The disorder of the inner ear induced by injection of SM and KM to the facial nerve through stylomatoid foramen was studied functionally by caloric test and brain stem evoked response. Surface specimens of the vestibular organ and the organ of Corti of guinea pigs were studied. The injection dose of SM and KM was about 0.03ml of 60mg/ml, 30mg/ml, 15mg/ml, 8mg/ml, and 4mg/ml respectively. The guinea pigs were tested by BSR using 1 cycle tone of 4, 000Hz, 8, 000Hz, 16, 000Hz, 20, 000Hz as auditory stimuli. The results were as follows: 1) When the concentration was over 60mg/ml, all the inner ear was damaged and when 4mg/ml was injected, a few disorder can be found. The higher the concentration, the more the damage of the inner ear increased. 2) The cause of disorder correlated with the ototoxic drugs infiltration. It runs along the facial nerve centrally and goes into cochlear and vestibular nerve through anastmosis in the inner ear canal. The shorter the distance between the anastmosis and the organ, the more the damage increased. There was no differences of the results between KM and SM in this study.
The acoustic far-field response (FFR) was observed in Kanamycin-treated guinea pigs from silvere wire electrodes chronically implanted in the epidural space of the temporal site. Binaural interaction was also checked by unilateral destruction of the anesthetized animal's cochlea. The early components of FFR, i.e., cochlear microphonics (CM) and a part of cochlear action potentials (AP) recorded from the temporal site were mainly contributed by the cochlea homolateral to the recording site. Later components, i.e., the brain stem responses, (BSR) and early phase of cortical evoked potentials (EP), were affected bilaterally and showed complex characteristics. Kanamycin was injected subcutaneously (400mg/kg) daily. CM disappeared primarily while the other neural responses persisted. EP was the last to be recorded. Abrupt decrease in amplitude of the responses of more than 80dB within 2 days occurred approximately 2 weeks later. The bioelectric correlates may suggest that CM is generated at the hair cells and plays a significant role in the hearing process.
The stapedial reflexes were measured in cases of acoustic neuromas, brainstem lesions and unilateral hearing loss, and their diagnostic significance for retrocochlear lesions were investigated. 1. The following findings could strongly suggest retrocochlear lesions or acoustic neuroma: a) when stapedial reflexes are absent in cases with hearing loss below 60dB in speech frequencies, b) when the reflex threshold in the diseased side is more than 15dB that in the normal side. 2. In small acoustic neuroma confined to the internal auditory meatus, reflex decay is frequently seen, even though the stapeidial reflex is within normal limits. 3. With the measurement of stapedial reflex threshold and reflex decay, the findings suggesting acoustic tumor or retrocochlear lesions were found in 78% of cases with hearing loss below 60dB in speech frequencies and in 86% of cases in which hearing could in any way be obtained within the measurable areas. 4. -Both the measurement of crossed and uncrossed stapedial reflex is useful in the diagnosis of brainstem lesions. The stapedial reflex was found to be normal in the central auditory pathways, such as cortical or subcortical lesions. 5. In intramedullary lesions, especially in lower pontine lesions, there are some cases with normal pure tone and speech audiogram, but with abnormal findings in directional hearing and with reflex decay. 6. The measurement of the stapedial reflex, together with the other audiometric tests could be applied as a diagnostic tool in central auditory disorders.
The intra-aural reflex is attributed mainly to the stapedius muscle in man. Using Grason-Stadler Otoadmittance Meter 1720, the response resembling the acoustic stapedius reflex was recorded from the ear on which the stapedectomy operation had been performed. To ascertain whether this response was attributed to the tensor tympani muscle or not the patients with bilateral total deafness and those underwent radical mastoidectomy were investigated. The same response as was recorded in cases after stapedectomy was recorded in these patients. But when acoustic stimulus was delivered through the earplug type earphone with high interaural attenuation, no response was detected. Therefore, the response was undoubtedly a false positive response elicited by the crossed sound energy to the ceramic microphone within the ear-piece. The false positive response was more readily observed when the 660Hz probe tone was used than 220Hz, and when the frequency of the stimulus was near to that of the probe tone. One should be aware of the false positive response in checking the acoustic reflex using Grason-Stadler Otoadmittance Meter.
An ear canal electrocochleographic electrode was newly designed and CM were recorded from the children of 5 years old. The electrode was mounted in a cuff which was attached at the tip of a silicon tube. The silicon tube was inserted easily and without pain into the bony part of the outer ear canal, and the cuff was inflated by pinch pump and fixed to the canal wall. The tone stimuli were delivered from a earphone in a metal box and conducted by a metal tube to the silicon tube in the canal. AP and CM were recorded by tone stimulus of 80dB. Electric and mechanic artifacts of tone stimuli were examined and excluded.
