Inhibition of shivering increases core temperature afterdrop and attenuates rewarming in hypothermic humans

Gordon G. Giesbrecht 1 , M. S. L. Goheen 1 , C. E. Johnston 1 , G. P. Kenny 1 , Gerald K. Bristow 1 , and John S. Hayward 2 1 Laboratory for Exercise and Environmental Medicine, at the Health, Leisure, and Human Performance Research Institute, and Department of Anesthesia, Faculty of Medicine, University of Manitoba, Manitoba R3T 2N2; and 2 Department of Biology, University of Victoria, Victoria, British Columbia, Canada V8W 2Y2 Received 1 October 1996; accepted in final form 7 July 1997. Giesbrecht, Gordon G., M. S. L. Goheen, C. E. Johnston, G. P. Kenny, Gerald K. Bristow, and John S. Hayward. Inhibition of shivering increases core temperature afterdrop and attenuates rewarming in hypothermic humans. J. Appl. Physiol. 83(5): 1630-1634, 1997. During severe hypothermia, shivering is absent. To simulate severe hypothermia, shivering in eight mildly hypothermic subjects was inhibited with meperidine (1.5 mg/kg). Subjects were cooled twice (meperidine and control trials) in 8°C water to a core temperature of 35.9 ± 0.5 (SD) °C, dried, and then placed in sleeping bags. Meperidine caused a 3.2-fold increase in core temperature afterdrop (1.1 ± 0.6 vs. 0.4 ± 0.2°C), a 4.3-fold increase in afterdrop duration (89.4 ± 31.4 vs. 20.9 ± 5.7 min), and a 37% decrease in rewarming rate (1.2 ± 0.5 vs. 1.9 ± 0.9°C/h). Meperidine inhibited overt shivering. Oxygen consumption, minute ventilation, and heart rate decreased after meperidine injection but subsequently returned toward preinjection values after 45 min postimmersion. This was likely due to the increased thermoregulatory drive with the greater afterdrop and the short half-life of meperidine. These results demonstrate the effectiveness of shivering heat production in attenuating the postcooling afterdrop of core temperature and potentiating core rewarming. The meperidine protocol may be valuable for comparing the efficacy of various hypothermia rewarming methods in the absence of shivering. first aid; rate of rewarming; shivering thermogenesis; hypothermia treatment 0161-7567/97 $5.00 Copyright © 1997 the American Physiological Society