Seventeen patients with Meniere's disease, six with inner ear deafness, and six normal subjects were tested using transtympanic electrocochleography after intravenous drip infusion or oral administration of 50g glycerol. In fourteen patients with Meniere's disease the negative SP decreased in amplitude following administration of glycerol. But the negative SP amplitude of each of the inner ear deafness and normal subjects was decreased. SP/AP ratio of the normal subjects after glycerol was investigated, and mean ±2 standard deviation was ranged from -8% to 5%, when preglycerol SP/AP ratio was 100%. When more than -8% decrease in SP/AP ratio was estimated as positive, there were nine positive patients with Meniere's disease. Thirteen patients with Meniere's disease were studied their serum osmorality and concentration of glycerol. All patients had maximum serum osmorality and concentration of glycerol one hour after glycerol was given. The serum osmorality of seven patients was changed more than 20mOsm/l and their electrocochleographyic findings were positive. We suggested the possibility of negativity of glycerol dehydration tests, if the dehydration effcts of glycerol was not normally done.
Cochlear nerve action potential (AP) was analyzed in normal and kanamycin (KM) treated guinea pigs. The stimuli were filtered bursts of 2, 4, 8, 12kHz and bone-conducted ultrasonic (98.8kHz) pip. The input-output function of the burst evoked AP (burst AP) in normal animals showed typical two segmented curve. On the other hand, that of ultrasonic evoked AP (UAP) showed steep and linear growth which closely resembles the burst AP input-output function of the KM poisoned animals. KM treatment elevated the burst AP threshold about 30-60dB but the UAP threshold elevation was only 10dB or so, although the AP latency was elongated significantly in the latter. Simultaneous masking of the burst AP by continuous ultrasonic sound was extraordinary effective despite of far higher masker frequency. This AP inhibition showed nonlinear growth as the masker intensity became stronger. And the higher the burst frequency became the more prominent the inhibition was. These results suggested that the ultrasonic receptor is not limited at the basal end of the cochlear partition but has rather wide distribution in the basal turn cochlea. And the upper frequency limit for the air-conducted sound was thought to be defined as the high frequency end of cochlear frequency tuning function as well as the problem of outer and middle ear sound conductance.
In a total of 103 subjects in a neonatal intensive care unit (NICU) consisting of sick neonates born maturely and low birth-weight infants with no central nervous complications, ABRs were measured when they were in undisturbed conditions immediately preceding their discharge from the hospital. The results showed that latencies of waves III, IV and V were longer in the group of neonates born inmature in terms of gestational age, then in the normal birth group. In the group of 38-41 weeks post-conceptional age, latencies of waves I and II tended to be shorter with the advancement of post-conceptional age. These results should be evaluated with regard to the rate of incidence of composite waveforms encountered during the measurement.
The investigation using digital filtering on the auditory middle latency response (MLR) to click was performed and the results were compared in infants and adults. The subjects were 10 children aged 8 to 10, and 7 children aged 11 to 14. All of them were proved to have normal hearing. The waveforms of the infants changed gradually into the waveforms of the adults during the age of 8 to 14. Pa detectability on high pass filtering of 40Hz and Pb detectability of 20-40Hz increased gradually with aging, and reached to the adults score (100%). The peak Pa and Nb decreased in latency with aging. From these results, the existence of the maturational effects on the MLR is recognized, and the infant MLR changes into the adult MLR in around 13 to 14 years old.
An effect of noise exposure on critical bandwidth (CBW) in acoustic refrex (AR) was investigated. CBW in AR was estimated in 100 workers using hand-held vibration tools (exposure group). The activating sounds for the reflex consisted of a 1000Hz pure tone, and thirteen kinds of noise centered 1000Hz with bandwidth of 100, 250, and 1/3-octave frequencies in 500-5000Hz. The results were compared with CBW in AR estimated in the control group previously reported by the author. The significant widening of CBW was observed in the exposed group compared to those in the control group (P<0.005); i.e. median value of CBW in AR was ≥4000Hz in the former, and 1138Hz in the latter group. To clarify the effect of noise exposure on CBW in AR, the exposed group was classified into four groups according to their hearing levels (HLs) at 3, 4, 6 and 8kHz; i.e. Group A (HLmean<25dB), Group B (25dB≤HLmean<50dB), Group C (50dB≤HLmean<75dB) and Group D (HLmean≥75dB). Median values of CBW in each of the groups were 1684Hz in Group A, 2312Hz in Group B, and ≥4000Hz in Groups C and D. It was noteworthy that CBW in AR was widened significantly (P<0.01) even in Group A with nearly normal hearing acuity (HLmean<25dB). The dose-effect relationship between noise exposure and widening of CBW in AR was confirmed.