Hearing loss due to combined effects of noise and sodium salicylate

This study reports on hearing loss due to the combined effects of noise and sodium salicylate. A group of 10 adult chinchillas was used to test the hypothesis that the combined effects of prolonged exposure to noise and continuous salicylate intoxication will result in a larger Temporary Threshold Shift (TTS) in the audibility curve than either of the agents alone can produce. Extensive behavioral training was used to determine hearing thresholds. Though use of shock avoidance techniques, the animals were trained to respond to tones by jumping a low barrier. After demonstrating sufficient ability in behavioral training, the animals were surgically rendered monaural. After recovery from surgery, monaural threshold data were obtained. The animals were exposed in a chamber to 85 dbA broadband noise for 48 h to measure TTS. The chinchillas were allowed to recover for a minimum of 45 days; then a second monaural audibility curve was obtained. The chinchillas were then injected subcutaneously with sodium salicylate at 6 h intervals to establish TTS-producing serum salicylate levels. After 36 h of salicylate exposure, the animals were placed in a noise chamber. For the next 42 h the animals were exposed to both sodium salicylate and 85 dbA noise. The results of this study indicated the chinchillas' hearing threshold is reduced in sensitivity by approximately 35 dB due to broad-band noise exposure of 85 dBA intensity. Serum salicylate levels of 20-40 mg per 100 ml resulted in a TTS of 30 dB on the average. The combination of noise and sodium salicylate exposure produced a temporary hearing loss of approximately 55 dB. These data suggested that the combination of prolonged noise and salicylate exposure may result in a larger hearing loss than either agent alone can produce.