Pulmonary respiration and acid-base state in hibernating marmots and hamsters

Abstract Ventilation has been measured in hibernating marmots, Marmota marmota , with a total body plethysmograph. Breaths were separated by variable periods ofapnea; the respiratory period ranged from O.5 to 6 min (mean 1.2 min). Mean ventilatory flow rate was 30.3 ± 7.0 ml btps · m −1 . An early sign of arousal was a great increase of ventilatory flow rate, before any significant increase in oxygen consumption and body temperature. Measurement of pH and P CO 2 of arterial blood samples via indwelling catheters gave the following values: euthermic hamster Cricetus cricetus (body temperature 37–38°C): pH = 7.40, P CO 2 = 45.3 torr, [HCO 3 − ] = 28.2 meq·L −1 ; hibernating hamster (body temperature 9°C): pH = 7.57, P CO 2 = 36.1 torr, [HCO 3 − ] = 53.8 meq·L −1 ; hibernating marmot (body temperature 8°C): pH = 7.57, P CO 2 = 33.3 torr, [HCO 3 − ] = 52.8 meq·L −1 . These data confirm the existence of a new, stable acid-base state in hibernating mammals, with a pH 0.17 unit higher than in euthermic conditions. In contrast, in poikilotherms, for the same decrease of body temperature blood pH would increase by about O.50 unit, i.e. by the same amount as the pH of neutrality of water, relative alkalinity remaining thus constant. Hibernating mammals may thus be viewed as relatively acidotic. The significance of these findings is discussed.