Takeo Fuse

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.

Pure-tone threshold prediction by 80-Hz amplitude-modulation following response.

The usefulness of 80-Hz amplitude-modulation following response (AMFR) detected by phase spectral analysis to predict the hearing threshold during sleep was evaluated in 20 normal adults, 8 normal children and 37 children with hearing impairment. The onset effect of tonal stimulus on 80-Hz steady state response was studied in normal adults during sleep and a threshold of 80-Hz AMFR detected by phase spectral analysis was compared with that of ABR elicited by tone pips in children during sleep. Although 80-Hz AMFR is not appropriate for the assessment of hearing in adults, it appears useful for evaluating hearing in young children during sleep. Hearing prediction by 80-Hz AMFR appears to be more accurate than that by ABR elicited with tone pips. The onset effect of stimulus on 80-Hz AMFR with modulation depth of 95% was less than 80-Hz SSR evoked by clicks.

CT detection of facial canal dehiscence and semicircular canal fistula : Comparison with surgical findings

OBJECTIVE The purpose of this study was to determine the accuracy of high resolution CT (HRCT) in the detection of facial canal dehiscence and semicircular canal fistula, the preoperative evaluation of both of which is clinically very important for ear surgery. MATERIALS AND METHODS We retrospectively reviewed the HRCT findings in 61 patients who underwent mastoidectomy at Yamagata University between 1989 and 1993. The HRCT images were obtained in the axial and semicoronal planes using 1 mm slice thickness and 1 mm intersection gap. RESULTS In 46 (75%) of the 61 patients, the HRCT image-based assessment of the facial canal dehiscence coincided with the surgical findings. The data for the facial canal revealed sensitivity of 66% and specificity of 84%. For semicircular canal fistula, in 59 (97%) of the 61 patients, the HRCT image-based assessment and the surgical findings coincided. The image-based assessment in the remaining two patients, who both had massive cholesteatoma, was false-positive. CONCLUSION HRCT is useful in the diagnosis of facial canal dehiscence and labyrinthine fistula, but its limitations should also be recognized.

Short-Term Outcome and Prognosis of Acute Low-Tone Sensorineural Hearing Loss by Administration of Steroid

Acute low-tone hearing loss (ALHL) is a typical type of hearing loss in Ménière’s disease and thought to be caused by endolymphatic hydrops in the inner ear. We treated 40 patients with ALHL by administration of the steroid and the early outcome and prognosis of the hearing level was retrospectively evaluated. The prognosis was generally determined within 7–10 days after administration of steroid. High-dose steroid cured some patients who failed to recover with low-dose steroid therapy. Our results showed that steroid is one of the effective therapies for ALHL and supported that etiology of ALHL involves an immune response.

Frequency specificity of amplitude-modulation following response detected by phase spectral analysis

To investigate the frequency specificity of steady-state responses elicited with a sinusoidally amplitude-modulated tone (amplitude-modulation-following response, AMFR), AMFR at different carrier frequencies were examined in 15 subjects with normal hearing, 12 patients with abrupt high-frequency hearing loss, 5 patients with low-frequency hearing loss and 1 patient with mid-frequency hearing loss. The stimulus was a sinusoidally amplitude-modulated tone with a modulation frequency of 40 Hz and modulation depth of 95%. Carrier frequencies were from 250 to 4000 Hz in normal subjects and from 250 to 8,000 Hz in hearing-impaired subjects. Fridmans phase spectral analysis was conducted for automatic detection of response. The thresholds of AMFR were distributed within 30 dB nHL at all carrier frequencies in normal subjects. In the hearing-impaired subjects, AMFR thresholds were between 0 and 25 dB above the behavioral threshold at all carrier frequencies. The threshold patterns of AMFR detected by phase spectral analysis very closely resembled the corresponding audiogram patterns in all types of hearing impairment. AMFR is thus shown to have a very good frequency specificity.

Immunological responses in acute low-tone sensorineural hearing loss and Ménière's disease.

