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F T Hambrecht

Publications and source records attributed to F T Hambrecht.

12 recordsLinked to original sources
PubMed1989

Functional electrical stimulation: an overview.

The development of future neural prostheses involves much more than connecting commercially available stimulators to disabled individuals. Safe and effective operation of prostheses requires fundamental studies of the electrode-tissue interface. The electrochemistry of the interface must be controlled to prevent toxic byproducts. Histopathological studies of stimulated tissue are necessary to establish safe limits of stimulation and to determine mechanisms of neural damage when it does occur. Electrophysiological studies elucidate which neural pathways are excited and help in the design of more selective electrode arrays. Biomaterials are required that protect the implant from the hostile environment of the body. Presently available materials are being improved and totally new materials are being developed. One of the goals of neural prostheses developers is a nonhermetic packaging material that can be applied to miniature implants without appreciably increasing their size. The techniques used to make integrated circuits on silicone substrates are ideally suited to making ultraminiature electrodes with self-contained electronic signal processing. Both integrated circuit stimulating and recording electrodes are being designed and fabricated.

Biocompatible Materials↗
PubMed1977

Neural prostheses.

Explore the source record for details and available documents.

Audiovisual Aids↗
PubMed1975

Electrical stimulation of the brain. III. The neural damage model.

A major concern in the use of neural prostheses is whether electrical stimualtion can cause irreversible damage to neurons. The Neural Damage Model was devised to study the problem and to provide guidlines. The cerebral cortex of cats was stimulated continuously for 36 hours with balanced, biphasic waveforms. The charge per phase, charge density and current density were varied in 16 separate tests. Of these stimulus parameters the charge per phase was more closely correlatable with neuronal damage than charge density and current density. Furthermore, the findings in this study suggest that current flow is more important than electrochemical reactions in causing neural damage. Correlation between blood-brain barrier (BBB) breakdown and neuronal damage was valid only in the group of animals sacrificed immediately following stimulation. The BBB is restored within one month following electrical injury. Convulsive seizures occurred in all but one of the animals during electrical stimulation. A technique for localizing the electrode sites at autopsy and in the microscopic sections is described.

Animals↗
PubMed1973

Capacitor electrode stimulates nerve or muscle without oxidation-reduction reactions.

Porous tantalum disks, available as "slugs" from the capacitor industry, have large available surface area and a thin insulating coating of tantalum pentoxide. When implanted, they fill with extracellular fluid and operate as capacitor-stimulating electrodes having high capacitance per unit volume. Capable of stimulating excitable tissute without generating electrochemical by-products, these electrodes should provide a safer interface between neural prosthetic devices and human tissue.

Animals↗
PubMedDate not supplied

Current status of multichannel cochlear protheses.

Multichannel cochlear prostheses are being developed and evaluated with emphasis on providing sensory deaf individuals enough information about their acoustic environment to permit communication by ordinary speech. Studies of the safety of the electrode arrays and stimulus values indicate that the remaining nerve fibers will not be damaged at the levels that will be typically used in human prostheses, but that a narrow safety range exists for suprathreshold stimuli. Early multichannel human implants have demonstrated that place pitch can be utilized with scali tympani implants, but this has not been demonstrated with modiolar electrode arrays. With both approaches, information about pitch can be conveyed by the frequency of stimulation. Research questions remain on the long-term viability of the eighth nerve with stimulated implants, on the interactions of closely spaced electrodes, on optimal methods of encoding the acoustic signal for multichannel nerve stimulation and on the ability of deaf individuals to utilize this information.

Cochlear Implants↗