Abstract:

Two issues will be reviewed: (1) combined effects of noise and aging on hearing and (2) protective effects of calcium-channel blockers (CCBs). There are no empirical data on the auditory effects of noise exposure and the aging process in humans. The only sources of information on combined effects of noise and age have been epidemiological studies. In recent experiments, gerbils were exposed monaurally at middle age to an intense tone which caused approximately 20 dB of noise-induced permanent threshold shift (NIPTS). At 36 months (lifespan of the gerbil), the threshold in the unexposed ear was considered the age-related loss and that in the exposed ear was considered the loss caused by aging plus noise. Data were examined in terms of published models which attempt to discriminate between NIPTS and presbycusis in older individuals. Most models significantly overestimated the noise-induced component of the hearing loss in the aged subjects. In the second series of experiments, gerbils were exposed to an intense noise while concurrently receiving CCBs or placebos. Nimodipine (a potent CCB) reduced the NIPTS. Furthermore, epidemiological data suggest that aged women taking CCBs have hearing levels 10--12 dB better than average. [Work supported by NIH-NIDCD and NOHR.]