Respiration in the Hibernation of the 13-Lined Ground Squirrel

Abstract

Respiratory rate, heart rate and body temperatures were recorded simultaneously in the 13-lined ground squirrel ( Citellus tridecemlineatus) throughout the hibernating cycle. An induction trend may appear at any time during the latter part of arousal. It may lead to the hibernating state, or it may give way to the continuation of arousal, hence neither induction nor arousal appears to be an ‘all-or-none’ phenomenon. In hibernation, respiration consists of one to two deep sighs followed by apnea of variable duration, averaging 1–3 breaths/min. The heart rate is often arrhythmic, but averages 7–8 beats/min. As the frequency of the sighs change, other shallow rhythmic breaths appear very early in arousal, and increase in rate and amplitude to marked hyperventilation. Heart rate also increases rapidly and without arrhythmia, but in late arousal various stimuli will elicit momentary respiratory and cardiac arrest. In transition stages, respiratory lead heart rate changes, except during early arousal and late induction when respiratory and heart rates are linearly related. The apparent initiatory action of respiration further implicates the respiratory muscles in the heat production of arousal.