Surgery – Surgically implanted vibratory hearing aid
Reexamination Certificate
2002-02-26
2004-03-30
Lacyk, John P. (Department: 3736)
Surgery
Surgically implanted vibratory hearing aid
C623S010000
Reexamination Certificate
active
06712754
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the field of implantable hearing aid devices, and more particularly, to non-invasive positioning of implanted actuators and interconnected componentry.
BACKGROUND OF THE INVENTION
Implantable hearing aid systems entail the subcutaneous positioning of various componentry on or within a patient's skull, typically at locations proximal to the mastoid process. In semi-implantable systems, a microphone, signal processor, and transmitter may be externally located to receive, process and inductively transmit a processed audio signal to an implanted receiver. Fully-implantable systems locate a microphone and signal processor subcutaneously. In either arrangement, a processed audio drive signal is provided to some form of actuator to stimulate the ossicular chain and/or tympanic membrane within the middle ear of a patient. In turn, the cochlea is stimulated to effect the sensation of sound.
By way of example, one type of implantable actuator comprises an electromechanical transducer having a magnetic coil that drives a vibratory member positioned to mechanically stimulate the ossicular chain via physical engagement. (See e.g. U.S. Pat. No. 5,702,342). In another approach, implanted excitation coils may be employed to electromagnetically stimulate magnets affixed within the middle ear. In each of these approaches, a changing magnetic field is employed to induce vibration. For purposes hereof, the term “electromechanical transducer” is used to refer to any type of implanted hearing aid actuator device that utilizes a changing magnetic field to induce a vibratory response.
In the case of actuators utilizing vibratory members, precise control of the engagement between the vibratory member and the ossicular chain is of critical importance. As will also be appreciated, the axial vibrations can only be effectively communicated to the ossicular chain when an appropriate interface exists (preferably a low mechanical bias or “no-load interface”) between the vibratory member and the ossicular chain. Overloading or biasing of the attachment can result in damage or degraded performance of the biological aspect (movement of the ossicular chain) as well as degraded performance of the mechanical aspect (movement of the vibratory member).
A number of arrangements have been proposed to precisely position actuators. These arrangements typically include among other things, a mechanical screw jack that controls the longitudinal movement of the actuator relative to the attachment interface. These screw jacks include a finely threaded screw that is manually adjusted, using a small tool, in or out to effect movement of a telescoping member that longitudinally positions the actuator relative to the attachment point.
Unfortunately, however, these devices suffer from several drawbacks. One drawback is that finite movements of the actuator are limited by the thread size of the screw. While it is often desirable to achieve a more finite adjustment of the actuator position, it is often not possible because of limitations in the available thread sizes. Another drawback is that regardless of tolerances in the system and screw design, a certain amount of “backlash” (movement of the screw in the reverse direction when forward pressure from the adjustment tool is released) exists in the system. To compensate for “backlash,” the screw is often adjusted slightly beyond the point where a desired position is reached. In some cases, several attempts at achieving the interface position must be made because of the unpredictability of the “backlash” in the system.
Also unfortunately, patients may experience a “drop-off” in hearing function after implantation due to changes in the physical engagement of the actuator caused by tissue growth. After implantation, however, it is difficult to readily assess the performance and adjust an implanted hearing aid actuator and interconnected componentry. For example, it is difficult to assess whether the vibratory member is in the desired physical engagement with the ossicular chain. Further, in the event of a “drop-off” in hearing after implantation, it is difficult to determine the cause, e.g. over/under loading of the interface or some other problem with the hearing aid, without invasive and potentially unnecessary surgery.
SUMMARY OF THE INVENTION
In view of the foregoing, a broad objective of the present invention is to provide a method and system that provides for non-invasive assessment of the performance of implanted hearing aid actuators and interconnected componentry. A related objective of the present invention is to provide a method and system for assessing the physical interface between a vibratory member of an implantable electromechanical transducer and the ossicular chain of a patient. Yet, another objective of the present invention is to provide for implantable hearing aid actuator performance assessment in a relatively simple and straightforward manner, thereby accommodating a simple office visit evaluation.
Another broad objective of the present invention is to provide a method and system for non or minimally-invasive adjustment of implanted actuators. A related objective is to provide a method and system for repositioning an electromechanical transducer to adjust the physical interface between the vibratory member and the ossicular chain of a patient. Yet, another object of the present invention is to provide a method and system for assessing the interface between an actuator and the ossicular chain of a patient and using the assessment to non-invasively reposition the electromechanical transducer to achieve a desirable interface between the transducer and the ossicular chain of the patient.
In carrying out the above objectives, and other objectives, features, and advantages of the present invention, a first aspect is provided, which includes a method and related system for externally assessing the performance of hearing aids that include implanted actuators. The method entails the positioning of a test device external to a patient having an implanted hearing aid actuator, and the use of the test device to obtain at least one test measure indicative of an electrical signal passing through the implanted actuator. In turn, the test measure(s) is employed to assess the performance of the implanted actuator.
In this regard, the present inventors have recognized that the electrical impedance of an implanted actuator (e.g. an electromechanical transducer) is indicative of the mechanical impedance present at the interface between the actuator and the middle ear of a patient (e.g. the ossicular chain). As such, the electrical impedance of an implanted actuator may be assessed to determine whether the desired actuator/middle ear interface is present.
The present inventors have also recognized that for a given implanted actuator driven by a predetermined test signal, the electrical impedance thereof may be determined either directly, (through a measure of the voltage and current of an electrical signal passing through the actuator in response to the test signal), or indirectly (from the magnetic field generated by the actuator in response to an electrical signal passing the implanted actuator.) In the latter case, the magnetic field strength is directly related to the amount of current passing through the actuator. In turn, all other things being equal, such current is inversely related to the electrical impedance present at the implanted actuator. That is, the smaller the electrical current passing through the actuator, the larger the electrical impedance thereof. Conversely, the larger the electrical current passing through the actuator, the smaller the electrical impedance. Such electrical impedance is directly related to the mechanical impedance present at the interface between the implanted actuator and middle ear of a patient. As such, by driving an implanted actuator at one or more predetermined frequencies, the resultant magnetic field measures or voltage and current-measures may be utilized to assess whether t
Miller Douglas Alan
Miller, III Scott Allan
Lacyk John P.
Marsh & Fischmann & Breyfogle LLP
Otologics LLC
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