PULMONARY GAS-EXCHANGE DURING HYPOXIC EXERCISE IN THE RAT

Pulmonary gas exchange and O-2 transport were studied at rest and duri ng maximal treadmill exercise in rats in acute hypoxia (PIO2 similar t o 71 Torr), and in littermates acclimatized to PB = 380 Torr (PIO2 sim ilar to 71 Torr) for 3 weeks (chronic hypoxia). To obtain valid estima tes 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 we re observed: alveolar and arterial P-O2 increased considerably, but th e difference, A-aP(O2), did not change significantly; arterial O-2 con centration (Ca-O2) decreased, and apparent pulmonary diffusing capacit y for O-2, D-app, increased. The increase in D-app, together with hype rventilation, may prevent further drop in Ca-O2 due to a large rightwa rd shift in the blood-O-2 equilibrium curve caused by lactic acidosis in conjunction with a large Bohr coefficient characteristic of this sp ecies. Comparison with corresponding results obtained in man reveals t hat 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.