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Does acute hypoxemia blunt sympathetic activity in hyperthermia?

L B Rowell1, G L Brengelmann, M V Savage

  • 1Department of Physiology, University of Washington School of Medicine, Seattle 98195.

Journal of Applied Physiology (Bethesda, Md. : 1985)
|January 1, 1989
PubMed
Summary

Acute moderate hypoxemia (low oxygen) does not impair the body's sweating or vasodilation responses to heat. However, it amplifies increases in stress hormones like norepinephrine and heart rate.

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Area of Science:

  • Autonomic Nervous System
  • Cardiovascular Physiology
  • Environmental Physiology

Background:

  • Sympathetic alpha-adrenergic function is known to be depressed by hypoxemia.
  • The impact of combined hypoxemia and sympathoexcitatory stimuli on other sympathetic pathways is less understood.

Purpose of the Study:

  • To investigate if combined hyperthermia and hypoxemia elicit normal sympathetic responses in alpha-adrenergic, beta-adrenergic, cholinergic, and peptidergic pathways.
  • To determine the effects of acute moderate hypoxemia on autonomic thermoregulation and cardiovascular responses.

Main Methods:

  • Human participants (normothermic men) were exposed to controlled hypoxemia and hyperthermia using a water-perfused suit.
  • Four sympathetic pathways were activated: alpha-adrenergic (norepinephrine release), beta-adrenergic (plasma renin activity), cholinergic (sweating), and peptidergic (active vasodilation).

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  • Measurements included body temperature, forearm blood flow, sweat rate, plasma catecholamines, plasma renin activity, and heart rate.

    • Main Results:

    • Heat-induced increases in body temperature, forearm blood flow, and sweat rate remained normal during hypoxemia.
    • Hypoxemia exaggerated increases in plasma norepinephrine, epinephrine, plasma renin activity, and heart rate.
    • Blood pressure responses were not significantly affected by the combined stimuli.

    Conclusions:

    • Acute moderate hypoxemia does not impair active cutaneous vasodilation or sweating during heat stress.
    • Peripheral autonomic functions, including thermoregulation, appear maintained under combined hypoxemia and hyperthermia.
    • Hypoxemia potentiates sympathoexcitatory responses to heat, particularly catecholamine release and heart rate elevation.