Also a review by Rösler (1994) reports the same amount of increase in age-corrected HTLs at 4 kHz, after the first 10 years of exposure. When comparing the age-corrected PTA3,4,6
values of the study population and the ISO predicted NIPTS as a function of exposure time, the greater inter-individual variation in the distribution of NIHL in exposed construction workers is remarkable. This suggests a high variation in factors influencing the susceptibility to hearing loss in each exposure year interval of the study group, such as HPD use, prior employment, non-occupational noise exposure, hearing disorders, and variability in noise intensity. However, the median values of both the noise-exposed workers and the ISO predictions have a similar slope, at least for exposure times between 10 and 40 years. An interesting aspect is the relationship during the first 10 years of noise exposure. Construction workers employed selleck inhibitor for less than 10 years show greater hearing losses than expected Ku-0059436 order based on the interpolation of ISO-1999. In addition, observed hearing loss increases over the first 10 years of exposure at the same rate as in
the following 10–40 years of exposure duration, where a pattern of strongly increasing thresholds would have been expected (ISO 1990; Rösler 1994; Prince 2002). To investigate the role of job history in this group with short exposure duration, this relationship is determined only for construction workers younger than 30 years of age that reported no prior employment. This selection of 2,190 employees shows the same pattern of median age-corrected PTA3,4,6 values that is about 10 dB higher than predicted by ISO. A number of previous studies also found a discrepancy between ISO predictions and measured hearing loss during the first years of exposure.
Acetophenone Analyses based on serial audiograms of railway workers showed that hearing thresholds exceed model predictions in the very beginning of noise exposure, showing age-corrected hearing loss at job entrance of 9 dB averaged over 2 and 4 kHz (Henderson and Saunders 1998). Another study, monitoring a cohort of newly enrolled construction apprentices, showed HTLs of 12.2 dB HL at 4 kHz at baseline (Seixas et al. 2004) without any change in audiometric hearing thresholds over the first 3 years of employment (Seixas et al. 2005). The reported hearing threshold levels at job entrance in these studies are all higher than 0 dB HL and correspond to the median age-corrected PTA3,4,6 of 10.9 dB HL found here. The ISO-1999 model depends on the interpolation of predicted hearing thresholds after 10 years of exposure and the assumed hearing thresholds of 0 dB HL at the beginning of employment. Our findings suggest that this may not correctly represent the true development of NIHL over this period of exposure.