Ventilatory and metabolic responses to hypoxia during moderate hypothermia in the anaesthetised rat. Frappell, Peter, Karen Westwood, and Michael Maskrey. School of Zoology, La Trobe University, Bundoora, Victoria, 3083 and Department of Physiology, University of Tasmania, Hobart, 7005.
APStracts 2:0081A, 1995.
In resting euthermic mammals hypoxia elicits a hyperventilation that results from a combination of hyperpnea and hypometabolism. Often accompanying the hypoxia induced hypometabolism is a drop in body temperature. In order to separate the synergic effects of hypothermia per se from the direct effects of hypoxia on metabolic rate, ventilation (E) and oxygen consumption (O2) were measured in anaesthetised rats fitted with abdominal heat exchangers and maintained at either normothermic (37.5 degrees C) or hypothermic (35 degrees C) body temperatures while exposed to either normoxia or hypoxia (7% O2). Hypothermia induced parallel decreases in E and O2, thereby maintaining E/O2 ratios. Hypoxia resulted in a hyperventilation achieved with the same relative decrease in O2 and increase in E in both normothermic and hypothermic rats. The results suggest that (1) the changes in metabolic rate and E during hypothermia reflect a direct effect of cold, and (2) that similar levels of hypoxic hyperventilation in the hypothermic and normothermic rats suggests that, relative to metabolic rate, respiratory gain has not been depressed in hypothermic rats. 

Received 18 August 1994; accepted in final form 27 February 1995.
APS Manuscript Number A873-4.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 10 March 1995.