Electrocochleography was performed on six patients with posterior cranial Fossa tumors which consist of three cases of acoustic neurinoma of grade II-III, a case of glioblastoma multiforme originating from cerebello-superior pons, a case of astrocytoma of grade III originating from medulla oblongata-inferior pons, and a case of meningioma originating from Meckel's cavity. Recording was made with the use of the transtympanic needle technique. AP input-output functions with acoustic neurinoma were very similar to those obtained in patients with sensorineural hearing loss showing the phenomenon of recruitment. In AP responses recorded from the patients with cerebello-superior pontine tumor and Meckel's cavity tumor, a loss of the positive portion of the potentials (P1) was characteristic. This phenomenon may be due to the compression on the auditory nerve by the growing tumor. The polarity of SP in all cases showed negative deflection without abnormal increment. CM responeses recorded from the patients were the same as in a normal subject. In the cases presented, although the abnormal changes in input-output functions as well as the changes in the wave form patterns of AP responses revealed a lesion of the portions corresponding to the sensory and/or to the neural structure, the presence of a well-developed CM may be explained by the fact that the hair cells remain unaffected. Therefore, it is thought that simultaneous recording of CM and AP gives great promise as a means of differential diagnosis between neural and cochlear pathology.
The purpose of this investigation is to study the site of lesions in mumps deafness by Electrocochleography. Sixteen affected ears of fifteen patients ranging in age from four to fourty-two with the average being 15.5 were investigated. Recording was made in an electrically shielded sound proof room with the use of the transtympanic needle electrode technique. Clicks for measurement of auditory nerve action potential (AP) and short tone-bursts for cochlear microphonics (CM) were used as sound stimuli. Although the audiometric examination in all cases confirmed no response, the following three categories of cochlear pathophysiological features in mumps deafness can be classified according to CM responses. 1) No AP response and the well-developed CM response: It seemed to indicate that the neural regions related to the source of AP response were impaired, but the organ of Corti was found to be functioning because the recorded CM responses were the same as in a normal hearing subject. 2) Neither AP nor CM response: It seemed to indicate that both the neural and the organ of Corti were impaired severely. 3) No AP response and the decreased CM responses: It seemed to indicate that the neural regions were impaired severely, but the organ of Corti were impaired only partially.
This study was performed to clarify characteristics of the brain stem auditory responses (BSR) to frequency modulated tones. The frequency of continuously presented 2, 000Hz tone was changed with a trapezoid shape of up- and down-ramp and plateau-duration of 1 msec. In animal experiment, this kind of stimuli caused frequency change and amplitude change in cochlear microphonics, and AP studies revealed that amplitude and latency curves refered to stimulus intensity were different from those of the response to tone bursts. The shape, the amplitude curve and latency curve of the human BSRs were also different from those of responses to click and tone bursts. The response to FM tones seems to be frequencyspecific and depends less on stimulus intensity than the one to tone bursts.
The availability of the BSR for assessing hearing thresholds at speech frequencies was studied by using a “selective masking”. Auditory stimuli consisted of 500Hz, 1kHz and 2kHz tone pips with 5msec rise and 5msec decay without a plateau. Several different maskings were applied using unfiltered weighted noise (B), 1800Hz highpass noise (C), 900Hz high-pass noise (D), 450Hz high-pass noise (E), 450-560Hz band-pass noise (F) and 900-1120Hz band-pass noise (G). Thresholds of the BSR at 500Hz, 1kHz and 2kHz were measured without masking (A) and then with varied masking noises (B-G). At each masking condition, thresholds obtained from BSR tests corresponded well to those from pure tone audiometry. The “BSR audiometry” appeared to be useful for the determination of hearing thresholds at frequencies of 500Hz, 1kHz and 2kHz.
BSRs were recorded in eighteen normal-hearing subjects. Auditory stimuli employed in this study consisted of tone bursts with 40msec duration; rise-time, frequency and intensity of the tone bursts were changed. BSR latency prolonged as rise-time of the tone bursts increased, and as stimulus frequency decreased. Latencies ranged between 7.0 and 15.4msec. At the stimulus intensity of 30dBSL, in all tested subjects BSR were provoked by 500Hz and 1kHz tone bursts with 10msec rise-time; mean latencies were 15.4 and 13.4msec, respectively. The above results suggested that hearing thresholds at 500Hz and 1kHz were predictable by the BSR. It was concluded that tone pips with 5msec rise and 5msec decay without a plateau was an appropriate stimulus for BSR audiometry.
Auditory brain stem responses in five patients with cerebellopontine angle tumor were studied and the results were compared between the acoustic tumor and other cerebellopontine angle tumors. In cases of acoustic tumor, all five waves were unable to record. In cases of other cerebellopontine angle tumors not originated from the acoustic nerve (meningioma and cholesteatoma), auditory brain stem responses showed only the initial wave I after the affected ear was stimulated. On the other hand, auditory brain stem responses showed only the initial three waves (I-III) after the not-affected ear was stimulated. The wave I represents the response of the auditory nerve and the latter four waves are generated in the brain stem auditory system. The wave V of the not-affected ear is suspectedly influenced crossly from the lesion mainly in the inferior colliculus.