, the largest artery in the body.

The right common carotid artery originates from the brachiocephalic trunk, while the left common carotid artery arises directly from the aortic arch. As they ascend through the neck, they split into two main branches: the internal and external carotid arteries.

The internal carotid artery supplies oxygenated blood to the brain, eyes, and other structures within the skull, while the external carotid artery provides blood to the face, scalp, and various regions of the neck.

Maintaining healthy carotid arteries is crucial for overall cardiovascular health and preventing serious conditions like stroke, which can occur when the arteries become narrowed or blocked due to the buildup of plaque or fatty deposits (atherosclerosis). Regular check-ups with healthcare professionals may include monitoring carotid artery health through ultrasound or other imaging techniques.

A heart valve prosthesis is a medical device that is implanted in the heart to replace a damaged or malfunctioning heart valve. The prosthetic valve can be made of biological tissue (such as from a pig or cow) or artificial materials (such as carbon or polyester). Its function is to allow for the proper directional flow of blood through the heart, opening and closing with each heartbeat to prevent backflow of blood.

There are several types of heart valve prostheses, including:

1. Mechanical valves: These are made entirely of artificial materials and have a longer lifespan than biological valves. However, they require the patient to take blood-thinning medication for the rest of their life to prevent blood clots from forming on the valve.
2. Bioprosthetic valves: These are made of biological tissue and typically last 10-15 years before needing replacement. They do not require the patient to take blood-thinning medication, but there is a higher risk of reoperation due to degeneration of the tissue over time.
3. Homografts or allografts: These are human heart valves that have been donated and preserved for transplantation. They have similar longevity to bioprosthetic valves and do not require blood-thinning medication.
4. Autografts: In this case, the patient's own pulmonary valve is removed and used to replace the damaged aortic valve. This procedure is called the Ross procedure and has excellent long-term results, but it requires advanced surgical skills and is not widely available.

The choice of heart valve prosthesis depends on various factors, including the patient's age, overall health, lifestyle, and personal preferences.

Perfusion, in medical terms, refers to the process of circulating blood through the body's organs and tissues to deliver oxygen and nutrients and remove waste products. It is a measure of the delivery of adequate blood flow to specific areas or tissues in the body. Perfusion can be assessed using various methods, including imaging techniques like computed tomography (CT) scans, magnetic resonance imaging (MRI), and perfusion scintigraphy.

Perfusion is critical for maintaining proper organ function and overall health. When perfusion is impaired or inadequate, it can lead to tissue hypoxia, acidosis, and cell death, which can result in organ dysfunction or failure. Conditions that can affect perfusion include cardiovascular disease, shock, trauma, and certain surgical procedures.

An intracranial aneurysm is a localized, blood-filled dilation or bulging in the wall of a cerebral artery within the skull (intracranial). These aneurysms typically occur at weak points in the arterial walls, often at branching points where the vessel divides into smaller branches. Over time, the repeated pressure from blood flow can cause the vessel wall to weaken and balloon out, forming a sac-like structure. Intracranial aneurysms can vary in size, ranging from a few millimeters to several centimeters in diameter.

There are three main types of intracranial aneurysms:

1. Saccular (berry) aneurysm: This is the most common type, characterized by a round or oval shape with a narrow neck and a bulging sac. They usually develop at branching points in the arteries due to congenital weaknesses in the vessel wall.
2. Fusiform aneurysm: These aneurysms have a dilated segment along the length of the artery, forming a cigar-shaped or spindle-like structure. They are often caused by atherosclerosis and can affect any part of the cerebral arteries.
3. Dissecting aneurysm: This type occurs when there is a tear in the inner lining (intima) of the artery, allowing blood to flow between the layers of the vessel wall. It can lead to narrowing or complete blockage of the affected artery and may cause subarachnoid hemorrhage if it ruptures.

Intracranial aneurysms can be asymptomatic and discovered incidentally during imaging studies for other conditions. However, when they grow larger or rupture, they can lead to severe complications such as subarachnoid hemorrhage, stroke, or even death. Treatment options include surgical clipping, endovascular coiling, or flow diversion techniques to prevent further growth and potential rupture of the aneurysm.

Arteries are blood vessels that carry oxygenated blood away from the heart to the rest of the body. They have thick, muscular walls that can withstand the high pressure of blood being pumped out of the heart. Arteries branch off into smaller vessels called arterioles, which further divide into a vast network of tiny capillaries where the exchange of oxygen, nutrients, and waste occurs between the blood and the body's cells. After passing through the capillary network, deoxygenated blood collects in venules, then merges into veins, which return the blood back to the heart.

I'm happy to help! However, I must clarify that "materials testing" is not a medical term per se. It is a term used in various fields, including engineering and materials science, to describe the process of subjecting materials to different tests to evaluate their properties and performance under various conditions.

In the context of medical devices or implants, materials testing may refer to the evaluation of the physical and mechanical properties of materials used in their construction. These tests can include assessments of strength, durability, biocompatibility, and other factors that are critical to ensuring the safety and efficacy of medical devices.

Medical device manufacturers must comply with regulatory standards for materials testing to ensure that their products meet specific requirements for performance, safety, and quality. These standards may vary depending on the type of device, its intended use, and the country or region in which it will be marketed and sold.

The endothelium is a thin layer of simple squamous epithelial cells that lines the interior surface of blood vessels, lymphatic vessels, and heart chambers. The vascular endothelium, specifically, refers to the endothelial cells that line the blood vessels. These cells play a crucial role in maintaining vascular homeostasis by regulating vasomotor tone, coagulation, platelet activation, inflammation, and permeability of the vessel wall. They also contribute to the growth and repair of the vascular system and are involved in various pathological processes such as atherosclerosis, hypertension, and diabetes.

A computer simulation is a process that involves creating a model of a real-world system or phenomenon on a computer and then using that model to run experiments and make predictions about how the system will behave under different conditions. In the medical field, computer simulations are used for a variety of purposes, including:

1. Training and education: Computer simulations can be used to create realistic virtual environments where medical students and professionals can practice their skills and learn new procedures without risk to actual patients. For example, surgeons may use simulation software to practice complex surgical techniques before performing them on real patients.
2. Research and development: Computer simulations can help medical researchers study the behavior of biological systems at a level of detail that would be difficult or impossible to achieve through experimental methods alone. By creating detailed models of cells, tissues, organs, or even entire organisms, researchers can use simulation software to explore how these systems function and how they respond to different stimuli.
3. Drug discovery and development: Computer simulations are an essential tool in modern drug discovery and development. By modeling the behavior of drugs at a molecular level, researchers can predict how they will interact with their targets in the body and identify potential side effects or toxicities. This information can help guide the design of new drugs and reduce the need for expensive and time-consuming clinical trials.
4. Personalized medicine: Computer simulations can be used to create personalized models of individual patients based on their unique genetic, physiological, and environmental characteristics. These models can then be used to predict how a patient will respond to different treatments and identify the most effective therapy for their specific condition.

Overall, computer simulations are a powerful tool in modern medicine, enabling researchers and clinicians to study complex systems and make predictions about how they will behave under a wide range of conditions. By providing insights into the behavior of biological systems at a level of detail that would be difficult or impossible to achieve through experimental methods alone, computer simulations are helping to advance our understanding of human health and disease.

Prosthesis design is a specialized field in medical device technology that involves creating and developing artificial substitutes to replace a missing body part, such as a limb, tooth, eye, or internal organ. The design process typically includes several stages: assessment of the patient's needs, selection of appropriate materials, creation of a prototype, testing and refinement, and final fabrication and fitting of the prosthesis.

The goal of prosthesis design is to create a device that functions as closely as possible to the natural body part it replaces, while also being comfortable, durable, and aesthetically pleasing for the patient. The design process may involve collaboration between medical professionals, engineers, and designers, and may take into account factors such as the patient's age, lifestyle, occupation, and overall health.

Prosthesis design can be highly complex, particularly for advanced devices such as robotic limbs or implantable organs. These devices often require sophisticated sensors, actuators, and control systems to mimic the natural functions of the body part they replace. As a result, prosthesis design is an active area of research and development in the medical field, with ongoing efforts to improve the functionality, comfort, and affordability of these devices for patients.

