Ernst Lehnhardt

Surgical Complications with the Cochlear Multiple-Channel Intracochlear Implant: Experience at Hannover and Melbourne

The surgical complications for the first 153 multiple-channel cochlear implant operations carried out at the Medizinische Hochschule in Hannover and the first 100 operations at the University of Melbourne Clinic, The Royal Victorian Eye and Ear Hospital, are presented. In the Hannover experience the major complications were wound breakdown, wound infection, electrode tie erosion through the external auditory canal, electrode slippage, a persistent increase in tinnitus, and facial nerve stimulation. The incidence of wound breakdown requiring removal of the package was 0.6% in Hannover and 1.0% in Melbourne. The complications for the operation at both clinics were at acceptable levels. It was considered that wound breakdown requiring implant removal could be kept to a minimum by making a generous incision and suturing the flap without tension.

Electrically Elicited Stapedius Reflex in Cochlear Implant Patients

Electrically elicited stapedius reflexes were examined in 25 deaf patients who had received a 22-channel Clark/NUCLEUS cochlear implant. Using an apical, a medial and a basal electrode pair, different stimulation positions within the cochlea and different stimulation modes were examined. For threshold determination, 10 reflexes were averaged with reflexes recorded on the nonoperated side. Reflexes were elicited in 19 of the 25 patients (76%); a saturation of reflex amplitude could be recorded in 14 (56%) subjects. In two additional cases, a reflex could be obtained by increasing the bipolar stimulation width (changing the stimulation mode). In comparison with different stimulation positions within the cochlea, the stimulation of apical electrodes produced more distinctive reflexes and required lower current levels. An increase in the bipolar stimulation width also decreased the intensity required for stapedius reflex threshold. Our data suggest that stapedius reflex evaluation may be a useful tool for speech processor fitting.

Instrumental Perforation of the Round Window: Animal Experiments Using Cochleography and ERA

The round window membrane of the inner ear of the guinea pig was perforated under Ketanest anaesthesia. A very rapid and almost total loss of cochlear microphonics, auditory nerve action potential and brain-stem response developed. Replacement of the perilymph with Ringers solution and surgical closure of the membrane damage had no effect on auditory nerve action potential or brain-stem response. Further decline in the amplitude of cochlear microphonics was halted, however. When perfusion of the round window membrane was carried out whilst the bulla was full with Ringers solution, no essential decline was seen in the amplitudes of microphonics and auditory nerve action. Only brain-stem response was reduced--temporarily by 40% of the original amplitudinal level--but this showed subsequent recovery. Preservation of cochlear microphonics and auditory nerve action after perforation in Ringers solution, i.e. excluding air, indicates that air entering the scala tympani is the cause of the sudden hearing loss after round window perforation. Using a simple physical model, an attempt is made to demonstrate this process. The anatomic connections between the round window, cochlear aqueduct and scala tympani are discussed, as are the different ways in which the round window membrane can be perforated.

Klinik der Innenohrschwerhörigkeiten

Trotz einer scheinbar klaren Aufgabenstellung mus die Gliederung eines Referats uber die Klinik der Innenohrschwerhorigkeiten logische Widerspruche in Kauf nehmen. Weder ist eine Ordnung allein nach der Ursache noch allein nach der Reaktionsform des Innenohres noch etwa allein nach dem Lebensalter moglich. Vielmehr wird man zwar die kindlichen Schwerhorigkeiten und die Altersschwerhorigkeit getrennt besprechen, aber auch die Tieftonschwerhorigkeiten gesondert abhandeln und ursachlich unterscheiden zwischen der ototoxischen, der stoffwechselbedingten oder der larmbedingten Schwerhorigkeit.

An integrity test battery for the Nucleus Mini 22 Cochlear Implant System.

