Risk of hearing loss from combined exposure to hand-arm vibrations and noise

Sammanfattning: Hearing loss from noise exposure is one of the most common occupational injuries, and exposure to vibrations may increase the risk of noise-induced hearing loss. Earlier cross-sectional and longitudinal studies found an increased risk of noise-induced hearing loss among workers with vibration-induced white fingers (VWF) symptoms compared to workers without such symptoms. It has been suggested that vibrations to the hand stimulate the sympathetic nervous system and cause vasoconstriction in both the exposed hand and the ears and that this contributes to noise-induced hearing loss. The overall aim of this thesis was to examine how hand-arm vibrations (HAV) interact with noise in the development of noise-induced hearing loss.The experimental study in this thesis examined the effects of HAV and noise, both separately and combined, on the temporary threshold shift (TTS) in hearing in 22 healthy male and female subjects. The two longitudinal studies in this thesis were based on a cohort of 189 male workers at a heavy engineering workshop. The first cohort study examined the risk of noise-induced hearing loss from long-term exposure to HAV and noise. The second cohort study examined if workers with VWF had an increased risk of noise-induced hearing loss compared to workers without such symptoms. Finally, the questionnaire study in this thesis examined the occurrence of Raynaud’s phenomenon among 133 men and women with noise-induced hearing loss in relation to exposure to vibrations.In the experimental study, no differences in TTS in hearing were observed after combined exposure to HAV and noise compared to exposure to only noise. In the first cohort study, there was an increased risk of noise-induced hearing loss with increased exposure to HAV in a noisy environment. In the second cohort study, it was found that workers with VWF had an increased risk of noise-induced hearing loss compared to workers without VWF. In the questionnaire study, many men and women with noise-induced hearing loss had used hand-held vibrating machines suggesting that vibrations might contribute to noise-induced hearing loss. A high prevalence of Raynaud’s phenomenon was found among men.This thesis demonstrated that there was a long-term effect on noise-induced hearing loss from combined exposure to noise and HAV, but no short-term effect, and that having Raynaud’s phenomenon may also increase the risk of noise-induced hearing loss.