Evaluation of cardiac function in active and hibernating grizzly bears.
OBJECTIVE
To evaluate cardiac function parameters in a group of active and hibernating grizzly bears.


METHODS
Prospective study.


METHODS
6 subadult grizzly bears.


METHODS
Indirect blood pressure, a 12-lead ECG, and a routine echocardiogram were obtained in each bear during the summer active phase and during hibernation.


RESULTS
All measurements of myocardial contractility were significantly lower in all bears during hibernation, compared with the active period. Mean rate of circumferential left ventricular shortening, percentage fractional shortening, and percentage left ventricular ejection fraction were significantly lower in bears during hibernation, compared with the active period. Certain indices of diastolic function appeared to indicate enhanced ventricular compliance during the hibernation period. Mean mitral inflow ratio and isovolumic relaxation time were greater during hibernation. Heart rate was significantly lower for hibernating bears, and mean cardiac index was lower but not significantly different from cardiac index during the active phase. Contrary to results obtained in hibernating rodent species, cardiac index was not significantly correlated with heart rate.


CONCLUSIONS
Cardiac function parameters in hibernating bears are opposite to the chronic bradycardic effects detected in nonhibernating species, likely because of intrinsic cardiac muscle adaptations during hibernation. Understanding mechanisms and responses of the myocardium during hibernation could yield insight into mechanisms of cardiac function regulation in various disease states in nonhibernating species.
Department of Veterinary Clinical Sciences, College of Veterinary Medicine, Washington State University, Pullman, WA 99164, USA.
O Lynne
OL
Nelson
Margaret-Mary
MM
McEwen
Charles T
CT
Robbins
Laura
L
Felicetti
William F
WF
Christensen
D000704:Analysis of Variance; D000818:Animals; D001794:Blood Pressure / Q000502:physiology; D004452:Echocardiography / Q000379:methods / Q000662:veterinary; D004562:Electrocardiography / Q000662:veterinary; D005260:Female; D006321:Heart / Q000502:physiology*; D006339:Heart Rate / Q000502:physiology; D006605:Hibernation / Q000502:physiology*; D008297:Male; D009200:Myocardial Contraction; D011446:Prospective Studies; D001503:Ursidae / Q000502:physiology*