Ventilation and metabolism in a large semifossorial marsupial: the effect of graded hypoxia and hypercapnia.

Metabolic and ventilatory variables were measured in a large semifossorial marsupial, the hairy-nosed wombat (Lasiorhinus latifrons, 21.9 kg). In normoxia, the rate of oxygen consumption was 63% of that predicted for a similar-sized marsupial, and the level of ventilation (V(E)) was such that the convective requirement (V(E)/VO2) was similar to other mammals. Exposure to hypercapnia (5% CO(2)) evoked a hyperventilatory response (3.55 x normoxia) that was no different to that observed for epigeal (surface-dwelling) marsupials; the increase in V(E) was primarily achieved with an increase in tidal volume. Exposure to hypoxia (15% to 8% O(2)) resulted in a hyperventilation (principally through an increase in frequency), although the response was blunted (in 8% O(2), 1.85 x normoxia) and only at the severest levels did hypometabolism contribute. The attenuated response to hypoxia in the wombat is presumably a reflection of a semifossorial lifestyle and a tolerance to this respiratory stimulant.