Hemodynamics: The movement and the forces involved in the movement of the blood through the CARDIOVASCULAR SYSTEM.Vascular Resistance: The force that opposes the flow of BLOOD through a vascular bed. It is equal to the difference in BLOOD PRESSURE across the vascular bed divided by the CARDIAC OUTPUT.Renal Circulation: The circulation of the BLOOD through the vessels of the KIDNEY.Blood Pressure: PRESSURE of the BLOOD on the ARTERIES and other BLOOD VESSELS.Blood Flow Velocity: A value equal to the total volume flow divided by the cross-sectional area of the vascular bed.Cardiac Output: The volume of BLOOD passing through the HEART per unit of time. It is usually expressed as liters (volume) per minute so as not to be confused with STROKE VOLUME (volume per beat).Regional Blood Flow: The flow of BLOOD through or around an organ or region of the body.Cerebrovascular Circulation: The circulation of blood through the BLOOD VESSELS of the BRAIN.Models, Cardiovascular: 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.Pulmonary Circulation: The circulation of the BLOOD through the LUNGS.Dogs: 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)Hypertension, Pulmonary: Increased VASCULAR RESISTANCE in the PULMONARY CIRCULATION, usually secondary to HEART DISEASES or LUNG DISEASES.Heart Rate: The number of times the HEART VENTRICLES contract per unit of time, usually per minute.Kidney: Body organ that filters blood for the secretion of URINE and that regulates ion concentrations.Blood Volume: Volume of circulating BLOOD. It is the sum of the PLASMA VOLUME and ERYTHROCYTE VOLUME.Pulsatile Flow: Rhythmic, intermittent propagation of a fluid through a BLOOD VESSEL or piping system, in contrast to constant, smooth propagation, which produces laminar flow.Glomerular Filtration Rate: The volume of water filtered out of plasma through glomerular capillary walls into Bowman's capsules per unit of time. It is considered to be equivalent to INULIN clearance.Liver Circulation: The circulation of BLOOD through the LIVER.Coronary Circulation: The circulation of blood through the CORONARY VESSELS of the HEART.Pulmonary Wedge Pressure: The blood pressure as recorded after wedging a CATHETER in a small PULMONARY ARTERY; believed to reflect the PRESSURE in the pulmonary CAPILLARIES.Splanchnic Circulation: The circulation of blood through the BLOOD VESSELS supplying the abdominal VISCERA.Cardiography, Impedance: A type of impedance plethysmography in which bioelectrical impedance is measured between electrodes positioned around the neck and around the lower thorax. It is used principally to calculate stroke volume and cardiac volume, but it is also related to myocardial contractility, thoracic fluid content, and circulation to the extremities.Pulmonary Artery: The short wide vessel arising from the conus arteriosus of the right ventricle and conveying unaerated blood to the lungs.Oxygen: An element with atomic symbol O, atomic number 8, and atomic weight [15.99903; 15.99977]. It is the most abundant element on earth and essential for respiration.Oxygen Consumption: The rate at which oxygen is used by a tissue; microliters of oxygen STPD used per milligram of tissue per hour; the rate at which oxygen enters the blood from alveolar gas, equal in the steady state to the consumption of oxygen by tissue metabolism throughout the body. (Stedman, 25th ed, p346)Ventricular Function, Left: The hemodynamic and electrophysiological action of the left HEART VENTRICLE. Its measurement is an important aspect of the clinical evaluation of patients with heart disease to determine the effects of the disease on cardiac performance.Hypertension, Portal: Abnormal increase of resistance to blood flow within the hepatic PORTAL SYSTEM, frequently seen in LIVER CIRRHOSIS and conditions with obstruction of the PORTAL VEIN.Blood Gas Analysis: Measurement of oxygen and carbon dioxide in the blood.Microcirculation: The circulation of the BLOOD through the MICROVASCULAR NETWORK.Time Factors: Elements of limited time intervals, contributing to particular results or situations.Ultrasonography, Doppler, Transcranial: A non-invasive technique using ultrasound for the measurement of cerebrovascular hemodynamics, particularly cerebral blood flow velocity and cerebral collateral flow. With a high-intensity, low-frequency pulse probe, the intracranial arteries may be studied transtemporally, transorbitally, or from below the foramen magnum.Spectroscopy, Near-Infrared: A noninvasive technique that uses