Pulmonary vascular resistance and vascular transmural gradient

Abstract

Perfusion studies were made on vascular beds of isolated dog lungs. Submerged, gas-free, fluid-distended lobes served for studies of resistance versus transmural pressure in a technique that abolished gravitational effects. Air-distended lobes with varying degrees of pulmonary edema were used to display the transmural gradient differences produced by height, and the effect alveolar fluid has on the apparent transmural gradient. Results indicate that the vascular bed behaves as a compliant tube of a limited maximal radius to which it may be distended while still in the normal pressure range. Vasopressors influence the wall distensibility and thus only the lower pressure portion of a pressure-flow curve. Flow continues through lobes distended at higher than arterial pressures with air. Progressive disappearance of this phenomenon as intra-alveolar fluid collects suggests that the effective transmural gradient differs from the vascular-alveolar gradient and is in part a function of alveolar surface tension. Submitted on October 16, 1959