Nitric Oxide Synthase Type III (NOS-III), also known as endothelial Nitric Oxide Synthase (eNOS), is an enzyme responsible for the production of nitric oxide (NO) in the endothelium, the lining of blood vessels. This enzyme catalyzes the conversion of L-arginine to L-citrulline, producing NO as a byproduct. The release of NO from eNOS plays an important role in regulating vascular tone and homeostasis, including the relaxation of smooth muscle cells in the blood vessel walls, inhibition of platelet aggregation, and modulation of immune function. Mutations or dysfunction in NOS-III can contribute to various cardiovascular diseases such as hypertension, atherosclerosis, and erectile dysfunction.

In the field of medicine, "time factors" refer to the duration of symptoms or time elapsed since the onset of a medical condition, which can have significant implications for diagnosis and treatment. Understanding time factors is crucial in determining the progression of a disease, evaluating the effectiveness of treatments, and making critical decisions regarding patient care.

For example, in stroke management, "time is brain," meaning that rapid intervention within a specific time frame (usually within 4.5 hours) is essential to administering tissue plasminogen activator (tPA), a clot-busting drug that can minimize brain damage and improve patient outcomes. Similarly, in trauma care, the "golden hour" concept emphasizes the importance of providing definitive care within the first 60 minutes after injury to increase survival rates and reduce morbidity.

Time factors also play a role in monitoring the progression of chronic conditions like diabetes or heart disease, where regular follow-ups and assessments help determine appropriate treatment adjustments and prevent complications. In infectious diseases, time factors are crucial for initiating antibiotic therapy and identifying potential outbreaks to control their spread.

Overall, "time factors" encompass the significance of recognizing and acting promptly in various medical scenarios to optimize patient outcomes and provide effective care.

Coronary vessels refer to the network of blood vessels that supply oxygenated blood and nutrients to the heart muscle, also known as the myocardium. The two main coronary arteries are the left main coronary artery and the right coronary artery.

The left main coronary artery branches off into the left anterior descending artery (LAD) and the left circumflex artery (LCx). The LAD supplies blood to the front of the heart, while the LCx supplies blood to the side and back of the heart.

The right coronary artery supplies blood to the right lower part of the heart, including the right atrium and ventricle, as well as the back of the heart.

Coronary vessel disease (CVD) occurs when these vessels become narrowed or blocked due to the buildup of plaque, leading to reduced blood flow to the heart muscle. This can result in chest pain, shortness of breath, or a heart attack.

The aorta is the largest artery in the human body, which originates from the left ventricle of the heart and carries oxygenated blood to the rest of the body. It can be divided into several parts, including the ascending aorta, aortic arch, and descending aorta. The ascending aorta gives rise to the coronary arteries that supply blood to the heart muscle. The aortic arch gives rise to the brachiocephalic, left common carotid, and left subclavian arteries, which supply blood to the head, neck, and upper extremities. The descending aorta travels through the thorax and abdomen, giving rise to various intercostal, visceral, and renal arteries that supply blood to the chest wall, organs, and kidneys.

Biomechanics is the application of mechanical laws to living structures and systems, particularly in the field of medicine and healthcare. A biomechanical phenomenon refers to a observable event or occurrence that involves the interaction of biological tissues or systems with mechanical forces. These phenomena can be studied at various levels, from the molecular and cellular level to the tissue, organ, and whole-body level.

Examples of biomechanical phenomena include:

1. The way that bones and muscles work together to produce movement (known as joint kinematics).
2. The mechanical behavior of biological tissues such as bone, cartilage, tendons, and ligaments under various loads and stresses.
3. The response of cells and tissues to mechanical stimuli, such as the way that bone tissue adapts to changes in loading conditions (known as Wolff's law).
4. The biomechanics of injury and disease processes, such as the mechanisms of joint injury or the development of osteoarthritis.
5. The use of mechanical devices and interventions to treat medical conditions, such as orthopedic implants or assistive devices for mobility impairments.

Understanding biomechanical phenomena is essential for developing effective treatments and prevention strategies for a wide range of medical conditions, from musculoskeletal injuries to neurological disorders.

Reproducibility of results in a medical context refers to the ability to obtain consistent and comparable findings when a particular experiment or study is repeated, either by the same researcher or by different researchers, following the same experimental protocol. It is an essential principle in scientific research that helps to ensure the validity and reliability of research findings.

In medical research, reproducibility of results is crucial for establishing the effectiveness and safety of new treatments, interventions, or diagnostic tools. It involves conducting well-designed studies with adequate sample sizes, appropriate statistical analyses, and transparent reporting of methods and findings to allow other researchers to replicate the study and confirm or refute the results.

The lack of reproducibility in medical research has become a significant concern in recent years, as several high-profile studies have failed to produce consistent findings when replicated by other researchers. This has led to increased scrutiny of research practices and a call for greater transparency, rigor, and standardization in the conduct and reporting of medical research.

"Swine" is a common term used to refer to even-toed ungulates of the family Suidae, including domestic pigs and wild boars. However, in a medical context, "swine" often appears in the phrase "swine flu," which is a strain of influenza virus that typically infects pigs but can also cause illness in humans. The 2009 H1N1 pandemic was caused by a new strain of swine-origin influenza A virus, which was commonly referred to as "swine flu." It's important to note that this virus is not transmitted through eating cooked pork products; it spreads from person to person, mainly through respiratory droplets produced when an infected person coughs or sneezes.

I believe there might be a misunderstanding in your question. "Dogs" is not a medical term or condition. It is the common name for a domesticated carnivore of the family Canidae, specifically the genus Canis, which includes wolves, foxes, and other extant and extinct species of mammals. Dogs are often kept as pets and companions, and they have been bred in a wide variety of forms and sizes for different purposes, such as hunting, herding, guarding, assisting police and military forces, and providing companionship and emotional support.

If you meant to ask about a specific medical condition or term related to dogs, please provide more context so I can give you an accurate answer.

Gene flow, also known as genetic migration or gene admixture, refers to the transfer of genetic variation from one population to another. It occurs when individuals reproduce and exchange genes with members of other populations through processes such as migration and interbreeding. This can result in an alteration of the genetic composition of both populations, increasing genetic diversity and reducing the differences between them. Gene flow is an important mechanism in evolutionary biology and population genetics, contributing to the distribution and frequency of alleles (versions of a gene) within and across populations.

Biological models, also known as physiological models or organismal models, are simplified representations of biological systems, processes, or mechanisms that are used to understand and explain the underlying principles and relationships. These models can be theoretical (conceptual or mathematical) or physical (such as anatomical models, cell cultures, or animal models). They are widely used in biomedical research to study various phenomena, including disease pathophysiology, drug action, and therapeutic interventions.

Examples of biological models include:

1. Mathematical models: These use mathematical equations and formulas to describe complex biological systems or processes, such as population dynamics, metabolic pathways, or gene regulation networks. They can help predict the behavior of these systems under different conditions and test hypotheses about their underlying mechanisms.
2. Cell cultures: These are collections of cells grown in a controlled environment, typically in a laboratory dish or flask. They can be used to study cellular processes, such as signal transduction, gene expression, or metabolism, and to test the effects of drugs or other treatments on these processes.
3. Animal models: These are living organisms, usually vertebrates like mice, rats, or non-human primates, that are used to study various aspects of human biology and disease. They can provide valuable insights into the pathophysiology of diseases, the mechanisms of drug action, and the safety and efficacy of new therapies.
4. Anatomical models: These are physical representations of biological structures or systems, such as plastic models of organs or tissues, that can be used for educational purposes or to plan surgical procedures. They can also serve as a basis for developing more sophisticated models, such as computer simulations or 3D-printed replicas.

Overall, biological models play a crucial role in advancing our understanding of biology and medicine, helping to identify new targets for therapeutic intervention, develop novel drugs and treatments, and improve human health.

