partial pressure

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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
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.
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.
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.

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 pressure

the 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.

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

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.
References in periodicals archive ?
The differences between total and partial pressure always need to be kept in mind, and this is especially important for cross-communication between vacuum practitioners.
However, negligible equilibrium effects were observed from the hydrogenation data leading to the following assumptions for developing the final kinetic model: (1) the surface reaction was rate limiting; (2) reaction is pseudo first order in the forward reaction; (3) the reaction occurred in a plug flow regime with negligible diffusion and mass transfer effects; (4) reaction occurred in excess amounts of hydrogen at constant partial pressure; (5) hydrogenation is inhibited by hydrogen sulphide that is produced from the HDS process and [H.sub.2]S is an ideal gas.
The pressure gradient for oxygen diffusion begins to establish itself when atmospheric air with a partial pressure of oxygen of 159 torr (i.e., [760 torr - 0 torr P[H.sub.2]O] 0.2093) enters the upper airway.
The small changes in real total or partial pressures that are hidden within gauge and RGA readouts that are statistical averages of the gas concentration within a chamber can be analyzed to some extent.
A gas load of this magnitude would require a pumping speed of 100 L/sec just to maintain a partial pressure of 1 x [10.sup.-7] torr of the gas emanating from the fingerprint.
On the other hand, CIS gas analyzers have a higher pressure limit of operation, but this is achieved at the cost of an increased minimal detectable partial pressure level relative to an OIS PPR.
Residual gas analysis revealed water vapor partial pressure reduction of more than 80% during subsequent deposition.
This provides for trace analysis; detection of positive and negative ions, as well as neutral particles; ultrasensitive leak testing; and partial pressure measurement down to <2 x [10.sup.-16] mbar.
* Partial pressures in the |10.sup.-10~ and |10.sup.-11~ torr range could be measured repeatedly while monitoring argon at a process pressure of 2 x |10.sup.-3~ torr.
Respiration rate in the fruits stored at 10[degrees]C was higher than that of the fruits stored at 0 and 5[degrees]C (Table 1), which may explain the difference in partial pressures of [O.sub.2] and C[O.sub.2] on the packs.
Increasing levels of backpressure resulted in increases in the exchange current densities of the electrochemical reactions, with the increase in the reactant partial pressures and determine an enhancement of the fuel cell performance by increasing the oxygen and hydrogen diffusion to the active sites of the catalyst layer (CL) [13, 14].
The law of partial pressures says that, if you introduce one gas into the presence of another, it will behave as if the other gas is not there.

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