Influence of Mixed Venous Oxygen Tension (PVO2) on Blood Flow to Atelectatic Lung

The influence of mixed venous oxygen tension (PVO2) on blood flow to the atelectatic left lung was studied at normal and reduced cardiac outputs (CO) using extracorporeal veno-venous bypass in six pentobarbital anesthetized, mechanically ventilated dogs. Aortic and left pulmonary artery flows; airway, left atrial, central venous, pulmonary, and systemic arterial pressures; hemoglobin, arterial, and mixed venous blood gases were measured. The blood flow reduction observed in atelectasis was altered by the PVO2. Approximately 50% of blood flow was diverted away from atelectatic lung when PVO2 was low (24 +/- 2 mmHg) or normal (46 +/- 2 mmHg) (mean left lung blood flow QL% was 23.2 +/- 4.6% with low PVO2 and 19.0 +/- 3.4%, with normal PVO2). When PVO2 was increased to greater than 100 mmHg, diversion of blood flow away from atelectatic lung did not occur and QL% was nearly the flow expected for normoxic ventilated left lung (mean QL% = 40.4 +/- 5.9%). Shunt (QS/QT%) was significantly greater when PVO2 was high than when it was normal or low (mean QS/QT% = 51.7 +/- 5.6%, 31.0 +/- 3.1%, 26.0 +/- 3.4% with high, normal, and low PVO2, respectively). Mean PaO2 was significantly greater when PVO2 was high than when PVO2 was normal or low, despite the increase in QL% and QS/QT% (PaO2 = 327 +/- 25 mmHg, 220 +/- 32 mmHg, 115 +/- 21 mmHg with high, normal, and low PVO2, respectively). A 40% reduction in cardiac output significantly decreased transmural pulmonary artery pressure but did not affect PaO2, QS/QT%, or QL%.(ABSTRACT TRUNCATED AT 250 WORDS)