• Animal Exposure to Infrasound

The AMRL dynamic pressure chamber (a hydraulic device that produces intense infrasound) recently became operational. Preliminary to human whole body exposures, a variety of experiments with animals are being performed in order to evaluate physiological limits. A monkey, a young baboon, and six dogs of various sizes anesthetized with pentobarbital were exposed from 1 to 4 h at the maximum levels the chamber is capable of producing (172.5 dB from 1 to 8 Hz and falling off 7.6 dB/oct to 158 dB at 30 Hz). EKG and respiration rate (via chest impedance measurements) were recorded. The only observed physiological effects were a decline in respiration rate and some reddening of the tympanic membrane. Except for three of the dogs, these animals were then given exposures in which they were not anesthetized. Exposure levels were gradually increased until all animals received the maximum chamber SPL for 1–14 h. Their behaviors were subjectively observed to be normally calm and occasionally restless. At no time did the animals appear in discomfort or show signs of nystagmus or dizziness. The lack of adverse results of these high exposure levels will be discussed.