Sotaro Funasaka

Dimensions of the scala tympani in the human and cat with reference to cochlear implants

The width, height, and cross-sectional area of the scala tympani in both the human and cat were measured to provide dimensional information relevant to the design of scala tympani electrode arrays. Both the height and width of the human scala tympani decrease rapidly within the first 1.5 mm from the round window. Thereafter, they exhibit a gradual reduction in their dimension with increasing distance from the round window. The cross-sectional area of the human scala tympani reflects the changes observed in both the height and width. In contrast, the cat scala tympani exhibits a rapid decrease in its dimensions over the first 6 to 8 mm from the round window. However, beyond this point the cat scala tympani also exhibits a more gradual decrease in its dimensions. Finally, the width of the scala tympani, in both human and cat, is consistently greater than the height.

Experimental Study on the Effect of Inferior Colliculus Lesions upon Auditory Brain Stem Response

The relationship between the activity of the inferior colliculus and each component of the auditory brain stem response (ABR) was investigated in rats using an electrical coagulation method. The ABR seems to be a composite of slow and fast waves, and the central nucleus of the inferior colliculus is more important for the slow wave than for the fast waves. There was little effect on the shape and latency of the fast waves of the ABR when the destruction was limited to the central nucleus. When the lesion was extended to or located in the lateroventral part of the inferior colliculus, where the nerve fibers of the lateral lemniscus penetrate into the inferior colliculus, potentials 5 and 6 were abolished, but potential 4 remained with a slightly prolonged latency. These findings suggest that the structures peripheral to the inferior colliculus play an important role for the generation of potential 4, and the inferior colliculus, particularly its lateroventral part, is essential for generation of potentials 5 and 6.

Effects of Chronic Electrical Stimulation on Spiral Ganglion Neuron Survival and Size in Deafened Kittens

We have studied spiral ganglion cell (SGC) survival and soma size in neonatally pharmacologically deafened kittens. They were implanted with a four‐electrode array in the left cochlea at 100 to 180 or more days of age. Eight animals were chronically stimulated approximately 1000 hours over approximately 60 days with charge‐balanced, biphasic current pulses; three were unstimulated controls. Using three‐dimensional computer‐aided reconstruction of the cochlea, the SGC position and cross‐sectional area were stored. SGC position was mapped to the organ of Corti by perpendicular projections, starting from the basal end. The basal region of the cochlea was divided into three 4‐mm segments. SGC survival (number per 0.1 mm of the length of the organ of Corti) and soma size for stimulated cochleae were compared statistically with implanted but unstimulated cochleae. There was no evidence of an effect of electrical stimulation on SGC survival under this protocol and with this duration. On the other hand, the cell size on the stimulated side was significantly larger than the control side in the middle segment (4 to 8 mm from the basal end). SGCs undergo a reduction in size after prolonged auditory deprivation; however, these changes may be partially moderated after chronic intracochlear electrical stimulation.

Congenital ossicular anomalies without malformations of the external ear

ZusammenfassungEs wird über 18 Ohren mit kongenitaler Gehörknöchelchenmißbildung ohne Deformierung des äußeren Ohres berichtet. Sie werden in drei Gruppen eingeteilt: 8 fehlende Incudostapedialverbindungen, 3 Malleus- oder Inkusfixationen und 7 Stapesfixationen.Für die Korrektur der ersten Gruppe wurde in der Regel ein Siliconröhrchen oder eine Drahtgelfoamprothese für eine Verbindung des Steigbügels mit dem Hammergriff verwendet. In dieser Gruppe konnte ein durchschnittlicher Hörgewinn von 35,4 dB in den Sprachfrequenzen erreicht werden. In der zweiten Gruppe brachte die Entfernung des fixierten Gehörknöchelchens in der Regel befriedigende Resultate, wogegen durch die reine Mobilisation kein Hörgewinn erzielt werden konnte. Bei der Gruppe mit Stapesfixation wurde in der Regel eine Stapedektomie mit Drahtgelfoamprothese durchgeführt. Die Resultate waren in einigen Fällen mit unterentwickelten ovalen Fenstern nicht befriedigend.Die genannten Mißbildungen werden nach embryologischen Gesichtspunkten analysiert.SummaryEighteen ears of congenital ossicular malformation without deformities of the external ear were presented. They were classified into three groups; eight incudostapedial joint separations, three malleus and/or incus fixations, and seven stapes fixations.The surgical correction for the first group was to connect the malleus handle to the stapes using a silicon tube specially designed or a gelfoam wire in the uncustomary way. This group showed the best surgical results with 35.4 dB of the average hearing gain in speech frequencies. In the second group, removal of the fixed part of the ossicles yielded satisfactory results, but mobilization failed to improve the hearing. For the group of stapes fixation, stapedectomy and the gelfoam wire prosthesis were performed. The result was not satisfactory in some cases with the undeveloped oval window.The embryological consideration leads us to the following conjecture; the incudostapedial joint separation results from the failure in build-up of “the secondary continuity”, the malleus and/or incus fixation is the result of disturbances in separation process by the undifferentiated mesenchyme, and the stapes fixation is due to maldevelopment of the stapedial lamina. This classification for the congenital ossicular malformation is practically valid as it would suggest the maldeveloped point in ossicular genesis and results of surgical correction.

