Heat- and Cold-Related Illness

1

What is the definition of a heat-related illness?

An illness resulting from inadequate acclimatization, impaired heat dissipation, increased heat production, and/or an elevated wet bulb globe temperature.

2

How does the human body respond to heat and humidity?

Sensors from the periphery alert the hypothalamus to an elevation in temperature. Signals are then sent to the sweat glands to begin producing sweat and to the vasculature to induce peripheral vasodilatation. In response to this vasodilation, the heart rate (HR) increases to maintain cardiac output (CO) (CO = HR × stroke volume [SV]).

3

What happens when physiologic cooling mechanisms fail?

Increases in core temperature trigger the release of inflammatory mediators, causing cell damage. As blood is directed to the peripheral circulation, tissue hypoperfusion leads to organ ischemia. Ultimately, coagulopathy and organ failure result in death.

4

What is acclimatization?

Acclimatization is the process of developing physiologic adaptations to environmental stress. After 7–14 days in heat and/or humidity, individuals experience an earlier onset of sweating (at lower core temperatures), increased sweat volume, and decreased sweat sodium concentration. During this time, aldosterone levels increase, expanding the plasma volume (increasing SV).

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