blood volume is normally about 450 mL (about 9% of total blood volume); about 70mL of this amount is contained within pulmonary capillaries, and the remainder is roughly equally distributed between the pulmonary arterial and venous systems.

The pulmonary blood pool may range from half of the normal amount to twice the normal amount as result of various physiological or pathological conditions. Vigorous expiration that creates high pressures within the lungs can cause as much as 250 mL of blood to be ejected from the pulmonary circulation.