the differential absorption properties of hemoglobin and myoglobin to evaluate tissue oxygenation and indirectly can measure regional hemodynamics and blood flow. Near-infrared light (NIR) can propagate through tissues and at particular wavelengths is differentially absorbed by oxygenated vs. deoxygenated forms of hemoglobin and myoglobin. Illumination of intact tissue with NIR allows qualitative assessment of changes in the tissue concentration of these molecules. The analysis is also used to determine body composition.Arterial Pressure: The blood pressure in the ARTERIES. It is commonly measured with a SPHYGMOMANOMETER on the upper arm which represents the arterial pressure in the BRACHIAL ARTERY.Stroke Volume: The amount of BLOOD pumped out of the HEART per beat, not to be confused with cardiac output (volume/time). It is calculated as the difference between the end-diastolic volume and the end-systolic volume.Arteries: The vessels carrying blood away from the heart.Vasodilator Agents: Drugs used to cause dilation of the blood vessels.Venous Pressure: The blood pressure in the VEINS. It is usually measured to assess the filling PRESSURE to the HEART VENTRICLE.Hypertension: Persistently high systemic arterial BLOOD PRESSURE. Based on multiple readings (BLOOD PRESSURE DETERMINATION), hypertension is currently defined as when SYSTOLIC PRESSURE is consistently greater than 140 mm Hg or when DIASTOLIC PRESSURE is consistently 90 mm Hg or more.Heart Failure: A heterogeneous condition in which the heart is unable to pump out sufficient blood to meet the metabolic need of the body. Heart failure can be caused by structural defects, functional abnormalities (VENTRICULAR DYSFUNCTION), or a sudden overload beyond its capacity. Chronic heart failure is more common than acute heart failure which results from sudden insult to cardiac function, such as MYOCARDIAL INFARCTION.Diuresis: An increase in the excretion of URINE. (McGraw-Hill Dictionary of Scientific and Technical Terms, 6th ed)Blood Circulation: The movement of the BLOOD as it is pumped through the CARDIOVASCULAR SYSTEM.Natriuresis: Sodium excretion by URINATION.Hematocrit: The volume of packed RED BLOOD CELLS in a blood specimen. The volume is measured by centrifugation in a tube with graduated markings, or with automated blood cell counters. It is an indicator of erythrocyte status in disease. For example, ANEMIA shows a low value; POLYCYTHEMIA, a high value.Swine: 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).Heart: The hollow, muscular organ that maintains the circulation of the blood.Disease Models, Animal: Naturally occurring or experimentally induced animal diseases with pathological processes sufficiently similar to those of human diseases. They are used as study models for human diseases.Pulmonary Gas Exchange: The exchange of OXYGEN and CARBON DIOXIDE between alveolar air and pulmonary capillary blood that occurs across the BLOOD-AIR BARRIER.Laser-Doppler Flowmetry: A method of non-invasive, continuous measurement of MICROCIRCULATION. The technique is based on the values of the DOPPLER EFFECT of low-power laser light scattered randomly by static structures and moving tissue particulates.Rats, Sprague-Dawley: A strain of albino rat used widely for experimental purposes because of its calmness and ease of handling. It was developed by the Sprague-Dawley Animal Company.Renal Plasma Flow: The amount of PLASMA that perfuses the KIDNEYS per unit time, approximately 10% greater than effective renal plasma flow (RENAL PLASMA FLOW, EFFECTIVE). It should be differentiated from the RENAL BLOOD FLOW; (RBF), which refers to the total volume of BLOOD flowing through the renal vasculature, while the renal plasma flow refers to the rate of plasma flow (RPF).Antihypertensive Agents: Drugs used in the treatment of acute or chronic vascular HYPERTENSION regardless of pharmacological mechanism. Among the antihypertensive agents are DIURETICS; (especially DIURETICS, THIAZIDE); ADRENERGIC BETA-ANTAGONISTS; ADRENERGIC ALPHA-ANTAGONISTS; ANGIOTENSIN-CONVERTING ENZYME INHIBITORS; CALCIUM CHANNEL BLOCKERS; GANGLIONIC BLOCKERS; and VASODILATOR AGENTS.Cardiac Catheterization: Procedures in which placement of CARDIAC CATHETERS is performed for therapeutic or diagnostic procedures.Nitric Oxide: A free radical gas produced endogenously by a variety of mammalian cells, synthesized from ARGININE by NITRIC OXIDE SYNTHASE. Nitric oxide is one of the ENDOTHELIUM-DEPENDENT RELAXING FACTORS released by the vascular