Surgery – Diagnostic testing – Sensitivity to electric stimulus
Reexamination Certificate
2000-02-02
2002-08-06
Schaetzle, Kennedy (Department: 2731)
Surgery
Diagnostic testing
Sensitivity to electric stimulus
C600S025000, C600S559000, C607S057000, C607S137000, C623S010000
Reexamination Certificate
active
06428484
ABSTRACT:
The present invention relates to apparatus for picking up electrical biological signals, and more specifically auditory evoked potentials generated by acoustic and/or electrical and/or mechanical stimulation of the cochlea, or of a portion of the auditory system in man or animal
BACKGROUND OF THE INVENTION
Traditionally, auditory evoked potentials are measured with extracorporeal devices using surface electrodes applied to the skin of the patient. Such equipment picks up far field auditory evoked potentials which mainly comprise:
early auditory evoked potentials (commonly referred to by the initials ABR). These potentials are normally made up of seven waves (“Les potentiels évoqués auditifs” [Auditory evoked potentials ] by J. M. Guerit, 1993 published by Masson, Paris at pages 87 to 99 on evoked potentials), with the wave
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being generated mainly by the ramifications of the auditory nerve along the internal hair cells;
medium latency auditory evoked potentials (referred to by the initials AMLR);
late auditory evoked potentials (referred to by the initials ALCR); and
cognitive evoked potentials (referred to by the initials ACR).
Such extracorporeal devices for picking up auditory potentials require a great deal of care and time to be put into operation. In addition, on safety grounds, it is essential to have complete metallic isolation between the machine and the person under test. The results obtained do not always accurately represent real auditory activity since standard equipment is specifically too sensitive to interfering electrical noise: stimulation artifacts; 50 Hz or 60 Hz from the electricity mains; high frequency interference; etc. . . . . Similarly, such equipment is disturbed by non-auditory biological activity. Furthermore, result reproducibility is degraded by fluctuations in the resistivity of the skin and by impedance drift due in particular to moving electrodes which can shift during a test, and which above all can be positioned differently from one examination to another. In order to restrict these drawbacks at least in part, it is possible to make use of anesthetics, in particular when performing tests on children, but that can give rise to other non-negligible drawbacks.
There also exist implanted devices for picking up auditory evoked potentials such as those described in U.S. Pat. No. 5,758,651 or application WO 97/48447, which measure cochlear activity following electrical stimulation thereof.
Document U.S. Pat. No. 5,758,651 describes a telemetry system for a hearing prosthesis, in particular for a cochlear implant. The system has a plurality of electrodes which are used to stimulate the auditory nerve and to detect the evoked potentials; in an example described in that document, the potential difference between an intracochlear electrode and an extracochlear electrode is measured; that potential difference is applied to the input of a “blanking” amplifier of gain adjustable over the range 40 dB to 80 dB; in a variant, that document proposes using a differential amplifier.
Document WO 97/48447 describes an adjustment system integrated in a cochlear stimulation implant; the system uses two means for measuring auditory perception by the patient: firstly an intracochlear electrode for measuring evoked potential, and secondly an electrode (or transducer) for measuring the activity of one of the two muscles of the middle ear (“stapedius” and “tensor tympani”).
The document by Carolyn J. Brown et al. published in J. Acous T Soc AM, Vol. 88, No. 3, September 1990, pages 1385 to 1391, describes a method of measuring evoked potentials in which use is made firstly of one of six intracochlear electrodes of the stimulation implant, and secondly of an electrode placed on the temporal muscle.
Those devices pick up solely a near field auditory evoked potential because one of the pickup electrodes is immersed in the cochlea and is as close as possible to the activity to be measured. That near field potential which represents the initial excitation of the auditory system is commonly referred to as evoked action potential (EAP). It does not give information about the other levels of the auditory system: cochlear nucleus, coliculus inferior, primary and secondary auditory areas, and associative areas. Furthermore, EAP cannot be recorded directly because of artifacts generated by electrical stimulation too close to the pickup electrodes. In order to obtain a meaningful EAP, it is necessary to make use of so-called “subtractive” techniques that serve to remove the artifacts and allow the EAP to be extracted on its own. Both techniques are described in particular in the above-mentioned document by Carolyn J. Brown et al.
OBJECTS AND SUMMARY OF THE INVENTION
The device of the invention makes it possible to remedy the drawbacks of existing evoked potential pickup devices.
In a first aspect, the invention consists of such a device which includes at least two extracochlear pickup electrodes for implanting, which pickup electrodes are connected to the (positive and negative) input terminals of a differential amplifier integrated in a package, likewise designed to be implanted; in addition, the package includes a system for transmission through the skin, with or without signal processing, thereby enabling an external device to receive information concerning the auditory evoked potentials that have been picked up. Such a device enables activity to be recorded at each level of the auditory system and to evaluate periodically the functional state of the auditory system as a whole from the cochlear to the associative cortex; measurements can be taken almost simultaneously, artifacts are practically non-existent, and the constant position and impedance of the pickup electrodes over time keeps down measurement inaccuracy and makes good reproducibility possible. Finally, the relative distance of the pickup electrodes from the cochlear site makes it possible to obtain direct and accurate measurements of all of the far field auditory evoked potentials described above: ABR, AMLR, ALCR, and ACR. In addition, ABR wave
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makes it possible by equivalence (cf. Buckard et al., J Acous Soc Am, 93 (4), pp. 2069-2076, April 1993) to measure the same activity as EAP activity and to do so without any need to resort to a “subtractive” technique. The device of the invention thus makes it possible to examine and evaluate overall activity of the auditory system in a single operation, including the possibility of recording results. When coupled with a cochlear implant, it also makes it possible to optimize the adjustments thereof, quickly and in “objective” manner, particularly on young children, which is not possible with any previously known device.
The invention relies in part on the observation whereby it is possible to measure in reliable manner the electrical potentials that result from neuronal activity of the auditory system by means of at least two electrodes that are remote from the cochlea; one advantage lies in the device being easier to implant surgically; another advantage lies in the measurement system being less sensitive to artifacts due to the cochlear being stimulated. An essential feature of the measurement method and device of the invention is that because of the external position (relative to the cochlea) of the measurement (i.e. pickup) electrodes, the potential differences that are measured represent physical phenomena that are quite distinct from those represented by measurements using an intracochlear electrode.
Another important advantage of the invention is that it is possible to make use of measurement electrodes that are larger than those which can be implanted in the cochlea; this gives rise to contact impedance between the electrode and tissue which is smaller and which can be kept substantially constant over time; the accuracy and the repeatability of measurements are thus improved; furthermore, the size of the electrode enables it to be associated with a screw passing through the electrode and enabling it to be secured to bony tissue, thereby improving bot
Battmer Rolf Dietter
Charvin Guy
Lenarz Thomas
Cohen & Pontani, Lieberman & Pavane
Droesch Kristen
Schaetzle Kennedy
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