Thermophysiological responses of human volunteers during controlled whole-body radio frequency exposure at 450 MHz.

Thermoregulatory responses of heat production and heat loss were measured in seven adult volunteers (four women and three men, aged 21-57 yr) during 45-min dorsal exposures of the whole body to 450 MHz continuous wave radio frequency (RF) fields. Two power densities (PD) (local peak PD = 18 and 24 mW/cm2; local peak specific absorption rate = 0.320 [W/kg]/[mW/cm2]) were tested in each of three ambient temperatures (Ta = 24, 28, and 31 degrees C) plus Ta controls (no RF). No changes in metabolic heat production occurred under any exposure conditions. Vigorous increases in sweating rate on back and chest, directly related to both Ta and PD, cooled the skin and ensured efficient regulation of the deep body (esophageal) temperature to within 0.1 degrees C of the normal level. Category judgments of thermal sensation, comfort, sweating, and thermal preference usually matched the measured changes in physiological responses. Some subtle effects related to gender were noted that confirm classic physiological data. Our results indicate that dorsal exposures of humans to a supraresonant frequency of 450 MHz at local peak specific absorption rates up to 7.68 W/kg are mildly thermogenic and are counteracted efficiently by normal thermophysiologic heat loss mechanisms, principally sweating.