Pulmonary mechanics of hibernating squirrels (Spermophilus lateralis)

In this study we examined the effects of hibernation on several aspects of pulmonary mechanics in golden mantled ground squirrels. Measurements were made on anesthetized animals that were active in late fall (FA, n = 7), maintained at 23 degrees C and normal photoperiod in mid-winter (WA, n = 0) and hibernating at 5 degrees C in mid-winter (H, n = 8). Compared with FA animals, WA animals showed an increase in inspiratory reserve volume (IRV) and in inspiratory, vital and total lung capacities (IC, VC, and TLC). Hibernating animals exhibited further increases in IRV, IC, VC and TLC, an elevated residual volume, and virtual elimination of the expiratory reserve volume. There was also a decrease in specific lung compliance and a sharp knee in the lower portion of the quasi-static volume-pressure curve. There was a significant increase in the elastic work required to ventilate the hibernating animals compared with FA animals. The data suggest that, despite an increase in compliance at TLC, there is decreased compliance at low volumes, gas trapping at functional residual capacity, and an increase in the work required to breathe in hibernating animals.