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. Heart disease may reduce the normal difference in the upper and lower zone clearance rates. To investigate this problem further we have studied a group of patients with congenital shunts between the left and right sides of the heart. These patients have a great variety ofpulmonary pressures and flows. This study was made with a specially selected group of such patients in whom complete hemodynamic investigations had been performed. The results demonstrate differences between the flow patterns in various disorders of the pulmonary circulation and throw some light on the factors that influence the partition of blood flow between different regions of the lung.