Respiration of a monotreme, the echidna, Tachyglossus aculeatus

Abstract

The minute volume, tidal volume, and respiratory frequency were measured in three echidnas breathing air and various air-CO2 mixtures. Increased concentration of CO2 in the inspired air caused large increases in minute and tidal volume but little change in respiratory rate. However, normal variation in minute volume of echidnas breathing air was principally the result of change in respiratory rate. The end-tidal (alveolar) CO2 concentration was 5-6% whereas the O2 was 14-15%, both values being similar to those of typical placemal mammals. Burrowing echidnas voluntarily tolerate CO2 concentrations of about 5%. The sensitivity of these animals to CO2 was compared to other homeotherms and found to be low, but definite conclusions cannot be drawn until results on more species are available.