endothelium and mediates VASODILATION. It also inhibits platelet aggregation, induces disaggregation of aggregated platelets, and inhibits platelet adhesion to the vascular endothelium. Nitric oxide activates cytosolic GUANYLATE CYCLASE and thus elevates intracellular levels of CYCLIC GMP.Renin: A highly specific (Leu-Leu) endopeptidase that generates ANGIOTENSIN I from its precursor ANGIOTENSINOGEN, leading to a cascade of reactions which elevate BLOOD PRESSURE and increase sodium retention by the kidney in the RENIN-ANGIOTENSIN SYSTEM. The enzyme was formerly listed as EC A state characterized by loss of feeling or sensation. This depression of nerve function is usually the result of pharmacologic action and is induced to allow performance of surgery or other painful procedures.Intracranial Aneurysm: 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)Portal Vein: A short thick vein formed by union of the superior mesenteric vein and the splenic vein.Kidney Glomerulus: A cluster of convoluted capillaries beginning at each nephric tubule in the kidney and held together by connective tissue.Catheterization, Swan-Ganz: Placement of a balloon-tipped catheter into the pulmonary artery through the antecubital, subclavian, and sometimes the femoral vein. It is used to measure pulmonary artery pressure and pulmonary artery wedge pressure which reflects left atrial pressure and left ventricular end-diastolic pressure. The catheter is threaded into the right atrium, the balloon is inflated and the catheter follows the blood flow through the tricuspid valve into the right ventricle and out into the pulmonary artery.Cerebral Arteries: The arterial blood vessels supplying the CEREBRUM.Hemorheology: The deformation and flow behavior of BLOOD and its elements i.e., PLASMA; ERYTHROCYTES; WHITE BLOOD CELLS; and BLOOD PLATELETS.Ultrasonography, Doppler, Color: 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.Resuscitation: The restoration to life or consciousness of one apparently dead. (Dorland, 27th ed)SulfonesShock, Hemorrhagic: Acute hemorrhage or excessive fluid loss resulting in HYPOVOLEMIA.Ultrasonography, Doppler: Ultrasonography applying the Doppler effect, with frequency-shifted ultrasound reflections produced by moving targets (usually red blood cells) in the bloodstream along the ultrasound axis in direct proportion to the velocity of movement of the targets, to determine both direction and velocity of blood flow. (Stedman, 25th ed)Magnetic Resonance Angiography: Non-invasive method of vascular imaging and determination of internal anatomy without injection of contrast media or radiation exposure. The technique is used especially in CEREBRAL ANGIOGRAPHY as well as for studies of other vascular structures.Veins: The vessels carrying blood away from the capillary beds.Hydrodynamics: The motion of fluids, especially noncompressible liquids, under the influence of internal and external forces.Acetazolamide: One of the CARBONIC ANHYDRASE INHIBITORS that is sometimes effective against absence seizures. It is sometimes useful also as an adjunct in the treatment of tonic-clonic, myoclonic, and atonic seizures, particularly in women whose seizures occur or are exacerbated at specific times in the menstrual cycle. However, its usefulness is transient often because of rapid development of tolerance. Its antiepileptic effect may be due to its inhibitory effect on brain carbonic anhydrase, which leads to an increased transneuronal chloride gradient, increased chloride current, and increased inhibition. (From Smith and Reynard, Textbook of Pharmacology, 1991, p337)Middle Cerebral Artery: The largest of the cerebral arteries. It trifurcates into temporal, frontal, and parietal branches supplying blood to most of the parenchyma of these lobes in the CEREBRAL CORTEX. These are the areas involved in motor, sensory, and speech activities.Heart Ventricles: The lower right and left chambers of the heart. The right ventricle pumps venous BLOOD into the LUNGS and the left ventricle pumps oxygenated blood into the systemic arterial circulation.Isoflurane: A stable, non-explosive inhalation anesthetic, relatively free from significant side effects.Carbon Dioxide: A colorless, odorless gas that can be formed by the body and is necessary for the respiration cycle of plants and animals.Myocardium: The muscle tissue of the HEART. It is composed of striated, involuntary muscle cells (MYOCYTES, CARDIAC) connected to form the contractile pump to generate blood flow.Treatment