Intraosseous transducers for hearing by bone conduction. Peroperative measurements

Now that it is possible to establish and maintain a reaction free skin penetration, there are new prospects for hearing through bone conduction. Peroperative hearing threshold measurements on patients entering hospital for ear surgery under local anaesthesia have been made. An electromagnetic transducer was temporarily cemented into the cortex of the mastoid process and the transducer current for threshold signals at different frequencies recorded. Considerable variability was found between patients but a distinct common pattern from 0.25 kHz to 8 kHz could be identified in the audiograms. With the transducers used, the power consumption was found to be low (1 mW) at threshold levels but to achieve a comfortable hearing level the electrical power needed was found to be as high as 4W.