Masuda H, Hirata A, Kawai H, Wake K, Watanabe S, Arima T, Poulletier de Gannes F, Lagroye I, Veyret B. Local exposure of the rat cortex to radiofrequency electromagnetic fields increases local cerebral blood flow along with temperature. J Appl Physiol. Oct 28, 2010. Ahead of print.
Humans and other mammals maintain internal temperature via autonomic thermoregulation. Excessive heat, for example, is dissipated through increases in blood flow and sweating. High-intensity exposure to radiofrequency (RF) electromagnetic fields results in temperature increases in exposed tissues, and in this way can affect physiological functions. In particular, local exposure to high intensity RF generates heat in the brain and can induce physiological changes. In the last three decades, few studies have been conducted on the effects of high intensity RF, most studies being focused on exposures to low levels of RF exposures that do not induce temperature rise in the brain.
The objective of the study was “to explore the effects of local RF exposure on the rat cerebrum and to clarify the intensity-dependent response”.
The experiments were conducted on anesthetized Sprague-Dawley rats (7 rats per exposure group). The target area of the cortex was exposed locally to 1,950 MHz RF at SAR 10.5, 40.3, 130 and 263 W/kg averaged over 4.04 mg . Two physiological parameters were measured: local cerebral blood flow (CBF) and temperature in three regions (target cortical area, rectum and calf hypodermis). Differences between RF-exposed and sham-exposed groups were evaluated at 6, 12 and 18 minutes of exposure. Associations between RF intensity and physiological parameters and associations among physiological parameters were evaluated at 18 minutes of exposure.
After 6 and 12 minutes of exposure, local cerebral blood flow was increased (compared to sham-exposed group) at higher SARs (40-263 W/kg). At the end of exposure (18 min), cerebral blood flow was increased at all SAR levels. The temperature in the target cortical area increased significantly at all SAR levels at 6, 12 and 18 minutes of exposure. Rectal temperature was significantly elevated at SAR 40-263 W/kg at 6, 12 and 18 minutes of exposure and hypodermal temperature – only after 12 and 18 minutes of exposure at 263 W/kg. These results suggest that local exposure at 10 W/kg alters only the local cerebral blood flow and the temperature in the target area, but not the temperature in the rectum and in the calf hypodermis. Local cerebral blood flow, temperature in the target area and temperature in the rectum were significantly associated with RF intensity (R2=0.71, R2=0.99 and R2=0.89, respectively). No significant association was seen between RF intensity and hypodermal temperature. Cerebral blood flow was significantly correlated with the target area temperature (R2=0.72) and with the rectal temperature (R2=0.61).
Interpretation and Conclusion
The authors have concluded: “These findings suggest that local RF exposure to rat cortex regions drives a regulation of cerebral blood flow accompanied by a local temperature elevation under the present exposure conditions. In spite of the large differences between humans and rats in terms of size and physiology, our findings may be helpful for discussing physiological changes in the human cortex locally exposed to RF.”
The basic restriction values established by the International Commission on Non-Ionizing Radiation Protection for local exposure to RF are 2W/kg for general public exposure and 10 W/kg for occupational exposure (averaged over 10 g of tissue for head and trunk).