"Cattle" is a term used in the agricultural and veterinary fields to refer to domesticated animals of the genus *Bos*, primarily *Bos taurus* (European cattle) and *Bos indicus* (Zebu). These animals are often raised for meat, milk, leather, and labor. They are also known as bovines or cows (for females), bulls (intact males), and steers/bullocks (castrated males). However, in a strict medical definition, "cattle" does not apply to humans or other animals.

"Cells, cultured" is a medical term that refers to cells that have been removed from an organism and grown in controlled laboratory conditions outside of the body. This process is called cell culture and it allows scientists to study cells in a more controlled and accessible environment than they would have inside the body. Cultured cells can be derived from a variety of sources, including tissues, organs, or fluids from humans, animals, or cell lines that have been previously established in the laboratory.

Cell culture involves several steps, including isolation of the cells from the tissue, purification and characterization of the cells, and maintenance of the cells in appropriate growth conditions. The cells are typically grown in specialized media that contain nutrients, growth factors, and other components necessary for their survival and proliferation. Cultured cells can be used for a variety of purposes, including basic research, drug development and testing, and production of biological products such as vaccines and gene therapies.

It is important to note that cultured cells may behave differently than they do in the body, and results obtained from cell culture studies may not always translate directly to human physiology or disease. Therefore, it is essential to validate findings from cell culture experiments using additional models and ultimately in clinical trials involving human subjects.