Outcome: Evaluation undertaken to assess the results or consequences of management and procedures used in combating disease in order to determine the efficacy, effectiveness, safety, and practicability of these interventions in individual cases or series.Portal System: A system of vessels in which blood, after passing through one capillary bed, is conveyed through a second set of capillaries before it returns to the systemic circulation. It pertains especially to the hepatic portal system.Shear Strength: 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.Norepinephrine: Precursor of epinephrine that is secreted by the adrenal medulla and is a widespread central and autonomic neurotransmitter. Norepinephrine is the principal transmitter of most postganglionic sympathetic fibers and of the diffuse projection system in the brain arising from the locus ceruleus. It is also found in plants and is used pharmacologically as a sympathomimetic.Atrial Natriuretic Factor: A potent natriuretic and vasodilatory peptide or mixture of different-sized low molecular weight PEPTIDES derived from a common precursor and secreted mainly by the HEART ATRIUM. All these peptides share a sequence of about 20 AMINO ACIDS.Oxyhemoglobins: A compound formed by the combination of hemoglobin and oxygen. It is a complex in which the oxygen is bound directly to the iron without causing a change from the ferrous to the ferric state.Vasodilation: The physiological widening of BLOOD VESSELS by relaxing the underlying VASCULAR SMOOTH MUSCLE.Renal Artery: A branch of the abdominal aorta which supplies the kidneys, adrenal glands and ureters.Stress, Mechanical: 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.Myocardial Contraction: Contractile activity of the MYOCARDIUM.Hypotension: Abnormally low BLOOD PRESSURE that can result in inadequate blood flow to the brain and other vital organs. Common symptom is DIZZINESS but greater negative impacts on the body occur when there is prolonged depravation of oxygen and nutrients.Prospective Studies: Observation of a population for a sufficient number of persons over a sufficient number of years to generate incidence or mortality rates subsequent to the selection of the study group.Fontan Procedure: A procedure in which total right atrial or total caval blood flow is channeled directly into the pulmonary artery or into a small right ventricle that serves only as a conduit. The principal congenital malformations for which this operation is useful are TRICUSPID ATRESIA and single ventricle with pulmonary stenosis.Hemodilution: Reduction of blood viscosity usually by the addition of cell free solutions. Used clinically (1) in states of impaired microcirculation, (2) for replacement of intraoperative blood loss without homologous blood transfusion, and (3) in cardiopulmonary bypass and hypothermia.Infusions, Intravenous: The long-term (minutes to hours) administration of a fluid into the vein through venipuncture, either by letting the fluid flow by gravity or by pumping it.Epoprostenol: A prostaglandin that is a powerful vasodilator and inhibits platelet aggregation. It is biosynthesized enzymatically from PROSTAGLANDIN ENDOPEROXIDES in human vascular tissue. The sodium salt has been also used to treat primary pulmonary hypertension (HYPERTENSION, PULMONARY).Ventricular Function, Right: The hemodynamic and electrophysiological action of the right HEART VENTRICLE.Shock: A pathological condition manifested by failure to perfuse or oxygenate vital organs.Ventricular Pressure: The pressure within a CARDIAC VENTRICLE. Ventricular pressure waveforms can be measured in the beating heart by catheterization or estimated using imaging techniques (e.g., DOPPLER ECHOCARDIOGRAPHY). The information is useful in evaluating the function of the MYOCARDIUM; CARDIAC VALVES; and PERICARDIUM, particularly with simultaneous measurement of other (e.g., aortic or atrial) pressures.Vascular Stiffness: Loss of vascular ELASTICITY due to factors such as AGING; and ARTERIOSCLEROSIS. Increased arterial stiffness is one of the RISK FACTORS for many CARDIOVASCULAR DISEASES.Receptors, Endothelin: Cell surface proteins that bind ENDOTHELINS with high affinity and trigger intracellular changes which influence the behavior of cells.Echocardiography: Ultrasonic recording of the size, motion, and composition of the heart and surrounding tissues. The standard approach is transthoracic.Angiotensin II: An octapeptide that is a potent but labile vasoconstrictor. It is produced from