The probability of system failures increases as the number of cochlear implants increases throughout the world. Whether a malfunction is a technical or physiological problem remains to be defined, particularly in very young children, while a psychogenic hearing disorder after implantation must not be excluded in adults. The battery of objective measurements used clinically at the Medizinische Hochschule, Hannover has provided useful diagnostic information for distinguishing possible causes of failure. In a normally functioning device, an electrical signal equivalent to the biphasic rectangular stimulation pulse can be recorded by measuring skin potentials from surface electrodes placed on the mastoid of the implant side and the forehead. The signal from the stimulated implanted electrodes is derived by applying a constant pulse rate. Signal averaging is not necessary. If no signals are observed, a non-functioning device should be suspected. If the device works normally, function of the auditory pathways can be examined by recording the electrically elicited stapedius reflex or electrically evoked brain-stem responses. In our experience with more than 450 cochlear implant patients, eight internal device failures occurred, while an additional three patients had either reduced or no hearing sensations due to a disorder of the auditory pathways.

Experience with the cochlear miniature speech processor in adults and children together with a comparison of unipolar and bipolar modes

Following the experience with nearly 150 patients with the Nucleus cochlear implant, a more sophisticated and lighter speech processor was tested successfully in terms of better speech understanding. In order to prepare further miniaturization, the standard bipolar stimulation mode was compared with an unipolar mode. It was found that unipolar stimulation needs less energy, without decreasing speech understanding. Preconditions for supplying very young children with a cochlear implant were the use of electrically elicited stapedius reflex thresholds, obtained intraoperatively, for the fitting of the speech processor and the setup of a special rehabilitation center, where children together with their mothers could be trained in hearing and understanding by special teachers and engineers for 12 weeks, distributed over the 1st postoperative year.

Long-term study after perforation of the round window. Animal experiments using electric response audiometry.

The round-window membrane of the inner ear of the guinea pig was perforated with a platinum wire under ketamine-xylazine anaesthesia. The latency times of waves I and V (Jewett) increased to 0.6 ms at 100 dB click HL stimulus loudness. The interpeak latencies did not change (4.0-4.2 ms). At 60 dB CHL stimulus loudness, no responses were discernible. Closure of the membrane damage by adhesive fibrin tissue had no effect on the auditory nerve potentials or the brain-stem responses. Normal latency times of waves I-V were seen 7 days after perforation. There was no difference between the animals with repaired and unrepaired membrane damage. We observed spontaneous healing of the round-window membrane 7 days after perforation, and a normal organ of Corti.

Zur Indikation und Prognose der transethmoidalen Opticusdekompression bei posttraumatischer Amaurose

