Effects of lung collapse on pulmonary blood volume, flow and resistance

Abstract

Pulmonary blood flow, pressures, volume and vascular resistance were measured when the lungs occupied an expiratory position in the closed chest and when they were collapsed by introducing air into the thorax. Circulation and innervation were intact. Variations due to respiratory movements or asphyxia were ruled out. Mongrel dogs were used, anesthetized with morphine and sodium pentobarbital. Pressures were measured from pulmonary artery, left atrium, aortic arch and intrapleural space. Pulmonary flow was evaluated utilizing the dye dilution method and the pulse contour method. Vascular volume was estimated by the product of mean circulation time and flow. When the lungs were collapsed there was an immediate elevation of intraluminal left atrial pressure but not a comparable rise in pulmonary arterial pressure. However, the direct records of arteriovenous pressure drop suggest that there was a delayed rise in pulmonary artery pressure. Flow, aortic pressure, heart rate and pulmonary vascular resistance showed no consistent changes. In 8 of 11 cases the pulmonary blood volume decreased when the lungs were collapsed.