Audiometric notch as a sign of noise induced hearing loss

Abstract

Objectives-To investigate the relation between diVerent types of exposure to noise and a classic sign of noise induced hearing loss (NIHL), the audiometric notch. Methods-The study sample had exposure to both continuous and impulse noise and was drawn from a population of electrical transmission workers. Audiograms, taken as part of a hearing conservation programme, were read by three clinicians experienced in the assessment of NIHL. Working independently and using their clinical judgment, they were asked to identify localised increases in the threshold of hearing (audiometric notches) which they would attribute to noise, had a suitable history of exposure been elicited. Prevalent cases of NIHL were identified by the presence of a notch in either ear. Risk factors for NIHL were assessed by a questionnaire which sought information about exposure to air blast circuit breaker noise; firearms; explosions, and continuous noise. The odds of exposure to these factors in those with and without hearing loss were calculated, and odds ratios (ORs) and 95% confidence intervals (95% CIs) were estimated by logistic regression. Results-Of the 648 questionnaires sent out 357 were returned, a response rate of 55%. Of these, at least two out of the three assessors identified 175 (49%) people with a notch at any audiometric frequency. There was no association between these cases and the NIHL risk factors identified by the questionnaire, but a further frequency specific analysis showed a small proportion of people (15 (4%)) with notches at 4 kHz who had the expected associations with exposure to noise and a significant OR for firearms of 4.25 (95% CI 1.28 to 14.1). The much larger proportion of people with 6 kHz notches (110 (31%)) did not show these associations. Conclusions-To diagnose NIHL it is important to elicit a detailed and accurate history of exposure to noise: although the notch at 4 kHz is a well established clinical sign and may be valuable in confirming the diagnosis, the 6 kHz notch is variable and of limited importance. (Occup Environ Med 2001;58:46-51)

Comparing the Effect of Different Permissible Exposure Limits on Hearing Threshold Levels above 25 dBA over Six Months

“…The hearing loss was more significant at 4000 and 6000 Hz. These findings are consistent with a study conducted in England and Wales [17] , where there were significant associations of exposure to noise and presence of notch at 4000 Hz but the findings were variable at 6000 Hz. According to Lawton [18] , noise levels above 80 dBA produced temporary threshold shifts that recovered quickly when the noise insult ceased.…”

The Association between Impaired Fasting Glucose and Noise‐induced Hearing Loss

“…Therefore, impaired fasting glucose and noiseinduced hearing loss were compared in this study. The audiometric notch at 4,000 Hz is a well-established clinical sign of noise-induced hearing loss and may be valuable in confirming the diagnosis; pure tone thresholds at 4,000 Hz were used in this study as a screening test for noiseinduced hearing loss 2) . The environmental noise levels in the workplace were measured to control for the In the statistical analyses, the significance level for the p-value was 0.05. a Continuous variables included age, environmental noise and initial hearing threshold; categorical variables included smoking (never, ex-and current smoker), alcohol drinking (social, moderate and heavy drinking), hypertension (no hypertension and existing hypertension), serum creatinine (<1.2 and ≥1.2 mg/dl) and fasting glucose (<100, 100-125 and ≥126 mg/dl or medication for diabetes).…”

“…Early noise-induced hearing loss can be detected by pure tone audiometry. Typically, the first sign of hearing loss due to noise exposure is a dip or notch in the audiogram at 4,000 Hz 2) . The notch broadens with increasing noise exposure and may be difficult to distinguish from hearing loss due to aging (presbycusis), which shows a gradual deterioration at high frequencies.…”

Self-employment in joinery: An occupational risk facor?

“…The audiogram was analyzed by a trained physician in order to determine if it would be compatible with a noise-induced hearing loss (NIHL). Selective 4000 Hz hearing loss is characteristic of the onset of NIHL, defined here as a hearing loss > 30 dB (uni-or bilateral) at 4000 Hz without a loss at 8000 Hz [9]. The global morbidity rate was defined by the presence of at least 1 functional symptom or an abnormal spiro metry or audiogram.…”