Effects of CO2 inhalation on acid-base balance and thermal recovery following cold water dives by the muskrat (Ondatra zibethicus).

Thermoregulatory, cardiac, and blood gas responses of muskrats to CO2 inhalation were examined during recovery from controlled dives in 3 degrees C water. It was shown that CO2 levels previously recorded in the winter lodges of this species are sufficient to reduce postdive oxygen consumption and rate of rewarming in unrestrained animals. Postdive exposure to 5-10% CO2 reduced recovery of abdominal and subcutaneous temperature (Tb) in the middorsal lumbar region, but did not affect interscapular warming overlying brown adipose tissue. Depressed recovery of deep Tb was matched by a prolonged acidosis in restrained muskrats breathing 5-10% CO2 following 90-s submergence in 3 degrees C water. This occurred despite a comparatively high whole body buffer value (delta H+/delta PaCO2) of 0.53 nM X l-1 X mmHg-1. Protracted recovery of arterial pH did not appear to involve retention of CO2 accumulated during diving, since in all trials, PaCO2 returned to the predive baseline within 5 min of surfacing. Perturbations in PaO2, like PaCO2, were restored within 5 min of surfacing, irrespective of inspired gas mixture. Predive exposure to 5-10% CO2 had no discernible effect on establishment of bradycardia in diving muskrats. Compared to predive values, postimmersion heart rate was significantly reduced in 5-10% CO2, but not in control runs.