angiotensin I after the removal of two amino acids at the C-terminal by ANGIOTENSIN CONVERTING ENZYME. The amino acid in position 5 varies in different species. To block VASOCONSTRICTION and HYPERTENSION effect of angiotensin II, patients are often treated with ACE INHIBITORS or with ANGIOTENSIN II TYPE 1 RECEPTOR BLOCKERS.Capillaries: The minute vessels that connect the arterioles and venules.Portal Pressure: The venous pressure measured in the PORTAL VEIN.Plasma Volume: Volume of PLASMA in the circulation. It is usually measured by INDICATOR DILUTION TECHNIQUES.Cerebral Veins: Veins draining the cerebrum.Vasoconstriction: The physiological narrowing of BLOOD VESSELS by contraction of the VASCULAR SMOOTH MUSCLE.Carotid Artery, Internal: Branch of the common carotid artery which supplies the anterior part of the brain, the eye and its appendages, the forehead and nose.Isotonic Solutions: Solutions having the same osmotic pressure as blood serum, or another solution with which they are compared. (From Grant & Hackh's Chemical Dictionary, 5th ed & Dorland, 28th ed)Hypotension, Controlled: Procedure in which arterial blood pressure is intentionally reduced in order to control blood loss during surgery. This procedure is performed either pharmacologically or by pre-surgical removal of blood.Arterioles: The smallest divisions of the arteries located between the muscular arteries and the capillaries.Sus scrofa: A species of SWINE, in the family Suidae, comprising a number of subspecies including the domestic pig Sus scrofa domestica.Heart Function Tests: Examinations used to diagnose and treat heart conditions.Meclofenamic Acid: A non-steroidal anti-inflammatory agent with antipyretic and antigranulation activities. It also inhibits prostaglandin biosynthesis.Plethysmography: Recording of change in the size of a part as modified by the circulation in it.Lung: Either of the pair of organs occupying the cavity of the thorax that effect the aeration of the blood.Systole: Period of contraction of the HEART, especially of the HEART VENTRICLES.Diastole: Post-systolic relaxation of the HEART, especially the HEART VENTRICLES.Purines: A series of heterocyclic compounds that are variously substituted in nature and are known also as purine bases. They include ADENINE and GUANINE, constituents of nucleic acids, as well as many alkaloids such as CAFFEINE and THEOPHYLLINE. Uric acid is the metabolic end product of purine metabolism.Hyperemia: The presence of an increased amount of blood in a body part or an organ leading to congestion or engorgement of blood vessels. Hyperemia can be due to increase of blood flow into the area (active or arterial), or due to obstruction of outflow of blood from the area (passive or venous).Sheep: Any of the ruminant mammals with curved horns in the genus Ovis, family Bovidae. They possess lachrymal grooves and interdigital glands, which are absent in GOATS.Cardiotonic Agents: Agents that have a strengthening effect on the heart or that can increase cardiac output. They may be CARDIAC GLYCOSIDES; SYMPATHOMIMETICS; or other drugs. They are used after MYOCARDIAL INFARCT; CARDIAC SURGICAL PROCEDURES; in SHOCK; or in congestive heart failure (HEART FAILURE).Ophthalmic Artery: Artery originating from the internal carotid artery and distributing to the eye, orbit and adjacent facial structures.Computer Simulation: Computer-based representation of physical systems and phenomena such as chemical processes.Milrinone: A positive inotropic cardiotonic agent with vasodilator properties. It inhibits cAMP phosphodiesterase type 3 activity in myocardium and vascular smooth muscle. Milrinone is a derivative of amrinone and has 20-30 times the inotropic potency of amrinone.Pressure: 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)Dose-Response Relationship, Drug: The relationship between the dose of an administered drug and the response of the organism to the drug.Vasoconstrictor Agents: Drugs used to cause constriction of the blood vessels.Endothelin-1: A 21-amino acid peptide produced in a variety of tissues including endothelial and vascular smooth-muscle cells, neurons and astrocytes in the central nervous system, and endometrial cells. It acts as a modulator of vasomotor tone, cell proliferation, and hormone production. (N Eng J Med 1995;333(6):356-63)Central Venous Pressure: The blood pressure in the central large VEINS of the body. It is distinguished from peripheral venous pressure which occurs in an extremity.Echocardiography, Doppler: