Relation between mixed venous oxygen tension and pulmonary vascular tone during normoxic, hyperoxic and hypoxic ventilation in dogs.

To evaluate the relation between the oxygen tension of pulmonary arterial blood (PvO2) and pulmonary vascular resistance (PVR), an extracorporeal circuit was used to vary the PvO2 of blood perfusing the left lung in 3 groups of open-chest dogs mechanically ventilated with an inspired fraction of oxygen of 0.35 (group I), 0.21 (group II), or 0.10 (group III). Left lung pulmonary blood flow, left atrial pressure and perfusate, and systemic pH and PCO2 did not change significantly as PvO2 was varied over a range of 11 to 52 mm Hg in groups I and II. There was no correlation between decreases in PvO2 and the percent change in left lung PVR compared with baseline (PvO2 approximately 40 mm Hg) in group I (r = 0.12, difference not significant). In contrast, there was a significant correlation between decreases in PvO2 and the percent change from baseline in PVR in group II (r = -0.50, p less than 0.02). Left lung alveolar oxygen tension (PAO2) decreased significantly when PvO2 was at its lowest in group II (p less than PAO2 0.05). Both groups I and II had a significant pulmonary vasoconstrictor response to hypoxic ventilation, indicating that vasoreactivity was preserved in this model. The increase in PVR with hypoxia was significantly blunted in dogs perfused with blood that had a high PvO2 (41 +/- 12.4 mm Hg, group IIIa) compared with dogs perfused with blood that had a low PvO2 (25 +/- 6 mm Hg, group IIIb), despite comparable values for PAO2.(ABSTRACT TRUNCATED AT 250 WORDS)