Journal of Applied Physiology, Vol 50, Issue 4 829-834, Copyright © 1981 by American Physiological Society
Metabolic response to respiratory heat loss-induced core cooling
C. A. Piantadosi, E. D. Thalmann and W. H. Spaur
To study the phenomenon of isolated core cooling, four resting men breathed
cooled helium-oxygen (T in = 14 +/- 2 degrees C, 40-60% relative humidity)
in a warm hyperbaric chamber at pressures equivalent to 640, 1,000, and
1,400, and 1,800 ft seawater (fsw). Rectal temperature (T re) fell by 0.43
+/- 0.13 degrees C at 640 fsw to 0.98 +/- 0.15 degrees C at 1,800 fsw after
60 min. The rate at which T re fell was linearly related to the product of
inspired gas density times specific heat. The metabolic response (VO2) to
this isolated core cooling was more closely related to the rate of fall in
T re than to the magnitude of this fall. A distinct threshold temperature,
below which a rise in VO2 would occur, was not demonstrable. However, when
the rate of fall of T re exceeded 0.70 degrees C . h-1, VO2 increased above
base line, in spite of high skin temperatures that may have blunted the VO2
response. When VO2 did increase, its net benefit on thermal homeostasis was
negated by the associated rise in pulmonary ventilation and its attendant
increase in respiratory heat loss. Breathing cool helium-oxygen under
hyperbaric conditions can rapidly lower deep body temperature, even in the
presence of a warm body surface.
