Abstract

OBJECTIVES
This study was undertaken to estimate the effect of hand transmitted vibration exposure for long time period on the auditory system in shipyard grinder workers.
METHODS
From 2006 to 2009, the study was carried out on 87 grinder workers for hand transmitted vibration exposure group, with 81 welders who were served as the control group. All subjects were male; at baseline, none of the participants had ear disease or diabetes mellitus. Auditory threshold at different frequencies ranged from 0.25 kHz to 8 kHz for both ear was recorded; the following were also collected from the subjects: age, exposure duration, noise exposure level of investigation year, total cholesterol, systolic/diastolic blood pressure, and smoking history.
RESULTS
In comparison of two groups, mean of age, exposure duration, noise level, total cholesterol, systolic/diastolic blood pressure, smoking rate were not significantly different between the groups. Auditory thresholds of 0.25, 0.5 kHz frequencies in both ear, 1 kHz frequency in right ear, and 8 kHz frequency in left ear were higher in hand-transmitted vibration exposure group than that in the control group at a statistically significant level. After stratification by age 50 years, there were no significant differences between the two groups in less than 50-years old age group, but auditory threshold of 0.25, 0.5, 1 and 8 kHz frequency were significantly different between the two groups in above 50-years old age group. The differences between two groups ranged from 0.4 dB(HL) to 6.7 dB(HL). Multiple linear regression analysis showed that hand transmitted vibration exposure was significant only in 0.25, 0.5 kHz frequency and the regression coefficients of vibration exposure ranged from 3.826 to 5.028 in those frequencies.
CONCLUSIONS
The differences of hearing threshold between two groups only in the 50-years old group were possibly owing to changed peripheral vascular system with autonomic nervous system, and significances only in low frequencies such as 0.25, 0.5 kHz probably mean that hand vibration exposure have been transmitted to auditory organ over long term. Collectively, older people can be more susceptible to hearing loss in the presence of hand transmitted vibration exposure and auditory threshold at low frequency may be more affected by the hand transmitted vibration exposure than high frequency.

• Keywords: Hearing loss;Hand-arm vibration syndrome;Autonomic nervous system;Cochlear;Auditory threshold