V/Q Ratio — FRCA Primary MCQ
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Correct answer: E — 0.8
The correct answer is E, 0.8. The V/Q ratio is alveolar ventilation divided by pulmonary perfusion. Typical resting values are approximately 4 L/min of alveolar ventilation and 5 L/min of pulmonary blood flow, giving 4/5 = 0.8. A value of 1.0 would imply equal alveolar ventilation and perfusion, which is not the usual whole-lung relationship. In an upright lung, both ventilation and perfusion increase from apex to base, but perfusion increases more steeply. Consequently, regional V/Q is greater than 1 toward the apex and less than 1 toward the base; 0.6 may therefore resemble a dependent regional value but is not the standard whole-lung average. Values of 0.4 are abnormally low, while 1.2 represents a relatively high V/Q ratio.
Reference: Zwart A, Seagrave RC, Van Dieren A. Ventilation-perfusion ratio obtained by a noninvasive frequency response technique. Journal of Applied Physiology. 1976;41(3):419-424. https://www.rcoa.ac.uk/media/49221