DEPENDENCE OF PULMONARY VENOUS ADMIXTURE ON INSPIRED OXYGEN FRACTION AND TIME DURING REGIONAL HYPOXIA IN THE RABBIT

In order to examine the value of assuming constant pulmonary venous ad mixture with respect to changes in inspired oxygen fraction (Fl(o2)) a nd time during sustained unilateral hypoxia, we studied venous admixtu re for 6 h in 27 anaesthetized rabbits in which the left lung was fill ed with liquid, isosmotic with plasma. In one group of 10 rabbits the right lung was ventilated for 6 h with Fl(o2) = 1: in a second group o f 10 the right lung was ventilated with Fl(o2) = 1 for 2.5 h and then with Fl(o2) = 0.3 for 3.5 h. A third group was similarly studied by ch anging from Fl(o2) = 1 to Fl(o2) = 0.5. We found that hypoxic pulmonar y vasoconstriction continued to intensify over 3 h. At 3-6 h, with Fl( o2) = 0.3, venous admixture (0.32 (SEM 0.03)) was higher than baseline (0.13 (0.01), t = 0 min during bilateral oxygenation) by twice the el evation above baseline of the venous admixture (0.22 (0.01)) in the gr oup with Fl(o2) = 1. The finding of a marked increase in venous admixt ure with decreasing Fl(o2) discussed in relation to current models of hypoxic pulmonary vasoconstriction.