Regional Pulmonary Blood Flow in Patients With Circulatory Shunts

Carbon dioxide labelled with oxygen-15 can be used to compare the blood flow in different regions of the lung. Results obtained with this technique in normal subjects at rest with the chest upright show that there is a much higher perfusion per unit of alveolar volume in the lower zone than in the upper zone. On moderate exercise the flow increases in both zones but the lower zone blood flow remains relatively greater than the upper zone (West and Dollery, 1960). Patients with mitral stenosis differ from the normal in that the moderately severe cases show almost equal perfusion in upper and lower zones and the severe cases have a higher perfusion in the upper than the lower zone (Dollery and West, 1960). This inversion of the normal distribution of blood flow has been observed also in patients with left ventricular failure and pulmonary cedema (Dollery and West, in preparation). The distribution of blood flow in normal subjects probably depends upon the effect of gravity on the low perfusion pressures in the pulmonary circulation.