Is it necessary to occlude the ear in bone-conduction testing at 4 kHz, in order to prevent air-borne radiation affecting the results?

Abstract

Objective: To re-evaluate the current BSA recommendation that the test ear should be occluded during the bone-conduction procedure at frequencies above 2 kHz to prevent audible air-borne radiation. Design:: Pure-tone audiometry was undertaken during routine hearing tests. The audiograms of fifty-two ears met the criteria for the study and were included. Bone conduction at 4 kHz was tested in three different conditions: test ear open/occluded by earplug and occluded by circumaural earphone. Study sample: Forty-four adults aged 41–77 years with average hearing levels from normal to severe loss. All complied fully with the test procedure. No audiogram had a significant conductive element. Results: There was no significant difference in each of the three test situations. Only two audiograms showed any (5 dB) difference at 4 kHz when bone conduction was retested with the ear occluded. Conclusions: The errors that result in a false air-bone gap at 4 kHz would not appear to be due to air-borne radiation. Failure to occlude the ear canal at 4 kHz, where air-borne radiation is greatest, makes no significant difference to the audiometric results. It is therefore suggested that it is unnecessary to block the test ear during routine pure-tone bone-conduction testing to prevent audible air-borne radiation, and that this should no longer form part of normal clinical practice.

Key Words:

• Air-bone gap
• air-borne radiation
• bone conduction
• earplug at 4 kHz
• recommended procedure

Declaration of interest

The authors report no conflicts of interest.

Notes

Notes

1. The specified background noise level of 35 dBA is the sum of spectral noise energy. Most of this energy is low-frequency noise (below 1 kHz) and although octave-band noise analysis was not undertaken for this study, the IAC audiometric booths used for these tests satisfy the requirements of ISO 8253-1 (2010) and are suitable for bone-conduction testing down to 0 dBHL. The noise component is minimal in the higher frequencies and audiometric booths offer a high degree of attenuation in this range.

2. Since the purpose of this study was to establish if it is necessary to occlude/cover the ear when testing bone conduction at 4 kHz, in order to show any BC threshold shift when the ear is occluded, only sensorineural hearing losses with an air-bone gap at the single frequency of 4 kHz were included.

3. No observable abnormalities of the canals or eardrums.

4. Any test subjects who gave unreliable responses, including any due to tinnitus, were excluded; all subjects included in the study provided reliable and repeatable responses.

5. Before they inserted the earplugs, patients were instructed on how to do this. The audiologist checked visually the position of the plug in the ear canal. Sound levels in the ear canal were not recorded; patients were asked whether their ear felt blocked and their hearing in that ear reduced.

6. For those who are not practising audiologists, 0 dBHL is regarded as average normal hearing, hence a minus reading simply refers to hearing that is better than average.

7. As there was no difference between ‘covered’ and ‘plugged’ results, and to simplify the table, only the latter is shown. Means and standard deviations also have been excluded from the table, again for simplicity, and, since there was near absence of any variability, it was considered that they would add little of value.