PULMONARY GAS-EXCHANGE DURING HYPOXIC EXERCISE IN THE RAT

Pulmonary gas exchange and O-2 transport were studied at rest and during maximal treadmill exercise in rats in acute hypoxia (PIO2 similar to 71 Torr), and in littermates acclimatized to PB = 380 Torr (PIO2 similar to 71 Torr) for 3 weeks (chronic hypoxia). To obtain valid estimates of blood gas partial pressures, particularly during exercise, the temperature coefficients of blood pH, P-O2 and P-CO2 were determined (Appendix). In both acute and chronic hypoxia, the following changes were observed: alveolar and arterial P-O2 increased considerably, but the difference, A-aP(O2), did not change significantly; arterial O-2 concentration (Ca-O2) decreased, and apparent pulmonary diffusing capacity for O-2, D-app, increased. The increase in D-app, together with hyperventilation, may prevent further drop in Ca-O2 due to a large rightward shift in the blood-O-2 equilibrium curve caused by lactic acidosis in conjunction with a large Bohr coefficient characteristic of this species. Comparison with corresponding results obtained in man reveals that during hypoxic exercise, the rat shows a larger increase in PA(O2), an increase, instead of a decrease, in Pa-O2, and a larger increase in D-app.