Physiological thermoregulatory responses of human volunteers exposed at two radio frequencies (450 and 1450 MHz)

Physiological thermoregulatory responses of heat production and heat loss were measured in two different groups of seven adult volunteers (both males and females) during 45-min dorsal exposures of the body to either 450 or 2450 MHz continuous wave (CW) radio frequency (RF) fields. At each frequency, two power densities (PD) were tested in each of three ambient temperatures (T_a=24, 28 and 31°C) plus T_a controls (no RF). Normalized peak surface specific absorption rates (SAR) of 6.0 and 7.7 W/kg, measured at the subject´s center back, were the same for comparable PD at both frequencies. No change in metabolic heat production occurred under any exposure condition at either frequency. Those skin areas under direct irradiation showed increases in temperature that were directly related to frequency, but local sweating rates on back and chest were related more to T_a and SAR. Both increased blood flow and increased sweating contributed to the regulation of the deep body (esophageal) temperature to within 0.1°C of the baseline level. Depth of penetration of the RF energy was directly related to the control of these heat loss mechanisms, as would be predicted by classical theory and data