Lower Body Negative Pressure: External decompression applied to the lower body. It is used to study orthostatic intolerance and the effects of gravitation and acceleration, to produce simulated hemorrhage in physiologic research, to assess cardiovascular function, and to reduce abdominal stress during childbirth.Hypovolemia: An abnormally low volume of blood circulating through the body. It may result in hypovolemic shock (see SHOCK).Forearm: Part of the arm in humans and primates extending from the ELBOW to the WRIST.Head-Down Tilt: Posture while lying with the head lower than the rest of the body. Extended time in this position is associated with temporary physiologic disturbances.Bed Rest: Confinement of an individual to bed for therapeutic or experimental reasons.Orthostatic Intolerance: Symptoms of cerebral hypoperfusion or autonomic overaction which develop while the subject is standing, but are relieved on recumbency. Types of this include NEUROCARDIOGENIC SYNCOPE; POSTURAL ORTHOSTATIC TACHYCARDIA SYNDROME; and neurogenic ORTHOSTATIC HYPOTENSION. (From Noseworthy, JH., Neurological Therapeutics Principles and Practice, 2007, p2575-2576)Vascular Capacitance: The measure of a BLOOD VESSEL's ability to increase the volume of BLOOD it holds without a large increase in BLOOD PRESSURE. The vascular capacitance is equal to the change in volume divided by the change in pressure.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.Dizziness: An imprecise term which may refer to a sense of spatial disorientation, motion of the environment, or lightheadedness.Blood Pressure: PRESSURE of the BLOOD on the ARTERIES and other BLOOD VESSELS.Pressoreceptors: Receptors in the vascular system, particularly the aorta and carotid sinus, which are sensitive to stretch of the vessel walls.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.Cardiovascular Deconditioning: A change in cardiovascular function resulting in a reduction in BLOOD VOLUME, and reflex DIURESIS. It occurs frequently after actual or simulated WEIGHTLESSNESS.Baroreflex: A response by the BARORECEPTORS to increased BLOOD PRESSURE. Increased pressure stretches BLOOD VESSELS which activates the baroreceptors in the vessel walls. The net response of the CENTRAL NERVOUS SYSTEM is a reduction of central sympathetic outflow. This reduces blood pressure both by decreasing peripheral VASCULAR RESISTANCE and by lowering CARDIAC OUTPUT. Because the baroreceptors are tonically active, the baroreflex can compensate rapidly for both increases and decreases in blood pressure.Heart Rate: The number of times the HEART VENTRICLES contract per unit of time, usually per minute.Gravity Suits: Double-layered inflatable suits which, when inflated, exert pressure on the lower part of the wearer's body. The suits are used to improve or stabilize the circulatory state, i.e., to prevent hypotension, control hemorrhage, and regulate blood pressure. The suits are also used by pilots under positive acceleration.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.Supine Position: The posture of an individual lying face up.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.Weightlessness Simulation: Condition under normal Earth gravity where the force of gravity itself is not actually altered but its influence or effect may be modified and studied. (From ASGSB Bull 1992;5(2):27)Weightlessness Countermeasures: Techniques and routines designed to prevent or reverse unwanted effects of weightlessness experienced during actual and simulated space flight, including physiologic changes related to removal of gravitational loading. Specific measures include creation of artificial gravity, exercise, low-level lower body negative pressure, and use of anti-deconditioning devices. (From Nicogossian, Space Physiology and Medicine, 2d ed, pp294-297)Space Flight: Travel beyond the earth's atmosphere.Regional Blood Flow: The flow of BLOOD through or around an organ or region of the body.Reflex: An involuntary movement or exercise of function in a part, excited in response to a stimulus applied to the periphery and transmitted to the brain or spinal cord.Syncope: A transient loss of consciousness and postural tone caused by diminished blood flow to the brain (i.e., BRAIN ISCHEMIA). Presyncope refers to the sensation of lightheadedness and loss of strength that precedes a syncopal event or accompanies an incomplete syncope. (From Adams et al., Principles of Neurology, 6th ed, pp367-9)Negative-Pressure Wound Therapy: The application of a vacuum across the surface of a wound through a foam dressing cut to fit the wound. This removes wound exudates, reduces build-up of inflammatory mediators, and increases the flow of nutrients to the wound thus promoting healing.Plethysmography: Recording of change in the size of a part as modified by the circulation in it.Ventilators, Negative-Pressure: Body ventilators that assist ventilation by applying intermittent subatmospheric pressure around the thorax, abdomen, or airway and periodically expand the chest wall and inflate the lungs. They are relatively simple to operate and do not require tracheostomy. These devices include the tank ventilators ("iron lung"), Portalung, Pneumowrap, and chest cuirass ("tortoise shell").Vasoconstriction: The physiological narrowing of BLOOD VESSELS by contraction of the VASCULAR SMOOTH MUSCLE.Tilt-Table Test: A standard and widely accepted diagnostic test used to identify patients who have a vasodepressive and/or cardioinhibitory response as a cause of syncope. (From Braunwald, Heart Disease, 7th ed)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)Hemodynamics: The movement and the forces involved in the movement of the blood through the CARDIOVASCULAR SYSTEM.