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Bone conduction audiometry. Aim: To determine the type of hearing loss by testing the sensorineural mechanism. Bone conduction actually works through three mechanisms: Distortion of the skull bones Activity of the ossicles Movement of the air column in the outer ear canal.
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Bone conduction audiometry • Aim: To determine the type of hearing loss by testing the sensorineural mechanism. • Bone conduction actually works through three mechanisms: • Distortion of the skull bones • Activity of the ossicles • Movement of the air column in the outer ear canal.
Issues with bone conduction • Placement: Mastoid or forehead? • Which ear is being tested? • Occlusion effect (Table 4.2, page 89) • Tactile responses • Procedure for testing similar to AC • Record thresholds in audiogram using appropriate symbols.
Audiogram interpretation • Based on AC and BC thresholds and relationship between them. • Difference between AC and BC: Air-Bone Gap (ABG). Shows amount of conductive component • If both AC and BC within normal limits: Normal hearing • 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 high (>10 dB): ?
Cross-hearing • Response by the non-test ear. • Inter-aural attenuation (IA; Table 4.3, page 96/105) • Cross-hearing for AC occurs when ACTE – IA ≥ BCNTE