In fluid dynamics, a flow with periodic variations is known as pulsatile flow, or as Womersley flow. The flow profiles was ... The cardiovascular system of chordate animals is a very good example where pulsatile flow is found, but pulsatile flow is also ... The pulsatile flow profile is given in a straight pipe by u ( r , t ) = R e { ∑ n = 0 N i P n ′ ρ n ω [ 1 − J 0 ( α n 1 / 2 i 3 ... The pressure gradient driving the pulsatile flow is decomposed in Fourier series, ∂ p ∂ x ( t ) = ∑ n = 0 N P n ′ e i n ω t ...
2007). "Comparisons of infection complications between continuous flow and pulsatile flow left ventricular assist devices". The ... and continuous-flow pumps. Pulsatile VADs use positive displacement pumps. In some pulsatile pumps (that use compressed air as ... less frequent adverse events and greater reliability with continuous flow LVADS compared to pulsatile flow devices. Of the 281 ... Continuous-flow VADs are smaller and have proven to be more durable than pulsatile VADs. They normally use either a centrifugal ...
EXCOR is a paracorporeal, pulsatile flow VAD. The device provides left ventricular, right ventricular or biventricular ... INCOR is an axial-flow pump for support of the left ventricle. In this system, the pump is implanted directly next to the heart ... The blood coming from the heart flows into the INCOR axial pump. The rotor in the pump has an active magnetic bearing while ... Like the heart, EXCOR blood pumps have valves which ensure that the blood only flows in one direction. The blood pumps are ...
In particular, wide-field imaging of pulsatile motion induced by blood flow can be measured on the thumb by digital holography ... Bencteux J, Pagnoux P, Kostas T, Bayat S, Atlan M (June 2015). "Holographic laser Doppler imaging of pulsatile blood flow". ... and achieve high temporal resolution and full-field imaging capability of pulsatile blood flow. Heart rate monitor Clitoral ... Because blood flow to the skin can be modulated by multiple other physiological systems, the PPG can also be used to monitor ...
It can be used for pulsatile blood flow imaging. Electronic speckle pattern interferometry Holography Interferometry Powell RL ... "Pulsatile microvascular blood flow imaging by short-time Fourier transform analysis of ultrafast laser holographic ... "Holographic laser Doppler imaging of pulsatile blood flow". Journal of Biomedical Optics. 20 (6): 066006. arXiv:1501.05776. ... It can also be used to detect optical path length variations in transparent media, which enables, for example, fluid flow to be ...
Recktenwald, Steffen M.; Wagner, Christian; John, Thomas (2021-06-29). "Optimizing pressure-driven pulsatile flows in ...
... and greater reliability with continuous-flow LVADs compared to pulsatile-flow devices. As of mid 2015, Thoratec has the only ... The material is currently[when?] used in the Thoratec PVAD pulsatile-flow biventricular device. By 2000, the Thoratec VAD ... In a two-year randomized controlled clinical trial published in 2009 comparing pulsatile and continuous-flow LVADs, survival ... The technology is for use in a minimally invasive, acute cardiac axial-flow pump that can be delivered percutaneously in a ...
Bookbinder; Engler; Hong; Miller (May 2001). "Comparison of Flow Measure Techniques during Continuous and Pulsatile Flow". 2001 ... Dimensionless numbers (or characteristic numbers) have an important role in analyzing the behavior of fluids and their flow as ... Petritsch, G.; Mewes, D. (1999). "Experimental investigations of the flow patterns in the hot leg of a pressurized water ... Science Applications International Corporation (2001). Performing Quality Flow Measurements at Mine Sites. Washington, DC: U.S ...
Painter, Page R; Edén, Patrik; Bengtsson, Hans-Uno (2006). "Pulsatile blood flow, shear force, energy dissipation and Murray's ... Since flow is leakless, the total flow rate into a junction must be the total flow rate out: ∑ in Q = ∑ out Q . {\displaystyle ... Although most derivations of Murray's law assume a steady state flow field, the same results apply for flow in tubes that have ... If network flow is smooth and leak-free, then systems that obey Murray's law minimize the resistance to flow through the ...
doi:10.1111/j.1365-2435.2006.01136.x. Painter PR, Edén P, Bengtsson HU (August 2006). "Pulsatile blood flow, shear force, ... Because fluid flow through a tubule is determined by the volume thereof, the total fluid flow is proportional to the total ... metabolism should scale proportionally to nutrient flow (or, equivalently, total fluid flow) in this circulatory system and (2 ... Thus, if B denotes the basal metabolic rate, Q the total fluid flow, and N the number of minimal tubules, B ∝ Q ∝ N . {\ ...
Pulsatile tinnitus is usually objective in nature, resulting from altered blood flow or increased blood turbulence near the ear ... Pulsatile tinnitus may also indicate vasculitis, or more specifically, giant cell arteritis. Pulsatile tinnitus may also ... but it can also arise as a subjective phenomenon from an increased awareness of blood flow in the ear. Rarely, pulsatile ... Pulsatile tinnitus can be a symptom of intracranial vascular abnormalities and should be evaluated for irregular noises of ...
Iberall, Arthur S.; Cardon, Samuel Z.; Young, Ed, On Pulsatile and Steady Arterial Flow - The GTS Contribution., Upper Darby, ... Effect of oxygen on cyclic red blood cell flow in unanesthetized mammalian striated muscle as determined by spectroscopy. ...
Nguyen, Quynh M.; Abouezzi, Joanna; Ristroph, Leif (17 May 2021). "Early turbulence and pulsatile flows enhance diodicity of ... the flow rate. The diodicity is then the ratio of the reversed flow resistance to the forward flow resistance: D i = R r R f {\ ... is the reverse flow pressure drop, and Δ p f {\displaystyle \Delta p_{\rm {f}}} the forward flow pressure drop for flow rate Q ... This difference in flow resistance causes a net directional flow rate in the forward direction in oscillating flows. The ...
Nguyen, Quynh M.; Abouezzi, Joanna; Ristroph, Leif (17 May 2021). "Early turbulence and pulsatile flows enhance diodicity of ... Flow through pipes can roughly be divided into two: Laminar flow - see Hagen-Poiseuille flow Turbulent flow - see Moody diagram ... Pipe flow does not have a free surface which is found in open-channel flow. Pipe flow, being confined within closed conduit, ... In fluid mechanics, pipe flow is a type of liquid flow within a closed conduit, such as a pipe or tube. The other type of flow ...
"Early turbulence and pulsatile flows enhance diodicity of Tesla's macrofluidic valve". Nature Communications. 12 (12): 2884. ... It's a leaky diode, i.e. the reverse flow is non-zero for any applied pressure difference. Tesla valve also has non-linear ... In thrust vectoring, in jet engine nozzles, swiveling parts are replaced by slots which inject fluid flows into jets. Such ... Scanned article available online from Google Books: Popular Science June 1967 Visualization of the flow field of a fluidic ...
Doppler examination shows anechoic cystic areas, with pulsatile flow in spectral analysis. Some chorioangiomas may be solid ... When chorioangiomas have deceased blood flow, fetal hemodynamics and clinical outcome are found to be improved. It is the most ... Large chorioangiomas with decreased echogenicity, decreased tumor volume and decreased blood flow in colour doppler images are ...
Rinderknecht, Derek Gresham (2008). "Development of a microimpedance pump for pulsatile flow transport : Part 1: Flow ... Tapping the end of a tube will cause flow of liquid inside the system. Very small versions of an impedance pump -- a micro ... Part 2: A systematic study of steady and pulsatile transport in microscale cavities.". Dissertation (Ph.D.), California ...
Pulsatile shear and Gja5 modulate arterial identity and remodeling events during flow-driven arteriogenesis. Buschmann I*, ... Resistance to blood flow in microvessels in vivo. Pries AR, Secomb TW, Gessner T, Sperandio MB, Gross JF, Gaehtgens P. Circ Res ... Blood flow in microvascular networks. Pries AR and Secomb TW. In: Handbook of Physiology: Microcirculation, edited by Tuma RF, ...
Before rupture, an AAA may present as a large, pulsatile mass above the umbilicus. A bruit may be heard from the turbulent flow ...
But without functioning atria, venous flow becomes pulsatile, and the overall circulation rate decreases significantly. Atria ... to be able to accept venous flow without interruption. By preventing the inertia of interrupted venous flow that would ... In an adult, an atrial septal defect results in the flow of blood in the reverse direction - from the left atrium to the right ... At birth, when the first breath is taken fetal blood flow is reversed to travel through the lungs. The foramen ovale is no ...
It is a dimensionless expression of the pulsatile flow frequency in relation to viscous effects. It is named after John R. ... In a flow distribution network that progresses from a large tube to many small tubes (e.g. a blood vessel network), the ... The Womersley number of human blood flow can be estimated as follows: α = L ( ω ρ μ ) 1 2 . {\displaystyle \alpha =L\left({\ ... In these regions the inertia force becomes less important and the flow is determined by the balance of viscous stresses and the ...
After his work on the G-Suit, Wood worked on techniques for measuring cardiac blood flow. He was granted a patent for the ear ... The water-filled, pulsatile pressure suits were developed to effect venous return. However, Wood and colleagues' detailed ... Grace, JB; Fox, IJ; Crowley, WP Jr; Wood, EH (November 1957). "Thoracic-aorta flow in man". J Appl Physiol. 11 (3): 405-418. ... Smith, HC; Sturm, RE; Wood, EH (August 1973). "Videodensitometric system for measurement of vessel blood flow, particularly in ...
Direct canalization to the right ventricle provides pulsatile blood flow compared to the Blalock-Taussig conduit. The Single ... In both cases a conduit is used to direct blood flow into the lungs, however anatomic anchoring varies. There are two different ... To accomplish this, blood flow to the lungs is disrupted, and therefore an alternative path must be created to provide blood ... Second step of the procedure establishes blood flow to the lungs. Variations to this step have been proposed over the years, ...
