Pulmonary gas exchange during hypoxic exercise in the rat

Pulmonary gas exchange and O2 transport were studied at rest and during maximal treadmill exercise in rats in acute hypoxia (PIO2 approximately 71 Torr), and in littermates acclimatized to PB = 380 Torr (PIO2 approximately 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, PO2 and PCO2 were determined (Appendix). In both acute and chronic hypoxia, the following changes were observed: alveolar and arterial PO2 increased considerably, but the difference, A-aPO2, did not change significantly; arterial O2 concentration (CaO2) decreased, and apparent pulmonary diffusing capacity for O2, Dapp, increased. The increase in Dapp, together with hyperventilation, may prevent further drop in CaO2 due to a large rightward shift in the blood-O2 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 PAO2, an increase, instead of a decrease, in PaO2, and a larger increase in Dapp.