EMF-Portal | Studies on microwave and blood-brain barrier interaction

Studies on microwave and blood-brain barrier interaction med./bio.

Aim of study (acc. to author)

Examination of interaction between microwaves and the blood-brain barriers, and correlation of any change in permeability with the quantity and distribution of the absorbed microwave energy.

Endpoint

Exposure

Exposure	Parameters
Exposure 1: 2.45 GHz Modulation type: pulsed Exposure duration: continuous for 20 min	power density: 1 W/cm² mean (80.0 mW/g corresponding average SAR in the brain at 20 µs pulse width and 500 pulses per second) power density: 5 W/m² mean (0.04 mW/g corresponding average SAR in the brain at 10 µs pulse width and 25 pulses per second) power density: 200 W/m² mean (1.6 mW/g corresponding average SAR in the brain at 20 µs pulse width and 500 pulses per second) power density: 50 W/m² mean (0.4 mW/g corresponding average SAR in the brain at 20 µs pulse width and 100 pulses per second) power density: 10 W/m² mean (0.08 mW/g corresponding average SAR in the brain at 10 µs pulse width and 50 pulses per second) power density: 145 mW/cm² mean (11.5 mW/g corresponding average SAR in the brain at 20 µs pulse width and 100 pulses per second)
Exposure 2: 2.45 GHz Modulation type: CW Exposure duration: 15 s	power: 20 W

Parameters

Exposure 1: 2.45 GHz

Modulation type: pulsed

Exposure duration: continuous for 20 min

power density: 1 W/cm² mean (80.0 mW/g corresponding average SAR in the brain at 20 µs pulse width and 500 pulses per second)
power density: 5 W/m² mean (0.04 mW/g corresponding average SAR in the brain at 10 µs pulse width and 25 pulses per second)
power density: 200 W/m² mean (1.6 mW/g corresponding average SAR in the brain at 20 µs pulse width and 500 pulses per second)
power density: 50 W/m² mean (0.4 mW/g corresponding average SAR in the brain at 20 µs pulse width and 100 pulses per second)
power density: 10 W/m² mean (0.08 mW/g corresponding average SAR in the brain at 10 µs pulse width and 50 pulses per second)
power density: 145 mW/cm² mean (11.5 mW/g corresponding average SAR in the brain at 20 µs pulse width and 100 pulses per second)

Exposure 2: 2.45 GHz

Modulation type: CW

Exposure duration: 15 s

power: 20 W

Exposure 1

Main characteristics

Frequency	2.45 GHz
Type	electromagnetic field
Polarization	unspecified
Exposure duration	continuous for 20 min

Modulation

Modulation type	pulsed
Additional info	rectangular shaped 10 and 20 µs pulses delivered at 25, 50, 100 and 500 pps.

Exposure setup

Exposure source	dielectrically loaded coaxial applicator, 14 mm diameter aperture
Distance between exposed object and exposure source	0 m
Setup	The applicator was in direct contact with the left side of head.

Parameters

Measurand	Value	Type	Method	Mass	Remarks
power density	1 W/cm²	mean	measured	-	80.0 mW/g corresponding average SAR in the brain at 20 µs pulse width and 500 pulses per second
power density	5 W/m²	mean	measured	-	0.04 mW/g corresponding average SAR in the brain at 10 µs pulse width and 25 pulses per second
power density	200 W/m²	mean	measured	-	1.6 mW/g corresponding average SAR in the brain at 20 µs pulse width and 500 pulses per second
power density	50 W/m²	mean	measured	-	0.4 mW/g corresponding average SAR in the brain at 20 µs pulse width and 100 pulses per second
power density	10 W/m²	mean	measured	-	0.08 mW/g corresponding average SAR in the brain at 10 µs pulse width and 50 pulses per second
power density	145 mW/cm²	mean	measured	-	11.5 mW/g corresponding average SAR in the brain at 20 µs pulse width and 100 pulses per second

Measurement and calculation details

Power flux density was calculated from reflected and forward powers. SAR was determined thermographically.

Exposure 2

Main characteristics

Frequency	2.45 GHz
Type	electromagnetic field
Waveform	sinusoidal
Polarization	linear
Exposure duration	15 s

Modulation

Modulation type	CW

Exposure setup

Exposure source	coaxial applicator

Parameters

Measurand	Value	Type	Method	Mass	Remarks
power	20 W	-	cf. remarks	-	-

Exposed system:

animal
rat/Wistar
partial body: brain

Methods Endpoint/measurement parameters/methodology

Investigated system:

tissue slices
isolated organ
investigation on living organism

Investigated organ system:

brain/CNS

Time of investigation:

during exposure
after exposure

Main outcome of study (acc. to author)

The rectal temperature showed a maximum increase of less than 0.75°C from a mean pre-exposure temperature of 36.6°C. The highest brain temperature recorded in a similar group of animals was less than 41°C. Brain temperatures must exceed 42°C for an appreciable length of time in order to effect changes in blood-brain barrier permeability. Consequently, barrier integrity was perserved. Conclusion: it appears that enhancement of blood-brain barrier permeation is not directly related to the strength of the microwave field in the tissue, but is associated with elevations of brain temperature.

Study character:

medical/biological study
experimental study
full/main study

Study funded by

Office of Naval Research (ONR), USA