Bone conduction audiometryBone conduction audiometry

Aim: To determine the type of hearing loss Aim: To determine the type of hearing loss by testing the sensorineural mechanism.by testing the sensorineural mechanism.

Bone conduction actually works through Bone conduction actually works through three mechanisms: three mechanisms:

Distortion of the skull bonesDistortion of the skull bonesActivity of the ossiclesActivity of the ossiclesMovement of the air column in the outer Movement of the air column in the outer

ear canal.ear canal.

Issues with bone conductionIssues with bone conduction

Placement: Mastoid or forehead?Placement: Mastoid or forehead?

Which ear is being tested?Which ear is being tested?

Occlusion effect (Table 4.2, page 89)Occlusion effect (Table 4.2, page 89)

Tactile responsesTactile responses

Procedure for testing similar to ACProcedure for testing similar to AC

Record thresholds in audiogram using appropriate Record thresholds in audiogram using appropriate symbols.symbols.

Audiogram interpretationAudiogram interpretation

Based on AC and BC thresholds and relationship between Based on AC and BC thresholds and relationship between them.them.

Difference between AC and BC: Air-Bone Gap (ABG). Shows Difference between AC and BC: Air-Bone Gap (ABG). Shows amount of conductive componentamount of conductive component

If both AC and BC within normal limits: Normal hearingIf both AC and BC within normal limits: Normal hearing

If AC thresholds elevated, BC normal: ?If AC thresholds elevated, BC normal: ?

If both AC and BC elevated, but ABG less (≤10 dB): ?If both AC and BC elevated, but ABG less (≤10 dB): ?

If both AC and BC elevated, but ABG high (>10 dB): ?If both AC and BC elevated, but ABG high (>10 dB): ?

Cross-hearingCross-hearing

Response by the non-test ear.Response by the non-test ear.

Inter-aural attenuation (IA; Table 4.3, page Inter-aural attenuation (IA; Table 4.3, page 96/105)96/105)

Cross-hearing for AC occurs when ACCross-hearing for AC occurs when ACTETE – IA – IA ≥ BC≥ BCNTENTE