Cerebrospinal fluid (CSF) flow MRI is used to assess pulsatile CSF flow both qualitatively and quantitatively. Time-resolved 2D ... CSF Fluid Flow MRI detects back and forth flow of Cerebrospinal fluid that corresponds to vascular pulsations from mostly the ... However, overestimating the VENC value leads to a lower acquired flow signal and a lower SNR. Typical CSF flow is 5-8 cm/s; ... The study of CSF flow became one of Phase-contrast MRI's major applications. The key to Phase-contrast MRI (PC-MRI) is the use ...
Bernstein, Donald P (2010). "Impedance cardiography: Pulsatile blood flow and the biophysical and electrodynamic basis for the ... This flow data can be used in a flow-versus-time graph. The area under the flow-versus-time curve for one cardiac cycle is the ... Cardiac output is a global blood flow parameter of interest in hemodynamics, the study of the flow of blood. The factors ... which is then multiplied by the VTI of the Doppler flow profile across the aortic valve to determine the flow volume per beat ( ...
Endothelial cell specific nitric oxide synthase (EcNOS) is activated by the pulsatile flow of blood through vessels. Nitric ... Continuous diffusion of oxygen (CDO) - CDO delivers continuous oxygen to an occluded, moist wound site at much lower flow rates ... and arms due to distal nerve damage and low blood flow. Autonomic neuropathy causes Sudomotor dysfunction and dryness of the ... oxide produced by EcNOS, maintains the diameter of blood vessels and proper blood flow to tissues. In addition to this, nitric ...
Lim, W. L.; Chew, Y. T.; Chew, T. C.; Low, H. T. (2001-11-01). "Pulsatile flow studies of a porcine bioprosthetic aortic valve ... These models can combine the constant supersaturation principle together with pulsatile flow, which is characteristic of the ... This model does not provide the flow or the mechanical stimuli to the tissue. Both flow and mechanical stimuli affect the ... Dynamic models can vary in terms of the means of providing the flow in the system, as well as in terms of the dynamic ...
Skala has developed organ-on-a-chip devices to study pulsatile flow and how it impacts cardiovascular disease. She is ... Mohns, Mariel (2020-11-16). "Measuring blood flow with a beating "heart-on-a-chip"". Morgridge Institute for Research. ...
Agarwal, R. K.; Okpara, E (2010). "Numerical Study of Pulsatile Flow through Models of Vascular and Aortic Valve Stenoses and ... In practical terms, the flow from the left ventricular outflow tract (LVOT) is compared to the flow at the level of the aortic ... The continuity equation states that the flow in one area must equal the flow in a second area if there are no shunts between ... The flow through the LVOT, or LV stroke volume (in cm3), can be calculated by measuring the LVOT diameter (in cm), squaring ...
He discovered that venous blood flow is pulsatile which, prior to Rai's discovery, was described only as linear flow. He is ...
In fluid dynamics, a flow with periodic variations is known as pulsatile flow, or as Womersley flow. The flow profiles was ... The cardiovascular system of chordate animals is a very good example where pulsatile flow is found, but pulsatile flow is also ... The pulsatile flow profile is given in a straight pipe by u ( r , t ) = R e { ∑ n = 0 N i P n ′ ρ n ω [ 1 − J 0 ( α n 1 / 2 i 3 ... The pressure gradient driving the pulsatile flow is decomposed in Fourier series, ∂ p ∂ x ( t ) = ∑ n = 0 N P n ′ e i n ω t ...
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Conclusions Pulsatile shear stress induces ubiquitin-proteasome-mediated degradation of PDCD4 via a PI3K/Akt pathway in HUVECs ... Application of unidirectional pulsatile shear stress to human umbilical vein endothelial cells (HUVECs) decreased PDCD4 protein ... Immunoprecipitation revealed that pulsatile shear stress induced the coupling of ubiquitin with PDCD4 expression. The ... Low PDCD4 level is associated with reduced proliferation for maintenance of HUVEC homeostasis under pulsatile shear stress. ...
A quantitative, comparative study was made of sound produced in vitro by pulsatile flow in and around three designs of ... A Quantitative, Comparative Study of Sound Produced in vitro by Pulsatile Flow in and Around Prosthetic, Aortic Heart-Valves ... Suobank, David Walter (1983) A Quantitative, Comparative Study of Sound Produced in vitro by Pulsatile Flow in and Around ... pulsatile states of normal valves than they were during the studies of normal/abnormal valves under normal pulsatile states. ...
Duijndam, J.M. (2020) Design and implementation of an in-vitro carotid artery flow circuit with pulsatile flow conditions. ... Design and implementation of an in-vitro carotid artery flow circuit with pulsatile flow conditions ... In the study an in-vitro ow circuit with pulsatile ow conditions is designed and implemented. The ow circuit will be used to ... The design includes a gear pump and a piston driven pump [ViVitro pump] that generate a pulsatile waveform, which is recorded ...
Leitner, D., Wassertheurer, S., Hessinger, M., & Holzinger, A. (2006). A Lattice Boltzmann Model for Pulsatile Blood Flow in ...
Various analytical expressions axial velocity, flow rate, wall shear stress and effective viscosity have been derived with the ... slip and inclination has been seen by plotting the graph and observed that axial velocity and flow rate increases with the ... help of MATLAB for understanding the fluid flow phenomena. The combined effect of catheterization, body acceleration, ... the pulsatile flow of blood through an inclined catheterized stenosed artery is analyzed. Perturbation method is used to solve ...
Aneurysms, Domes (Structural elements), Flow (Dynamics), Hemodynamics, Vortices, Shear stress, Cavities, Inflow, Pulsatile flow ... Blood Flow in Abdominal Aortic Aneurysms: Pulsatile Flow Hemodynamics J Biomech Eng (October,2001) ... Pulsatile Flow Effects on the Hemodynamics of Intracranial Aneurysms Trung B. Le, Trung B. Le ... Pulsatile Flow and Athersclerosia in the Human Carotid Bifurcation. Positive Correlation Between Plaque Location and Low ...
A simple conceptual model of blood flow in the microcirculation, including small arteries, arterioles, capillaries, venules, ... A simple conceptual model of blood flow in the microcirculation, including small arteries, arterioles, capillaries, venules, ...
How should investigators compare different perfusion modes or different types of pulsatile flow during chronic support? ASAIO ... How should investigators compare different perfusion modes or different types of pulsatile flow during chronic support? / Ündar ... How should investigators compare different perfusion modes or different types of pulsatile flow during chronic support?. ... T1 - How should investigators compare different perfusion modes or different types of pulsatile flow during chronic support? ...
Preclinic Medtech has you covered with their top-of-the-line pulsatile flow blood pumps. Get accurate and reliable results with ... Looking for a reliable and high-precision pulsatile pump system manufacturer? Look no further! ... It is used to provide blood flow power source for human blood flow simulation device, and can accurately adjust the required ... Specifications of High-precision Pulsatile Pump. High-precision pulsatile pump. MODEL: PLAB1001. ...
Since flow and pressure inside AAA are non-uniform, the dynamic interaction between the pulsatile flow and wall may influence ... Influence of pulsatile flow on LDL transport in the arterial wall. , ANNALS OF BIOMEDICAL ENGINEERING, Vol: 35, Pages: 1782- ... Analysis of complex flow and the relationship between blood pressure, wall shear stress, and intima-media thickness in the ... It is demonstrated that including fluid flow can change local wall stresses slightly. However, as far as the peak wall stress ...
... ... A mathematical model for the pulsatile blood flow in a small vessel in a cardiovascular system with a mild stenosis is analyzed ...
Pulsatile Perfusion Therapy: A novel approach for improving cerebral tissue blood flow and oxygenation. Posted on September 29 ... "Pulsatile Perfusion Therapy: A novel approach for improving cerebral tissue blood flow and oxygenation" ... to take part in a study that will assess the response of cerebral blood flow and oxygenation to cyclical variations in arterial ...
Effect of pulsatile flow on liquid phase packed bed adsorption. Lau, A. (Author). 23 Oct 1997 ...
Pulsatile tinnitus occurs when the sounds throb in time to the beat of their pulse. This article explores the causes, symptoms ... Pulsatile tinnitus occurs when the ear becomes aware of a change in blood flow in nearby blood vessels. These include the ... Localised increased flow. Sometimes, blood flow increases in just one or one group of vessels. Tumors in the head and neck can ... Generalised increased blood flow. When blood is flowing quickly, such as during strenuous exercise or pregnancy, it makes more ...
Pulsatile Flow * Risk * Stroke / classification * Stroke / physiopathology* * Vascular Resistance* ...
Role of flow reversals in transition to turbulence and relaminarization of pulsatile flows. Journal of Fluid Mechanics, 917 ... "Role of flow reversals in transition to turbulence and relaminarization of pulsatile flows". Journal of Fluid Mechanics 917 ... Role of flow reversals in transition to turbulence and relaminarization of pulsatile flows ... The instability and transition to turbulence and its evolution in pulsatile flows, which involve reverse flows and unsteady ...
Pulsatile Flow * Regional Blood Flow * Transducers, Pressure * Ultrasonography, Doppler* / instrumentation Grants and funding * ... and left main coronary velocity for the estimation of coronary flow reserve. These noninvasive methods are convenient and easy ...
