7th February 2024

Regional variations of ventilation and perfusion

Consider a person standing upright; the upper lung zones (non-dependent areas) will be expanded at rest compared to the lower lung zones (dependent areas). During inspiration, the upper lung zones will increase in size to a lesser degree than the lower lung zones. Hence, ventilation of the upper lung zone is less compared to the lower lung zone.

Perfusion of the upper lung zone will be less than the lower lung zone due to the effect of gravity. However, the increase in perfusion is more significant than the increase in ventilation as we move from upper to lower lung zones. The overall V/Q ratio of a normal lung is 0.9.