Longitudinal Changes in Hearing and Speech Perception in Older Adults

Address correspondence to: Medical University of South Carolina, Judy R. Dubno, Department of Otolaryngology-Head and Neck Surgery, 135 Rutledge Avenue, MSC 550, Charleston, SC 29425-5500 US, Phone: (843) 792-7978, Fax: (843) 792-7736, [email protected]. In addition to its high prevalence, age-related hearing loss was considered a significant area of scientific focus because of its complex etiology. Many factors contribute to age-related hearing loss in older humans, including genetic and aging factors; a lifetime of exposures to noise and ototoxic drugs; diet; trauma; and otologic and other diseases. As a result of these multiple, complex factors, it is not feasible in older humans to determine the unique contribution of age-related changes to the auditory system, independent of the accumulated effects due to environmental and other ototoxic factors. To determine the magnitude and effects of an aging component, research on age-related hearing loss has been conducted with laboratory animals raised under strict experimental control. At MUSC, the gerbil animal model has been used extensively, due, in part, to audiometric profiles in older animals that are similar to audiograms of 65to 70-year-old human males and females (Mills et al., 1990). In this model, gerbils are raised during their three-year lifespan in a controlled environment, whereby noise and ototoxic drug exposures are kept to a minimum, and humidity, nutrition, and diet are carefully monitored. Under these conditions, hearing loss observed in older gerbils relates only to changes due to age or genetic factors. Age-related changes observed in the gerbil’s auditory anatomy and physiology contribute to our understanding of age-related hearing loss in older humans, for whom environmental and other ototoxic factors cannot be controlled or even monitored over the lifespan. An initial focus of the program at MUSC has been the audiometric configuration typical of older adults who have not experienced long-term exposures to noise. This configuration is characterized by a relatively flat loss of 10–40 dB HL in lower frequencies, coupled with a gradually sloping loss in the higher frequencies (e.g., Jerger et al., 1993), a pattern of hearing loss