The effects of hypoxia on pulmonary function and maximal rates of oxygen consumption in two anuran amphibians

Abstract

1. The effects of ambient\(P_{O_2 } \) on the maximal rate of oxygen consumption, alveolar\(P_{O_2 } \) and alveolar ventilation rate were measured for two species of anuran amphibians during forced activity. The maximal rates of oxygen consumption were independent of ambient\(P_{O_2 } \) values as low as 80 Torr for bothBufo cognatus (1.5 ml O2 g−1 h−1) andRana pipiens (0.64 ml g−1 h−1), and were linearly proportional to ambient\(P_{O_2 } \) at less than 80 Torr. 2. The alveolar\(P_{O_2 } \) ofB. cognatus andR. pipiens during forced activity at a normal ambient\(P_{O_2 } \) was 125–135 Torr. Alveolar\(P_{O_2 } \) declined linearly for both species under hypoxic conditions. 3. The alveolar ventilation rate was calculated from maximal oxygen consumption rate and alveolar\(P_{O_2 } \) at various ambient\(P_{O_2 } \) values. The alveolar ventilation rate at 153 Torr was 32 ml min−1atpd forB. cognatus and 19 forR. pipiens during forced activity. Theatpd alveolar ventilation increased substantially at lowered ambient\(P_{O_2 } \), although thestpd alveolar ventilation declined markedly. The interspecific differences in maximal rates of oxygen consumption were correlated with the interspecific differences in alveolar ventilation rates. 4. The relationship between maximal rate of oxygen consumption and ambient\(P_{O_2 } \) forB. cognatus andR. pipiens indicates that ambient\(P_{O_2 } \) and pulmonary ventilation rates do not normally limit the maximal rates of respiratory gas exchange in anuran amphibians. The critical\(P_{O_2 } \) (80 Torr), below which the maximal rate of oxygen consumption declines, corresponds to an altitude of about 4500 m, and is less than the ambient\(P_{O_2 } \) encountered by terrestrial anuran amphibians in their natural environments.