Journal of Applied Physiology, Vol 59, Issue 5 1423-1427, Copyright © 1985 by American Physiological Society
Respiration during hypothermia: effect of rewarming intermediate areas of ventral medulla
J. P. Kiley, F. L. Eldridge and D. E. Millhorn
We studied respiration (phrenic nerve activity) during progressive
hypothermia to as low as 30.5 degrees C in five anesthetized, paralyzed,
glomectomized, and vagotomized cats. PCO2 was maintained at a constant
level throughout the experiments. We confirmed the results of a previous
study (J. P. Kiley, F. L. Eldridge, and D. E. Millhorn, J. Appl. Physiol.
58: 295-312, 1985) in which respiratory minute output decreased
progressively with cooling and respiratory frequency decreased markedly. In
addition we show that focal rewarming to normal temperature (37.5 degrees
C) of the structures in the intermediate areas on the ventral surface of
the medulla resulted in a significant reversal of the depressed respiratory
minute activity observed with hypothermia. Respiratory frequency, however,
was unaffected by intermediate area rewarming. We conclude that the
decreased respiratory activity during hypothermia is due to a generalized
interference with neural function. A major portion of these effects is due
to cooling of the intermediate areas, but the slowing of respiratory
frequency appears to be an independent effect.