Blood Flow in Abdominal Aortic Aneurysms: Pulsatile Flow Hemodynamics J Biomech Eng (October,2001) ... Flow (Dynamics), Pressure, Blood vessels, Fluids, Incompressible fluids, Phase shift, Pulsatile flow, Shear stress ... Pulsatile Blood Flow in a Channel of Small Exponential Divergence-I. The Linear Approximation for Low Mean Reynolds Number D. J ... Pulsatile Blood Flow Effects on Temperature Distribution and Heat Transfer in Rigid Vessels J Biomech Eng (October,2001) ...
This iwhat is known as a pulsatile tinnitus.. Other medical problems: These include changes in your inner ear bones, an inner ... Blood vessels close to your middle and inner ear become less stretchy, so your blood flow is stronger and seems louder. ...
"Speech Production and Pulsatile Flow over a Surface Protuberance". Michael W. Plesniak, Mechanical and Aerospace Engineering , ...
Viscous Fluid Flow. - Pulsatile Flow, Bolus Flow, Turbulence. 14,15. 9. 17-18. November 9. - Turbulence, Aneurysms. - Perrins ...
Wall shear stress (WSS), a tangential force per unit area exerted on the inner wall of a vessel by blood flow, plays an ... The key is to determine the local normal direction of the wall in image-based flow domains. We present a novel computation ... Session W07: Biological Fluid Dynamics: Physiological Cardiac Flows (10:00am - 10:45am CST). 10:00 AM, Tuesday, November 24, ... Abstract: W07.00001 : A Novel Computational Framework for Pulsatile Wall-shear Stress in Image-based Computational Fluid ...
... we show that monolayer-graphene single microelectrodes harvesting charge from continuous aqueous flow provide an effective flow ... Here, self-powered monolayer graphene microelectrodes are shown to enable real-time interrogation of whole-blood flows with 6- ... However, existing nano-based electrical flow sensing technologies remain lacking in precision and stability and are typically ... over six-months stability and sub-micrometer/second resolution in real-time quantification of whole-blood flows with multiscale ...
I. Marshall, S. Zhao, P. Papathanasopoulou, P. Hoskins, and X. Y. Xu, "MRI and CFD studies of pulsatile flow in healthy and ... Pulsatile continuous pressure, not flow, is the peculiar parameter related to arterial disease. Compliance, capacitance, and ... There is evidence that flow shear stress arises from disturbed flow from protruding plaque with vacuolation and turbulence that ... K. T. Nguyen, C. D. Clark, T. J. Chancellor, and D. V. Papavassiliou, "Carotid geometry effects on blood flow and on risk for ...
The results show that the loss coefficient decreases and the flow coefficient increases with the increase of the Reynolds ... but the flow coefficient increases if the Reynolds number is larger than 10,000. In addition, the effects of the gaps between ... and the groove depth varying from 2.3 mm to 9 mm are chosen to investigate their effects on the flow and loss coefficients of ... 14] focused on the pulsatile flow of a mechanical heart valve, Chen et al. [15] investigated the thermal stress of a pressure- ...
The feasibility of using a compressed interwoven Supera stent as a flow diverting device for popliteal aneurysms was recently ... The pulsatile flow in the popliteal artery generated distinct flow features in the straight and bent models. In the straight ... Physiologic flow loop (left) used to recreate pulsatile triphasic flow (right) as present in the popliteal aneurysm cohort. ... Six rigid PAA models were created and integrated into a flow set-up that reproduced physiologic pulsatile flow. The anatomy and ...
  • What's to know about pulsatile tinnitus? (medicalnewstoday.com)
  • Pulsatile tinnitus is characterized by hearing noises that beat in time with your pulse . (medicalnewstoday.com)
  • What is pulsatile tinnitus? (medicalnewstoday.com)
  • Pulsatile tinnitus is a rhythmical noise that beats at the same rate as the heart and is the sound of blood circulating the body. (medicalnewstoday.com)
  • Unlike other forms of tinnitus, which are thought to be caused by a disconnect between the sounds the ears hear and the way the brain interprets them, pulsatile tinnitus has a physical source. (medicalnewstoday.com)
  • Pulsatile tinnitus occurs when the ear becomes aware of a change in blood flow in nearby blood vessels. (medicalnewstoday.com)
  • Tumors in the head and neck can lead to the development of abnormal blood vessels, which can result in pulsatile tinnitus. (medicalnewstoday.com)
  • The majority of tumors associated with pulsatile tinnitus are benign, meaning they are not cancerous. (medicalnewstoday.com)
  • This could lead to pulsatile tinnitus. (medicalnewstoday.com)
  • A condition called benign or idiopathic intracranial hypertension can cause pulsatile tinnitus, as well as headaches and sight problems. (medicalnewstoday.com)
  • In people with pulsatile tinnitus, doctors may suggest that they have additional tests, such as an MRI or ultrasound scan , to study the blood vessels and check the pressure inside the head. (medicalnewstoday.com)
  • If a specific cause is found for pulsatile tinnitus, doctors can treat the underlying condition. (medicalnewstoday.com)
  • This iwhat is known as a pulsatile tinnitus. (webmd.com)
  • Pulsatile tinnitus is a rare type of tinnitus that sounds like a rhythmic pulsing in the ear, usually in time with your heartbeat. (banishtinnitus.net)
  • This kind of tinnitus is most often caused by problems with blood flow in the head or neck. (banishtinnitus.net)
  • Pulsatile tinnitus also may be caused by brain tumors or abnormalities in brain structure. (banishtinnitus.net)
  • There are two main categories of Pulsatile Tinnitus - Objective or Subjective. (festivalofthephotograph.org)
  • Pulsatile tinnitus is triggered by a change of blood flow within the large arteries and veins within the neck, base from the skull, or the smaller blood vessels inside the ear. (festivalofthephotograph.org)
  • The extra circulation generates noise and can consequence in Pulsatile tinnitus. (festivalofthephotograph.org)
  • When Pulsatile tinnitus is suspected, additional tests may be required to study the blood vessels and check the pressure inside the head. (festivalofthephotograph.org)
  • Sufferers with Pulsatile tinnitus will usually undergo some kind of medical imaging like Ultrasound, CT scanning, Magnetic resonance scanning (MRI), Magnetic resonance angiography (MRA), or Angiography. (festivalofthephotograph.org)
  • This is one of the main causes of Pulsatile Tinnitus, and affects the vast majority of tinnitus patients. (festivalofthephotograph.org)
  • Due to the inflammation of the inner ear, blood flow to the damaged tissue increases and causes pulsating tinnitus or ringing in the ears. (festivalofthephotograph.org)
  • Normally, the middle ear is an air free space, and this fluid build up causes Pulsatile Tinnitus. (festivalofthephotograph.org)
  • Sinus infection medication could also be one of the causes of Pulsatile Tinnitus. (festivalofthephotograph.org)
  • Thyroid Dysfunction can also cause pulsatile tinnitus. (festivalofthephotograph.org)
  • Pulsatile (like a heartbeat) tinnitus is often caused by sounds created by muscle movements near the ear, changes in the ear canal, or blood flow (vascular) problems in the face or neck. (healthwise.net)
  • Application of unidirectional pulsatile shear stress to human umbilical vein endothelial cells (HUVECs) decreased PDCD4 protein but not mRNA level. (plos.org)
  • The flow profiles was first derived by John R. Womersley (1907-1958) in his work with blood flow in arteries. (wikipedia.org)
  • In recent years, the study of blood flow through obstructed arteries has received much attention, due to its ample importance in human cardiovascular system. (scirp.org)
  • Since heart pumps of the blood are periodic in nature, the blood flow in narrow arteries can be assumed as pulsatile. (scirp.org)
  • A simple conceptual model of blood flow in the microcirculation, including small arteries, arterioles, capillaries, venules, and small veins, with linearized equations of motion and simplifying assumptions. (rand.org)
  • This causes the arteries to become narrow and possibly blocking the flow of blood. (festivalofthephotograph.org)
  • It represents actual noise created by structures near the ear such as noise generated by blood flowing through arteries or veins. (msdmanuals.com)
  • This leads to a turbulent and louder blood flow. (medicalnewstoday.com)
  • In past experiments, simulations and theoretical analysis, rotation has been shown to dramatically effect the characteristics of turbulent flows, such as causing the mean velocity profile to appear laminar, leading to an overall drag reduction, as well as affecting the Reynolds stress tensor. (nsf.gov)
  • The axially rotating pipe is an exemplary prototypical model problem that exhibits these complex turbulent flow physics. (nsf.gov)
  • In this work, Direct Numerical Simulations (DNS) of rotating turbulent pipe flows are conducted at moderate Reynolds numbers (Re=5300, 11,700, and 19,000) and rotation numbers of N=0 to 3. (nsf.gov)
  • The main objectives of this work are to firstly quantify turbulence suppression for rotating turbulent pipe flows at different Reynolds numbers as well as study the effects of rotation on turbulence by analyzing the characteristics of the Reynolds stress tensor and the production and dissipation terms of the turbulence budgets. (nsf.gov)
  • The feasibility of using a compressed interwoven Supera stent as a flow diverting device for popliteal aneurysms was recently demonstrated in patients. (springer.com)
  • It is unclear, however, what the optimal flow diverting strategy is, because of the fusiform shape of popliteal aneurysms and their exposure to triphasic flow. (springer.com)
  • To assess this flow diverting strategy for popliteal aneurysms, flow profiles and thrombus formation likelihood were investigated in popliteal aneurysm models. (springer.com)
  • In cerebral aneurysms, flow diverters effectively reduce flow in the aneurysm and promote aneurysm thrombosis and subsequent shrinkage [ 4 ]. (springer.com)
  • Moreover, the system must enable to study different pulsatile hemodynamic patterns in different geometries such as aneurysms (a n aneurysm is a balloon-like expansion of weakened blood vessels which can rupture causing haemorrhages). (ni.com)