Measurement of intracardiac blood flow using an M-mode and/or two-dimensional (2-D) echocardiogram while simultaneously recording the spectrum of the audible Doppler signal (e.g., velocity, direction, amplitude, intensity, timing) reflected from the moving column of red blood cells.Medetomidine: An agonist of RECEPTORS, ADRENERGIC ALPHA-2 that is used in veterinary medicine for its analgesic and sedative properties. It is the racemate of DEXMEDETOMIDINE.Cyclic Nucleotide Phosphodiesterases, Type 5: A cyclic nucleotide phosphodiesterase subfamily that is highly specific for CYCLIC GMP. It is found predominantly in vascular tissue and plays an important role in regulating VASCULAR SMOOTH MUSCLE contraction.Hypotension, Orthostatic: A significant drop in BLOOD PRESSURE after assuming a standing position. Orthostatic hypotension is a finding, and defined as a 20-mm Hg decrease in systolic pressure or a 10-mm Hg decrease in diastolic pressure 3 minutes after the person has risen from supine to standing. Symptoms generally include DIZZINESS, blurred vision, and SYNCOPE.Angiotensin-Converting Enzyme Inhibitors: A class of drugs whose main indications are the treatment of hypertension and heart failure. They exert their hemodynamic effect mainly by inhibiting the renin-angiotensin system. They also modulate sympathetic nervous system activity and increase prostaglandin synthesis. They cause mainly vasodilation and mild natriuresis without affecting heart rate and contractility.NG-Nitroarginine Methyl Ester: A non-selective inhibitor of nitric oxide synthase. It has been used experimentally to induce hypertension.Sympathetic Nervous System: The thoracolumbar division of the autonomic nervous system. Sympathetic preganglionic fibers originate in neurons of the intermediolateral column of the spinal cord and project to the paravertebral and prevertebral ganglia, which in turn project to target organs. The sympathetic nervous system mediates the body's response to stressful situations, i.e., the fight or flight reactions. It often acts reciprocally to the parasympathetic system.Chronic Disease: Diseases which have one or more of the following characteristics: they are permanent, leave residual disability, are caused by nonreversible pathological alteration, require special training of the patient for rehabilitation, or may be expected to require a long period of supervision, observation, or care. (Dictionary of Health Services Management, 2d ed)Blood Viscosity: The internal resistance of the BLOOD to shear forces. The in vitro measure of whole blood viscosity is of limited clinical utility because it bears little relationship to the actual viscosity within the circulation, but an increase in the viscosity of circulating blood can contribute to morbidity in patients suffering from disorders such as SICKLE CELL ANEMIA and POLYCYTHEMIA.Kidney Function Tests: Laboratory tests used to evaluate how well the kidneys are working through examination of blood and urine.Aorta: The main trunk of the systemic arteries.Rats, Wistar: A strain of albino rat developed at the Wistar Institute that has spread widely at other institutions. This has markedly diluted the original strain.Nitric Oxide Synthase: An NADPH-dependent enzyme that catalyzes the conversion of L-ARGININE and OXYGEN to produce CITRULLINE and NITRIC OXIDE.Venae Cavae: The inferior and superior venae cavae.Ultrasonography, Doppler, Pulsed: Ultrasonography applying the Doppler effect, with velocity detection combined with range discrimination. Short bursts of ultrasound are transmitted at regular intervals and the echoes are demodulated as they return.Analysis of Variance: A statistical technique that isolates and assesses the contributions of categorical independent variables to variation in the mean of a continuous dependent variable.Hypertrophy, Right Ventricular: Enlargement of the RIGHT VENTRICLE of the heart. This increase in ventricular mass is often attributed to PULMONARY HYPERTENSION and is a contributor to cardiovascular morbidity and mortality.Reference Values: The range or frequency distribution of a measurement in a population (of organisms, organs or things) that has not been selected for the presence of disease or abnormality.Plasma Substitutes: Any liquid used to replace blood plasma, usually a saline solution, often with serum albumins, dextrans or other preparations. These substances do not enhance the oxygen- carrying capacity of blood, but merely replace the volume. They are also used to