This retrospective study was conducted at the audiology clinic of UKM in the year 2000. It was intended to detect the effect of walkman on the hearing system of its users and to investigate whether distortion product otoacoustic emission test can provide an early and reliable sign of cochlear damage or not. Distortion product otoacoustic emission test helps to determine the function of outer hair cell. Outer hair cells get damaged with exposure to loud sound, drugs and aging. Thirty subjects (20 in the study group and 10 in the control group), between the ages of 19-25 years, who fulfilled all the criteria of selection, were investigated. There were two sets of criteria (general and specific). Anyone, in the control or study group, failing in any of these criteria was excluded from the study. According to the general criteria, it was essential for all the subjects to have clean ear canals, normal hearing at all the frequencies (250Hz- 8000Hz), normal middle ear function (Type A tympanogram), no middle ear problem, not used/using any ototoxic medicine, no family history of hearing loss, no history of ear surgery, not exposed to any form of loud noise like disco, concert, F1 racing or gun shooting. According to the special criteria it was essential for the subjects in the control group to have never used a walkman and those in the study group must have been using a walkman for at least 6 months. Comparison of distortion product emission levels between control and study groups revealed that emissions were significantly lower in the study group, across all the frequencies, suggesting outer hair cell damage in the walkman users. These differences reached level of statistical significance (p<0.05) at 2, 4, 6 and 8kHz. Using walkman at an intensity unsafe for hearing and a duration longer than recommended is suspected for the outer hair cell damage in our study group. Those using walkman for longer duration and higher intensity manifested much lower emission levels. Our study supports the literature that distortion product emission test is a much sensitive test than pure-tone audiometry, as it can detect cochlear damage long before it appears in an audiogram. It is recommended that people who are exposed to loud noise regularly should be monitored with distortion product emission test. It is suggested that the use of walkman.
Study site: Audiology clinic, Pusat Perubatan Universiti Kebangsaan Malaysia, Kuala Lumpur, Malaysia