Sweep-Frequency Tympanometry: Its Development and Diagnostic Value

This reports a newly developed tympanometric system using a sweep-frequency probe tone. For a sweep-frequency tone ranging from 220 to 2 000 Hz, measurements of sound pressure (P) and phase were performed at ear canal pressures of 0 and -200 mm H2O. The results were expressed as a sound pressure curve (P0-P-200 in decibels), a phase curve (formula: see text) and a polar curve (formula: see text) against probe tone frequency. Both the frequency at which the sound pressure curve crossed the 0-dB difference line and the peak frequency of the phase curve shifted lower than normal for ossicular disruption and higher than normal for ossicular fixation. Changes in the sound pressure curve and in the phase curve were exaggerated for ossicular disruption and limited for fixation. As the result of these, the polar curve showed an expanded type for disruption and a compressed type for fixation. A review of 220-Hz tympanograms and of the polar curves for 10 patients demonstrated that the latter permitted a better discrimination among ossicular disorders.

Tympanometry using a Sweep-Frequency Probe Tone and Its Clinical Evaluation

In this new tympanometric system, air pressure in the external meatus is kept constant at either -200 daPa or 0 daPa. The frequency of the probe tone is swept from 220 to 2,000 Hz (or 2,500 Hz, if necessary) in 4 s. During this frequency sweep, sound pressure in decibels and phase angle in degrees in the external meatus are sampled and the differences in sound pressure and phase angle measured at -200 and 0 daPa pressures are computed. These results are figured as a frequency-sound pressure curve and a frequency-phase angle curve. From the study on 8 fresh human cadaver temporal bones, four parameters in these curves are selected by discriminant analysis to provide diagnostic criteria: the minimum value and the 0-cross frequency of the frequency-sound pressure curve and the maximum value and its frequency of the frequency-phase angle curve. Normal parameters were determined in 50 normal ears. Evaluation of 40 patients with ossicular disorders revealed that 10 out of 12 cases of ossicular discontinuity and 5 out of 6 cases of malleus and/or incus fixation were correctly diagnosed. For stapes fixation, the diagnosis was correct in 12 out of 22 ears. This system is useful in the clinical diagnosis of ossicular disorders, producing a collection of curves and parameters that are distinctively different for the ossicular discontinuity and the ossicular fixation.

Effects of intracochlear factors on spiral ganglion cells and auditory brain stem response after long-term electrical stimulation in deafened kittens.

Using an animal model, we have studied the response of the auditory brain stem to cochlear implantation and the effect of intracochlear factors on this response. Neonatally, pharmacologically deafened cats (100 to more than 180 days old) were implanted with a 4-electrode array in both cochleas. Then, the left cochlea of each cat was electrically stimulated for total periods of up to 1000 hours. After a terminal 14C-2-deoxyglucose (2DG) experiment, the fraction of the right inferior colliculus with a significant accumulation of 2DG label was calculated. Using 3-dimensional computer-aided reconstruction, we examined the cochleas of these animals for spiral ganglion cell (SGC) survival and intracochlear factors such as electrode positions, degeneration of the organ of Corti, and the degree of fibrosis of the scala tympani. The distribution of each parameter was calculated along the organ of Corti from the basal end. There was a positive correlation between SGC survival and the level of fibrosis in the scala tympani, and a negative correlation between SGC survival and the degree of organ of Corti degeneration. Finally, there was a negative correlation between the 2DG-labeled inferior colliculus volume fraction and the degree of fibrosis, particularly in the 1-mm region nearest the pair of electrodes, and presumably in the basal turn.

The Auditory Stimuli to Evoke a clear Average Response at Behavioral Threshold

One of the difficulties in evoked response audiometry is identification of the response at lower stimulus intensities. It was thought that frequency change could evoke the response somewhat independently of the intensity of the tone, and averaged responses evoked by frequency-modulated (FM) tones were studied in order to learn whether this stimulus was suitable as a stimulus for obtaining a clear response at threshold intensityThe typical response evoked by a FM tone, which was presented in a continuous pure tone of 1 000 Hz by changing its frequency at intervals, was characterized by there vertex positive and two negative waves, which were refered to as P1, P2, P3, N1, and N2. The P1, N1, and P2 peaks were the most prominent. The latency of the response decreased with both increase in frequency increment and increase in tone intensity. The P1-N1 and N1-P2 amplitudes increased with increase in frequency increment, and this increase was more conspicuous for tones of lower intensity. Amplitude increment wit...

Use of Frequency Modulation Combined with Amplitude Change to Elicit Frequency-Specific Whole-Nerve Response

The averaged whole-nerve response to frequency modulation combined with amplitude change was recorded from the round window of the guinea pig. A downward shift of 20% in the frequency of a 500-Hz, 1-kHz or 2-kHz pure tone with an amplitude increase elicited the responses. The latency for each frequency was investigated at different intensities. The latency is greater for lower-frequency tones and this latency increase agrees well with the traveling wave delay for the intensity range used in this study. A downward shift with an amplitude decrease failed to yield the response. These findings suggest that the response to a downward shift of frequency with an amplitude increase results from new activation due to an apical extension of the envelope of the traveling wave and thus represents the activity in a restricted area of the basilar membrane. Thus, the frequency-modulated tone in downward direction with increased amplitude can be a frequency-specific stimulus.

Use of Sintered Hydroxylapatite and Inert Collagen in Middle Ear Surgery

In the surgery of chronic otitis media with cholesteatoma, it is absolutely necessary to remove the cholesteatoma and all other diseased tissue completely. The cholesteatoma arises at the invaginated pocket of the pars flaccida of the tympanic membrane and expands gradually to the attic and the mastoid antrum in most cases. Thus it is usually required to excavate the antrum first and then to proceed to the attic. In order to accomplish a complete clearance of the cholesteatoma occupying these areas, the surgeon must reduce the party wall between the attic and the external meatus until a very thin bridge of bone remains, and not infrequently the bridge must be removed.