ventilation:perfusion ratio

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ven·ti·la·tion:per·fu·sion ra·ti·o

(V̇V˙A:Q˙) (ven'ti-lā'shŭn-pĕr-fyū'zhŭn rā'shē-ō)
The ratio of alveolar ventilation to simultaneous alveolar capillary blood flow in any part of the lung; because both ventilation and perfusion are expressed per unit volume of tissue and per unit of time, which cancel, the units become liters of gas per liter of blood.


renewal or exchange of gas in an enclosed space.
1. the process or act of supplying a building or part of it continuously with fresh air.
2. in respiratory physiology, the process of exchange of air between the lungs and the ambient air. Pulmonary ventilation (usually measured in liters per minute) refers to the total exchange, whereas alveolar ventilation refers to the effective ventilation of the alveoli, where gas exchange with the blood takes place. See also air movement.

alveolar ventilation
the amount of gas expelled from the alveoli to the outside of the body per minute.
artificial ventilation
see artificial respiration.
assisted ventilation
the depth of spontaneous ventilation is augmented by the anesthetist, as by squeezing the rebreathing bag.
controlled ventilation
breathing is done entirely by a mechanical device or the anesthetist squeezing the rebreathing bag.
dead space ventilation
see dead space.
high frequency ventilation
mechanical ventilation that delivers gas at more than four times the normal rate of breathing.
intermittent mandatory ventilation (IMV)
a type of mechanical ventilation in which the ventilator is set to deliver a prescribed tidal volume at specified intervals and a high-flow gas system permits the patient to breathe spontaneously between cycles. The ventilator rate is set to maintain the patient's Paco2 at normal levels and is reduced gradually to zero as the patient's condition improves.
intermittent positive-pressure ventilation (IPPV)
the provision of mechanical ventilation by a machine designed to deliver breathing gas until equilibrium is established between the patient's lungs and the ventilator. IPPV machines are positive-pressure, pressure-cycled, assister-controller (pneumatic) devices.
Because of their compact size and capability of operating independently of an electrical current, the IPPV machines have the most widespread applicability in the employment of a form of treatment called intermittent positive-pressure breathing.
maximal voluntary ventilation (MVV)
the maximal volume that can be exhaled per minute by the patient breathing as rapidly and deeply as possible.
mechanical ventilation
that accomplished by extrinsic means.
minute ventilation
the total amount of gas (in liters) expelled from the lungs per minute.
ventilation mismatch
mismatches of ventilation and blood flow, as in chronic obstructive lung disease, are a common cause of hypoxemia.
ventilation:perfusion ratio
the ratio of air ventilation to the blood perfused. Called also VA/Q. The degree of oxygenation of the blood and the proportional excretion of CO2 are both dependent on both variables being optimal.
positive pressure ventilation
administration of oxygen under pressure, usually by use of an anesthetic bag or mechanical ventilator. See also continuous positive airway pressure, positive end-expiratory pressure.
spontaneous ventilation
breathing without the assistance of any ventilator or mechanical device.
total ventilation
the amount of air moved out of (or into) the airways and alveoli over a specified time period.