The effect of hypoglycemia on thermoregulatory responses.
Passias, Thanasis C., Graydon S. Meneilly, and Igor B. Mekjavie.
School of Kinesiology, Simon Fraser University, Burnaby, British
Columbia, Canada V5A 1S6, Faculty of Medicine, University of British
Columbia, British Columbia, Canada V6T IZ3
APStracts 2:0466A, 1995.
The effects of hypogycemia on sweating, skin blood perfusion and
shivering responses were investigated in ten healthy male volunteers.
They exercised on an underwater cycle ergometer while immersed to the
neck in 28 C water for 20 minutes at 50% of their maximal work rate.
The exercise-induced elevation in esophageal temperature (Tes)
initiated the sweating response (Esw) and increased skin blood
perfusion (SkBP), as measured at the forehead. In the 99 min post
-exercise immersion period the [lambda]Tes (Tes relative to resting
level) values at which Esw abated, SkBP reached pre-exercise values,
and shivering commenced were defined as the [lambda]Tes thresholds
for cessation of sweating, passive vasodilation and onset of
shivering, respectively. Two trials were conducted one week apart. In
one trial the subject was hypoglycemic and in the other euglycemic
(plasma glucose was maintained at 2.8 and 5 mM, respectively) with
the use of the hyperinsulinemic (insulin infusion rate = 60 mU.m
-2.min-1) glucose clamp technique. Oxygen uptake (VO2), Esw, Tes, mean
skin temperature (Tsk), heat flux (Q) from the skin and SkBP were
recorded at minute intervals. Although Q and SkBP attained
significantly higher end-exercise levels during euglycemia, the
responses were similar during the post-exercise cooling period.
Hypoglycemia did not affect the Esw response during the exercise and
cooling periods. Whereas the exercise [lambda]Tes response was
unaffected by hypoglycemia, the decrease in Tes was greater (p <
0.005) during the hypoglycemic than the euglycemic condition.
Hypoglycemia did not alter the [lambda]Tes threshold for cessation of
sweating and passive vasodilation but reduced (p < 0.001) the
[lambda]Tes threshold for onset of shivering (from -0.09 + 0.07 C in
the euglycemic condition to -0.65 + 0.12 C in the hypoglycemic
condition). The present results indicate that hypoglycemia (2.8 mM)
does not affect the [lambda]Tes threshold for cessation of
thermoregulatory sweating nor the threshold for passive vasodilation
during recovery from exercise-induced moderate heat stress, but
decreases the core temperature threshold for shivering during cold
exposure.
Received 30 November 1993; accepted in final form 16 October
1995.
APS Manuscript Number A1149-3.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 6 November 95