Study type: Medical/biological study (experimental study)

Regional brain heating during microwave exposure (2.06 GHz), warm-water immersion, environmental heating and exercise med./bio.

By: Walters TJ, Ryan KL, Belcher JC, Doyle JM, Tehrany MR, Mason PA
Published in: Bioelectromagnetics 1998; 19 (6): 341-353
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Aim of study (acc. to author)

To examine the possibility of different pattern of brain heating by high-powered microwave exposure in rats. Temperatures were measured directly in the hypothalamus and cortex during heating by high-powered microwaves, warm water immersion (WWI), environmental heating (warm ambient environment, WSED), or exercise-induced heating (exercised on a treadmill in a warm ambient environment, WEX).

Endpoint

Exposure

Exposure Parameters
Exposure 1: 2.06 GHz
Exposure duration: 240 s
Exposure 2: 2.06 GHz
Exposure duration: 30 s

General information

Experiment 1: rats were implated with rectal and brain temperature probes in the hypothalamus and cortex. Experiment 2: rats were implated with a single brain temperature probe , either in the hypothalamus or cortex.

Exposure 1

Main characteristics
Frequency 2.06 GHz
Type
Waveform
Charakteristic
Polarization
Exposure duration 240 s
Exposure setup
Exposure source
Chamber anechoic chamber
Setup rats were maintained in k-orientation by placing them in a rectangular shaped Styrofoam restrainer (9 cm x 6 cm x 27 cm whl) with a PVC head and Plexiglas tail gate.
Parameters
Measurand Value Type Method Mass Remarks
SAR 122.4 mW/g - cf. remarks cf. remarks hypothalamus
power density 170 mW/cm² mean measured - in front of the retainer's headgate
SAR 49.3 mW/g - cf. remarks cf. remarks cortex

Exposure 2

Main characteristics
Frequency 2.06 GHz
Type
Waveform
Charakteristic
Polarization
Exposure duration 30 s
Exposure setup
Exposure source
Chamber anechoic chamber
Setup rats were maintained in k-orientation by placing them in a rectangular shaped Styrofoam restrainer (9 cm x 6 cm x 27 cm whl) with a PVC head and Plexiglas tail gate.
Parameters
Measurand Value Type Method Mass Remarks
SAR 1.224 W/g - cf. remarks cf. remarks hypothalamus
power density 1.7 W/cm² mean measured - in front of the retainer's headgate
SAR 493 mW/g - cf. remarks cf. remarks cortex

Exposed system:

Methods Endpoint/measurement parameters/methodology

Investigated system:
Time of investigation:
  • during exposure

Main outcome of study (acc. to author)

The increase in hypothalamic temperature was significantly greater than those in cortical or rectal temperatures when animals were exposed to high-power density. Low-power density produced more homogenous heating. Quantitatively similar results were observed whether animals were implanted with probes in two brain sites or a single probe in one or the other of two sites. WWI produced uniform heating in the regions measured. Similar rates of temperature increase occured among regions following WSED or WEX, thus maintaining the pre-existing gradient between hypothalamic temperature and cortical temperature. The results indicate that high-power density produced a 2-2.5-fold difference in the rate-of-heating within brain regions that were separated by only a few millimeters. In contrast, more homogenous heating was found during low-power density or nonmicrowave modalities of heating.

Study character:

Study funded by

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