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The Hearing Aid and the Role of the Audiologist


In practice, the earliest efforts to assist people with hearing difficulties began long before there was any reliable method to measure the nature or extent of their problem. The so-called ear trumpet was first introduced during the 17th century and, together with the speaking tube, remained in everyday use until the latter years of the 18th century when the invention of the telephone led to the first electric hearing aid, while the first audiologist only appeared around three decades later. Today, these specialised healthcare professionals employ state-of-the-art technology to measure the severity of hearing loss, using their findings to recommend the most effective form of remediation.


In health, the threshold of human hearing is equivalent to a sound pressure of 20 micropascals, which is the equivalent of around 0 decibels, at frequencies of between 20 Hz to 20 kHz. The natural ageing process tends to raise the threshold figure while reducing the range of audible frequencies. However, other factors can cause similar effects. Before recommending a hearing aid, an audiologist will first need to conduct some tests.


A GP may make a preliminary diagnosis of deafness by testing a patient’s response to instructions whispered from varying distances. However, only an audiogram can provide a reliable measure of the extent of a subject’s hearing loss across the entire audible spectrum. Those outsized, old-fashioned trumpets and tubes were simple acoustic devices equivalent to shouting directly into the user’s ear. In practice, loss of audition is generally more pronounced at some frequencies than others. Consequently, tunability has become an essential feature of the modern hearing aid. An audiologist can conduct an audiogram to identify the affected frequencies and the level of amplification that each will require.


The audiogram is a non-invasive procedure during which a sound is played at increasing volumes and selected frequencies in the audible range. The sound is relayed to the subject through an earphone. The subject presses a button to indicate the point at which the sound becomes audible. The action generates points on a graph corresponding to the loudness and frequency of the sound. The test is then repeated for the other ear. However, before it is feasible to prescribe a hearing aid, the audiologist must also determine whether the deafness is due to conductive or sensory damage or both.


To differentiate, the specialist uses a vibrating tuning fork to perform two further tests. The former involves holding the handle of the device against the forehead or bridge of the nose. Normal subjects detect the sound in both ears, while someone with one-sided sensorineural deafness will hear it only in the good ear. The Rinne test detects conductive deafness by the relative sound volumes when the fork is placed on the mastoid bone or held in front of the ear. The audiologist can only prescribe a hearing aid once armed with the complete set of test results.


In more extreme cases, referring a patient to an ENT surgeon for a cochlear implant may be necessary. However, when seeking help early enough, such stringent measures are rarely needed. Perhaps you have concerns about your ability to hear and believe you might need a hearing aid. Why not consult an expert audiologist at The Hearing Clinic in Pretoria.

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