Medical/biological study (experimental study)

Human exposure at two radio frequencies (450 and 2450 MHz): similarities and differences in physiological response med./bio.

By: Adair ER, Cobb BL, Mylacraine KS, Kelleher SA

Published in: Bioelectromagnetics 1999; 20 Suppl 4: 12-20

Aim of study (acc. to author)

To study thermoregulatory responses of heat production and heat loss in seven volunteers during exposure to 2450 MHz continuous wave radiofrequency fields.
The results of this study were compared to results of an earlier study at 450 MHz (publication 2256).

Background/further details

Two power densities were tested at each of three ambient temperatures (24, 28, and 31°C).

Endpoint

thermoregulation: thermoregulatory responses of heat production and heat loss

Exposure

- 2.45 GHz
- microwaves

Exposure	Parameters
Exposure 1: 2,450 MHz Modulation type: CW Exposure duration: continuous for 45 min	power density: 27 mW/cm² maximum SAR: 5.94 W/kg maximum (at the surface) power density: 35 mW/cm² maximum SAR: 7.7 W/kg maximum (at the surface)

Exposure 1

Main characteristics

Frequency	2,450 MHz
Type	electromagnetic field
Charakteristic	far field
Exposure duration	continuous for 45 min
Additional info	A report on the comparable earlier 450 MHz study (using identical procedures) can be found in the reference article.

Modulation

Modulation type	CW

Exposure setup

Exposure source	horn antenna anechoic chamber Klystron amplifier
Distance between exposed object and exposure source	1 m
Chamber	The electrically shielded anechoic chamber was 2.45 m x 2.45 m x 3.66 m. A small climate-conditioned cubicle of 1.47 m x 2.00 m x 2.06 m was created by a 5-cm thick Styrofoam partition.
Setup	Subjects wearing a bathing suit sat in a light plastic chair with their back towards the 15-dB standard-gain horn antenna. The electric field vector was aligned with the long axis of the subject's body (E-polarization).
Sham exposure	A sham exposure was conducted.
Additional info	After 30 min of equilibration to the prevailing temperature (24, 28, or 31 °C), the subjects were exposed or sham exposed for 45 min.

Parameters

Measurand	Value	Type	Method	Mass	Remarks
power density	27 mW/cm²	maximum	measured	-	-
SAR	5.94 W/kg	maximum	measured	-	at the surface
power density	35 mW/cm²	maximum	measured	-	-
SAR	7.7 W/kg	maximum	measured	-	at the surface

Additional parameter details

Power densities (PD) specified above were determined with the E-field probe placed on the antenna boresight at the location of the subject's center back. These PDs were verified every few weeks during the course of the study.

Measurement and calculation details

Forward and reflected powers were monitored by power meters with the power sensors located in the waveguide between transmitter and antenna. Field uniformity at the subject's location was determined over two 65 x 80 cm planes centered on the boresight and at 1 and 1.5 m from the leading edge of the antenna using a broadband isotropic radiation detector fitted with an E-field probe. PD across the central 25 x 45 cm portion of each plane showed a 13% nonuniformity with the chair absent. Dosimetric evaluations were conducted on a 70-kg soft plastic mannequin model filled with simulated muscle tissue and placed on the chair [Adair et al., 1998]. After equilibration, the model was irradiated for 10 min at three PD values. The maximum surface SAR of 0.22 W/kg per mW/cm² was calculated from the greatest temperature rise occurring at the lower back [Chou et al., 1996, publication 1466].

Reference articles

Adair ER et al. (1998): Thermophysiological responses of human volunteers during controlled whole-body radio frequency exposure at 450 MHz

Exposed system:

human
partial body: back

Methods Endpoint/measurement parameters/methodology

effects on the cardiovascular system: local skin blood flow at three sites (anterior forearm, anterior thigh, upper back)
thermoregulation: deep body (esophageal) temperature; skin temperature at six sites (anterior thigh, upper chest, forearm, upper and lower back, forehead); metabolic heat production (fractions of oxygen and carbon dioxide in the expired air); local sweating rate

Investigated system:

investigation on living organism

Investigated organ system:

cardiovascular system

Time of investigation:

during exposure
after exposure

Main outcome of study (acc. to author)

No alteration in metabolic heat production occurred under any irradiation conditions at either frequency (450 and 2450 MHz). The magnitude of increase in those skin temperatures under direct exposure was directly related to frequency, but local sweating rates on back and chest were related more to ambient temperature and SAR. Both efficient sweating and increased local skin blood flow contributed to the regulation of the deep body temperature to within 0.1°C of the baseline level.

Study character:

medical/biological study
experimental study
full/main study

Study funded by

not stated/no funding

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Adair ER et al. (2001): Partial-body exposure of human volunteers to 2450 MHz pulsed or CW fields provokes similar thermoregulatory responses
Adair ER et al. (2001): Human exposure to 2450 MHz CW energy at levels outside the IEEE C95.1 standard does not increase core temperature
Adair ER et al. (1998): Thermophysiological responses of human volunteers during controlled whole-body radio frequency exposure at 450 MHz