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The V/Q ratio quantifies the relationship of lung ventilation to perfusion and in ideal physiology, the ratio is 1. V/Q mismatch on the other hand...
by Adele Shenoy, MD
V/Q mismatch is an imbalance in the relationship between ventilation (V) and perfusion (Q) of the respiratory units within the lung. The V/Q ratio quantifies the relationship of ventilation to perfusion and in ideal physiology, the ratio is 1. V/Q mismatch with a high ratio describes areas of the lung that are well-ventilated and poorly perfused. V/Q mismatch with a low ratio is seen when there are areas of the lung that are poorly ventilated and well-perfused.
V/Q mismatch is a common cause of hypoxemia.
Interruptions of blood flow within the pulmonary circulation, such as seen with a pulmonary embolism, will lead to impaired gas exchange and an increase in respiratory dead space. This will lead to high ratio V/Q mismatch.
Airways disease leading to obstruction and poor ventilation, such as observed in pneumonia, COPD, or atelectasis, will lead to perfusion of unventilated lung, also known as intrapulmonary shunt. This will cause low ratio V/Q mismatch.
Both situations will decrease the delivery of oxygen from the lungs.
Edited by Charles L Fishman, MD
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Sarkar M, Niranjan N, Banyal PK. Mechanisms of hypoxemia. Lung India. 2017 Jan-Feb;34(1):47-60