Cold Water Immersion: The Gold Standard for Exertional Heatstroke Treatment

Douglas J. Casa; Brendon P. McDermott; Elaine C. Lee; Susan W. Yeargin; Lawrence E. Armstrong; Carl M. Maresh

Disclosures

Exerc Sport Sci Rev. 2007;35(3):141-149. 

In This Article

Physiology of CWI

Basic Dynamics and Cooling Capacity of Humans in Water

Water has many physical characteristics that differentiate it from air, helping to explain the powerful cooling that occurs when an athlete with EHS is treated with CWI. For example, water has a thermal conductivity of 630.5 mW/m2 per °K, whereas air is only 26.2 mW/m2 per °K. This 24-fold greater capacity for thermal conductivity translates into a much greater potential for heat transfer.[15,29] Given that in water, the immersed portion has a surface area that is nearly 100% in direct contact with water that surrounds it, the conductive potential is enormous and far superior to air. In addition, the specific heat of water is 4.2 J/g per °K compared with 1.0 J/g per °K for air, and the density of water is 0.9922 g/cm3 compared with 0.0012 g/cm3 for air. The resulting volume-specific heat capacity of water is nearly 3500 times greater than that of air.[15,29] Thus, a person cools four times faster in water than in air of the same temperature.[15] To put it another way, water provides the same cooling capacity as air that is 11°C (20°F) cooler.[15] These principles of the cooling capacity of water apply when a normothermic person is subjected to cold water (as in the case of a person initially capsized in the north Atlantic) and to a hyperthermic individual (from EHS or illness). The initial physiological responses to the cold water are different.[10,12,15,22,23,29] A normothermic person defends body temperature via PVC and shivering (discussed later), whereas a hyperthermic individual blunts these responses so as to cool rapidly (as noted by the immediate drop in temperature, compared with a short period of maintenance for a normorthermic person when both are subjected to CWI).

Peripheral/Central Control of Body Temperature

The degree of PVC and shivering that occurs for an individual during CWI is dictated by the current state of the peripheral and central receptors for body temperature regulation. A great proportion (some have speculated approximately a 9:1 ratio when considering sweat production) of the response is regulated by changes in core body temperature via sensors in the hypothalamus.[25] The remainder of the response is determined by skin temperature. In other words, a 1°C (1.8°F) change in core body temperature elicits an approximately nine-fold greater thermoregulatory response than a 1°C (1.8°F) change in skin temperature.[25] Obviously, skin temperature fluctuates more rapidly and across a greater range of temperatures than core body temperature during daily living.[25] The sensitivity of the responses to fluctuations in skin temperature helps to generate rapid changes in skin blood flow, sweating, and shivering, depending on the change in skin temperature which is influenced by the temperature of the surrounding environment, the degree of skin exposed, exercise, etc.

In EHS, the large change in core body temperature (approximately 5°C/10°F higher than at rest) provides a powerful influence that can partially or completely negate the influence of CWI on lowering skin temperature and the resultant PVC and shivering. Although PVC and shivering likely happen to some degree, the rapid cooling seen in a severely hyperthermic person in CWI shows that the central responses are quite different than initially in a normothermic individual during CWI. In addition, given the powerful cooling that eventually occurs (beginning after about 20 min) for a normothermic individual, the magnitude of thermal conductivity and convection of moving water over the entire body surface shows that adequate perfusion (shunted away because of PVC) may not be necessary to extract the heat of the body in a rapid manner and that these processes can overpower the heat preserved via PVC or shivering.[15,22]

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