Jiro Harada

Application of fast Fourier transform to auditory evoked brainstem response

The current application of fast Fourier transform (FFT) to the analysis of auditory evoked brainstem response (ABR) is reviewed under four categories: (1) digital filtering, which facilitates isolation of fast and slow components from the same ABR wave, is the most common use of FFT; (2) power spectral analysis: this seems significant in ABR for isolating and analysing slow, middle and fast components from the Fourier components around each peak of the power spectrum with a three-peak pattern by inverse fast Fourier transform; (3) cross correlation function shows the relationship between two signals being analysed from the viewpoint of their phase. Clinical applications are used in the diagnosis of multiple sclerosis and for automatic detection of ABR; and (4) phase spectral analysis: the synchrony measure method (Fridman, 1984) is a type of phase spectral analysis. In this method, the phase variances of selected Fourier components are calculated, from among 10 averaging groups of 200 sweeps in the same stimulating conditions, to determine the presence or absence of a response. The clinical application of this method to the automatic evaluation of ABR is discussed.

A Study on the Phase Spectral Analysis of Middle Latency Response and 40-Hz Event-related Potential in Central Nervous System Disorders

The synchrony measure method, or SM method, a phase spectral analysis described by Fridman in 1984 for ABR, was applied to 40-Hz event-related potential (40-Hz ERP), and was found to be a useful method for automatic detection in predicting hearing thresholds across the audiometric frequencies. Although 40-Hz ERP was claimed by Galambos to be the summation of middle latency responses (MLR), its origin is still controversial. Moreover, only a few articles have reported on the clinical use of 40-Hz ERP in patients with neurological disorders. We recorded ABRs, MLRs, and 40-Hz ERPs in 59 patients with central nervous system (CNS) disorders, and analyzed the relationship between central lesions and MLR or 40-Hz ERP using phase spectral analysis. Abnormal findings in 40-Hz ERP were observed in 43 (72.9%) out of 59 cases with CNS disorders, and most of the abnormal cases had disorders involving the midbrain or thalamic lesions, especially on the side contralateral to stimuli. The results suggest that phase spectral analysis of 40-Hz ERP is useful in the detection of CNS disorders.

Phase Spectral Analysis of Auditory Brainstem Response in Cats

In order to apply the phase spectral analysis of auditory brainstem response (ABR) to the clinical diagnostic test, the following studies in cats were performed. At first, the phase spectra of normal ABRs were investigated under adequate stimulus intensities. In addition the component synchrony measures (CSM) of ABRs were calculated at each stimulus level. Moreover the waveforms and phase spectra of ABRs were investigated before and after the destructions of cochlear nerve and brainstem auditory pathways in cats. The results were as follows; (1) In normal ABRs, the phase spectra were mainly composed of three frequency components at 0-300Hz (component A), 300-900Hz (component B) and 900-1500Hz (component C). The CSMs of component A represented the degree of synchrony for a slow component of the ABR and the CSMs of components B and C represented the degree of synchrony for a fast component. (2) A decrease in stimulus intensity resulted in a decrease in each average of the CSMs of the three components. (3) A greater decrease of the CSM occurred if ipsilateral destruction was performed in a peripheral lesion. Lesions of the auditory pathway were followed by a decrease of the CSM of component C to contralateral stimulation. These results suggest that the phase spectral analysis of ABRs has significant clinical value in the detection of brainstem lesions.

Non-Clostridial Gas Gangrene in the Neck; A Case Report.

A 23-year-old female presented with high fever, throat pain, trismus and swelling of the right side of the neck. Odontogenic infection was suspected as the primary focus with infection spreading over the omohyoid muscle. X-ray examination showed gas formation in the soft tissues of the neck. She was treated with drainage and chemotherapy. The therapy was effective and successful, and she recovered from this illness completely. Culture of the muscle revealed Bacteroides melaninogenicuss. We diagnosed non-clostridia) gas gangrene.