Quantifying the Carhart effect in otosclerosis.

The Carhart effect consists of a depression in bone conduction thresholds in the presence of a conductive hearing loss. However, the mathematical relationship between the degree of conductive hearing loss and the degree of depression of bone conduction has not before been described. We have reviewed pre- and post-operative pure-tone audiograms performed on 102 consecutive patients having stapedectomy in an attempt to identify relationships between changes in bone conduction and air conduction and air-bone gap closure. Significant linear relationships were found between bone conduction and air conduction at 0.5. 1, 2 & kHz. Bone conduction was linearly related to air bone gap closure at 2 kHz.