Meeting Abstract

14.5  Jan. 4  Circulatory and cardiac physiology of hibernating black bears TOIEN, O.*; BLAKE, J.; EFIMOV, I. R.; GRAHN, D.; HELLER, H. C.; BARNES, B. M.; Institute of Arctic Biology, University of Alaska Fairbanks oivind.toien@uaf.edu

Black bears depress metabolic rate to about 25% of normal resting levels during hibernation with a decrease of core temperature by only 2-8�C. Along with the needs for reduced perfusion, mean heart rate is profoundly decreased. There is a strong sinus arrhythmia on the heart rate pattern. During breathing events HR is close to normal, while between breathing events inter-beat intervals can be prolonged to typically 8-12 seconds with the extreme recorded at 23 s. Therefore, can bears perfuse the tissues during the long inter-beat intervals, and how do they avoid uncontrolled arrhythmias? We present preliminary recordings of intra-arterial blood pressure in hibernating non-anesthetized bears recorded through a mesenteric artery in- or close to- abdominal aorta. Temperature loggers, a radio telemetry temperature transmitter and a transmitter for blood pressure, ECG and EMG were implanted into the peritoneal cavity or in the neck area (ECG /EMG only). Air was collected from the hibernaculum and passed to a respirometry system. Breathing was detected with a differential pressure transducer connected to the den. The periods of high heart rate during breathing episodes pushed blood pressure up to very high levels, often with a systolic pressure of 200 mmHg at the end of this period, representing a very high load. During long inter-beat intervals, blood pressure slowly decreased to about 60 mm Hg adequate for tissue perfusion and indicates a high degree of vasoconstriction. Observed changes of interrelationships in the ECG pattern during breathing cycles may indicate adaptations to avoid fibrillation. – Supported by the NSF Alaska EPSCoR program. We thank Alaska Department of Fish and Game for supplying bears.