treat dehydration.Vena Cava, Inferior: The venous trunk which receives blood from the lower extremities and from the pelvic and abdominal organs.Rats, Inbred SHR: A strain of Rattus norvegicus with elevated blood pressure used as a model for studying hypertension and stroke.Compliance: Distensibility measure of a chamber such as the lungs (LUNG COMPLIANCE) or bladder. Compliance is expressed as a change in volume per unit change in pressure.Hypertension, Renal: Persistent high BLOOD PRESSURE due to KIDNEY DISEASES, such as those involving the renal parenchyma, the renal vasculature, or tumors that secrete RENIN.Random Allocation: A process involving chance used in therapeutic trials or other research endeavor for allocating experimental subjects, human or animal, between treatment and control groups, or among treatment groups. It may also apply to experiments on inanimate objects.Fentanyl: A potent narcotic analgesic, abuse of which leads to habituation or addiction. It is primarily a mu-opioid agonist. Fentanyl is also used as an adjunct to general anesthetics, and as an anesthetic for induction and maintenance. (From Martindale, The Extra Pharmacopoeia, 30th ed, p1078)Heart Defects, Congenital: Developmental abnormalities involving structures of the heart. These defects are present at birth but may be discovered later in life.Femoral Vein: The vein accompanying the femoral artery in the same sheath; it is a continuation of the popliteal vein and becomes the external iliac vein.Cardiac Pacing, Artificial: Regulation of the rate of contraction of the heart muscles by an artificial pacemaker.Liver Cirrhosis: Liver disease in which the normal microcirculation, the gross vascular anatomy, and the hepatic architecture have been variably destroyed and altered with fibrous septa surrounding regenerated or regenerating parenchymal nodules.Sodium: A member of the alkali group of metals. It has the atomic symbol Na, atomic number 11, and atomic weight 23.Venous Insufficiency: Impaired venous blood flow or venous return (venous stasis), usually caused by inadequate venous valves. Venous insufficiency often occurs in the legs, and is associated with EDEMA and sometimes with VENOUS STASIS ULCERS at the ankle.Hemoglobins: The oxygen-carrying proteins of ERYTHROCYTES. They are found in all vertebrates and some invertebrates. The number of globin subunits in the hemoglobin quaternary structure differs between species. Structures range from monomeric to a variety of multimeric arrangements.Collateral Circulation: Maintenance of blood flow to an organ despite obstruction of a principal vessel. Blood flow is maintained through small vessels.Models, Anatomic: Three-dimensional representation to show anatomic structures. Models may be used in place of intact animals or organisms for teaching, practice, and study.Shock, Septic: Sepsis associated with HYPOTENSION or hypoperfusion despite adequate fluid resuscitation. Perfusion abnormalities may include, but are not limited to LACTIC ACIDOSIS; OLIGURIA; or acute alteration in mental status.Cardiovascular Physiological Phenomena: Processes and properties of the CARDIOVASCULAR SYSTEM as a whole or of any of its parts.Cardiovascular System: The HEART and the BLOOD VESSELS by which BLOOD is pumped and circulated through the body.Magnetic Resonance Imaging: Non-invasive method of demonstrating internal anatomy based on the principle that atomic nuclei in a strong magnetic field absorb pulses of radiofrequency energy and emit them as radiowaves which can be reconstructed into computerized images. The concept includes proton spin tomographic techniques.Enalapril: An angiotensin-converting enzyme inhibitor that is used to treat HYPERTENSION and HEART FAILURE.Pulmonary Edema: Excessive accumulation of extravascular fluid in the lung, an indication of a serious underlying disease or disorder. Pulmonary edema prevents efficient PULMONARY GAS EXCHANGE in the PULMONARY ALVEOLI, and can be life-threatening.Anesthesia, IntratrachealPartial Pressure: The pressure that would be exerted by one component of a mixture of gases if it were present alone in a container. (From McGraw-Hill Dictionary of Scientific and Technical Terms, 6th ed)Prostaglandins: A group of compounds derived from unsaturated 20-carbon fatty acids, primarily arachidonic acid, via the cyclooxygenase pathway. They are extremely potent mediators of a diverse group of physiological processes.TetrazolesPhenylpropionatesAortic Valve Stenosis: A pathological constriction that