Thermophysiological Responses of Human Volunteers to Whole Body RF Exposure at 220 MHz
Abstract
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/cm2 1 MW/cm2 10 W/m2, whole body average normalized specific absorption rate SAR =0.045 W/kg/MW/cm2 =0.0045 W/kg/ W/m2) were tested at each of three ambient temperatures (Ta = 24, 28, and 31 deg C) plus Ta controls (no RF). Measured responses included esophageal (Tesoph) and seven skin temperatures (Tsk), 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 Tesoph showed small changes (less than 0.35 deg C) but never exceeded 37.3 C. As with similar exposures at 100 MHz, local Tsk changed little and modest increases in SkBF were recorded. At 220 MHz, vigorous sweating occurred at PD = 12 and 15 mW/cm2, 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.
Document Details
- Document Type
- Technical Report
- Publication Date
- May 19, 2005
- Accession Number
- ADA438453
Entities
People
- Dennis M. Scholl
- Dennis W. Blick
- Eleanor R. Adair
- John M. Ziriax
- Kevin S. Mylacraine
- Stewart J. Allen