THE VENTILATORY RESPONSE TO HYPERCAPNIA IN HIBERNATING GOLDEN-MANTLED GROUND-SQUIRRELS, SPERMOPHILUS-LATERALIS

The hypercapnic ventilatory response of golden-mantled ground squirrels was characterized an consecutive days throughout single bouts of hibernation and on the third day of hibernation bouts during the early, middle, and late portions of the hibernation season, to determine whether ventilatory responses during hibernation are a function of body temperature or hibernation depth. Our measurements confirm that the hypercapnic ventilatory response of this species during hibernation consists almost exclusively of increases in respiratory frequency (f(R)); tidal volume (V-T) changed little. No change in f(R) or V-T occurred as inspired CO2 was increased from 0% to 2%. Between 2% and 8% inspired CO2, f(R) increased linearly. Respiratory frequency remained constant or decreased slightly as CO2 was elevated beyond 8%. At levels of inspired CO2 between 10% and 13%:, animals would initiate arousal from hibernation and ventilation would increase again through increases in V-T and further increases in f(R). No significant interbout or intrabout variations were observed in any aspect of the hypercapnic ventilatory response. These data indicate that hypercapnic ventilatory sensitivity, if not exclusively a function of body temperature, is consistent between periods of equal body temperature regardless of possible temperature-independent changes in hibernation depth.