Effect of the volume history of the isolated lung on distribution of blood flow.

Abstract

The distribution of pulmonary blood flow in an isolated dog lung preparation was measured using radioactive xenon. The pattern found when the lung was inflated to a transpulmonary pressure of 12 cm H2O from a near collapsed state was contrasted with the pattern found when the lung was deflated to the same transpulmonary pressure, or volume, after a full expansion. It was found that pulmonary blood flow rose 4.0 cm (Se mean 0.4 cm) higher up the lung (for the same vascular and alveolar pressures) when in its inflation state than in its deflation state at isovolume conditions. The effect on the distribution of blood flow of approaching the same pulmonary arterial pressure from above and below was also examined. The consequent vessel hysteresis was found to be small and inconstant. Pulmonary vascular resistance was found to be higher in the deflation state compared with the inflation state. The differences between the distribution of blood flow on inflation and deflation presumably reflect changes in the surface tension of the alveolar lining layer which alter the perivascular pressure of intra-alveolar vessels.