Thermoregulation: Its Role in Microwave Exposure

Abstract

The thermogenic properties of exposure to radio frequency (RF) and microwave fields are well recognized. Indeed, most current safety guidelines are based on the premise that significant increases in tissue temperature of RF-exposed human beings should not be permitted. While some investigators have argued that there are other responses that can be initiated at “non-thermal” levels of RF energy, concrete evidence to support this view is lacking. The term “non-thermal” is often defined in terms of the lack of a measurable increase in the temperature of exposed tissues. However, even when no changes can be measured in the deep or peripheral temperatures of the body, sensitive thermoregulatory mechanisms are mobilized to dissipate any heat generated in body tissues by the absorption of thermalizing energy from RF sources in the environment. When RF field strengths are significant, these mechanisms are so efficient that only modest increments in body temperatures may occur. However, when RF fields are very intense, as is the case with high-power microwave applications, regions of localized high specific absorption rate (SAR) may occur in which heat is generated faster than it can be dissipated. This condition poses a challenge for the thermoregulatory system of the exposed organism. In describing the role of thermoregulation in microwave exposure, this paper presents information on the organization and function of the controlling system for thermoregulation and some insights on the importance of both SAR and frequency to behavioral and autonomic thermoregulatory responses.