Thermal Mechanisms of Interaction of Radiofrequency Energy With Biological Systems With Relevance to Exposure Guidelines

Abstract

This article reviews thermal mechanisms of interaction between radiofrequency (RF) fields and biological systems, focusing on theoretical frameworks that are of potential use in setting guidelines for human exposure to RF energy. Several classes of thermal mechanisms are reviewed that depend on the temperature increase or rate of temperature increase and the relevant dosimetric considerations associated with these mechanisms. In addition, attention is drawn to possible molecular and physiological reactions that could be induced by temperature elevations below 0.1 degrees, which are normal physiological responses to heat, and to the so-called microwave auditory effect, which is a physiologically trivial effect resulting from thermally-induced acoustic stimuli. It is suggested that some reported "nonthermal" effects of RF energy may be thermal in nature; also that subtle thermal effects from RF energy exist but have no consequence to health or safety. It is proposed that future revisions of exposure guidelines make more explicit use of thermal models and empirical data on thermal effects in quantifying potential hazards of RF fields.

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

“…This present writer notes that a rough analysis, based on Pennes' bioheat equation [26], is consistent with these findings. Considering only heat transport by blood perfusion, and ignoring the effects of heat conduction and loss of heat to the outside environment, the bioheat equation predicts a steady-state increase in temperature of…”

“…suggests, to help clarify the sometimes confusing RF bioeffects literature, it would be useful to develop a better understanding of biological phenomena associated with such important processes as development of thermotolerance and temperature sensing by the thermoregulatory system, which can be highly sensitive to small temperature increases above normal [26]. A better understanding of biological effects of small temperature changes, apart from thermal damage, might help clarify some reported 'non-thermal' effects of radiofrequency energy, some of which may in fact be 'thermal' after all.…”

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

“…For a temperature elevation above a certain level, blood perfusion was activated in order to carry away the excess heat produced [20,28]. As to the blood perfusion for all tissues except the skin, the regulation mechanism was governed by the local tissue temperature.…”

Letter to the Editor

“…If exposure continues indefinitely it may be necessary to consider whether long-term dependence on these mechanisms may exact any penalty on the body. As discussed by Foster and Glaser [5], the understanding of thermal transfer mechanisms is important to the secondary aspects of exposure standards, those that specify spatial and temporal averaging.…”

“…The possibility of subtle effects due to even small temperature rises can make interpretation of other effects very difficult. An example, discussed by Foster and Glaser [5], is the work of de Pomerai and associates on gene expression and development in the nematode Caenorhabditis elegans and the evolving understanding of the role of heating in explaining experimental observations. While early work showed an apparently non-thermal heat-shock response [6] and changes in growth and maturation [7][8], subsequent refinement of technique and equipment identified the presence of unexpected heating and of a biological response to a very small temperature change [9].…”