Sound intolerance : characteristics, psychosocial work factors and reactions to exposure

Abstract: Sound intolerance refers to an adverse reaction to sounds at sound pressure levels most people do not find bothersome. It is sometimes associated with hearing loss and tinnitus, but neither conditions are a prerequisite for being intolerant to sounds. The processes underlying the heightened reactions to sound, or how sound intolerance is related to other afflictions is not fully known, and research in this area can still be described as being in an early stage. This thesis aims to broaden the knowledge about sound intolerance and the sub-category of hyperacusis by using cross-sectional epidemiological and quasi-experimental methods of inquiry.The thesis consists of three studies, each approaching the subject from a different perspective with the aim to better understand various characteristics of sound intolerance in general, its relation to psychosocial factors in the work environment, and its effects during noise exposure. Studies I & II are cross-sectional studies using two different data sets with similar design. Study I was based on data from a stratified sample in the Västerbotten Environmental Health Study. It examined the characteristics, background descriptions and comorbidities of self-reported and physician diagnosed individuals with hyperacusis, and compared them to a healthy referent group. Analyses revealed that a majority of both hyperacusis groups actively tried to avoid sound sources, and experienced that they for the most part could affect the environment to make it less noisy. There were significantly increased risks for other diagnosed illnesses in the hyperacusis groups compared to the healthy referent group, with large odds ratios (ORs) for the psychiatric illnesses anxiety, depression, post-traumatic stress disorder and exhaustion syndrome. Other common illnesses were tinnitus, hearing impairment and musculoskeletal disorders. Study II used data from the Österbotten Environmental Health Study and focused on the psychosocial work environment for people with hyperacusis. Working participants with hyperacusis who were employed/on leave of absence/paternal leave/long-term sick listed were compared to a working sample without hyperacusis on measures of effort-reward imbalance, work over commitment, emotional and social support and worry at work. The hyperacusis group scored significantly higher on worry, social support, and reward, whereas the groups did not differ significantly with respect to emotional support, over commitment or effort. In the final study, a quasi-experimental design was employed to investigate how individuals with sound intolerance react to noise exposure over time, in terms of perceived sound intensity, unpleasantness, rated distractibility, symptoms, heart rate variability and cognitive performance. Participants were divided into three groups of equal size based on their self-rated sound intolerance, which resulted in low, medium, and high sound intolerance groups. Results revealed large variations across individuals in several outcome variables. Compared to the other two groups, the high sound intolerance group perceived the noise as more unpleasant, stronger, and more distracting. They further rated the symptoms as higher in intensity, showed deviations in heart rate variability, and performed poorer on a cognitive task selected to measure inhibition.In conclusion, the results suggest that persons with sound intolerance have relatively poor general health and hearing as well as high odds of comorbidity with various symptoms, including psychiatric diagnoses and functional somatic syndromes. In a working population, the sound intolerant show high odds for worrying about things at work, perceiving low social support at work and not feeling rewarded at work. Finally, the results suggest that persons with high sound intolerance have increased distractibility, sound unpleasantness, symptoms over time as well as lowered heart rate variability and cognitive performance when exposed to sounds.