Thermophysiological Effects of Electromagnetic Radiation

Eleanor R. Adair production; a positive load error will yield heat loss. John B. Pierce Foundation and Yale University The particular thermoregulatory response that is mobilized, as well as its vigor, depends on the prevailing thermal environment. Figure 1 presents a schematic "thermoregulaTHERMOREGULATION AND tory profile" of a typical endotherm, illustrating how the PHYSIOLOGICAL RESPONSES principal effector responses of heat production, thermal H UMAN BEINGS function most efficiently when the temconductance, and evaporative heat loss depend on the perature of their vital internal organs is maintained at a ambient temperature. The responses (coded as Rl, R2, and relatively constant level near 37°C (98.6°F). The usual range R3) are considered to be steady-state, rather than transient, of "normal" body temperatures (35.5 to 39°C) results from and the air is considered to have minimal movement and circadian variation, variations in ambient temperature, sewater content. The profile exhibits three distinct zones, quelae of food intake, vigorous exercise, age factors, cyclical delineated in terms of the prevailing effector response. Below variation in women, illness, and emotional factors. Temperasome lower critical ambient temperature (LCT), thermoregutures outside this range must be related to major disease lation is brought about by changes in metabolic heat producstates, pharmacological intervention, unusual activity, or tion (R1), and other responses (R2 and R3) remain at minimal extraordinary environmental conditions. strength (resting level). Both shivering and non-shivering Humans are classified as endotherms, species characterthermogenesis contribute to Rl. In general, the lower the ized by the ability to produce heat in their bodies through ambient temperature, the greater is the heat production, up to metabolic processes (M). When humans are exposed to some maximum that varies with species. As detailed below, electromagnetic (EM) radiation, frictional heat can also be EM energy absorbed by an endotherm in a cool environment generated passively in body tissues as the water molecules will spare Rl in proportion to the field strength. This fact oscillate at the frequency of the imposed field. To avoid a rise derives from the heat balance equation and forms the basis of in body temperature, this heat must be continually transferthe recent proposal [1, 2, 3] that microwave radiation be used red to the environment by radiation (R), conduction (K), and to comfort-heat humans in otherwise-cool interior spaces. convection (C), the mechanisms of dry heat loss, or by At ambient temperatures (T8) above LCT, R1 is at a low, evaporation of water from the skin and respiratory tract (E). resting level that is characteristic of the species; R3 is also The primary environmental variables that regulate the transminimal; and thermoregulation is accomplished by changes in fer of heat away from the body are the air temperature (T.), thermal conductance (R2). Conductance is a measure of heat air movement (V), and humidity (RH); also important are the flow from the body core to the skin and reflects the mean radiant temperatures of surfaces surrounding the body vasomotor tone of the peripheral blood vessels. In the cold, and the amount of body insulation (fur, fat, clothing, etc.). the blood vessels of the skin are vasoconstricted, effectively Under steady-state conditions, when the energy produced in increasing the thickness of the body's insulation. In neutral the body is balanced by that lost to the environment, storage Ta, as the constricted skin vessels begin to vasodilate, warm (S) of heat is minimal and deep body temperature remains blood from the body core is brought to the surface so that stable. This condition may be expressed in an energy (heat) heat may be lost to the environment by radiation and balance equation convection. These vasomotor adjustments take place within