VENTILATION OF A FOSSORIAL MAMMAL (SPALAX-EHRENBERGI) IN HYPOXIC AND HYPERCAPNIC CONDITIONS

An improved barometric method was tested and employed to measure tidal volume (VT), ventilation frequency (f) and ventilation rate (.ovrhdot.VE) in the unrestrained awake fossorial mole rat in conditions of normoxia, hypoxia, hypercapnia and their combination. Values were compared with those measured in the laboratory rat and the common mammal pattern. The .ovrhdot.VE of the mole rat at rest, 72 .+-. 13 (SD) ml .cntdot. min-1, was about 2/3 that expected from allometric predictions. The .ovrhdot.VE of the rat was not significantly different from what was expected. The low .ovrhdot.VE of the mole rat together with normal O2 consumption and the normal anatomic features of its respiratory system predict high alveolar CO2 pressure (PACO2) (calculated value 48 Torr). .ovrhdot.VE increase in response to hypercapnia started above an inspired CO2 pressure (PICO2) of 35 Torr and to hypoxia below an inspired O2 pressure (PIO2) of 41 Torr. The response to hypercapnic hypoxia was similar to hypercapnia alone. The .ovrhdot.VE increased with increasing PICO2 up to 115 Torr. In hypoxic hypercapnia there was no further increase at PIO2 < 35 and PICO2 > 99 Torr. In the rat, .ovrhdot.VE began to increase at higher PIO2 and lower PICO2. This increase was arrested at PICO2 > 85 Torr in hypercapnia alone and at PIO2 < 55 and PICO2 > 75 Torr in hypoxic hypercapnia. Compared to the rat, the ventilation of the mole rat at rest did not respond to moderate hypercapnia and hypoxia, increased in extreme hypercapnia and hypoxia and was inhibited only below 5% O2 and above 14% CO2.