pressure
force per unit area; the SI unit is the pascal.
abdominal pressure, intra-abdominal p.
after pressure, a sense of pressure that lasts for a short period after removal of the actual pressure.
alveolar pressure, the pressure exerted by the air in the pulmonary alveoli.
arterial pressure, arterial blood pressure, blood p. (def. 2).
atmospheric pressure, the pressure exerted by the atmosphere, usually considered as the downward pressure of air onto a unit of area of the earth's surface; the unit of pressure at sea level is one atmosphere. Pressure decreases with increasing altitude. See also atmosphere (def. 2).
back pressure, the pressure caused by the damming back of the blood in a heart chamber and its tributaries, due to an obstructive heart valve or failing myocardium.
barometric pressure, atmospheric p.
biting pressure, occlusal p.
bladder pressure, intravesical p.
blood pressure, the pressure of blood against the walls of any blood vessel.the pressure of the blood on the walls of the arteries, dependent on the energy of the heart action, the elasticity of the walls of the arteries, and the volume and viscosity of the blood. The maximum or systolic blood pressure occurs near the end of the stroke output of the left ventricle of the heart. The minimum or diastolic blood pressure occurs late in ventricular diastole. Mean blood pressure is the average of the blood pressure levels, and basic blood pressure is that during quiet rest or basal conditions. See also hypertension and hypotension.
capillary pressure, the blood pressure in the capillaries.
central venous pressure, the venous pressure as measured at the right atrium, obtained by means of a central venous catheter whose distal end is attached to a manometer.
cerebral perfusion pressure, the difference between the mean arterial pressure and the intracranial pressure, normally 70–95 mm Hg.
cerebrospinal pressure, the pressure or tension of the cerebrospinal fluid, normally 100–150 mm Hg as measured by the manometer.
continuous positive airway pressure, a method of positive pressure ventilation used with patients who are breathing spontaneously, in which pressure in the airway is maintained above the level of atmospheric pressure throughout the respiratory cycle. The purpose is to keep the alveoli open at the end of exhalation and thus increase oxygenation and reduce the work of breathing. Cf. positive end-expiratory p.
critical pressure, the smallest amount of pressure necessary to liquefy a gas at the critical temperature.
detrusor pressure, the pressure exerted inward by the detrusor urinae muscles of the bladder wall, one of the components of the total intravesical pressure.
detrusor leak point pressure, as the bladder fills without an increase in abdominal pressure, the level of pressure at which leakage of urine through the urethra occurs; this is a measure of both strength of the urethral sphincters and compliance of the detrusor urinae muscle.
diastolic pressure, diastolic blood pressure, see blood p.
Donders pressure, increase of manometric pressure with the instrument placed on the trachea on opening the chest of a dead body; due to collapse of the lung.
end-diastolic pressure, the pressure in the ventricles of the heart at the end of diastole, usually measured in the left ventricle as an approximation of the end-diastolic volume, or preload.
endocardial pressure, pressure of blood within the heart.
filling pressure, see mean circulatory filling p.
hydrostatic pressure, the pressure at any level in fluid at rest due solely to the weight of the fluid above it.
intra-abdominal pressure, the pressure between the viscera within the abdominal cavity. Called also abdominal p.
intracranial pressure, the pressure in the space between the skull and the brain, i.e., the pressure of the subarachnoidal fluid.
intraocular pressure, the pressure of the fluids of the eye against the tunics. It is produced by continual renewal of the fluids within the interior of the eye, and is altered in certain pathological conditions (e.g., glaucoma). It may be roughly estimated by palpation of the eye or measured, directly or indirectly, with specially devised instruments called tonometers. Normal intraocular pressure is symbolized Tn. Called also intraocular tension.
intrapleural pressure, pleural p.
intrathecal pressure, pressure within a sheath, particularly the pressure of the cerebrospinal fluid within the subarachnoid membrane.
intrathoracic pressure, pleural p.
intraventricular pressure, the pressure within one ventricle of the heart.
intravesical pressure, the pressure exerted on the contents of the urinary bladder, being the sum of the intra-abdominal pressure from outside the bladder and the detrusor pressure exerted by the bladder wall musculature itself. Called also bladder p. and vesical p.
