Human exposure at two radio frequencies (450 and 2450 MHz): Similarities and differences in physiological response

Thermoregulatory responses of heat production and heat loss were measured i n two different groups of seven adult volunteers (males and females) during 45-min dorsal exposures of the whole body to 450 or 2450 MHz continuous-wa ve radio frequency (RF) fields. At each frequency, two power densities (PD) were tested at each of three ambient temperatures (T-a = 24, 28, and 31 de grees C) plus T-a controls (no RP). The normalized peak surface specific ab sorption rate (SAR), measured at the location of the subject's center back, was the same for comparable PD at both frequencies, i.e., peak surface SAR = 6.0 and 7.7 W/kg. No change in metabolic heat production occurred under any exposure conditions at either frequency. The magnitude of increase in t hose skin temperatures under direct irradiation was directly related to fre quency, but local sweating rates on back and chest were related more to T-a and SAR. Both efficient sweating and increased local skin blood flow contr ibuted to the regulation of the deep body (esophageal) temperature to withi n 0.1 degrees C of the baseline level. At both frequencies, normalized peak SARs in excess of ANSI/IEEE C95.1 guidelines were easily counteracted by n ormal thermophysiological mechanisms. The observed frequency-related respon se differences agree with classical data concerning the control of heat los s mechanisms in human beings. However, more practical dosimetry than is cur rently available will be necessary to evaluate realistic human exposures to RF energy in the natural environment. Bioelectromagnetics 20:12-20, 1999. Published 1999 Wiley-Liss, Inc.dagger.