Pulmonary ventilation and cardiac activity in hibernating and arousing golden-mantled ground squirrels (Spermophilus lateralis)

Pulmonary ventilation was assessed in the hibernating and arousing golden-mantled ground squirrel by plethysmography and end-tidal gas analysis. The heart rate and electrocardiogram were monitored simultaneously with ventilation. The hibernating squirrels displayed a periodic respiratory pattern characterized by a variable breathing frequency and tidal volume and often exhibited characteristics of Cheyne-Stokes respiration. Apneic periods averaging 8 to 9 min resulted in a low overall breathing frequency. Cardiac activity in the hibernating ground squirrel was characterized by arrhythmias which correlated with ventilation and by alterations in the electrocardiogram typically seen in hibernating animals. Arousal from hibernation was accompanied by: (i) a replacement of periodic by continuous ventilation, (ii) a 25-fold increase in V_E in the first hour which was accounted for by the increment in breathing frequency, and (iii) a marked decrease in the ratio of heart beats to breaths. The techniques developed in the present study will permit further quantitative investigations of pulmonary ventilation and its control in hibernating animals.