Ventilation/perfusion ratio

In respiratory physiology, the ventilation/perfusion ratio (V/Q ratio) is a ratio used to assess the efficiency and adequacy of the ventilation-perfusion coupling and thus the matching of two variables: V – ventilation – the air that reaches the alveoli Q – perfusion – the blood that reaches the alveoli via the capillaries The V/Q ratio can therefore be defined as the ratio of the amount of air reaching the alveoli per minute to the amount of blood reaching the alveoli per minute—a ratio of volumetric flow rates. These two variables, V and Q, constitute the main determinants of the blood oxygen (O2) and carbon dioxide (CO2) concentration.

Source: Wikipedia — Ventilation/perfusion ratio (CC BY-SA 4.0)