Ventilation (V, air reaching the lung alveoli) / Perfusion (Q, blood reaching lung alveoli via capillaries) is an important concept in respiratory physiology.

The V/Q ratio refers to the ratio of the amount of air reaching the alveoli per minute to the amount of blood reaching the alveoli per minute. V and Q are the main determinants of blood oxygen and carbon dioxide concentration.

V/Q mismatch occurs when one or more areas of the lung receive oxygen but no/little blood flow, or they receive blood flow but no/little oxygen.

V/Q ratio can be determined using a V/Q lung scan, medical imaging using scintigraphy and medical isotopes to evaluate the circulation of air and blood within the lungs. The V/Q scan is used in preference to a CTPA for the investigation of PE in patients with kidney failure or in pregnancy, to avoid significant radiation exposure.

Radiopaedia - V/Q scan

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