01 level Italic values represent percentages Hearing threshold

levels To examine the hearing ability of the employees, median hearing threshold levels of the noise-exposed workers are compared to median HTLs of the non-exposed controls and to age-matched thresholds reported in annex A of the ISO-1999 standard (Fig. 1). Fig. 1 Measured hearing thresholds levels of the exposed workers (thick black lines), compared to the non-exposed internal controls (grey area) and age-matched ISO predictions of annex A (crosses), for five age groups All curves show the well-known deterioration of hearing with age, which is most prominent in the high frequency region. Both the exposed workers and the internal controls show significantly poorer hearing threshold levels relative to the ISO predicted values, across the complete range of test frequencies. In addition,

both groups show a slight worsening in the high frequencies in the two youngest groups. Dasatinib order In the older age groups, the differences between median HTLs of the exposed workers and the internal controls increase. These differences are greatest for hearing thresholds at 4 and 6 kHz. With selleckchem increasing age, the exposed group develops a typical NIHL notching pattern in the high frequency range, which broadens from 4 to 6 kHz to the lower frequencies. Figure 1 shows that hearing thresholds strongly depend on age. Therefore, measured HTLs are corrected for age effects. After these corrections, the differences between the noise-exposed workers and controls remain statistically significant for all frequencies (p < 0.001). These differences are relatively small at 0.5 and 1 kHz

(<1 dB) Verteporfin supplier but become more pronounced at higher frequencies, with a maximum mean difference of 7.0 dB at 4 kHz. Relationship of noise and hearing loss In order to assess the relationship between hearing loss and noise exposure, multivariate regression analyses are performed, with age as covariate. Both noise parameters and the interaction term show a significant bivariate association with the PTA-values. However, the interaction term does not contribute Fossariinae significantly to both multivariate regression models and is excluded from further analyses. For PTA1,2,4, the model accounts for 24.3% of the variance. The age-adjusted regression coefficient for noise level is 0.14 (99% CI 0.11–0.19), for years of exposure this is 0.07 (99% CI 0.05–0.09). The regression model for PTA3,4,6 accounts for 32.4% of the variance. Also the age-adjusted regression coefficients for noise level and exposure time are higher for PTA3,4,6, 0.27 (99% CI 0.22–0.32) and 0.12 (99% CI 0.09–0.15), respectively. To gain more insight into the relationship between hearing loss and noise exposure, the impact of both parameters on hearing loss is further explored in separate analyses. The age-corrected hearing thresholds enable comparison to the noise-induced permanent threshold shift (NIPTS) predicted by ISO-1999.