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.Blood Volume: Volume of circulating BLOOD. It is the sum of the PLASMA VOLUME and ERYTHROCYTE VOLUME.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.Gravitation: Acceleration produced by the mutual attraction of two masses, and of magnitude inversely proportional to the square of the distance between the two centers of mass. It is also the force imparted by the earth, moon, or a planet to an object near its surface. (From NASA Thesaurus, 1988)Leg: The inferior part of the lower extremity between the KNEE and the ANKLE.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).Weightlessness: Condition in which no acceleration, whether due to gravity or any other force, can be detected by an observer within a system. It also means the absence of weight or the absence of the force of gravity acting on a body. Microgravity, gravitational force between 0 and 10 -6 g, is included here. (From NASA Thesaurus, 1988)Posture: The position or attitude of the body.Blood Flow Velocity: A value equal to the total volume flow divided by the cross-sectional area of the vascular bed.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.Vasomotor System: The neural systems which act on VASCULAR SMOOTH MUSCLE to control blood vessel diameter. The major neural control is through the sympathetic nervous system.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.Cold Temperature: An absence of warmth or heat or a temperature notably below an accustomed norm.Veins: The vessels carrying blood away from the capillary beds.Skin Temperature: The TEMPERATURE at the outer surface of the body.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.Pelvis: The space or compartment surrounded by the pelvic girdle (bony pelvis). It is subdivided into the greater pelvis and LESSER PELVIS. The pelvic girdle is formed by the PELVIC BONES and SACRUM.Autonomic Nervous System: The ENTERIC NERVOUS SYSTEM; PARASYMPATHETIC NERVOUS SYSTEM; and SYMPATHETIC NERVOUS SYSTEM taken together. Generally speaking, the autonomic nervous system regulates the internal environment during both peaceful activity and physical or emotional stress. Autonomic activity is controlled and integrated by the CENTRAL NERVOUS SYSTEM, especially the HYPOTHALAMUS and the SOLITARY NUCLEUS, which receive information relayed from VISCERAL AFFERENTS.Hand Strength: Force exerted when gripping or grasping.Cardiovascular Physiological Phenomena: Processes and properties of the CARDIOVASCULAR SYSTEM as a whole or of any of its parts.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.Rest: Freedom from activity.Exercise: Physical activity which is usually regular and done with the intention of improving or maintaining PHYSICAL FITNESS or HEALTH. Contrast with PHYSICAL EXERTION which is concerned largely with the physiologic and metabolic response to energy expenditure.Brachial Artery: The continuation of the axillary artery; it branches into the radial and ulnar arteries.Muscle, Skeletal: A subtype of striated muscle, attached by TENDONS to the SKELETON. Skeletal muscles are innervated and their movement can be consciously controlled. They are also called voluntary muscles.Stress, Physiological: The unfavorable effect of environmental factors (stressors) on the physiological functions of an organism. Prolonged unresolved physiological stress can affect HOMEOSTASIS of the organism, and may lead to damaging or pathological conditions.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.Cerebrovascular Circulation: The circulation of blood through the BLOOD VESSELS of the BRAIN.Time Factors: Elements of limited time intervals, contributing to particular results or situations.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)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.Epinephrine: The active sympathomimetic hormone from the ADRENAL MEDULLA. It stimulates both the alpha- and beta- adrenergic systems, causes systemic VASOCONSTRICTION and gastrointestinal relaxation, stimulates the HEART, and dilates BRONCHI and cerebral vessels. It is used in ASTHMA and CARDIAC FAILURE and to delay absorption of local ANESTHETICS.Skin: The outer covering of the body that protects it from the environment. It is composed of the DERMIS and the EPIDERMIS.Muscles: Contractile tissue that produces movement in animals.Air Pressure: The force per unit area that the air exerts on any surface in contact with it. Primarily used for articles pertaining to air pressure within a closed environment.Electrocardiography: Recording of the moment-to-moment electromotive forces of the HEART as projected onto various sites on the body's surface, delineated as a scalar function of time. The recording is monitored by a tracing on slow moving chart paper or by observing it on a cardioscope, which is a CATHODE RAY TUBE DISPLAY.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.Heart: The hollow, muscular organ that maintains the circulation of the blood.Suction: The removal of secretions, gas or fluid from hollow or tubular organs or cavities by means of a tube and a device that acts on negative pressure.Abdominal Wound Closure Techniques: Methods to repair breaks in abdominal tissues caused by trauma or to close surgical incisions during abdominal surgery.Skin Care: Maintenance of the hygienic state of the skin under optimal conditions of cleanliness and comfort. Effective in skin care are proper washing, bathing, cleansing, and the use of soaps, detergents, oils, etc. In various disease states, therapeutic and protective solutions and ointments are useful. The care of the skin is particularly important in various occupations, in exposure to sunlight, in neonates, and in PRESSURE ULCER.