DISTRIBUTION OF PULMONARY BLOOD-FLOW IN CONSCIOUS RESTING RATS

The pattern of pulmonary blood flow (PBF) distribution was determined in the rat, in which lung gravitational forces are minimal. Microspher es were infused into the inferior vena cava of 15 conscious, and 5 ane sthetized rats. Relative scatter of specific PBF [(sample activity/sam ple weight)/(total activity/total weight)] in 28 lung samples was calc ulated. In 5 of the conscious rats, consecutive determinations were ma de 30 min apart. In 5 anesthetized rats, PBF was determined in prone a nd supine positions. Relative scatter of specific PBF varied from 0.84 to 1.12, with PBF being distributed preferentially to the hilar, cent ral regions. There was a high correlation between consecutive measurem ents: y = 0.88 x + 0.11 (n = 140, r = 0.92). By changing from prone to supine position, PBF to the topmost regions increased, and that to th e lowermost regions decreased, by only 3 percent. The results indicate that in the conscious resting rat, PBF has a small but significant pr eferential distribution to the hilar, central regions, with lower bloo d flow to the peripheral regions of the lung.