Assessment of Cochlear Damage after Microwave Irradiation

The objective of this project was to determine whether or not excessive exposure to microwaves results in permanent damage to the inner ear. A group of 15 chinchillas was exposed for one hour to pulsed microwaves (1250 MHz) of 20 usec duration and 0.1-Hz repetition rate and an average power of 1 Watt. The specific absorption rate of various measurement sites in the head ranged from 2-8 Wkg. The exposures were done at the WRAIR Microwave Laboratory, Washington, D.C. Seven animals were sham-exposed for one hour using the same apparatus and sedation. For the sham exposures, the microwave equipment was powered but no radiation was delivered. The cochleas from 20 control chinchillas of the same age range as the animals in the present study were available for comparison purposes. The controls had spent their entire lives in sound-treated animal quarters at Washington University in St. Louis, MO. The cochleas from all animals were processed for histological evaluation as plastic-embedded flat preparations. Some animals were processed less than 24 hour after their exposures; the rest were processed after a month or more of recovery. In each cochlea, the following quantitative data were obtained: the extent and pattern of degeneration in the sensory cell populations; the number of missing pillar cells; the extent and location of degeneration of the stria vascularis and of the myelinated nerve fibers in the osseous spiral lamina.