leak point pressure, as the bladder fills, the pressure at which leakage occurs through the urethra, used as a measure of strength of the urethral sphincters. See detrusor leak point p. and Valsalva leak point p.
maximum expiratory pressure, a measure of the strength of respiratory muscles, obtained by having the patient exhale as strongly as possible against a mouthpiece; the maximum value is near total lung capacity.
maximum inspiratory pressure, a measure of the strength of respiratory muscles, obtained by having the patient inhale as strongly as possible with the mouth against a mouthpiece; the maximum value is near the residual volume.
mean arterial pressure, the average pressure within an artery over a complete cycle of one heartbeat; in the brachial artery,
MAP=
systolic pressure - diastolic pressure
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mean circulatory filling pressure, a measure of the average (arterial and venous) pressure necessary to cause filling of the circulation with blood; it varies with blood volume and is directly proportional to the rate of venous return and thus to cardiac output.
negative pressure, a pressure less than that of the atmosphere.
occlusal pressure, pressure exerted on the occlusal surfaces of the teeth when the jaws are brought into apposition. Called also biting p.
oncotic pressure, the osmotic pressure due to the presence of colloids in a solution; in the case of plasma–interstitial fluid interaction, it is the force that tends to counterbalance the capillary pressure.
osmotic pressure, the pressure required to stop osmosis through a semipermeable membrane between a solution and pure solvent; it is proportional to the osmolality of the solution and also to other colligative properties of the solution, including freezing point depression, vapor pressure depression, and boiling point elevation. Symbol π.
osmotic pressure, effective, that part of the total osmotic pressure of a solution that governs the tendency of its solvent to pass through a bordering semipermeable membrane or across another boundary.
partial pressure, the pressure exerted by each of the components of a gas mixture, such as of gases in the blood.
perfusion pressure, the difference between the arterial and venous pressures through an organ or capillary bed.
pleural pressure, the pressure between the visceral pleura and the parietal pleura in the pleural cavity. Called also intrapleural or intrathoracic p.
positive pressure, pressure greater than that of the atmosphere.
positive end-expiratory pressure, a method of positive pressure ventilation used in conjunction with mechanical ventilation; pressure is maintained above the level of atmospheric pressure at the end of exhalation. This is achieved by preventing the complete release of gas during exhalation, usually by means of a valve within the circuit. The purpose is to increase the volume of gas remaining in the lungs at the end of exhalation, thus reducing the shunting of blood through the lungs and improving gas exchange; done in acute respiratory failure to allow reduction of inspired O2 concentrations. Cf. continuous positive airway p.
pulmonary artery wedge pressure, pulmonary capillary wedge pressure, blood pressure measured by a catheter wedged into the distal pulmonary artery; it permits indirect measurement of the mean blood pressure in the left atrium.
pulse pressure, the difference between the systolic and diastolic blood pressures.
selection pressure, an effect produced by a given gene that determines the frequency of a given allele; it may be advantageous for survival (positive selection pressure) or disadvantageous (negative selection pressure).
solution pressure, the force that tends to bring into solution the molecules of a solid contained in the solvent.
systolic pressure, systolic blood pressure, see blood p.
transpulmonary pressure, the pressure difference between the inner and outer surfaces of the lung, i.e., the pressure tending to inflate or deflate the lungs; equal to the difference between the alveolar pressure and the pleural pressure.
urethral pressure, the inward pressure exerted by the walls of the urethra, which must be counteracted in order for urine to flow through; see also under profile.
Valsalva leak point pressure, the amount of pressure on the bladder by a Valsalva maneuver at which leakage of urine from the urethra occurs; this is a measure of strength of the urethral sphincters.
venous pressure, the blood pressure in a vein, such as central venous pressure or wedged hepatic vein pressure.
vesical pressure, intravesical p.
wedge pressure, blood pressure measured by a small catheter wedged into a vessel, occluding it; see pulmonary capillary wedge p. and wedged hepatic vein p.
wedged hepatic vein pressure, the venous pressure measured with a catheter wedged into the hepatic vein. The difference between wedged and free hepatic vein pressures is used to locate the site of obstruction in portal hypertension; it is elevated in that due to cirrhosis but low in cardiac ascites or portal vein thrombosis.