  • The design includes a gear pump and a piston driven pump [ViVitro pump] that generate a pulsatile waveform, which is recorded with a mass ow meter. (utwente.nl)
  • Moreover, the resistance and compliance visibly in uence the pulsatile ow profile, but the resulting waveform largely resembles the in-vivo waveform. (utwente.nl)
  • High-resolution numerical simulations are carried out to systematically investigate the effect of the incoming flow waveform on the hemodynamics and wall shear stress patterns of an anatomic sidewall intracranial aneurysm model. (asme.org)
  • We show that the waveform PI is the key parameter that governs the vortex dynamics across the aneurysm neck and the flow patterns within the dome. (asme.org)
  • We finally argue that the ratio between the characteristic time scale of transport by the mean flow across the neck and the time scale of vortex ring formation can be used to predict for a given sidewall aneurysm model the critical value of the waveform PI for which the hemodynamics will transition from the cavity mode to the vortex ring mode. (asme.org)
  • Due to the reduction in blood flow, the sensor may not be able to pick up adequately the pulsatile waveform resulting in no signal or loss of accuracy. (amperordirect.com)
  • We investigated whether atheroprotective unidirectional pulsatile shear stress affects the expression of PDCD4 in endothelial cells. (plos.org)
  • En face co-immunostaining of the mouse aortic arch revealed a low level of PDCD4 in endothelial cells undergoing pulsatile shear stress. (plos.org)
  • Immunoprecipitation revealed that pulsatile shear stress induced the coupling of ubiquitin with PDCD4 expression. (plos.org)
  • Low PDCD4 level was associated with reduced proliferation but not apoptosis or phosphorylation of endothelial nitric oxide synthase caused by pulsatile shear stress to help maintain the homeostasis of endothelial cells. (plos.org)
  • Pulsatile shear stress induces ubiquitin-proteasome-mediated degradation of PDCD4 via a PI3K/Akt pathway in HUVECs. (plos.org)
  • Low PDCD4 level is associated with reduced proliferation for maintenance of HUVEC homeostasis under pulsatile shear stress. (plos.org)
  • Atherosclerosis plaques preferentially develop at arterial branches and curvatures under low and oscillatory or even static shear stress induced by disturbed blood flow as opposed to in straight parts, featuring protective unidirectional pulsatile shear stress [14] , [15] . (plos.org)
  • Ample evidence shows that pro-atherosclerotic disturbed flow induces sustained activation of atherogenic genes in endothelial cells to promote their oxidation, inflammation, cell cycle progression and proliferation, whereas pulsatile shear stress tends to maintain endothelial cells in a quiescent and less proliferative state with a low level of oxidation and inflammation [16] , [17] . (plos.org)
  • Various analytical expressions axial velocity, flow rate, wall shear stress and effective viscosity have been derived with the help of MATLAB for understanding the fluid flow phenomena. (scirp.org)
  • Presence of atherosclerosis (stenosis), increased the resistance and therefore blood flow reduced inside the artery and also the remarkable change occurred in pressure distribution and wall shear stress. (scirp.org)
  • Utilizing data relevant to basal conditions existing in the major blood vessels of the human coronary circulation, it is found (in the absence of any persistent flow anomalies) that the shear stress at the wall is at least one to two orders of magnitude lower than values reported to be damaging to vascular endothelium. (silverchair.com)
  • Wall shear stress (WSS), a tangential force per unit area exerted on the inner wall of a vessel by blood flow, plays an important role in the prevention, pathogenesis, and treatment of cardiovascular diseases. (aps.org)
  • There is evidence that flow shear stress arises from disturbed flow from protruding plaque with vacuolation and turbulence that cause further intimal disruption, and this has been suggested as a mechanism for excess blood lipids to fuel deposition into plaques from the lumen of the vessel. (hindawi.com)
  • The cardiovascular system of chordate animals is a very good example where pulsatile flow is found, but pulsatile flow is also observed in engines and hydraulic systems, as a result of rotating mechanisms pumping the fluid. (wikipedia.org)
  • A mathematical model for the pulsatile blood flow in a small vessel in a cardiovascular system with a mild stenosis is analyzed. (ub.bw)
  • Current topics include the modeling of blood flows in the cardiovascular system, the development of multiscale methods for the simulation of vascularized tissues and biomaterials. (wias-berlin.de)
  • Professor Alfio Quarteroni of the École Polytechnique Fédérale de Lausanne (EPFL, Switzerland) is leading the Mathcard project in developing mathematical models of the blood flow in our cardiovascular system. (europa.eu)
  • The University of North Texas Health Science Center is recruiting up to 50 subjects (male and female) to take part in a study that will assess the response of cerebral blood flow and oxygenation to cyclical variations in arterial pressure. (unthsc.edu)
  • Pulsatile continuous pressure, not flow, is the peculiar parameter related to arterial disease. (hindawi.com)
  • Initially, retrograde arterial flow was observed and since it was appropriate for primary repair.The repair was performed primarily (Figure 10). (ispub.com)
  • Pulse oximetry assumes that arterial blood is the only pulsatile absorber and other sources of fluctuations could contribute to erroneous readings. (amperordirect.com)
  • In the study an in-vitro ow circuit with pulsatile ow conditions is designed and implemented. (utwente.nl)
  • 16 While in vitro systems such as parallel plate and T-chamber flow systems provide an opportunity for highly controlled investigations of cellular response to various types of hemodynamic stresses, such model systems are limited to short-duration studies. (ajnr.org)
  • The object is to provide a device capable of reproducing in vitro, the exact pulsatile signals encountered in the blood vessels. (ni.com)
  • Vascular endothelial cells, as a monolayer in direct contact with the flowing blood, bear the most of the wall shear stresses and have important homeostatic functions in response to stress [16] . (plos.org)
  • This ability should enable signals to be generated and applied to ECs (endothelial cells) or bilayer culture systems containing ECs and VSMCs ( vascular smooth muscle cells) seeded in a transparent test chamber or any geometry that allows observation under the microscope, recording of flow parameters and cell harvest after treatments. (ni.com)
  • Next, we plan to use advanced intestinal tissue models using primary human epithelial cells and apply a constant flow of medium in the apical chamber and pulsatile flow in the vascular compartment within a bioreactor. (uni-wuerzburg.de)
  • Blood vessels close to your middle and inner ear become less stretchy, so your blood flow is stronger and seems louder. (webmd.com)
  • How the Supera flow diverting configuration alters hemodynamics in a PAA has not yet been investigated. (springer.com)
  • Attention was given to understanding effects of valvar and pulsatile conditions upon the frequency characteristics of the opening, systolic, and closing sounds. (caltech.edu)
  • A piston driven by a programmable DC servo motor was used to set-up a water flow system and provide the pulsation characteristics. (nsf.gov)
  • However, existing nano-based electrical flow sensing technologies remain lacking in precision and stability and are typically only applicable to simple aqueous solutions or liquid/gas dual-phase mixtures, making them unsuitable for monitoring low-flow (~micrometer/second) yet important characteristics of continuous biofluids (such as hemorheological behaviors in microcirculation). (nature.com)
  • In particular, over six-months stability and sub-micrometer/second resolution in real-time quantification of whole-blood flows with multiscale amplitude-temporal characteristics are obtained in a microfluidic chip. (nature.com)
  • Note that, P 0 ′ {\displaystyle P'_{0}} (standing for n = 0 {\displaystyle n=0} ) is the steady-state pressure gradient, whose sign is opposed to the steady-state velocity (i.e., a negative pressure gradient yields positive flow). (wikipedia.org)
  • The combined effect of catheterization, body acceleration, slip and inclination has been seen by plotting the graph and observed that axial velocity and flow rate increases with the increase in body acceleration, inclination angle and slip velocity while axial velocity diminishes on increasing the catheter radius. (scirp.org)
  • With these methods one can measure cardiac filling and ejection velocities, velocity pulse arrival times for determining pulse wave velocity, peripheral blood velocity and vessel wall motion waveforms, jet velocities for the calculation of the pressure drop across stenoses, and left main coronary velocity for the estimation of coronary flow reserve. (nih.gov)
  • When the Reynolds number and channel divergence are each small, the flow does not separate, but there is a downstream attenuation of both flow and pressure, together with the appearance of a finite radial velocity component. (silverchair.com)
  • All-electronic interrogation of biofluid flow velocity by electrical nanosensors incorporated in ultra-low-power or self-sustained systems offers the promise of enabling multifarious emerging research and applications. (nature.com)
  • Alternatively, triboelectric charge harvested from a liquid flow by a micro/nanoelectrode device can be quantified for gauging the flow velocity. (nature.com)
  • A flow of EDTA-anticoagulated whole bovine blood (pH = 7.0, ionic strength = 150 mM) with precisely controlled velocity was driven through the microfluidic channel by a syringe pump. (nature.com)
  • In fluid dynamics, a flow with periodic variations is known as pulsatile flow, or as Womersley flow. (wikipedia.org)