SummaryIn 8 patients with unilateral posttraumatic amaurosis a transethmoidal decompression of the optical nerve was performed. In 4 patients the vision returned completely after operation, 1 patient showed only a partial improvement and in 3 cases the amaurosis remained unchanged. These results agree with those reported by Japanese authors (Sugita et al., 1965; Fukado, 1968) and suggest, that opposite to the neurosurgical transfrontal-intradural resection of the roof of the optical canal the rhinosurgical transethmoidal decompression of the optical nerve may improve the prognosis of the posttraumatic amaurosis, especially, if the decompression can be done as soon after trauma as possible. Further advantages of this surgical method are the smaller risk, the shorter operation time and the preservation of olfaction. It is emphasized that the rhinologist cannot indicate the decompression of the optical nerve without consulting the ophthalmologist and the neurologist. Contraindications are lesions of the bulbus oculi and the fundus, lesions of the chiasma opticum and a posttraumatic amaurosis caused by a sinus-cavernosus-fistula. Regarding the experiences gained by rhinosurgeons so far the early transethmoidal decompression seems to be indicated, if a unilateral impairment of vision exists right after the trauma or develops within the next 24–48 hrs and if there is no damage to the bulbus and the fundus.ZusammenfassungEs wird über 8 Patienten mit einseitiger posttraumatischer Amaurose berichtet, bei denen die transethmoidale Opticusdekompression durchgeführt wurde. In 4 Fällen erholte sich das Sehvermögen postoperativ vollständig, in einem weiteren teilweise und in den übrigen 3 Fällen blieb die Amaurose bestehen. In Übereinstimmung mit den Mitteilungen japanischer Autoren (Sugita et al., 196 S. Fukado, 1968) läßt dieses Ergebnis erwarten, daß die rhinochirurgische transethmoidale Opticusdekompression im Gegensatz zur neurochirurgischen transfrontal-intraduralen Opticuskanaldachresektion die Prognose der posttraumatischen Amaurose verbessern kann, besonders wenn die Dekompression zum möglichst frühen Zeitpunkt durchgeführt wird. Weitere Vorteile dieser Operationsmethode sind geringeres Risiko, geringerer Zeitaufwand und die Erhaltung des Riechvermögens. Auf die große Bedeutung einer interdisziplinären neurologisch-ophthalmologisch-rhinologischen Diagnostik vor Indikationsstellung zur Opticusdekompression wird hingewiesen. Kontraindikationen sind Bulbus- und Augenhintergrundverletzungen, Läsionen im Bereich des Chiasma opticum sowie eine posttraumatische Amaurose infolge einer Sinus-Cavernosus-Fistel. Aufgrund der bisher auf rhinochirurgischer Seite gewonnenen Erfahrungen erscheint die transethmoidale Frühdekompression indiziert, wenn eine einseitige Visusverschlechterung unmittelbar nach dem Trauma besteht oder sich innerhalb der ersten 24–48 Std entwickelt und wenn Bulbus und Augenhintergrund unverletzt sind.In 8 patients with unilateral posttraumatic amaurosis a transethmoidal decompression of the optical nerve was performed. In 4 patients the vision returned completely after operation, 1 patient showed only a partial improvement and in 3 cases the amaurosis remained unchanged. These results agree with those reported by Japanese authors (Sugita et al., 1965; Fukado, 1968) and suggest, that opposite to the neurosurgical transfrontal-intradural resection of the roof of the optical canal the rhinosurgical transethmoidal decompression of the optical nerve may improve the prognosis of the posttraumatic amaurosis, espcially, if the decompression can be done as soon after trauma as possible. Further advantages of this surgical method are the smaller risk, the shorter operation time and the preservation of olfaction. It is emphasized that the rhinologist cannot indicate the decompression of the optical nerve without consulting the ophthalmologist and the neurologist. Contraindications are lesions of the bulbus oculi and the fundus, lesions of the chiasma opticum and a posttraumatic amaurosis caused by a sinus-cavernosus-fistula. Regarding the experiences gained by rhinosurgeons so far the early transethmoidal decompression seems to be indicated, if a unilateral impairment of vision exists right after the trauma or develops within the next 24-48 hrs and if there is no damage to the bulbus and the fundus.

The brain stem response SN10, its frequency selectivity, and its value in classifying neural hearing lesions

