Abstract
It is important to determine what frequencies and auditory perceptual measures are the most sensitive early indicators of noise-induced hearing impairment. To examine whether hearing loss among shipyard workers increases more rapidly at extended high frequencies than at clinical frequencies and whether subtle auditory processing deficits are present in those with extensive noise exposure but little or no hearing loss. This cross-sectional study collected audiometric data (0.25-16 kHz), survey questionnaires, and noise exposure levels from 7890 shipyard workers in a Shanghai shipyard from 2015 to 2019. Worsening hearing loss was evaluated in the group with hearing loss. Speech processing and temporal processing were evaluated in 610 participants with noise exposure and clinically normal hearing to identify early biomarkers of noise-induced hearing impairment. Data analysis was conducted from November to December 2020. Linear regression was performed to model the increase in hearing loss as function of cumulative noise exposure and compared with a group who were monitored longitudinally for 4 years. Auditory processing tests included speech-in-noise tests, competing sentence tests, dichotic listening tests, and gap detection threshold tests and were compared with a control group without history of noise exposure. Of the 5539 participants (median [interquartile range (IQR)] age, 41.0 [34.0-47.0] years; 3861 [86.6%] men) included in the cross-sectional analysis, 4459 (80.5%) were hearing loss positive and 1080 (19.5%) were hearing loss negative. In younger participants (ie, ≤40 years), the maximum rate of increase in hearing loss was 0.40 (95% CI, 0.39-0.42) dB per A-weighted dB-year (dB/dBA-year) at 12.5 kHz, higher than the growth rates of 0.36 (95% CI, 0.35-0.36) dB/dBA-year at 4 kHz, 0.32 (95% CI, 0.31-0.33) dB/dBA-year at 10 kHz, 0.31 (95% CI, 0.30-0.31) dB/dBA-year at 6 kHz, 0.27 (95% CI, 0.26-0.27) dB/dBA-year at 3 kHz, and 0.27 (95% CI, 0.27-0.28) dB/dBA-year at 8 kHz. In the 4-year longitudinal analysis of hearing loss among 403 participants, the mean (SD) annual deterioration in hearing was 2.70 (2.98) dB/y at 12.5 kHz, almost twice as that observed at lower frequencies (eg, at 3kHz: 1.18 [2.15] dB/y). The auditory processing scores of participants with clinically normal hearing and a history of noise exposure were significantly lower than those of control participants (eg, median [IQR] score on speech-in-noise test, noise-exposed group 1 vs control group: 0.63 [0.55-0.66] vs 0.78 [0.76-0.80]; P < .001). These findings suggest that the increase in hearing loss among shipyard workers was more rapid at 12.5 kHz than at other frequencies; workers with clinically normal hearing but high cumulative noise exposure are likely to exhibit deficits in speech and temporal processing.
Highlights
In younger participants, the maximum rate of increase in hearing loss was 0.40 dB per A-weighted dB–year at 12.5 kHz, higher than the growth rates of 0.36 dB/dBA-year at 4 kHz, 0.32 dB/dBA-year at 10 kHz, 0.31 dB/dBA-year at 6 kHz, 0.27 dB/dBA-year at 3 kHz, and 0.27 dB/dBA-year at 8 kHz
The auditory processing scores of participants with clinically normal hearing and a history of noise exposure were significantly lower than those of control participants. These findings suggest that the increase in hearing loss among shipyard workers was more rapid at 12.5 kHz than at other frequencies; workers with clinically normal
The median (IQR) pure-tone audiometry (PTA) at 0.25 to 2 kHz in noise-exposed group (NG) 1 (9.7 [6.7-11.9] dB) and noise-exposed group 2 (NG 2) (12.5 [9.4-15.0] dB) groups were significantly different from those in the control group (10.6 [8.8-12.5] dB; noise-exposed group 1 (NG 1) vs control group: H = −2.247; P = .02; NG 2 vs control group: H = −4.675; P < .001), while there was no statistical difference between NG 1 and NG 2
Summary
Prolonged and/or intense noise exposure contributes to numerous health problems, in particular noise-induced hearing loss (NIHL) that damages the cochlea.[1,2] Noise-induced damage leads to hearing loss but can make it difficult to understand speech.[3,4,5] many countries have established health and safety regulations,[6] early detection of NIHL is of great importance for prevention.The most common biomarker used to identify NIHL is the shape of the audiogram.[7,8,9] Historically, the so-called 4-kHz noise notch has been considered a hallmark of NIHL and is used to distinguish it from other types of sensorineural hearing losses associated with aging, ototoxic effects, and genetic factors.[7,8,10,11,12] On the other hand, it has been suggested that notches can occur in the absence of a positive noise history.[8]. Advocates point out the advantage of EHF in early identification of hearing loss due to ototoxic drugs and noise exposure.[13,14,15,16] a systematic review failed to arrive at a robust conclusion regarding the advantage of EHF vs conventional audiometry.[15] Most of the conclusions have been derived from a pool of participants with unclear durations and/or doses of noise exposure.[16,17] In addition, many studies lacked longitudinal measurement of hearing. The utility of EHF audiometry to test for early onset NIHL remains an open question
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