Thermophysiological consequences of whole body resonant RF exposure (100 MHz) in human volunteers

Abstract

Thermophysiological responses of heat production and heat loss were measured in seven adult volunteers (six males and one female, aged 31-74 years) during 45 min dorsal exposures of the whole body to 100 MHz continuous wave (CW) radio frequency (RF) energy. Three power densities (PD) (average PD = 4, 6, and 8 mW/cm(2); whole body specific absorption rate [SAR] = 0.068 [W/kg]/[mW/cm(2)]) were tested in each of three ambient temperatures (T(a) = 24, 28, and 31 degrees C), as well as in T(a) controls (no RF). A standardized protocol (30 min baseline, 45 min RF or sham exposure, 10 min baseline) was used. Measured responses included esophageal and seven skin temperatures, metabolic heat production, local sweat rate, and local skin blood flow. No changes in metabolic heat production occurred under any test condition. Unlike published results of similar exposures at 450 and 2450 MHz, local skin temperatures, even those on the back that were irradiated directly, changed little or not at all during 100 MHz exposures. The sole exception was the temperature of the ankle skin, which increased by 3-4 degrees C in some subjects at PD = 8 mW/cm(2). During the 45 min RF exposure, esophageal temperature showed modest changes (range = -0.15 to 0.13 degrees C) and never exceeded 37.2 degrees C. Thermoregulation was principally controlled by appropriate increases in evaporative heat loss (sweating) and, to a lesser extent, by changes in skin blood flow. Because of the deep penetration of RF energy at this frequency, effectively bypassing the skin, these changes must have been stimulated by thermal receptors deep in the body rather than those located in the skin.

The relation between the specific absorption rate and electromagnetic field intensity for heterogeneous exposure conditions at mobile communications frequencies

“…Looking at both scenarios together, 12% of the examined cases lead to lower averaged electric field strengths required to reach the whole-body SAR limit of 0.08 W/kg at 946 MHz, 15% at 1840 MHz, and 22% at 2140 MHz. For 946 MHz, these results are shown in Figure 4; an overview of the results of this work [Neubauer et al, 2006] being in line with results from [Bernardi et al, 2000[Bernardi et al, , 2002Adair et al, 2003] is given in Figure 5. It is interesting to note that more cases with higher heterogeneous exposure can be found both at 946 and 1840 MHz for scenario 1, but not for 2140 MHz, where more cases with higher heterogeneous exposure can be found for scenario 2.…”

Comment on “Scaling the thermophysiological effects of radiofrequency radiation—revisited”

“…I believe that the data collected by Adair et al [2003] validates the concept that body mass is a critical factor that predicts the sensitivity to RF radiation under most environmental conditions. This validation should help researchers interested in extrapolating their bioeffects data collected in experimental species to humans.…”

“…I would be remiss if I did not comment on the similarity between the threshold SARs reported by Adair et al [2003] and the predicted threshold SARs for human responses that I made in 1982 [Gordon, 1982]. At the time of publication there were no data on the thermophysiological responses of humans when exposed to RF radiation.…”

“…Eleanor Adair and colleagues have published results of an excellent study on the thermophysiological consequences of whole-body resonant exposure to 100 MHz in humans [Adair et al, 2003]. They recorded sweating and several other thermoeffectors in humans (in swim suits) exposed for 45 min to 100 MHz when maintained at ambient temperatures (T a ) of 24, 28, and 31 8C.…”

“…However, when the regression line is extrapolated to the mass of an 83 kg adult human, the average weight of subjects in Adair et al, 2003, the threshold SAR is predicted to be 0.26 W/kg. This threshold is equal to or slightly below the threshold SARs that were recently published by Adair et al [2003]. I have plotted their threshold SARs for the elicitation of sweating in humans at T a 's of 24-31 8C (Fig.…”