Minato Hirabayashi

Frequency Composition of Auditory Middle Responses

Power spectral analysis and digital filtration were performed on the auditory middle responses (AMR) to click stimuli in six subjects with normal hearing. The spectral analysis revealed that the main power of the AMR was located at frequencies between 30 and 50 Hz with a peak at 40 Hz. A small elevation of power observed in the spectrum between 90 and 180 Hz was considered to be due to the ABR and the earliest part of the AMR. Typical AMR components, namely Na, Pa, Nb and Pb, were constantly recognised with digital high-pass (HP) filtration at 30 Hz. With increasing cut-off frequencies up to 50 Hz, the peak latencies of Na and Pa remained unchanged, while their magnitudes markedly decreased. On the other hand, Pb completely disappeared with 40 Hz filtration, forming two distinct positive peaks at about 55 and 80 ms after the stimulus onset. In some cases, three small positive peaks were seen following Pa with HP filtration at 50 Hz. With 60 Hz HP filtration, main components of the AMR substantially disapp...

Age-Related Morphological Changes in Auditory Middle-Latency Response

Age-related changes in the waveforms of the middle latency response (MLR) were investigated in 9 adults and 28 children aged between 4 and 14 years. The children were classified into three groups according to their age. For obtaining characteristic configurations in the responses for each group, composite group averaging was performed by summating the individual recordings in each group. With high-pass digital filtering at 20 Hz, composite MLR for adults showed a well-defined Na-Pa-Nb-Pb complex with peak latencies at about 17, 30, 45 and 63 ms, respectively. The composite response for children aged 4-7 years was characterized by a broad positive deflection (Pa) followed by a negative peak (Nb) at about 40 and 60 ms after stimulus onset, respectively. The peak latency of Pa was close to the adult value in the composite MLR for subjects aged 8-11 years, while the complete adult pattern in the later part of the response was not reached even in the composite response for subjects aged 12-14 years.

Auditory middle responses in young children.

In order to ascertain if any substantial difference exists in the auditory middle responses (AMR) between adults and young children, a digital high-pass (HP) filtering technique was applied to the responses in 26 young children aged 1-7 years and nine adults with normal hearing. Two significant differences were found between the HP-filtered responses in children and those in adults. Pa in the responses from adults was consistently recognized with HP filtering up to 50 Hz, while Pa in young children was effectively detected only with 20 Hz HP filtering. It was mostly eliminated when the HP filter was set at 30 or 40 Hz. Pb was identified in most of the adult responses, particularly with HP filtering at 30 Hz. On the other hand, it was not visually distinguished in the responses from young children with any HP filter setting.

Effects of Analog and Digital Filtering on Auditory Middle Latency Responses in Adults and Young Children

Effects of analog high pass (HP) filtering were compared with those of zero phase-shift digital filtering on the auditory middle latency responses (MLR) from nine adults and 16 young children with normal hearing. Analog HP filtering exerted several prominent effects on the MLR waveforms in both adults and young children, such as suppression of Po (ABR), enhancement of Nb, enhancement or emergence of Pb, and latency decrements for Pa and the later components. Analog HP filtering at 20 Hz produced more pronounced waveform distortions in the responses from young children than from adults. Much greater latency decrements for Pa and Nb were observed for young children than for adults in the analog HP-filtered responses at 20 Hz. A large positive peak (Pb) emerged at about 65 ms after the stimulus onset. From these results, the use of digital HP filtering at 20 Hz is strongly recommended for obtaining unbiased and stable MLR in young children.

Facial reconstruction with latissimus dorsi myocutaneous island flap following total maxillectomy

Following total maxillectomy for maxillary cancer, facial reconstruction was performed using a latissimus dorsi myocutaneous island flap. Postreconstructive deformity was studied in 10 patients. In 5 patients, after simple total maxillectomy the inner raw surface of the facial skin and orbito was covered by the flap, and the other extended total maxillectomy patients where the orbital contents and facial skin were involved, reconstruction was by means of the folded flap. In the patients with simple total maxillectomy, cicatricial contracture of the facial skin and cicatricial ectropion of the lower eyelid were quite small, and in the patients with extended total maxillectomy, reconstructed facial skin did not give rise to cicatricial contracture.

Auditory brainstem response (ABR) to tone pips in hearing-impaired children.

The correspondence between ABR thresholds to tone pips and behavioral thresholds at 500, 1000 and 2000 Hz was studied in 13 normal and 55 hearing-impaired children, including 42 sensori-neural losses and 13 conductive losses. The childrens ages ranged from 1 year 3 months to 8 years. Tone pips were provided with 2-cycle rise-fall times and 2-cycle plateaus. The correlations between the two measures were highly significant at 3 frequencies both in sensori-neural losses and conductive losses. In the subjects with sensori-neural losses, the ABR thresholds tended to be lower than the behavioral thresholds. Mean threshold differences between the ABR and behavioral audiometry at each frequency in sensori-neural losses were 1.6, 0.26 and 5.8 dB, respectively. On the other hand, in the subjects with conductive losses, the ABR thresholds were higher than the behavioral ones by 9.6, 7.8 and 7.5 dB at respective frequencies. Therefore, the hearing acuity in young children with sensori-neural losses can be predicted with accuracy from the ABR thresholds to tone-pips at 500, 1000 and 2000 Hz.