Ventilation-perfusion mismatch pathophysiology

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Aida Javanbakht, M.D.

Overview

Any disruption between blood flow and ventilation is called V/Q mismatch.

Pathogenesis

In the upright position of the normal lung, the amount of ventilation and perfusion is higher in the base of the lung compare to apex of the lung. Although ventilation and perfusion are low in the apex of the lung, the perfusion is lower than ventilation in the apex. So, the V/Q is higher in the apex of the lung compare to the base. In a normal lung V/Q is 0.8 which means 4 liters of oxygen and 5 liters of blood transfer in the lung per minute. V/Q mismatch is one of the reason of hypoxemia in patients with lung disease like obstructive lung diseases, pulmonary vascular diseases, and interstitial diseases . Usually hypoxemia due to V/Q mismatch will resolve by oxygen therapy.

In normal condition when there is a low ventilation, the body tries to keep this ratio in a normal range by restricting the perfusion in that specific area of the lung. This unique mechanism is called hypoxic pulmonary vasoconstriction. If this process happens for a long time it can cause pulmonary hypertension.

Associated Conditions

Some conditions that cause decrease in V/Q are:

• Bronchitis
• Asthma
• Foreign body aspiration

Some conditions that cause increase in V/Q are:

• Pulmonary embolism
• Emphysema