Thermoregulatory responses to RF energy absorption

Abstract

This white paper combines a tutorial on the fundamentals of thermoregulation with a review of the current literature concerned with physiological thermoregulatory responses of humans and laboratory animals in the presence of radio frequency (RF) and microwave fields. The ultimate goal of research involving whole body RF exposure of intact organisms is the prediction of effects of such exposure on human beings. Most of the published research on physiological thermoregulation has been conducted on laboratory animals, with a heavy emphasis on laboratory rodents. Because their physiological heat loss mechanisms are limited, these small animals are very poor models for human beings. Basic information about the thermoregulatory capabilities of animal models relative to human capability is essential for the appropriate evaluation and extrapolation of animal data to humans. In general, reliance on data collected on humans and nonhuman primates, however fragmentary, yields a more accurate understanding of how RF fields interact with humans. Such data are featured in this review, including data from both clinic and laboratory. Featured topics include thermal sensation, human RF overexposures, exposures attending magnetic resonance imaging (MRI), predictions based on simulation models, and laboratory studies of human volunteers. Supporting data from animal studies include the thermoregulatory profile, response thresholds, physiological responses of heat production and heat loss, intense or prolonged exposure, RF effects on early development, circadian variation, and additive drug-microwave interactions. The conclusion is inescapable that humans demonstrate far superior thermoregulatory ability over other tested organisms during RF exposure at, or even above current human exposure guidelines. Bioelectromagnetics Supplement 6:S17-S38, 2003.

Estimation of Core Temperature Elevation in Humans and Animals for Whole-Body Averaged Sar

“…Heat dissipation due to the perspiration rate is not sufficient in the rabbit, leading to excess temperature elevation. This result coincides with the claim in [6]. Figure 3 shows the difference in the core temperature elevations between FDTD results and results with (13) at 6, 30, and 60 mins.…”

“…Based on the formula, the WBA-SAR, which is a metric of international safety standard/guidelines, is shown to be a good measure for estimating core temperature elevation. However, it depends on the species, as pointed out in [6]. We clarified the main factors influencing the core temperature elevation as the body surface area-to-weight ratio and perspiration rate.…”

“…As expected from [12], core temperature elevation in humans exposed at the allowable limit in the safety guidelines/standards is comparable to a fluoroptic thermometer resolution of 0.1 • C. The computational method of our thermal dosimetry is given briefly, since it is based on our formula. The air temperature is 28 • C as a thermoneutral condition, and thus we do not need to consider metabolic adjustments [6]. Note that computational thermal dosimetry in humans has been conducted extensively for whole-body exposures in different scenarios [18][19][20].…”

“…This threshold is based on the fact that RF exposure of laboratory animals in excess of approximately 4 W/kg has revealed a characteristic pattern of thermoregulatory response [4]. In addition, decreased task performance by rats and monkeys has been observed at WBA-SAR in the range of 1-3 W/kg [5] According to Adair and Black [6], the physiological heat loss mechanisms are different for different species. In particular, small animals would be poor models for human beings.…”

Thermal aspects of exposure to radiofrequency energy: Report of a workshop

“…In these studies, human volunteers were exposed to RF energy at several frequencies (100, 450 and 2450 MHz) for extended times (45 min) at different environmental temperatures (24 , 28 , 31 C) [18]). In these experiments, the whole body average SAR ranged up to about 1 W/ kg (more than twice the basic restriction in the IEEE and ICNIRP limits for occupational exposures, and more than 12 times the basic restriction for the general public).…”