can occur above (supravalvular stenosis), below (subvalvular stenosis), or at the AORTIC VALVE. It is characterized by restricted outflow from the LEFT VENTRICLE into the AORTA.Ritodrine: An adrenergic beta-2 agonist used to control PREMATURE LABOR.Receptor, Endothelin A: A subtype of endothelin receptor found predominantly in the VASCULAR SMOOTH MUSCLE. It has a high affinity for ENDOTHELIN-1 and ENDOTHELIN-2.Rheology: 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.Rest: Freedom from activity.Ventricular Remodeling: The geometric and structural changes that the HEART VENTRICLES undergo, usually following MYOCARDIAL INFARCTION. It comprises expansion of the infarct and dilatation of the healthy ventricle segments. While most prevalent in the left ventricle, it can also occur in the right ventricle.Hepatic Veins: Veins which drain the liver.Teprotide: A synthetic nonapeptide (Pyr-Trp-Pro-Arg-Pro-Gln-Ile-Pro-Pro) which is identical to the peptide from the venom of the snake, Bothrops jararaca. It inhibits kininase II and ANGIOTENSIN I and has been proposed as an antihypertensive agent.Retinal Vessels: The blood vessels which supply and drain the RETINA.Anoxia: Relatively complete absence of oxygen in one or more tissues.Brain: The part of CENTRAL NERVOUS SYSTEM that is contained within the skull (CRANIUM). Arising from the NEURAL TUBE, the embryonic brain is comprised of three major parts including PROSENCEPHALON (the forebrain); MESENCEPHALON (the midbrain); and RHOMBENCEPHALON (the hindbrain). The developed brain consists of CEREBRUM; CEREBELLUM; and other structures in the BRAIN STEM.Anesthesia, General: Procedure in which patients are induced into an unconscious state through use of various medications so that they do not feel pain during surgery.Angiotensin Receptor Antagonists: Agents that antagonize ANGIOTENSIN RECEPTORS. Many drugs in this class specifically target the ANGIOTENSIN TYPE 1 RECEPTOR.Heart-Assist Devices: 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.Respiratory Physiological Processes: Biological actions and events that support the functions of the RESPIRATORY SYSTEM.Phosphodiesterase Inhibitors: Compounds which inhibit or antagonize the biosynthesis or actions of phosphodiesterases.Aortic Valve: The valve between the left ventricle and the ascending aorta which prevents backflow into the left ventricle.Lypressin: The porcine antidiuretic hormone (VASOPRESSINS). It is a cyclic nonapeptide that differs from ARG-VASOPRESSIN by one amino acid, containing a LYSINE at residue 8 instead of an ARGININE. Lys-vasopressin is used to treat DIABETES INSIPIDUS or to improve vasomotor tone and BLOOD PRESSURE.Natriuretic Agents: Endogenous or exogenous chemicals that regulate the WATER-ELECTROLYTE BALANCE in the body. They consist of peptides and non-peptide compounds.Double-Blind Method: A method of studying a drug or procedure in which both the subjects and investigators are kept unaware of who is actually getting which specific treatment.Cardiopulmonary Bypass: Diversion of the flow of blood from the entrance of the right atrium directly to the aorta (or femoral artery) via an oxygenator thus bypassing both the heart and lungs.Sodium Chloride: A ubiquitous sodium salt that is commonly used to season food.Sulfonamides: A group of compounds that contain the structure SO2NH2.Carotid Stenosis: Narrowing or stricture of any part of the CAROTID ARTERIES, most often due to atherosclerotic plaque formation. Ulcerations may form in atherosclerotic plaques and induce THROMBUS formation. Platelet or cholesterol emboli may arise from stenotic carotid lesions and induce a TRANSIENT ISCHEMIC ATTACK; CEREBROVASCULAR ACCIDENT; or temporary blindness (AMAUROSIS FUGAX). (From Adams et al., Principles of Neurology, 6th ed, pp 822-3)Retinal Artery: Central retinal artery and its branches. It arises from the ophthalmic artery, pierces the optic nerve and runs through its center, enters the eye through the porus opticus and branches to supply the retina.Prostaglandin Antagonists: Compounds that inhibit the action of prostaglandins.Hypertension, Renovascular: Hypertension due to RENAL ARTERY OBSTRUCTION or compression.Carotid Arteries: 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.Hemofiltration: Extracorporeal ULTRAFILTRATION technique without HEMODIALYSIS for treatment of fluid overload and electrolyte disturbances affecting renal, cardiac, or pulmonary function.omega-N-Methylarginine: A competitive inhibitor of nitric oxide synthetase.