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.
Medical Dictionary for the Health Professions and Nursing © Farlex 2012