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High-peak-power microwave pulses: effects on heart rate and blood pressure in unanesthetized rats
1Biological Effects Branch, Radiofrequency Radiation Division, U.S. Air Force Armstrong Laboratory, Brooks Air Force Base, TX, USA.
Introduction:
Exposure sources capable of generating high-peak-power microwave pulses, with relatively short pulse widths, have recently been developed. Studies of the effect of these sources on the cardiovascular systems of animals have not been reported previously.
Methods:
We exposed 14 unanesthetized male Sprague-Dawley rats to 10 high-peak-power microwave pulses generated by a transformer-energized megawatt pulsed output (TEMPO) microwave source, at frequencies ranging from 1.2-1.8 GHz. Peak power densities were as high as 51.6 kW/cm2. At 14 d prior to irradiation, the animals were implanted with chronic aortic cannulae. With appropriate shielding of the transducer, blood pressure recordings were obtained during microwave pulsing.
Results:
In a preliminary series of exposures at 1.7-1.8 GHz (peak power density 3.3-6.5 kW/cm2), an immediate but transient increase in mean arterial blood pressure (significant) and decrease in heart rate (non-significant) were observed. A loud noise was associated with each pulse produced by the TEMPO; this factor was subsequently attenuated. In a second series of exposures at 1.2-1.4 GHz (peak power density 14.6-51.6 kW/cm2), there were no significant changes in mean arterial blood pressure or heart rate during microwave exposure.
Conclusions:
The earlier significant increase in blood pressure that occurred during microwave exposure appeared to be related to the sharp noise produced by the TEMPO source. After appropriate sound attenuation, there were no significant effects of exposure to the microwave pulses.