Objective--The autoimmune response appears to play an important role in some types of acute sensorineural hearing loss. Endolymphatic hydrops associated with fluctuating hearing loss has also been suggested to be caused by an immunological mechanism. Acute low-tone hearing loss (ALHL) associated with Ménières disease (MD) is characterized by fluctuating hearing loss, and its etiology is thought to involve endolymphatic hydrops. The aim of this study was to attempt to determine the etiology of ALHL in MD. Material and methods--A flow cytometer was used to analyze intracellular cytokine levels in peripheral blood from 19 patients with ALHL and 26 patients with MD and the data compared to those obtained from age- and gender-matched healthy volunteers. Results--The patients with ALHL showed significantly increased levels of Th1 subsets (interferon-gamma-producing helper T cells) as compared to those in normal controls. The levels of Th2 (IL-4-producing helper T cells) subsets did not differ from those in the control group and thus Th1 predominated in ALHL patients. The patients with MD showed significantly increased natural killer cell activity but no Th1 dominance. These patients had no obvious systemic or local disease except in the inner ear. Conclusion--An abnormality of the Th1/Th2 balance in ALHL and increased natural killer cell activity in MD are thought to relate to inner ear disorder. These results are consistent with the possibility that the etiology of ALHL and MD involves an immune response.

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.

Effects of Aging on Amplitude-modulation Following Response

Phase spectral analysis as developed by Fridman (1982) was used to detect amplitude-modulation following response (AMFR). The threshold of AMFR was determined with greater sensitivity and accuracy by phase spectral analysis than by visual analysis. Using this method, a modulation frequency (MF) of 80 Hz was found optimal for detecting AMFR in young children (ranging in age from 2 to 4 years) during sleep, for whom there is no advantage in recording 40-Hz steady-state responses. To determine the optimal MF for detecting AMFR during sleep in children less than 2 years of age and age limitation for using 80-Hz MAFR in objective audiometry, AMFR as a function of MF was investigated during sleep in 25 children with normal hearing ranging from 4 months to 15 years of age, and 10 normal hearing adults. The stimulus was a 1000 Hz, 50 dBnHL sinusoidally amplitude modulated tone with a modulation depth of 95%. MF 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. Phase spectral analysis showed AMFR at MF of 80 Hz to be the most stable and reliable in all children during sleep among MFs from 20 to 200 Hz. Spectral amplitude analysis demonstrated 80-Hz AMFR to have a high S/N ratio in all children.(ABSTRACT TRUNCATED AT 250 WORDS)

Diagnosis of the Ossicular Chain in the Middle Ear by High-Resolution CT

This study was conducted to assess the usefulness and limitation of high-resolution CT for evaluating the condition of ossicular chain in the middle ear. Preoperative CT findings of the ossicular chain were compared with the operative findings of ossicles in 26 patients with chronic otitis media or congenital ossicular anomaly who underwent tympanoplasty. Total defect of head of the malleus, body of the incus and long process of the incus were completely detected by high-resolution CT. But the reliability in detecting the defect of handle of the malleus and superstructure of the stapes were 33.3% and 60%, respectively. Defect of the I-S joint (1 case) and partial defect of stapes crus (2 cases) could not be diagnosed correctly in the preoperative estimation. Although these findings demonstrate the limitations of high-resolution CT in the diagnosis of ossicular chain, it will be diminished by the advanced space resolution of CT in the future.

Angiomyoma of the retropharyngeal space.

We encountered a 59-year-old man with angiomyoma of the retropharyngeal space. He had been referred to our hospital because of a six-month history of a sensation of a narrowed pharynx. A smooth-surfaced tumour arising from the posterior wall in the hypopharynx was observed by indirect laryngoscopy. Radiographical imaging revealed a solitary tumour with homogenous contents in the retropharyngeal space. The tumour was successfully removed via a lateral pharyngotomy approach under general anaesthesia. Histopathologically, the tumour was composed of numerous veins with thick muscular walls. To the best of our knowledge, this is the first report of an angiomyoma arising in the retropharyngeal space.