Journal of Comparative Physiology B

, Volume 180, Issue 3, pp 465–473

Cardiac function adaptations in hibernating grizzly bears (Ursus arctos horribilis)

Original Paper

DOI: 10.1007/s00360-009-0421-x

Cite this article as:
Nelson, O.L. & Robbins, C.T. J Comp Physiol B (2010) 180: 465. doi:10.1007/s00360-009-0421-x


Research on the cardiovascular physiology of hibernating mammals may provide insight into evolutionary adaptations; however, anesthesia used to handle wild animals may affect the cardiovascular parameters of interest. To overcome these potential biases, we investigated the functional cardiac phenotype of the hibernating grizzly bear (Ursus arctos horribilis) during the active, transitional and hibernating phases over a 4 year period in conscious rather than anesthetized bears. The bears were captive born and serially studied from the age of 5 months to 4 years. Heart rate was significantly different from active (82.6 ± 7.7 beats/min) to hibernating states (17.8 ± 2.8 beats/min). There was no difference from the active to the hibernating state in diastolic and stroke volume parameters or in left atrial area. Left ventricular volume:mass was significantly increased during hibernation indicating decreased ventricular mass. Ejection fraction of the left ventricle was not different between active and hibernating states. In contrast, total left atrial emptying fraction was significantly reduced during hibernation (17.8 ± 2.8%) as compared to the active state (40.8 ± 1.9%). Reduced atrial chamber function was also supported by reduced atrial contraction blood flow velocities and atrial contraction ejection fraction during hibernation; 7.1 ± 2.8% as compared to 20.7 ± 3% during the active state. Changes in the diastolic cardiac filling cycle, especially atrial chamber contribution to ventricular filling, appear to be the most prominent macroscopic functional change during hibernation. Thus, we propose that these changes in atrial chamber function constitute a major adaptation during hibernation which allows the myocardium to conserve energy, avoid chamber dilation and remain healthy during a period of extremely low heart rates. These findings will aid in rational approaches to identifying underlying molecular mechanisms.


Atrial chamber Bradycardia Cardiac function Diastolic function Ursus arctos horribilis 

Supplementary material

Supplementary material (MPG 502 kb)

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Copyright information

© Springer-Verlag 2009

Authors and Affiliations

  1. 1.Department of Veterinary Clinical SciencesWashington State UniversityPullmanUSA
  2. 2.Department of Natural Resource Sciences, School of Biological SciencesWashington State UniversityPullmanUSA

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