Wilderness and Rescue Medicine 7th Edition Jeffrey Isaac, PA-C and David E. Johnson, MD

Chapter 17: Thermoregulation

The core of the human body operates most effi- ciently at or very near a temperature of 37°C. The brain automatically adjusts heat production and retention based on information from temperature sensors in the skin and body core. This thermo- regulatory system uses muscles to generate heat, the skin to dissipate heat, and the endocrine sys- tem to control metabolism. Blood vessels in the skin dilate to dissipate or release heat or constrict to preserve heat. Sweat glands release fluid to enhance cooling by evaporation. Shivering pro- duces heat with involuntary exercise. You can watch this compensation mechanism work, but it is not under your direct control.

When heat energy is released into your skin by contact with a warm object, you feel warmth. When heat energy is removed from your skin, you feel cold. In the healthy individual the perception of being warm or cold, and the need to produce or dissipate heat, is based primarily on conditions affecting the body shell. A number of things can influence this per- ception. Alcohol in a beverage, for example, is a vasodilator that allows more warm blood to perfuse the skin surface, reversing the shell/core compensation. It impairs normal shivering and inhibits effective thermoregulatory sensation and response. Additionally, too much alcohol will impair a person’s ability and desire to care for themselves in cold weather. This example reminds us that our conscious efforts are important to thermoregulation, too. Even the best body morphology will not keep you healthy if you do not pay attention to hydration, calories, and shelter. Problems with heat and cold often have their origins in poor judgment. Problems with thermoregulation can also devel- op when the function of the system is impaired by illness, injury, toxins, or medication. The sys- tem can also be overwhelmed by environmental extremes. Maintaining the function of the ther- moregulatory system is a key element of patient care in the wilderness setting.

General Principles

Thermoregulation

Structure: • Temperature sensors • Endocrine system • Muscles • Skin Function: • Maintain body core at 37°C Problem:

• Too little heat • Too much heat

©2018WMA

Because your body core is always at a tempera- ture of about 37°C, your conscious perception of hot or cold comes from sensors in your skin.