Marchbanks in England developed Tympanic Displacement Analyser (TDA). Accurate tympanic membrane (TM) movement during accoustic stapedial reflex was thought to be measurable by the TDA. In this paper, the TM volume displacement of normal subject and patients were measured. The results were compared with those by impedance meter (IM). The TM volume displacement increased with an increase in stimulus intensity. The TM displacement obtained with subjects in supine position were smaller than those obtained with subjects in sitting. This would be caused by the pressure alteration of perilymphatic fluid due to postural changes. Acoustic Reflex Threshold (ART) measured by the TDA was nearly the same as that by the IM, but the TDA was able to measure TM movement more accurately than the IM, owing to the TDA original measuring method.
The present study was designed to improve the method of the chronic measurement of cochlear nerve compound action potentials (CAP) reported by Hildesheimer et al (1979). After removing the facial nerve, a silver/silver-chloride wire was inserted into the facial canal approximately 6mm from the stylomastoid foramen so as to reach the second gene of the canal. The electrode was insulated with teflon except the cut end which was coated with silver chloride. Dental cement was used to fix the electrode to the mastoid bone. A sufficiently large CAP (50-120μV at 80 dBSPL) was evoked with this method and 4μV CAP was obtained at the sound stimulation of the CAP threshold (10μV with the round window recording). Although the CAP threshold was unstable within the first one week after the implantation of the electrode, the values were consistent and reproducible thereafter. This method does not require any difficult procedure and the success rate is very high. It is our conclusion that this method is quite suitable for the long term observation of the cochlear potentials.
The Fast Fourier Transform (FFT) is the conventional method to analyze the power spectrum of evoked otoacoustic emission (EOAE) and it can be carried out conveniently. But in this conventional method, so called time-invariant spectrum, the power spectrum of EOAE depends on the modality of the averaged EOAE its self but lacks the information of the frequency-latency function. So the instantaneous time-varying spectral analysis was adopted and tried to evaluate the EOAE recorded from normal hearing young adults. The instantaneous spectrum was calculated mainly based on the method of Ackroyd (1970) and printed out in 3 dimensional display. The instantaneous spectrum was examined in two different ways, one was instantaneous spectrum of averaged EOAE and the other was ensemble average of instantaneous spectra of responses evoked with each stimulus. In the instantaneous spectrum of averaged EOAE, interpretation of the frequency-latency function was easier than the conventional maneuver because of its information for latency. In the ensemble average of instantaneous spectra, EOAE and spontaneous otoacoustic emission (SOAE) were simultaneously and clearly recorded.
Single unit responses to click stimuli were recorded from the inferior colliculus of guina pigs with retrocochlear disorders which were produced by a silicon balloon of 5mm diameter inserted into the subtentorium above the 4th ventricule and induced compression of the lower brain stem. The retrocochlear disorders were confirmed by abnormal ABRs. The normal responses were also recorded from the inferior colliculus of animals without compression of the brain stem. In the normal group, a response latency to 95.5dB peSPL click stimuli ranged between 5 and 10ms, and there were few neurons with latencies longer than 15ms. On the other band, in the compressed brain stem group, the latency ranged widely between 6 and 20ms. Moreover, fewer neurons could follow click stimuli at high rates in the compressed brain stem group than in the normal. In the compressed brain stem group, fewer neurons showed band pass function for stimulus rates than in the normal. These results suggested that neural firing was desynchronized and at high stimulus rates neural excitation was disturbed in the inferior colliculus of animals with abnormal ABRs resulting from the compressed brain stem.
To identify the damaged cochlear region which might be responsible for sudden deafness (SD), pure tone audiometry and evoked otoacoustic emissions (EOAEs) were studied during treatment of patients with SD. Measurement was carried out once a week as a rule until hearing level was fixed. The patients with SD were classified into four (complete, prominent, partial recovery and unchanged) groups according to the degree of hearing improvement. At the initial measurement, the pure tone hearing levels and minimum detectable levels of EOAEs were mostly well matched in the complete recovery group while the former elevated more than in the other incomplete recovery groups. Using a linear regression analysis, the complete recovery group had a moderate correlation between them during the clinical course. Also correlation was found in the prominent and partial recovery groups in some degree while no correlation was found in the unchanged group, and even discrepancy was seen in some cases. These complicated results suggested multiple involvement of cochlea regions in SD. These damages seemed to exist sole or combined influence to the outer hair cells (OHCs) which are the generator of EOAEs in various extent. Main damaged region in SD seemed to be OHCs in the complete recovery group while multiple regions of the cochlea in the other groups even with a possibility of central part.
Effect of antineoplastic agent, cisplatin (CDDP) on distortion product otoacoustic emissions (DPOAE) were measured in 4 young patients without any ear problems. All of them had orthopedic malignancies and had repeated CDDP administrations during the DPOAE measuring program. Dose dependent decrease of DPOAE level, especially in high frequencies and in low input primary levels, and partial recovery of them were obserued, where no apparent change in pure tone audiometry was detected. Although some limitations exist, early detection of cochlear damage by CDDP and other ototoxic agents is possible by DPOAE measurements. Further study to find better indexes that should reflect state of cochlear damage is necessary to make this method an easy and useful clinical indicator of ototoxicity.
We recorded OAEs from 21 patients who recieved CDDP treatment. The sound pressure levels of all distortion product OAEs (DPOAEs) and a part of the evoked OAEs (EOAEs) were reduced in the patients with reduced hearing levels during therapeutic course of CDDP. Furthermore the sound pressure levels of some OAEs were reduced in the patients without hearing impairments at the frequency of the stimulation sound for OAEs. It was concluded that OAEs could be one of the objective evaluations for hearing impairments induced by CDDP, and in some cases the early damages of the outer hair cells by CDDP which were not reflected on audiogram might be detectable with OAEs.
It was recently revealed that DPOAEs were highly frequency specific, therefore the pattern of DP-audiogram was similar to Békésy audiogram. DPOAEs and FDLs were recorded in 6 ears sensorineural hearing loss with dips. Patterns of FDLs and DPOAEs were similar in these cases with dips. These results suggested that FDLs may be measured objectively by DPOAEs.