Abstract

Wilmot, T. J. (1972).Brit. J. industr. Med.,29, 125-133. The meaning of modern audiological tests in relation to noise-induced deafness: a review. If noise-induced deafness becomes a prescribed disease, it is inevitable that a very large number of workers with hearing difficulties will be discovered and will pose serious problems for both industrial medical officers and otologists working in the National Health Service.

The two main problems are detection of deafness and a decision whether the hearing loss is attributable to noise damage. This paper is concerned largely with the second problem, and outlines in general terms the procedures likely to be required.

After a short discussion of the initial screening procedure the paper concentrates upon those who fail to pass the requisite standard, and describes how modern hearing tests help to differentiate between various types of hearing loss. The traditional belief that conductive deafness and sensorineural deafness are easily differentiated holds true only in classical examples. In practice, in many cases, there are often mixed elements of both. In these individuals the acoustic impedance meter may give important objective evidence on the functions of the Eustachian tube, the tympanic membrane and ossicular chain, and the small but important intratympanic muscles.

Even a pure sensorineural deafness may be present without being caused by noise, and the uses of speech tests and tests for `recruitment' are invaluable in the differential diagnosis of this type of hearing loss.

Whereas noise-induced deafness is usually bilateral, unilateral deafness can be caused or aggravated by noise, and our problems are increased in these cases as efficient `masking' of the good ear is essential before we can obtain any true information about the impaired hearing ear.

One of the other problems is malingering. This may be deliberate, or a person with good hearing may believe it to be impaired; both varieties are now usually known as non-organic hearing loss. Usually the simplest differentiating factor is the ability of someone with non-organic hearing loss to hear the spoken word much more easily than pure tones, and this sign should always make one suspicious of this type of disorder.

Modern auditory analysis should enable the otologist who is equipped with suitable apparatus to diagnose with some precision the site and extent of most auditory disorders and to evaluate the proportion of noise-induced hearing loss in each individual affected.