O. Lynne Nelson, DVM, MS, DACVIM (Internal Medicine and Cardiology)
Veterinary Clinical Sciences and WSU Bear Research, Education and Conservation Center, Washington State University, Pullman, WA, USA
Hibernation is a remarkable feat of extreme metabolism that results in a radical departure from the normal homeostasis that is seen in most mammals. Adapting research methods to understand this complex process in the bear can be quite challenging. Anesthesia is often used to obtain measures when studying wild animal biology. This is particularly troubling for cardiovascular physiology interpretation as anesthesia profoundly affects cardiac responses. The cardiac phenotype of the hibernating grizzly bear (Ursus arctos horribilis) was recently described using captive, trained animals to avoid the confounding effects of drugs. This study revealed unique differences that had not been previously assessed using anesthetized animals. For example, heart rate was mildly elevated by the anesthetic protocol during the active period but dramatically increased during hibernation over that of bears that were not anesthetized. Parameters of left ventricular systolic performance were impaired to a greater extent by anesthesia in the summer but less so in the winter. In contrast, anesthesia appeared to have greater depressive effects on diastolic filling cardiac parameters during hibernation. Thus, the effect of a drug protocol on cardiac function is discordant from one season to another. The striking effect of hibernation on atrial chamber ejection was only identified when unanesthetized bears were studied. These bears have since been trained for various research projects. Endocrine rhythms including cortisol and melatonin rhythms are also profoundly affected by common anesthesia protocols. When possible, using trained animals can avoid erroneous interpretation of results and shed immense light on native physiology understanding.