Biomedical subjects

Michael Tykocinski

Publications and source records attributed to Michael Tykocinski.

5 recordsLinked to original sources

PubMed2006

Comparison of round window and cochleostomy approaches with a prototype hearing preservation electrode.

INTRODUCTION: Preservation of residual hearing in cochlear implant recipients has been demonstrated to be possible and provides the potential benefit of combined electric and acoustic auditory stimulation. A prototype 16-mm multichannel array has been designed to facilitate placement of 22 electrodes without damage to intracochlear structures. The electrode array is suitable for insertion via the round window membrane (RWM) or a small cochleostomy. AIM: To evaluate the insertion trajectory and the presence of trauma to intracochlear structures with the prototype electrode inserted by either the RWM or a scala tympani cochleostomy. MATERIALS AND METHODS: Eighteen fresh frozen human temporal bones were prepared for cochlear implantation using a standard transmastoid facial recess technique. Twelve electrodes were implanted at the University of Melbourne and 6 at the Medizinische Hochschule Hannover. In Melbourne fluoroscopy was used to monitor the insertions. Twelve prototype electrodes were inserted via the RWM. A further 6 electrodes were inserted via a small scala tympani cochleostomy. The cochleostomy was sited inferior to the RWM to avoid trauma to the basilar membrane and spiral ligament. Specimens were embedded and fixed with acrylic resin and the cochleae then examined histologically at 200-mum intervals using a grinding and polishing technique. RESULTS: Full insertion of the electrode was achieved without significant resistance in all RWM and cochleostomy specimens. In two RWM specimens fold-over of the electrode tip occurred, and in one specimen the electrode penetrated the spiral ligament to lie in an 'endosteal 'position. In one cochleostomy specimen the electrode was rotated within the cochlea to face laterally rather than towards the modiolus. The final electrode position differed for the two groups, with the electrodes inserted via the RWM lying in a more perimodiolar position along the first part of the basal turn. The average depth of insertion was 240 degrees for the RWM electrodes and 255 degrees for the cochleostomy electrodes. Histologic examination showed no damage in any specimen to the modiolus, osseous spiral lamina or basilar membrane. CONCLUSIONS: A prototype hearing preservation electrode array was inserted by either a RWM or a scala tympani cochleostomy without evidence of significant intracochlear trauma.

Basilar Membrane↗

PubMed2006

Airway fire during tracheotomy.

We report a case of airway fire during surgical tracheotomy using diathermy for the incision into the trachea. A literature review of airway fire during tracheotomy was carried out, and the management of airway fire is discussed. Recommendations are made to prevent this adverse outcome.

Aged↗

PubMed2005

Cochleostomy site: implications for electrode placement and hearing preservation.

CONCLUSIONS: With recent increased interest in minimizing intracochlear trauma and preserving residual hearing during cochlear implantation, increased attention must be paid to the cochleostomy site. The results of this paper demonstrate that the cochleostomy must be made inferior, rather than anterior, to the round window to ensure scala tympani insertion and to decrease the likelihood of insertion-induced intracochlear damage during electrode insertion. OBJECTIVE: To describe the complex anatomy of the hook region of the cochlea, specifically in relation to the optimal placement of the cochleostomy for cochlear implant electrode insertion to potentially achieve hearing preservation. The authors believe that previous industry recommendations and described surgical techniques have resulted in cochleostomies being placed in anatomical positions that possibly result in electrode insertions that damage the basilar membrane and/or other cochlear structures. MATERIAL AND METHODS: The results of a number of temporal bone studies were reviewed with attention being paid to the anatomical relationship of the basilar membrane and spiral ligament to the round window membrane. For different cochleostomy sites the potential for damage to intracochlear structures, particularly the basilar membrane and organ of Corti, was assessed. RESULTS: The review of electrode insertion studies into human temporal bones, as well as a post-mortem anatomical study of implanted temporal bones, showed an increased risk of scala vestibuli insertions and insertion-induced damage to intracochlear structures when the cochleostomy was performed more anterior to the round window. These results were endorsed by studies detailing the anatomy of the hook region of the cochlea.

Basilar Membrane↗

PubMed2005

Measurement and analysis of access resistance and polarization impedance in cochlear implant recipients.

BACKGROUND: Impedance measurements are commonly performed at the end of cochlear implant surgery, not only to confirm that all electrodes are working but also to monitor the impedances of the newly implanted electrodes. The current method of testing allows the determination of only the overall electrode impedance but not its components, access resistance and polarization impedance. To determine whether any longitudinal change in the electrode impedance is caused by a change in the endocochlear environment or rather caused by a change in the surface quality of the electrode, it is necessary to extract access resistance and polarization impedance. METHODS: We applied an impedance model that enabled us to calculate access resistance and polarization impedance after measurement of electrode impedance at three points along the voltage waveform. RESULTS: The results show that the value of the components of electrode impedance varied with time after surgery: access resistance increased slowly over time, whereas polarization impedance increased up to Week 2 but decreased after commencement of electrical stimulation at that stage. These results are consistent with the hypothesis that a layer of fibrous tissue forms around the electrode within the cochlear canal, resulting in a slow increase of access resistance, whereas a layer of proteins forms on the surface of the electrode in the early phase after implantation. Electrical stimulation appears to disperse this surface layer, thereby reducing both the polarization impedance and electrode impedance. CONCLUSION: The method presented enables the extraction of more detailed information about the longitudinal changes in the intracochlear environment after cochlear implantation.

Acoustic Impedance Tests↗

PubMed2002

Threshold, comfortable level and impedance changes as a function of electrode-modiolar distance.

OBJECTIVE: The study investigated the hypothesis that threshold and comfortable levels recorded from cochlear implant patients would reduce, and dynamic range increase, as distance of the electrode from the modiolar wall (radial distance) decreases. Two groups of cochlear implant patients participated; one group using the Nucleus' 24 Contour electrode array, and one group using the Nucleus standard straight (banded) array. The Nucleus 24 Contour array has been shown in temporal bone studies to lie closer to the modiolus than the banded array. The relationship of electrode impedance and radial distance is also investigated. DESIGN: The study, conducted at three centers, evaluated 21 patients using the Contour array, and 36 patients using the banded array. For each patient, threshold, comfortable levels and dynamic range were measured at four time points. Common ground electrode impedance was recorded clinically from each patient, at time intervals up to 12 wk. An estimate of the radial distance of the electrode from the modiolus was made by analysis of Cochlear view x-rays. RESULTS: Threshold and comfortable levels were significantly lower for the Nucleus 24 Contour array than for the banded array. However, dynamic range measurements did not show the predicted increase. In a majority of subjects, a significant correlation was found between the estimated radial distance of the electrode from the modiolus and the measured threshold and comfortable levels. This trend was not observed for dynamic range. The analysis indicates that other factors than radial distance are involved in the resultant psychophysical levels. Clinical impedance measures (common ground) were found to be significantly higher for the Contour array. However, the electrodes on the Contour array are half-rings, which are approximately only half the geometric size of the full rings as electrodes of the standard array. When the geometric electrode area in the two array designs are normalized, the trends in the electrode impedance behavior are similar. CONCLUSIONS: The results support the hypothesis that the relationship between the radial distance of the electrode and the psychophysical measures are influenced by patterns of fibrous tissue growth and individual patient differences, such as etiology and neural survival. Impedance measures for the Nucleus 24 Contour electrode array were higher than the banded electrode array, but this is primarily due to the reduction in electrode surface area. The different outcomes in impedance over time suggest differences in the relative contributions of the components of impedance with the two arrays.

Acoustic Impedance Tests↗