QUICK INCREASE OF PULMONARY BLOOD FLOW IN RESPONSE TO AN ACUTE ALVEOLAR HYPDXIA IN HUMAN SUBJECTS

The effects of acute alveolar hypoxia on pulmonary blood flow were studied in upright standing human subjects by means of a constant expiration technique combined with continuous analysis of the C2H2 fraction in the expired gas. The subject rapidly and deeply inhaled a gas mixture containing 4.87% C2H2, 0.99% O2, N2 for balance and exhaled the alveolar gas via a constant flow valve. The PO2 of the alveolar gas fell to 37.6±5.6 mmHg. The C2H2 curve showed a clear downward inflection 7 to 10 sec after the completion of washout of the dead space gas. This inflection indicates an increase of the C2H2 uptake rate produced by an increase in pulmonary blood flow. The pulmonary blood flow calculated for the time range of 10.0 to 12.5 sec after the establishment of acute alveolar hypoxia (6.5±1.1 1/min) was significantly larger than the blood flow under normoxia (5.5±0.91/min). This increase associated with a quick rise in systemic arterial blood pressure which was probably induced by a chemical reflex.