Audiological evaluation

The doseBadge being a very small unit has a memory limitations. It has a high cut-off point where noise exposure data of less than 75dB is discarded. This is not entirely suitable for children, which gives a conservative estimate of the children’s exposure. Information on levels of noise, which will cause damage to young children, is problematic due to lack of information on this topic. The best guidance on this is given by the World Health Organization (1999), where they estimate that time-average levels over an 8-hour day of 75dB are unlikely to cause significant harm across the population. A lower cut-off point at 65dB would have been useful, but the meter did not have this capability.

Note: the time scale is GMT (the default setting on the meter)

Figure 7-4 typical time-history from a doseBadge

7.11 Audiological evaluation

There are three parts to this study: completion of case history, comprehensive hearing evaluation, and longitudinal study of hearing loss development with prolonged exposure to music.

7.11.1 Completion of case history

All participants completed a self-reporting case history form, and the form was usually completed just before hearing evaluation. The questionnaire consisted of relevant questions related to ear and hearing problems, questions about behaviour towards loud music and noise, questions about personal hearing complaints, the type

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and use of hearing protection during rehearsal and performance, and subjective judgments of own hearing capacity.

There were also questions relating to musical instrument playing habits, number of years playing musical instruments, other noise and/or music exposure, practice and performance time per week, primary music genre, and instrument played and use of amplification systems.

The medical history included middle ear infection, family history of any hearing problem, tinnitus (ringing in the ear), giddiness and/or balancing difficulties, major illness, medications taken, other history of noise exposure, duration of employment in the orchestra or attending the academy of music, and also information relating to awareness about noise induced hearing loss, the duration of training time per week, leisure time activities, and in particular, for the occurrence of noise in leisure time.

The case history also included when they were last exposed to noise and/or music (Appendices E&G). When appropriate, answers were supplied in a multiple-choice format. Open-ended answers could not be avoided for specific questions, and the investigator subjectively interpreted those data.

7.11.2 Hearing evaluation

7.11.2.1 Ear examination

An otoscopy examination was performed on all the participants. This is a non-invasive procedure by which the external ear is examined for presence of earwax, and to assess the eardrum status. It takes only a minute or so. Those with excessive cerumen or abnormalities of ear canal and/or ear drum were referred to an otolaryngology department for medical management.

Three different types of hearing assessment were performed on all participants. They are as follows.

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7.11.2.2 Impedance audiometry

The test was performed with a Grason-Stadler- GSI Middle Ear Analyzer, Version 2, (220/660Hz) for evaluation of middle ear functioning. Those with measurements indicative of tympanic membrane and/or middle ear disorder were referred to an otolaryngology department for medical management. The criteria used for referral in this study were static compliance <0.3 mmhos, ear canal volume >5.0ml or abnormal asymmetry, and tymponometric peak pressure less than -150 daPa.

7.11.2.3 Pure-tone audiometry

This test was performed with an aim to assess the degree and type of hearing loss in a client. Pure-tone audiometric air conduction thresholds were obtained at 0.25, 0.5, 1, 1.5, 2, 3, 4, 6 and 8kHz, and bone conduction thresholds were obtained at 0.25, 0.5, 1, 2, 3 and 4kHz, using the Hughson-Westlake technique. Each participant’s hearing ability of the right and left ears was tested.

This test was performed with a GSI 61 (Grason-Stadler- GSI) Pure-tone audiometer, which is a fully featured two channel clinical audiometer providing air, bone, masking and speech facilities through a range of transducers and stimulus variations with intensity steps of 1, 2 or 5dBHL. The standard frequency range is 125Hz–8kHz giving dose % and Pa²h with a high frequency option up to 20kHz with the maximum output of 120dB. The calibration of the audiometer and headphone was checked and found to be in compliance with ANSI S 3.6-1969 (R 1973) audiometer specifications, OSHA 1983 Exhaustive Calibration Specifications and manufacturer specification. The hearing tests were performed by the researcher in a certified purpose built sound treated booth at the Wellington Hospital Audiology department.

Background sound levels were monitored in the beginning of the study with the Quest model 2900 Impulse Sound level Meter, and the sound level measurements were within allowable specifications. The biological calibration checks of audiometer function were also carried out before each day of use.

According to the National Institute for Occupational Safety and Health (NIOSH) 1998, to ensure that the worker is free from the effect of previous noise exposure, the

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individual must not be exposed to noise level at or above 85dB(A) for a minimum of 12 hours before the audiometric test. Hence all the musicians’ hearing was tested according to these guidelines.

7.11.2.3.1 Classification of audiograms

Hearing within normal limits: An individual musician is considered to have normal hearing if hearing threshold is 20dB or less in all the frequencies (250-8000Hz) in both the ears.

Hearing loss: In this study we have adopted a very strict criterion (a musician is considered to have a hearing loss if their hearing threshold is ≥ 25dB at least in one of the frequencies and at least in one ear) to account for hearing loss in orchestra musicians.

Normal dips in the audiograms: A dip in the audiogram is considered normal if hearing is within normal limits ≥ 20dB HL in all the frequencies and the dip observed is within those limits. (Hearing is reduced in one frequency and the threshold is ≥ 10dB in two of the adjacent frequencies.)

Abnormal dips in the audiograms: A dip in the audiogram is considered abnormal if the dip is outside the normal limits ≥ 20dB HL. (Hearing is reduced in one frequency and the threshold is ≥10dB in two of the adjacent frequencies.)

7.11.2.4 Diagnostic Oto-acoustic Emission testing

Distortion Product Oto-acoustic Emission (DPOAE) testing was only performed on 31 adult musicians (50.8%), 34 youth musicians (40.0%), and 28 children musicians (75.7%) because of the time constraints and non-availability of the instrument. Oto-acoustic emissions are considered to reflect the outer hair cell activity of the cochlea, which in turn is recognised as the site most affected by noise exposure. Emissions appear to be more sensitive to cochlear changes following noise exposure and therefore more appropriate for screening and monitoring ears at risk of noise induced hearing loss (NIHL). The objectivity of the measurements and the short test time

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required further enhance their usefulness as a cochlear measure. The tests were performed with the latest ILO 292 USB-11 DPEchoport – an objective, frequency specific analyser of cochlear status with binaural testing capabilities.

The instrument’s probe was calibrated on a daily basis, and Distortion Product Oto-acoustic Emission was investigated in the frequency range from 1.0 to 8.0kHz (f1/f2 = 1.22, I1 = I2 = 70dB) in all subjects. Distortion Product Oto-acoustic Emission was evoked using pairs of tones f1 and f2 with particular intensity and frequency relations (f1:f2 ratio). The evoked response from these stimuli occurs at a third frequency, the distortion product frequency fdp, which is calculated as fdp = 2 £ f1¡f2. The levels of the primary tones, of the Distortion Product Oto-acoustic Emission: L1 and L2, were 75 and 70dB SPL respectively. The frequency ratio of f2/f1 was 1.22. Distortion Product Oto-acoustic Emission was measured at the frequency 2f1¡f2 for 27 f2 frequencies ranging from 1000 to 8000Hz. The emission level was established on the basis of three presentations. In case of high noise floors, the measurement was repeated manually at particular frequencies, usually below 2kHz.

Following completion of testing, the test results were explained to each musician and a copy of the test results were provided on request. Those with results indicating the presence of hearing loss were advised to use ear protection on a regular basis, and on a case-by-case basis had a brief counselling on prevention of hearing loss.