Human exposure to 2450 MHz CW energy at levels outside the IEEE C95.1 standard does not increase core temperature

Permission was received from the Brooks AFB Institutional Review Board and the AF Surgeon General's Office to exceed the peak power density (PD = 35 mW/cm(2)) we had previously studied during partial body exposure of human volunteers at 2450 MHz. Two additional peak PD were tested (50 and 70 mW/cm(2)). The higher of these PD (normalized peak local SAR = 15.4 W/kg) is well outside the IEEE C95.1 guidelines for partial body exposure, as is the estimated whole body SAR approximately 1.0 W/kg. Seven volunteers (four males, three females) were tested at each PD in three ambient temperatures (T(a) = 24, 28, and 31 degrees C) under our standard protocol (30 min baseline, 45 min RF exposure, 10 min baseline). The thermophysiological data (esophageal and six skin temperatures, metabolic heat production, local sweat rate, and local skin blood flow) were combined with comparable data at PD = 0, 27, and 35 mW/cm(2) from our 1999 study to generate response functions across PD. No change in esophageal temperature or metabolic heat production was recorded at any PD in any T(a). At PD = 70 mW/cm(2), skin temperature on the upper back (irradiated directly) increased 4.0 degrees C in T(a) = 24 degrees C, 2.6 degrees C in T(a) = 28 degrees C, and 1.8 degrees C in T(a) = 31 degrees C. These differences were primarily due to the increase in local sweat rate, which was greatest in T(a) = 31 degrees C. Also at PD = 70 mW/cm(2), local skin blood flow on the back increased 65% over baseline levels in T(a) = 31 degrees C, but only 40% in T(a) = 24 degrees C. Although T(a) becomes an important variable when RF exposure exceeds the C95.1 partial body exposure limits, vigorous heat loss responses of blood flow and sweating maintain thermal homeostasis efficiently. It is also clear that strong sensations of heat and thermal discomfort will motivate a timely retreat from a strong RF field, long before these physiological responses are exhausted. Published 2001 Wiley-Liss, Inc.