Study type: Medical/biological study (experimental study)

Physiological interaction processes and radio-frequency energy absorption. med./bio.

Published in: Bioelectromagnetics 1992; 13 (6): 497-512

Aim of study (acc. to author)

The question was tested whether the thermoregulatory system might somehow be overwhelmed by exposures at resonance at higher whole-body SARs, even in environments conducive to efficient heat dissipation.

Background/further details

Hyperthermia has been examined in an animal model to determine both the thresholds for response change and the steady-state thermoregulatory compensation for body heating during exposure at resonant (450 MHz) and supra-resonant (2450 MHz, data previously collected) frequencies.

Endpoint

Exposure

Exposure Parameters
Exposure 1: 450 MHz
Modulation type: CW
Exposure duration: repeated exposures for 5 x 10 min separated by 20-min intervals
  • power density: 6 mW/cm² (2, 3, 4, 5, and 6 mW/cm²)
  • SAR: 2.5 W/kg mean (whole body) (0.83, 1.24, 1.65, 2.08, and 2.48 W/kg)
Exposure 2: 450 MHz
Modulation type: CW
Exposure duration: continuous for 90 min
  • power density: 15 mW/cm² (2, 5, 8, 11, and 15 mW/cm²)
  • SAR: 6 W/kg mean (whole body) (0.83, 2.08, 3.3, 4.54, and 6.1 W/kg)
Exposure 3: 2,450 MHz
Modulation type: CW
Exposure duration: repeated exposures for 5 x 10 min separated by re-equilibration intervals
  • SAR: 3.75 W/kg mean (whole body) (0.5-3.75 W/kg)
Exposure 4: 2,450 MHz
Modulation type: CW
Exposure duration: continuous for 90 min
  • SAR: 9 W/kg mean (whole body) (0.5-9 W/kg)

Exposure 1

Main characteristics
Frequency 450 MHz
Type
Charakteristic
Exposure duration repeated exposures for 5 x 10 min separated by 20-min intervals
Modulation
Modulation type CW
Exposure setup
Exposure source
Distance between exposed object and exposure source 130 cm
Chamber The anechoic chamber was 2.44 m x 2.44 m x 3.05 m. The half-wave dipole antenna was mounted in a 90° corner reflector.
Setup Monkeys were restrained in a chair inside a ventilated Styrofoam test compartment (30 cm x 33 cm x 78 cm). The electric field vector of the incident plane wave was aligned with the long axis of the animal's body (E-polarization).
Sham exposure A sham exposure was conducted.
Additional info After 90 min of equilibration, the monkey received five 10-min MW exposures of increasing power density separated by 20-min intervals. Three such sessions were conducted on each monkey at each ambient temperature (15, 20, 25, or 30 °C).
Parameters
Measurand Value Type Method Mass Remarks
power density 6 mW/cm² - measured - 2, 3, 4, 5, and 6 mW/cm²
SAR 2.5 W/kg mean measured whole body 0.83, 1.24, 1.65, 2.08, and 2.48 W/kg

Exposure 2

Main characteristics
Frequency 450 MHz
Type
Charakteristic
Exposure duration continuous for 90 min
Modulation
Modulation type CW
Exposure setup
Exposure source
Sham exposure A sham exposure was conducted.
Additional info Following equilibration, the monkey was exposed to a single power density for 90 min at 20 °C. Three sessions were conducted on each monkey at each power density.
Parameters
Measurand Value Type Method Mass Remarks
power density 15 mW/cm² - measured - 2, 5, 8, 11, and 15 mW/cm²
SAR 6 W/kg mean measured whole body 0.83, 2.08, 3.3, 4.54, and 6.1 W/kg

Exposure 3

Main characteristics
Frequency 2,450 MHz
Type
Charakteristic
Exposure duration repeated exposures for 5 x 10 min separated by re-equilibration intervals
Modulation
Modulation type CW
Exposure setup
Exposure source
  • not specified
Additional info Earlier data collected on comparable groups of animals, exposed to 2,450-MHz CW fields in environments similar to E1 [Adair and Adams, 1982; Adair, 1987] was compared to data from the present experiments.
Parameters
Measurand Value Type Method Mass Remarks
SAR 3.75 W/kg mean measured whole body 0.5-3.75 W/kg

Exposure 4

Main characteristics
Frequency 2,450 MHz
Type
Charakteristic
Exposure duration continuous for 90 min
Additional info Adair ER (1987): Microwave challenges to the thermoregulatory system. USAF Report SAM-TR-87-7, August. Brooks AFB, TX: School of Aerospace Medicine.
Modulation
Modulation type CW
Exposure setup
Exposure source
  • not specified
Additional info Earlier 2,450-MHz data collected under protocols identical to E2 [Adair, 1987] was compared to data from the present experiments.
Parameters
Measurand Value Type Method Mass Remarks
SAR 9 W/kg mean measured whole body 0.5-9 W/kg

Reference articles

Exposed system:

Methods Endpoint/measurement parameters/methodology

Investigated system:
Investigated organ system:
Time of investigation:
  • during exposure

Main outcome of study (acc. to author)

The reduction of metabolic heat production was directly proportional to the SAR during brief radiofrequency exposures in the cold. 2450 MHz energy was a more efficient stimulus than was 450 MHz. In the steady state, a regulated increase in deep body temperature accompanied exposure at resonance, not unlike that which occurs during exercise. The results indicate that temperature changes in the skin are the primary source of the neural signal for a change in physiological interaction processes during radiofrequency exposure in the cold.

Study character:

Study funded by

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