PubMed Health⌕ Search

Biomedical subjects

Todd Hillman

Publications and source records attributed to Todd Hillman.

5 recordsLinked to original sources
PubMed2006

An evaluation of the risk of cerebrospinal fluid leakage as a function of the surgical approach to the cochlear nerve.

OBJECTIVE: Direct implantation into the cochlear nerve can bypass the potential limitations of conventional cochlear implants. Implantable electrical arrays increase the number of stimulation sites, broaden frequency selectivity, require less activating current, and are not dependent on cochlear anatomy. Cochlear nerve implantation demands a unique surgical exposure to the modiolus. This study comprises an assessment of the risk of generating an intraoperative cerebrospinal fluid (CSF) leak using this approach. METHODS: Five fresh cadavers were obtained for dissection. Using dyed normal saline as an indicator, the central nervous system was pressurized to physiological parameters. Surgical approaches to the cochlear nerve were initiated. Leakage of indicator fluid for each approach was quantitatively and qualitatively assessed. Indicator dye in the surgical field was considered a CSF breech. Indicator fluid was collected and quantified. RESULTS: Eighty percent of the surgical approaches caused quantifiable leaks with rates ranging from 0.1 mL/minute to 6 mL/minute. For directly implanted microarrays, the utilization of a modified facial recess approach with cochleostomy and modiolar drillout carries significant risk for generating a CSF leak during the procedure.

Aged, 80 and over↗
PubMed2004

Dominant optic atrophy, sensorineural hearing loss, ptosis, and ophthalmoplegia: a syndrome caused by a missense mutation in OPA1.

PURPOSE: To describe the clinical features of and identify the disease-causing mutation in a large Utah family segregating a dominantly inherited syndrome of optic atrophy, sensorineural hearing loss, ptosis, and ophthalmoplegia. DESIGN: Observational case series. METHODS: Thirty individuals at risk for a syndrome of optic atrophy, sensorineural hearing loss, ptosis, and ophthalmoplegia in a single family underwent clinical examinations and venipuncture. Linkage analysis and mutation screening of the optic atrophy 1 gene (OPA1) were performed. RESULTS: Eighteen individuals demonstrated characteristics of the syndrome. Genetic analysis identified a G-->A substitution at nucleotide position 1334 in exon 14 of OPA1 causing an arginine-to-histidine change (R445H) in all affected members of the family. This change segregated with the disease phenotype in the study family with a LOD score of 7.02 at theta; = 0 and was not found in 200 normal control subjects. Analysis of an unrelated Belgian family with a similar phenotype revealed the same R445H mutation segregating with the disease phenotype. CONCLUSIONS: This study describes a mutation in OPA1 causing a unique syndrome of optic atrophy, sensorineural hearing loss, ptosis, and ophthalmoplegia. These results expand the spectrum of human disease associated with mutations of OPA1 and indicate that ophthalmologists caring for patients with optic atrophy should inquire about possible associated hearing loss. Although OPA1 is a nuclear gene, the gene product localizes to mitochondria, suggesting that mitochondrial dysfunction may be the final common pathway for many forms of syndromic and nonsyndromic optic atrophy, hearing loss, and external ophthalmoplegia.

Adolescent↗
PubMed2003

Cochlear nerve stimulation with a 3-dimensional penetrating electrode array.

HYPOTHESIS: An array of penetrating microelectrodes can be implanted into the cochlear nerve to produce stable evoked responses with important electrophysiologic advantages over conventional electrode technology. BACKGROUND: A totally implantable cochlear implant system would benefit from new electrode technology that lowers the current required for stimulation. Modern cochlear implant arrays placed in the scala tympani have an appreciable distance between the electrodes and the cochlear nerve, the site of intended stimulation. This distance can create the problem of cross-talk, limiting the number of electrodes that can represent discrete frequencies over a given length as well as significantly increasing stimulation thresholds and producing nonfocal stimulation of the fibers in the nerve. An electrode in direct contact with neurons in the cochlear nerve could reduce these problems. The Utah Electrode Array is a novel, three-dimensional, penetrating electrode array intended for direct neural stimulation with the potential ability to implant up to 200 electrodes directly into the cochlear nerve. METHODS: Arrays containing 6 to 19 electrodes were implanted acutely into six separate cat cochlear nerves for analysis. Thresholds and input/output functions were measured with electrically induced auditory brainstem responses. RESULTS: Current injections in 38 of 70 implanted electrodes produced stable brainstem responses after implantation. The median threshold was 15 microA. CONCLUSIONS: An array of penetrating electrodes can be implanted into the cochlear nerve and used to evoke brainstem responses. The responses are of low threshold and are stable. Arrays of electrodes, inserted into auditory nerve, could form the neural interfaces for the next generation of auditory prostheses.

Animals↗
PubMed2002

A technique for implantation of a 3-dimensional penetrating electrode array in the modiolar nerve of cats and humans.

BACKGROUND: We believe that direct intraneural stimulation of the modiolar nerve using an array of electrodes will have lower thresholds, offer greater frequency selectivity and more stimulation sites, and have a greater frequency representation than conventional cochlear implants. OBJECTIVES: To describe a potential auditory prosthesis based on electrical stimulation of the modiolar cochlear nerve and to report the development of a surgical approach in human and animal models. DESIGN: Cadaveric human and animal studies conducted in temporal bones indicated that an array of penetrating microelectrodes could be implanted in the modiolar nerve. Cat studies using anesthesia were performed to develop the surgical procedure in an animal model. Nerve viability was assessed by measurement of electrically evoked auditory brainstem responses at different stages of the surgery. SUBJECTS: Two fresh cadaveric human temporal bones, 3 cat cadavers, 1 pig cadaver, and 6 anesthetized cats were used in the experiments. RESULTS: We were able to implant arrays containing 20 microelectrodes in the human modiolar nerve after exposure by a modified extended facial recess approach. In animals, the modiolar nerve was accessed by the transbulla and the middle fossa approach. The cat was chosen as the appropriate animal model, and the transbulla approach was selected. The round window was exposed by ventral access to the bulla and after cochleostomy; drilling the modiolar bone exposed the modiolar nerve. The mean +/- SD diameter of the exposed nerve in cats was 1.64 +/- 0.07 mm (n = 9), and the mean +/- SD exposed length was 2.50 +/- 0.11 mm (n = 9); this is adequate to accommodate 20 microelectrodes. The electrically evoked auditory brainstem responses indicated nerve survival during and after the surgery. CONCLUSIONS: The surgical technique allows implantation of up to 20 microelectrodes in the cat and human modiolar nerve. The nerve survives the surgical procedure. This work enables studies in the electrophysiological properties and consequences of long-term implantation.

Animals↗