Minute ventilation (VE) in the semifossorial ground squirrel (Spermophilus tridecemlineatus) increased with increased levels of hypoxia. 2. The increase in VE was brought about primarily by an increase in breathing frequency (f). There was no significant change in tidal volume (VT). 3. The PiO2 threshold for the ventilatory response to hypoxia and position of the ventilatory response curve in the ground squirrel were closer to the semifossorial echidna (Tachyglossus aculeatus) than the completely fossorial mole rate (Spalax ehrenbergi); both the ground squirrel and echidna had a higher PiO2 threshold than the mole rat. 4. The ventilatory response curve was shifted to the left in the mole rat. 5. These observations indicate that the mole rat is the least responsive to hypoxia of the three species.
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