ZusammenfassungDie Komponente P6 der Hirnstammreizantwort ist nur auf das Hören im Hochtonbereich ≥2 kHz zu beziehen, läßt sich aber bis an die Hörschwelle verfolgen. Die Hirnrindenreizantwort N90 dagegen ist frequenzspezifisch, bis an die subjektive Hörschwelle heran jedoch kaum zu erfassen. Die langsame Hirnstammkomponente SN10 (Davis und Hirsh 1979) soll unbeeinflußt durch medikamentösen Schlaf Auskunft auch über das Hörvermögen im Tief- und Mittelfrequenzbereich geben und wäre damit eine ideale Ergänzung zur schnellen Komponente P6.An einem Kollektiv von Normalhörenden und Innenohrkranken mit unterschiedlichen Frequenzgängen wurden die Hirnstammreizantworten P6 und SN10 simultan abgeleitet. Als Reiz verwendeten wir Tonpips frequenzunabhängiger An- und Abstiegsflanke von je 2 ms und einem Plateau von ebenfalls 2 ms. Die Schwelle der SN10-Reizantwort liegt im Mittel um ∼ 10 dB über der subjektiven Hörschwelle. Die Konstanz der Latenzen entspricht derjenigen von P6. Die Frequenzspezifität dieser relativ langsamen Hirnstammreizantwort ließ sich durch Vergleich der P6- und SN10-Reizantworten mit dem Verlauf der subjektiven Hörschwelle belegen.Die topodiagnostische Bedeutung der Komponente SN10 in Verbindung mit der Hirnstammreizantwort P6 und der Hirnrindenreizantwort N90 wird an einem Fall neuraler Hörstörung aufgezeigt.SummaryThe component P6 of the brain stem is only to be related to the hearing ability in the high tone range of ≥2 kHz, but it can be traced up to the hearing threshold. The cortex response N90, on the other hand, is frequency-specific, but it can hardly be recorded up to the subjective hearing threshold. The slow brain stem response SN10 (Davis and Hirsh 1979), unaffected by medicamented sleep, shall give information about hearing ability in the low and medium frequency range and may thus be an ideal complement to the fast response P6.In a number of normal hearing people and patients with sensorial hearing impairment of different frequency characteristics the brain stem responses P6 and SN10 were simultaneously recorded. As stimuli we used tone pips of a rise and fall time independent of frequency of about 2 ms and with a plateau of 2 ms as well. The mean threshold of the SN10 response is about 10 dB above the subjective hearing threshold. The constancy of the latencies corresponds to that of P6. The frequency selectivity of this relatively slow brain stem response is proved by comparing the P6 and SN10 responses with the course of the subjective hearing threshold.The topodiagnostic significance of the wave SN10 in connection with the brain stem response P6 and the cortical response N90 is shown in a case of neural hearing impairment.

Storage of audiometric data — Online — with a small computer

ZusammenfassungMit Hilfe eines Audiometers, das über einen zusätzlichen seriellen Ausgang verfügt, eines Rechners (DEC PDP 11/03) sowie eines Eingabe- und Sichtgerätes (DEC VT 55) lassen sich audiometrische Meßdaten on-line speichern, digital ordnen und diagraphisch wiedergeben. Die Eingabe kann man auf dem Display jederzeit kontrollieren und wie ein Audiogramm lesen. Für die Übertragung ist jeweils lediglich die Betätigung eines Knopfes am Audiometer notwendig. Ton- und Sprachaudiogramm erscheinen auf dem Display in getrennten Diagrammen; unter der Tonschwelle sind außerdem die Ergebnisse des SISI- und des Lüscher-Tests sowie die Stapediusreflexschwelle vermerkt, innerhalb des Tonschwellenaudiogramms die Meßpunkte des Fowler- und des Langenbeck-Tests. Für zusätzliche Befunde stehen drei Zeilen Bemerkungen zur Verfügung; sie werden über die Tastatur des Sichtgerätes eingegeben.Wahlweise kann eine rechnergesteuerte Vertäubungshilfe genutzt werden; unabhängig davon werden auch die Überhörwerte und die genutzten Geräuschlautstärken gespeichert.Die Papierdokumentation kann in Form einer Hardcopy oder gegebenenfalls als vierfarbiger Plotterausdruck erfolgen. Statistische Zusammenstellungen sind ohne weitere Aufbereitung möglich.SummaryFor online storage of audiometric measuring data we use an audiometer with serial operating output, a computer (DEC PDP 11/03), and a graphic terminal (DEC VT 55). The data can be controlled at any given time on the display and read like an audiogram. To transmit the data it is mainly only necessary to activate one button on the audiometer in addition.Pure tone and speech audiograms appear on the display in separate diagrams; in addition, beneath the pure tone threshold the results of the suprathreshold tests and the impedance measurement are indicated. For additional observations three lines are left available. If desired, a computer-supported masking aid can be used; independent of this, cross-heard values and applied masking noise intensities are stored.Paper documentations can achieve success as a hardcopy or as a four-coloured plotter print. Statistical groupings are possible without further processing.