  • Sud and Sekhon [5] studied on pulsatile flow of blood through a rigid circular tube subjected to periodic body acceleration considering blood as Newtonian fluid. (scirp.org)
  • Hemodynamic simulation provides simulated fluid for the cardiovascular model and can adjust the temperature, flow rate, and pressure of the simulated fluid. (preclinic-sim.com)
  • The pulsating flow of a viscous, incompressible fluid through rigid circular channels having walls which diverge at a slow exponential rate is examined analytically. (silverchair.com)
  • Linearized solutions for low mean Reynolds numbers reveal that viscous effects lead to radially dependent phase shifts between different layers of fluid oscillating in the axial direction, and characteristic phase lags between flow and pressure curves. (silverchair.com)
  • His research interests are in Applied Mathematics, Fluid Dynamics including Porous Media Flows, Mathematical Modeling and Simulation, Numerical Analysis, and Scientific Computing. (researchgate.net)
  • Sufficient conditions for an injection rate that maintains a stable flow are analytically derived for flows with an arbitrary number of fluid layers. (researchgate.net)
  • The elements of the designed circuit mimic the pulsatile ow conditions of the carotid artery in the body. (utwente.nl)
  • Visualization of the valve and particle trajectories and simultaneous recording of sound, flow rate, and upstream and downstream pressure, provided direct evidence of the cause of many of the acoustical events. (caltech.edu)
  • Liepsch [9] compared the details of flow behaviors with hemodynamic approach and observed that flow rate varies due to pulsatile nature of blood. (scirp.org)
  • Sometimes, blood flow increases in just one or one group of vessels. (medicalnewstoday.com)
  • One of the most common reasons for its development is a change in blood flow to the vessels located near the ears. (connecthearing.ca)
  • BACKGROUND: Weaning of patients from mechanical cardiac support after myocardial recovery has always involved multiple, interacting factors, particularly the training of the myocardium during reduction of pump flow. (perfusion.com)
  • Under low-flow conditions, the heart imposes an oscillating forward-backward flow through the non-occlusive rotary pump, causing an increase in ventricular work. (perfusion.com)
  • Bennett [1] has observed that the presence of wall slip at the flow boundaries decreases the apparent (effective) viscosity. (scirp.org)
  • We perform a linear stability analysis of three-layer radial porous media and Hele-Shaw flows with variable viscosity in the middle layer. (researchgate.net)
  • At high PI, on the other hand, the flow is dominated by vortex ring formation, transport across the neck, and impingement and breakdown at the distal wall of the aneurysm dome. (asme.org)
  • Strouhal numbers were estimated from center-frequencies of resonance peaks associated with sounds that were related to periodic vortex shedding in flows past the struts, annular gaps and phonocatheter. (caltech.edu)
  • How should investigators compare different perfusion modes or different types of pulsatile flow during chronic support? (psu.edu)
  • Color flow Doppler evaluation of St. Jude Medical prosthetic valves. (meduniver.com)
  • 21. Chambers J, Monaghan M, Jackson G. Colour flow Doppler mapping in the assessment of prosthetic valve regurgitation. (meduniver.com)
  • The location of peaks within the power density spectra of opening, systolic and closing sounds were more similar during the studies of alternate, non-normal, pulsatile states of normal valves than they were during the studies of normal/abnormal valves under normal pulsatile states. (caltech.edu)
  • When blood is flowing quickly, such as during strenuous exercise or pregnancy, it makes more noise. (medicalnewstoday.com)
  • Generalized increased blood flow throughout the body which occurs throughout strenuous exercise or could be triggered by severe anemia. (festivalofthephotograph.org)
  • Comparison of continuous-flow and pulsatile-flow blood pumps on reducing pulmonary artery pressure in patients with fixed pulmonary hypertension. (ksbu.edu.tr)
  • Rotary pumps offer training advantages when support flow is reduced, even to nearly zero. (perfusion.com)
  • Turbulence appears to be produced at the locations of maximum or minimum vorticity within the attached WVL, in the ridges between the K-H vortices around the separated WVL and the upstream side of the secondary vortex where the flow impinges on the wall. (nsf.gov)
  • In this paper, the pulsatile flow of blood through an inclined catheterized stenosed artery is analyzed. (scirp.org)
  • MacDonald [14] considered the pulsatile blood flow in a catheterized artery and obtained theoretical estimates for pressure gradient corrections for catheters, which are positioned eccentrically, as well as coaxially with the artery. (scirp.org)
  • At low PI, the flow in the dome is similar to a driven cavity flow and is characterized by a quasi-stationary shear layer that delineates the parent artery flow from the recirculating flow within the dome. (asme.org)
  • High levels of cholesterol can cause an obstruction of blood flow by depositing fatty deposits in the inner lining of an artery near the inner ear. (festivalofthephotograph.org)
  • In this T1-weighted midline sagittal MR image without contrast, a flow void can be seen at the anterior edge of this mass, which represents the distal right posteriorinferior cerebellar artery. (medscape.com)
  • The Reynolds number varying from 200 to 500,000, and the valve opening degree varying from 20% to 100%, and the groove depth varying from 2.3 mm to 9 mm are chosen to investigate their effects on the flow and loss coefficients of the gate valve. (mdpi.com)
  • The results show that the loss coefficient decreases and the flow coefficient increases with the increase of the Reynolds number and the valve opening degree, while with the increase of the groove depth, the loss coefficient barely changes, but the flow coefficient increases if the Reynolds number is larger than 10,000. (mdpi.com)
  • Flow diversion may stimulate both routes, by augmenting particle residence time in the aneurysm, or by shear-induced platelet activation when blood is expulsed through the stent struts [ 7 ]. (springer.com)
  • It is used to provide blood flow power source for human blood flow simulation device, and can accurately adjust the required simulation parameters. (preclinic-sim.com)
  • Further research concentrates on the development, the analysis, and the simulation of mathematical models for a better understanding of biological flows and biological tissues. (wias-berlin.de)
  • An application study is to quantify WSS of Womersley flow in ducts. (aps.org)
  • Tu and Deville [2] observed the blood flow in diseased conditions. (scirp.org)
  • These conditions cannot be achieved with pulsatile systems. (perfusion.com)
  • Comparison of continuous-flow and pulsat. (ksbu.edu.tr)
  • Here, we show that monolayer-graphene single microelectrodes harvesting charge from continuous aqueous flow provide an effective flow sensing strategy that delivers key performance metrics orders of magnitude higher than other electrical approaches. (nature.com)
  • Here, we show self-powered graphene microdevices that transduce in real time the flow of continuous blood in a microfluidic channel to charge-transfer current in response to the flow-sensory rearrangement (not formation/deformation) of EDL at the graphene-aqueous interface. (nature.com)
  • Transesophageal color flow Doppler and echocardiogra-phic features of normal and regurgitant St. Jude medical prostheses in the mitral valve position. (meduniver.com)
  • The physical mechanisms causing turbulence suppression are currently not well-understood, and a deeper understanding of these mechanisms is of great value for many practical examples involving swirling or rotating flows, such as swirl generators, wing-tip vortices, axial compressors, hurricanes, etc. (nsf.gov)
  • The flow transduction of the devices is based on a single microelectrode of monolayer graphene that harvests charge from flowing blood through contact electrification without the need for an external current supply. (nature.com)
  • At higher Re numbers, the strength and extent of the vortices are larger and substantial disturbances appear in the free stream region of the flow, which are typical of pipe flows at transitional Re numbers. (nsf.gov)
  • Effects of pulse rate, mean flow-rate, and mean aortic pressure associated with the normal valvar sounds were investigated. (caltech.edu)
  • Under alternate pulsatile states, the total power of the opening and closing sounds were influenced primarily by the rate of change of the ventricular pressure prior to these events. (caltech.edu)
  • This will alter the flow field, modify the pressure distribution and increase the resistance. (scirp.org)
  • Direct pressure should be placed on the wound to stem the flow of blood until your veterinarian arrives. (lbemc.com)
  • Two-dimensional flow velocities were visualized by laser particle image velocimetry. (springer.com)
  • The instability and transition to turbulence and its evolution in pulsatile flows, which involve reverse flows and unsteady flow separations, is the primary focus of this experimental work. (nsf.gov)
  • Flow diverters are expected to decrease velocities in the aneurysm, but it is unknown whether this holds for PAA, where flow reversal, i.e. a diastolic retrograde flow, is typically present. (springer.com)
  • Both of these flow types are commonly observed in human IAs. (ajnr.org)
  • A pulsation artifact, known as phase ghosting, indicates that flowing blood is present within the mass, which suggests that the mass could be an aneurysm. (medscape.com)
  • Six popliteal aneurysm models were created and integrated into a pulsatile flow set-up. (springer.com)
  • Effect of trabeculectomy on pulsatile ocular blood flow. (bmj.com)
  • Inflectional instability leads to flow separation and the formation of a major roll-up structure with the K-H vortices superimposed. (nsf.gov)