Effect of hypoxia on distribution of pulmonary blood flow.

Abstract

The effect of alveolar hypoxia on the distribution of pulmonary blood flow was studied in 9 anesthetized, spontaneously breathing mongrel dogs, using a modified Xe133 [Xenon133] technique. Observations were made over a wide range of H+ concentration induced by adding CO2 to the inspired gas. In the upright (head up) position perfusion increased linearly with distance down the lung except near the bottom where a zone of decreased perfusion was frequently noted. The slope of the line relating relative perfusion to distance down the lung decreased during hypoxia indicating more uniform perfusion. No effect on the distribution of ventilation was noted. The magnitude of the change in relative perfusion gradient was affected by both the degree of hypoxia and the coincident H+ concentration but correlated best with the change in pulmonary artery pressure. In a few instances, however, when acidosis was especially severe, the perfusion gradient was reversed indicating a disproportionate increase in vascular resistance in lower lung zones.