The Effect of Time and Stress on the Heart Rate-Oxygen Consumption Relationship of Uinta Ground Squirrels

Uinta ground squirrels (Spermophilus armatus) were instrumented with ECG radio-transmitters. Heart rate and oxygen consumption were monitored for one hour at ambient temperatures above, within and below the thermoneutral zone. These measures were made at predetermined intervals throughout the active season of squirrels to determine if the heart rate-oxygen consumption relationship was a stable linear regression within and between squirrels during this period. Heart rate and oxygen consumption were also monitored for squirrels exposed to artificial and natural stressors. These squirrels were then released in an outdoor enclosure. Heart rate and behavior of animals were monitored simultaneously during above and below ground activity. Heart rate-oxygen consumption regressions were stable during measurements through a 25°C temperature range. Regressions of heart rate versus oxygen consumption did vary between and within squirrels over four days. Heart rate tended to decrease initially after presentation of natural stressors. Heart rate tended to increase when artificial stressors were presented. Regressions of heart rate versus oxygen consumption for these stressors tended to be linear, but heart rate would not be a good predictor of oxygen consumption during rapid heart rate changes because, in most cases, heart rate-oxygen consumption regressions were not statistically significant. In some tests with rapidly decreasing initial heart rates, the heart rate-oxygen consumption relationship was negative. that is, oxygen consumption remained constant as heart rate decreased. Possible causes of negative responses are discussed. Heart rate responses generated in laboratory stress tests were similar to semi free-living heart rate responses. During the major portion of time spent above and below ground, heart rate of squirrels was found to be quite stable. During these periods, heart rate should be a reasonable predictor of oxygen consumption. In summary, average heart rate should be a reasonable predictor of oxygen consumption of free-living squirrels over daily periods. In using this method, it would be necessary to calculate regressions of heart rate and oxygen consumption in the laboratory before and after free-living studies to examine the stability of the regression lines during this period. An average regression line could be used to compensate in part for a change of the heart rate-oxygen consumption relationship during study periods