partial pressure(redirected from gas pressure)
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force per unit area.
arterial pressure (arterial blood pressure) blood pressure (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.
barometric pressure atmospheric p.
1. see blood pressure.
2. pressure of blood on walls of any blood vessel.
capillary pressure the blood pressure in the capillaries.
central venous pressure see central venous pressure.
cerebral perfusion pressure the mean arterial pressure minus the intracranial pressure; a measure of the adequacy of cerebral blood flow.
cerebrospinal pressure the pressure of the cerebrospinal fluid, normally 100 to 150 mm Hg.
continuous positive airway pressure see continuous positive airway pressure.
filling pressure see mean circulatory filling pressure.
high blood pressure hypertension.
intracranial pressure see intracranial pressure.
intraocular pressure the pressure exerted against the outer coats by the contents of the eyeball.
intrapleural pressure (intrathoracic pressure) pleural pressure.
intrinsic positive end-expiratory pressure elevated positive end-expiratory pressure and dynamic pulmonary hyperinflation caused by insufficient expiratory time or a limitation on expiratory flow. It cannot be routinely measured by a ventilator's pressure monitoring system but is measurable only using an expiratory hold maneuver done by the clinician. Its presence increases the work needed to trigger the ventilator, causes errors in the calculation of pulmonary compliance, may cause hemodynamic compromise, and complicates interpretation of hemodynamic measurements. Called also auto-PEEP and intrinsic PEEP.
maximal expiratory pressure maximum expiratory pressure.
maximal inspiratory pressure the pressure during inhalation against a completely occluded airway; used to evaluate inspiratory respiratory muscle strength and readiness for weaning from mechanical ventilation. A maximum inspiratory pressure above −25 cm H2O is associated with successful weaning.
maximum expiratory pressure (MEP) 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 (MIP) the inspiratory pressure generated against a completely occluded airway; used to evaluate inspiratory respiratory muscle strength and readiness for weaning from mechanical ventilation. A maximum inspiratory pressure above −25 cm H2O is associated with successful weaning.
mean airway pressure the average pressure generated during the respiratory cycle.
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 pressure less than that of the atmosphere.
oncotic pressure the osmotic pressure of a colloid in solution.
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. Symbol π.
partial pressure the pressure exerted by each of the constituents of a mixture of gases.
peak pressure in mechanical ventilation, the highest pressure that occurs during inhalation.
plateau pressure in mechanical ventilation, the pressure measured at the proximal airway during an end-inspiratory pause; a reflection of alveolar pressure.
pleural pressure the pressure between the visceral pleura and the thoracic pleura in the pleural cavity. Called also intrapleural or intrathoracic pressure.
positive pressure pressure greater than that of the atmosphere.
positive end-expiratory pressure (PEEP) a method of control mode ventilation in which positive pressure is maintained during expiration to increase the volume of gas remaining in the lungs at the end of expiration, thus reducing the shunting of blood through the lungs and improving gas exchange. A PEEP higher than the critical closing pressure prevents alveolar collapse and can markedly improve the arterial Po2 in patients with a lowered functional residual capacity, as in acute respiratory failure.
pulmonary artery wedge pressure (PAWP) (pulmonary capillary wedge pressure (PCWP)) intravascular pressure, reflecting the left ventricular end diastolic pressure, measured by a swan-ganz catheter wedged into a small pulmonary artery to block the flow from behind.
pulse pressure the difference between the systolic and diastolic pressures. If the systolic pressure is 120 mm Hg and the diastolic pressure is 80 mm Hg, the pulse pressure is 40 mm Hg; the normal pulse pressure is between 30 and 40 mm Hg.
urethral pressure the pressure inwards exerted by the walls of the urethra, which must be counteracted in order for urine to flow through; see also urethral pressure profile.
venous pressure the blood pressure in the veins; see also central venous pressure.
water vapor pressure the tension exerted by water vapor molecules, 47 mm Hg at normal body temperature.
wedge pressure blood pressure measured by a small catheter wedged into a vessel, occluding it; see also pulmonary capillary wedge pressure and wedged hepatic vein pressure.
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.
par·tial pres·sure (P),
the pressure exerted by a single component of a mixture of gases, commonly expressed in mm Hg or torr; for a gas dissolved in a liquid, the partial pressure is that of a gas that would be in equilibrium with the dissolved gas. Formerly, symbolized by p, followed by the chemical symbol in capital letters (for example, pCO2, pO2); now, in respiratory physiology, P, followed by subscripts denoting location and/or chemical species (for example, Pco2, Po2, Paco2.
the pressure exerted by any one gas in a mixture of gases or in a liquid, with the pressure directly related to the concentration of that gas to the total pressure of the mixture. The concentration of oxygen in the atmosphere represents approximately 21% of the total atmospheric pressure, calculated at 760 mm Hg under standard conditions. Therefore, the partial pressure of atmospheric oxygen is about 160 mm Hg (760 mm Hg × 0.21).
par·tial pres·sure(pahr'shăl presh'ŭr)
The pressure exerted by a single component of a mixture of gases, commonly expressed in mm/Hg or torr; for a gas dissolved in a liquid, the partial pressure is that of a gas that would be in equilibrium with the dissolved gas. In respiratory physiology, symbolized by P, followed by subscripts denoting location and/or chemical species (e.g., PCO2, PO2, PaCO2).
partial pressurethe total pressure of the mixture of gases within which a gas occurs, multiplied by the percentage of the total volume the gas occupies. Thus if the normal total pressure of the atmospheric gases is 760 mm Hg and there is 21% oxygen in this mixture, the partial pressure of O2 is: 760×0.21 = 160 mm Hg.
The pressure exerted by one of the gases in a mixture of gases. The partial pressure of the gas is proportional to its concentration in the mixture. The total pressure of the gas mixture is the sum of the partial pressures of the gases in it (Dalton's Law) and as the total pressure increases, each partial pressure increases proportionally.
Mentioned in: Nitrogen Narcosis
partial pressurethe component of the total gas pressure accounted for by one gas in a mixture of gases, e.g. in air at 1 standard atmosphere (1 bar, ∼101 kPa, 760 mmHg or torr), 21% is oxygen and the partial pressure of oxygen ( P O2) is ∼21 kPa or 160 mmHg (torr). Partial pressure ( syn tension) of a gas dissolved in a liquid is defined as the partial pressure of that gas in the gaseous phase with which the liquid is, has been or would be, in equilibrium. So, given near-perfect diffusion equilibrium across the alveolar-capillary membranes, blood leaves the lungs with virtually the same P O2 and P CO2 as in alveolar gas (normally close to 100 mmHg P O2 and 40 mmHg P CO2). When blood reaches capillaries in active tissues, the lower P O2 and higher P CO2 in tissue fluids cause net molecular movement towards equilibrium, so that O2 is removed from the blood and CO2 taken up. See also carbon dioxide, diffusing capacity, gas exchange, nitrogen, oxygen, oxyhaemoglobin dissociation curve.
par·tial pres·sure(pahr'shăl presh'ŭr)
The pressure exerted by a single component of a mixture of gases, commonly expressed in mm/Hg or torr.
pertaining to or having the characteristics of a part of something.
see partial budget.
the pressure exerted by a specific gas in a mixture of gases. Because the amount of the gas dissolved in a liquid is proportional to the pressure of the gas on the fluid the concentration of a gas in a fluid is expressed as its partial pressure.
partial thromboplastin time (PTT)
see activated partial thromboplastin time.