Abstract
We have developed an implantable hearing aid using an ossicular vibrator of piezoelectric ceramic bimorph. In order to determine output power level of the device and to utilize the device to the human ear, it was required to develop a method to assess hearing induced by direct oscillation of auditory ossicle using piezoelectric ceramic bimorph element. During tympanoplastic operation under local anesthesia, the element was attached to either the head of the stapes, tip of columella or the short process of the incus. Then pure tone signals from an audiometer were supplied to the element and the lowest audible intensity level of vibration was measured in dB/V p-p. This value was termed as vibratory hearing threshold. From this value, the sensitivity, equivalent dB SPL at the ear drum, for a given length of vibrator element was calculated. The sensitivity of the element of 7mm was 91dB in 1KHz and 100dB in 4KHz respectively, when it was applied to the head of the stapes of normal motility. In order to establish indication of implantation of the device, it is crucial to assess the sensitivity in the patient. In this sense, we termed this method "intra-operative vibratory audiometry".
