Adair Eleanor R, Blick Dennis W, Allen Stewart J, Mylacraine Kevin S, Ziriax John M, Scholl Dennis M
Air Force, Hamden, CT 06517, USA.
Bioelectromagnetics. 2005 Sep;26(6):448-61. doi: 10.1002/bem.20105.
Since 1994, our research has demonstrated how thermophysiological responses are mobilized in human volunteers exposed to three radio frequencies, 100, 450, and 2450 MHz. A significant gap in this frequency range is now filled by the present study, conducted at 220 MHz. Thermoregulatory responses of heat loss and heat production were measured in six adult volunteers (five males, one female, aged 24-63 years) during 45 min whole body dorsal exposures to 220 MHz radio frequency (RF) energy. Three power densities (PD = 9, 12, and 15 mW/cm(2) [1 mW/cm(2) = 10 W/m(2)], whole body average normalized specific absorption rate [SAR] = 0.045 [W/kg]/[mW/cm(2)] = 0.0045 [W/kg]/[W/m(2)]) were tested at each of three ambient temperatures (T(a) = 24, 28, and 31 degrees C) plus T(a) controls (no RF). Measured responses included esophageal (T(esoph)) and seven skin temperatures (T(sk)), metabolic rate (M), local sweat rate, and local skin blood flow (SkBF). Derived measures included heart rate (HR), respiration rate, and total evaporative water loss (EWL). Finite difference-time domain (FDTD) modeling of a seated 70 kg human exposed to 220 MHz predicted six localized "hot spots" at which local temperatures were also measured. No changes in M occurred under any test condition, while T(esoph) showed small changes (< or =0.35 degrees C) but never exceeded 37.3 degrees C. As with similar exposures at 100 MHz, local T(sk) changed little and modest increases in SkBF were recorded. At 220 MHz, vigorous sweating occurred at PD = 12 and 15 mW/cm(2), with sweating levels higher than those observed for equivalent PD at 100 MHz. Predicted "hot spots" were confirmed by local temperature measurements. The FDTD model showed the local SAR in deep neural tissues that harbor temperature-sensitive neurons (e.g., brainstem, spinal cord) to be greater at 220 than at 100 MHz. Human exposure at both 220 and 100 MHz results in far less skin heating than occurs during exposure at 450 MHz. However, the exposed subjects thermoregulate efficiently because of increased heat loss responses, particularly sweating. It is clear that these responses are controlled by neural signals from thermosensors deep in the brainstem and spinal cord, rather than those in the skin.
自1994年以来，我们的研究已经证明了人类志愿者在暴露于100、450和2450兆赫这三种射频时，热生理反应是如何被调动起来的。目前这项在220兆赫进行的研究填补了该频率范围内的一个显著空白。在六名成年志愿者（五名男性，一名女性，年龄在24 - 63岁之间）全身背部暴露于220兆赫射频（RF）能量45分钟的过程中，测量了散热和产热的体温调节反应。在三种环境温度（Ta = 24、28和31摄氏度）以及Ta对照（无射频）下，分别测试了三种功率密度（PD = 9、12和15毫瓦/平方厘米[1毫瓦/平方厘米 = 10瓦/平方米]，全身平均归一化比吸收率[SAR] = 0.045[瓦/千克]/[毫瓦/平方厘米] = 0.0045[瓦/千克]/[瓦/平方米]）。测量的反应包括食管温度（Tesoph）和七个皮肤温度（Tsk）、代谢率（M）、局部出汗率和局部皮肤血流量（SkBF）。推导得出的指标包括心率（HR）、呼吸频率和总蒸发失水量（EWL）。对一名70千克坐姿人体暴露于220兆赫的有限差分时域（FDTD）建模预测了六个局部“热点”，并在这些位置测量了局部温度。在任何测试条件下，M均未发生变化，而Tesoph有小的变化（≤0.35摄氏度），但从未超过37.3摄氏度。与100兆赫的类似暴露情况一样，局部Tsk变化很小，SkBF有适度增加。在220兆赫时，PD = 12和15毫瓦/平方厘米时出现大量出汗，出汗水平高于在100兆赫时相同PD下观察到的水平。预测的“热点”通过局部温度测量得到了证实。FDTD模型显示，在含有温度敏感神经元的深部神经组织（如脑干、脊髓）中，220兆赫时的局部SAR比100兆赫时更高。220兆赫和100兆赫的人体暴露导致的皮肤加热远低于450兆赫暴露时的情况。然而，由于散热反应增加，尤其是出汗，暴露的受试者能够有效地进行体温调节。很明显，这些反应是由来自脑干和脊髓深处的热传感器的神经信号控制的，而不是由皮肤中的热传感器控制的。
