Ventilation/perfusion ratio

In respiratory physiology, the ventilation/perfusion ratio (or V/Q ratio) is a measurement used to the efficiency and adequacy of the matching of two variables:


 * "V" - ventilation - the air which reaches the lungs
 * "Q" - perfusion - the blood which reaches the lungs

A normal value is approximately 0.8.

Because the lung is centered vertically around the heart, part of the lung is superior to the heart, and part is inferior. This has a major impact on the V/Q ratio:


 * apex of lung - higher
 * base of lung - lower

The V/Q ratio can be measured with a ventilation/perfusion scan.

An area with no ventilation (and thus a V/Q of zero) is termed a shunt. An area with no perfusion (and thus a V/Q of infinitiy) is termed "dead space"