Output capabilities of personal music players and assessment of preferred listening levels of test subjects: outlining recommendations for preventing music-induced hearing loss.

OBJECTIVES/HYPOTHESIS: Our goal was to assess the impact of personal music players, earphones, and music styles on output, the subject's preferred listening levels, and outline recommendations for the prevention of music-induced hearing loss. STUDY DESIGN: Experimental study. Personal music players' output capabilities and volunteers' preferred output levels were assessed in different settings. Based on current noise-induced hearing loss exposure limits, recommendations were outlined. METHODS: On three different devices and earphone types and 10 music styles, free field equivalent sound pressure output levels were assessed by applying a microphone probe inside the auditory canal. Forty-five hearing-healthy volunteers were asked to select preferred listening levels in different background noise scenarios. RESULTS: Sound pressure output reached 126 dB. No difference was found between device types, whereas earbud and supra-aural earphones showed significantly lower outputs than in-ear earphones (P < .001). Three distinct music style groups were identified with as much as 14.4 dB difference between them. In silence, 17.8% of volunteers spontaneously selected a listening level above 85 dB. With 90 dB background noise, 40% selected a level above 94 dB. Earphone attenuation capability was found to correlate significantly with preferred level reductions (r = 0.585, P < .001). In-ear and especially supra-aural earphones reduced preferred listening levels the most. CONCLUSIONS: Safe-use recommendations were outlined, whereas selecting the lowest volume setting comfortable remained the main suggestion. High background noise attenuating earphones may help in reducing comfortable listening levels and should be preferred. A risk table was elaborated, presenting time limits before reaching a risky exposure.

Mitochondrial diabetes and deafness: possible dysfunction of strial marginal cells of the inner ear.

OBJECTIVE: Some patients with the syndrome of mitochondrial diabetes and deafness (MIDD) have a m.3243A>G mutation of the MTTL1 gene encoding transfer ribonucleic acid for the amino acid leucine (tRNALeu(UUR)). One of our MIDD patients inspired us to propose an integrated view on how a single mutation of the mitochondrial deoxyribonucleic acid (DNA) affects both the glucose metabolism and the inner ear physiology. DESIGN: (a) Study of mitochondrial DNA in a patient with MIDD. (b) REVIEW OF THE LITERATURE on the impact of the m.3243A>G mutation on glucose metabolism and on the physiology of the hearing process. SETTINGS: Outpatient diabetes and nutrition department and molecular nutrition laboratory. METHODS: (a) Polymerase chain reaction followed by restriction fragment analysis identified the m.3243A>G mutation. (b) REVIEW OF THE LITERATURE from 1994 to 2009. RESULTS: (a) Molecular study: the m.3243A>G mutation was detected with an appreciable level of heteroplasmy. (b) REVIEW OF THE LITERATURE: the strial marginal cells located near the organ of Corti fulfill two characteristics: they are rich in mitochondria, and their dysfunction may produce neurosensorial deafness by means of a reduction in the potassium ion concentration of the endolymph. CONCLUSIONS: The m.3243A>G mutation not only underlies a dysfunction of the insulin-producing beta cell of the pancreas but also results in a reduction in adenosine triphosphate production of the strial marginal cells of the inner ear, thus diminishing the energy (in the form of potassium ion gradient) needed for the outer hair cells of the organ of Corti to amplify the soundwaves, particularly at high frequencies.