HEAD-TEMPERATURE EFFECTS ON PHYSIOLOGY, COMFORT, AND PERFORMANCE DURING HYPERTHERMIA

  • 1 January 1982
    • journal article
    • research article
    • Vol. 53  (7) , 623-628
Abstract
The effects of head temperature on subjects under hyperthermic conditions were assessed. Six volunteers were trained to plateau on a manikin task that tested cognitive performance and reaction time. A subject''s core temperature was driven with a full-length, liquid-conditioned garment perfused with water at 30.degree. or 43.degree. C, and head temperature was controlled by a cap with an inlet temperature of 8.degree. or 43.degree. C. Heavy insulation was worn overall; ambient temperature was 30.degree. C. Subjects were heated and cooled twice during each experiment to include all possible cap/suit temperature combinations. Each subject did 1 control and 4 stress experiments. Comfort and performance were measured as the subject''s esophageal temperature (Tes) rose and fell through the range 37.5-39.0.degree. C. Cap temperature did not affect rectal temperature (Tre) but significantly altered the Tes rate of change; a cool head sometimes truncated the peak Tes value. Although the cap covered only 3-4% of the body surface, the head was a major determinant of subjective comfort. Body heating tended to shorten reaction time and diminish performance accuracy, while head cooling largely reversed these trends. Possible mechanisms include the following: change in overall heat balance; countercurrent exchanges in the neck; and change in sensory output. Head cooling deserves serious consideration for machinery operators where whole-body thermoneutrality is impractical.

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