Head-temperature effects on physiology, comfort, and performance during hyperthermia

Area of Science:

• Environmental Physiology
• Human Factors Engineering

Background:

• Maintaining thermal comfort and cognitive function is crucial in occupational settings.
• Hyperthermic conditions can impair physiological and psychological performance.

Purpose of the Study:

• To investigate the impact of head temperature on physiological responses and cognitive performance under hyperthermic conditions.
• To determine if localized head cooling can mitigate negative effects of whole-body heating.

Main Methods:

• Six volunteers underwent experiments involving a liquid-conditioned garment and a temperature-controlled cap.
• Esophageal temperature (Tes) and rectal temperature (Tre) were monitored, alongside cognitive performance and reaction time.
• Subjects experienced various combinations of suit and cap temperatures in a controlled 30°C ambient environment.

Main Results:

• Head temperature significantly altered the rate of change in esophageal temperature (Tes), with cool heads sometimes limiting peak Tes.
• Head cooling, despite covering minimal body surface area, was a major factor in subjective comfort.
• Body heating impaired cognitive performance and reaction time, while head cooling largely reversed these impairments.

Conclusions:

• Localized head temperature exerts a significant influence on thermal comfort and cognitive performance, independent of core body temperature.
• Head cooling presents a viable strategy to improve operator performance and comfort in hot environments where full-body thermoneutrality is unachievable.
• Potential mechanisms include altered heat balance, countercurrent heat exchange in the neck, and modified sensory input.