Yoshinori Kim

Optimal modulation frequency for amplitude-modulation following response in young children during sleep

In young children, there appears to be no advantage to recording steady-state response (SSR) at a stimulus rate of 40 Hz. To determine the optimal modulation frequency in auditory SSR evoked by sinusoidally amplitude-modulated (SAM) tones (amplitude-modulation following response: AMFR) in children during sleep and compare response patterns of AMFR at different modulation frequencies while awake with those during sleep, AMFR was examined in 10 adults with normal hearing while awake and during sleep and in 10 young children with normal hearing during sleep. The stimulus was a 1000 Hz, 50 dBnHL SAM tone with a modulation depth of 95%. Modulation frequency was varied from 20 to 200 Hz in 20 Hz steps. Response was determined by phase spectral analysis and the S/N ratio calculated by spectral amplitude at the modulation frequency and noise level around the modulation frequency using fast Fourier transform. Although AMFR was clearly evoked only by a modulation frequency of 40 Hz in adults while awake, AMFRs at modulation frequencies of 80 and 100 Hz were detected during sleep, in addition to 40 Hz AMFR. In children, 40 Hz AMFR was difficult to detect, but response could be clearly detected at higher modulation rates, especially at modulation frequencies of 80 and 100 Hz, compared with response in adults during sleep. Modulation frequencies from 80 to 100 Hz would thus appear optimal for detecting AMFR during sleep in children.

An application of phase spectral analysis to amplitude-modulation following response

A phase spectral analysis developed by Fridman (1982) was applied to the detection of amplitude-modulated frequency following response (AMFR) and its clinical usefulness was evaluated. A 1000 Hz sinusoidally amplitude-modulated tone with a modulation frequency of 40 Hz and a modulation depth of 90% was delivered to the right ear of 10 normal-hearing subjects. According to Fridmans technique, an ensemble of sweeps was divided into 10 groups and group averages were obtained. Then phase variances were calculated using fast Fourier transform for the group averages. In order to determine the optimal conditions of analysis for constructing an automatic detection program using phase spectral analysis, frequency spacing, number of sampling points and number of sweeps averaged per group were investigated. The sensitivity of phase spectral analysis for automatic detection of AMFR was also evaluated. The results suggested that the optimal number of sampling points and frequency spacing are 512 points and 4.9 Hz (observation window 204.8 ms), respectively. Concerning the average number of sweeps, the synchrony measure of the frequency component corresponding to the modulation frequency increased as the number of sweeps increased. Furthermore, it was demonstrated that threshold determination by phase spectral analysis is more sensitive than detection of the threshold by visual analysis of waveform configuration.

Measurement of Cochlear Basilar Membrane Traveling Wave Velocity by Derived ABR

Auditory brainstem response (ABR) can be used to measure the basilar membrane traveling wave velocity (TWV). Traveling wave velocity was calculated from the latency difference between wave V of different derived ABR and the cochlear location distance between the appropriate derived band center frequency. The latency of wave V of derived ABR produced by 6 noise-masked ABR using high pass filtered noise and the location of the corresponding cochlear partition (distance from the stapes foot-plate) were measured, and five traveling wave velocities were estimated based on this parameter. Ten subjects with normal hearing, 7 patients with Menieres disease, and 8 patients with sensorineural hearing loss were used in this study. The traveling wave velocity in the sensorineural hearing loss group was within normal limits at all frequencies, whereas the traveling wave velocity at 8 kHz in the Meniere group greatly exceeded that of the normal and sensorineural hearing loss group.

Hearing Preservation and Improvement of Auditory Brainstem Response Findings after Acoustic Neuroma Surgery

Among 9 patients with acoustic neuroma who underwent tumor removal by the middle cranial fossa approach during the past 5 years, 6 were selected for hearing preservation surgery which was successful in 5 cases (83.3%). For the prediction of success in hearing-preservation, factors related to hearing preservation, including preoperative findings of neurotological examination, were analyzed. Postoperative hearing threshold correlated significantly with wave V latency and I-V interpeak latency of preoperative auditory brainstem response (ABR) and the SP/AP ratio of preoperative electrocochleogram and postoperative facial palsy. The size of tumors and preoperative results of speech audiometry did not correlate with hearing results. Postoperative ABR findings were normalized within the observation period from 5 days to 10 months in 3 hearing-preserved patients. Possible mechanisms for improvement of ABR findings after the removal of acoustic neuroma are discussed.

Results of Treatment of Laryngeal Cancer

Eighty-one laryngeal cancer patients treated at our clinic during the past ten years were studied clinically. The proportion of patients in their sixties was highest and the number of males was much larger than that of females, at a ratio of 15:1. Laryngeal cancer was classified as glottic, supraglottic, and subglottic in 58, 19, and 4 cases, respectively, and glottic cancer patients accounted for more than half of these. The cumulative 5-year survival rate in all patients was 79.6%, and the rates in glottic and supraglottic cancer patients were 82.2% and 83.3%, respectively. Cumulative 5-year survival rates in patients in Stages I, II, III and IV were 83.7%, 83.9%, 83.3%, and 55.5%, respectively. Recurrence after radiotherapy was controlled by salvage operations satisfactorily in Stages I and II, but the prognosis of recurrent cancer was poor for patients in Stages III and IV. A selective review is given.

Modified Method of Submucosal Turbinectomy: Mucosal Flap Method

Sixteen patients with nasal obstructions were treated by use of a new technique of submucosal turbinectomy (mucosal flap method) which can reduce a large volume of the turbinate without leaving any mucosal defect. Subjective nasal obstruction showed improvement in all of the cases at 1 month after operation, and objective nasal obstruction examined with rhinomanometry was improved in 13 out of 16 sides of the noses (8 cases). Mucosal flaps were made from the turbinate mucosa facing the common meatus. After excision of the turbinate bone with the mucosa, the bone stump and mucosal defect were covered with the newly repositioned mucosal flap. It is considered that this mucosal flap method can reduce a large volume of the turbinate without leaving any mucosal defect.

Evaluation of Neurotological Examinations in Patients with Trigeminal Neuralgia and Hemifacial Spasm

Pure-tone audiometry, auditory evoked brainstem response (ABR) and electronystagmographic examination (ENG) were studied before and after microvascular decompression (MVD) in 41 patients with trigeminal neuralgia (TN) and 39 patients with hemifacial spasm (HFS). Fourteen patients (34.1%) with TN and 16 (41.0%) with HFS suffered from hearing loss postoperatively, while 1 patient (2.4%) with TN and 2 (12.8%) with HFS had a hearing gain after MVD. Latencies of peak V of ABR were longer on the affected side than on the unaffected side before MVD in 6 patients with TN and 3 with HFS. Among these 9 patients, decreased latency of peak V were observed after MVD in 4 patients. Latencies of peak V were increased after MVD in 13 (33.3%) patients with TN and 25 (73.5%) with HFS. Various abnormalities were observed in ENG before MVD in 15 patients (45.5%) with TN and 10 (29.4%) with HFS. Abnormalities in optokinetic nystagmus (OKN) and/or eye tracking test (ETT) were detected before surgery in 7 patients (45.5%) with TN and disappeared after MVD in 5 patients, whereas no abnormality in OKN and ETT was observed in patients with HFS. Postoperative improvements in spontaneous and/or positional nystagmus were observed in 2 patients with HFS. These postoperative improvements of the abnormalities in neurotological examinations suggest that the effect of causative vessels extend to the 8th cranial nerve and brain stem, although no patient complained of any otological symptoms before surgery.