partial pressure

pressure /pres·sure/ (P ) (presh´er) force per unit area.

arterial pressure blood p. (2).

blood pressure

1. the pressure of blood against the walls of any blood vessel.

2. the pressure of blood on the walls of the arteries, dependent on the energy of the heart action, elasticity of the arterial walls, and volume and viscosity of the blood; the maximum or systolic pressure occurs near the end of the stroke output of the left ventricle, and the minimum or diastolic late in ventricular diastole.

central venous pressure (CVP) the venous pressure as measured at the right atrium, done by means of a catheter introduced through the median cubital vein to the superior vena cava.

cerebrospinal pressure the pressure or tension of the cerebrospinal fluid, normally 100–150 mm. as measured by the manometer.

detrusor pressure the pressure exerted inwards by the detrusor urinae muscles of the bladder wall.

diastolic pressure , diastolic blood pressure see blood p.

end-diastolic pressure the pressure in the ventricles at the end of diastole, usually measured in the left ventricle as an approximation of the end-diastolic volume, or preload.

intracranial pressure (ICP) pressure of the subarachnoidal fluid.

intraocular pressure the pressure exerted against the outer coats by the contents of the eyeball.

intravesical pressure the pressure exerted on the contents of the urinary bladder; the sum of the intra-abdominal pressure from outside the bladder and the detrusor pressure.

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) 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 (MAP) the average pressure within an artery over a complete cycle of one heartbeat.

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 due to the presence of colloids in solution.

osmotic pressure the pressure required to prevent 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.

positive pressure pressure greater than that of the atmosphere.

positive end-expiratory pressure (PEEP) a method of mechanical ventilation in which pressure is maintained to increase the volume of gas left in the lungs at the end of exhalation, reducing shunting of blood through the lungs and improving gas exchange.

pulmonary artery wedge pressure (PAWP), pulmonary capillary wedge pressure (PCWP) intravascular pressure as measured by a catheter wedged into the distal pulmonary artery ; used to measure indirectly the mean left atrial pressure.

pulse pressure the difference between systolic and diastolic pressures.

systolic pressure , systolic blood pressure see blood p.

Valsalva leak point pressure the amount of pressure on the bladder by a Valsalva maneuver at which leakage of urine occurs; a measure of strength of the urethral sphincters.

venous pressure the pressure of blood in the veins.

wedge pressure blood pressure measured by a small catheter wedged into a vessel, occluding it, e.g., pulmonary capillary wedge p.

wedged hepatic vein pressure the venous pressure measured with a catheter wedged into the hepatic vein; used to locate the site of obstruction in portal hypertension.

partial pressure

The pressure that one component of a mixture of gases would exert if it were alone in a container.

Partial pressure

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 pressure,

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).

pressure (P) [presh´ur]

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.

blood pressure

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 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.

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.

Effects of the application of positive end-expiratory pressure (PEEP) on the alveoli. A, Atelectatic alveoli before PEEP application. B, Optimal PEEP application has reinflated alveoli to normal volume. C, Excessive PEEP application overdistends the alveoli and compresses adjacent pulmonary capillaries, creating dead space with its attendant hypercapnia. From Pierce, 1995.

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