A retrospective analysis of noise-induced hearing loss in the Dutch construction industry

Purpose Noise exposure is an important and highly prevalent occupational hazard in the construction industry. This study examines hearing threshold levels of a large population of Dutch construction workers and compares their hearing thresholds to those predicted by ISO-1999. Methods In this retrospective study, medical records of periodic occupational health examinations of 29,644 construction workers are analysed. Pure-tone audiometric thresholds of noise-exposed workers are compared to a non-exposed control group and to ISO-1999 predictions. Regression analyses are conducted to explore the relationship between hearing loss and noise intensity, noise exposure time and the use of hearing protection. Results Noise-exposed workers had greater hearing losses compared to their non-noise-exposed colleagues and to the reference population reported in ISO-1999. Noise exposure explained only a small proportion of hearing loss. When the daily noise exposure level rose from 80 dB(A) towards 96 dB(A), only a minor increase in hearing loss is shown. The relation of exposure time and hearing loss found was similar to ISO-1999 predictions when looking at durations of 10 years or more. For the first decade, the population medians show poorer hearing than predicted by ISO-1999. Discussion Duration of noise exposure was a better predictor than noise exposure levels, probably because of the limitations in noise exposure estimations. In this population, noise-induced hearing loss was already present at the beginning of employment and increased at the same rate as is predicted for longer exposure duration

The morphological structure of the chick's basilar papilla: a light and transmission electron microscopic study

The basilar papilla corresponds to the cochlea of mammals and is becoming a common model of assessment of the regeneration process which takes place after the damage to the inner ear caused by noise or ototoxic drugs. In this study the morphology of a chick's basilar papilla in light and electron microscopy is described. There are two types of hair cells (sensory cells): the tall hair cells and the short hair cells, whose morphology and pattern of innervation are different. The tall hair cells correspond to the inner, hair cells in mammals, which are responsible for sound transduction. They are mainly innervated by the afferent (cochlear) fibers. The short hair cells correspond to the outer hair cells in mammals, which are responsible for the sound amplification. They are mainly innervated by the efferent fibers. The supporting cells, whose morphology is also described in the study, separate the hair cells from each other and from the basilar membrane. They are considered to be a source for regenerating hair cells