Patent ID: 12186559

DETAILED DESCRIPTION

There are several hearing loss causing mechanisms that can occur during the electrode insertion into the patient's cochlea. Most of these mechanisms can be avoided or reversed by controlling the force and speed of the insertion and timely maneuvering of the electrode during the insertion. Thus embodiments of the present invention are directed to arrangements to create an automated system for controlling cochlear implantation surgery to navigate the surgeon during insertion of the electrode array into the cochlea. In real time or near real time while the array is being inserted, at least one measurement difference value is determined for at least one electrode contact that is currently located at a given insertion depth into the patient cochlea, based on comparing current stimulus response data for the at least one electrode contact to prior stimulus response data for at least one prior electrode contact that was previously located at the given insertion depth. A potential trauma response is then identified when the at least one measurement difference value exceeds a defined difference value, and the surgical insertion is then paused.

FIG.2shows various functional blocks in a system andFIGS.3A-3Bshow various logical steps in a corresponding method of surgical insertion of a cochlear implant electrode array according to an embodiment of the present invention. An insertion tool202is configured for inserting an electrode array203with multiple electrode contacts204distributed along its outer surface into a cochlea205of an implanted patient206. An insertion controller201includes at least one hardware implanted processor device which is controlled by software instructions to control the insertion process by instructing the insertion tool202to control the inserting of the electrode array203. The program instructions that are executed by the insertion controller201include program instructions to commence insertion of the electrode array301.

As the electrode array203starts to enter the cochlea205,FIG.4A, once the first electrode contact E1enters into the cochlea205and valid impedance is present on that contact,FIG.4B, the stimulus response is measured and recorded for that contact at that location, step302. The insertion controller201controls the insertion tool202to continue insertion of the electrode array203into the cochlea205until the next contact E2enters, step303,FIG.4C. The stimulus response is measured and recorded for each inserted contact at its current location, step304.

The stimulus response measurements and recordings may include, for example, parameters such as response latencies, amplitudes and/or frequencies and phases of the evoked response signals, which may be recorded and evaluated continuously (with the electrode array being inserted at a controlled speed) or step-wise where the electrode array203is inserted into the cochlea205in steps and after each stopping the response measurement and recording is performed. The stimulus response signal amplitudes should be greater than the noise floor. For example, the amplitude of the stimulus response signals typically may vary from approximately 0.2 uV up to 800 uV recorded over a period up 8 sec. Typical recording time is 5-8 sec. Generally, the larger the signal, the smaller the recording period. Response measurement and record can be successfully performed even in patients with relatively poor hearing, even with low frequency thresholds at around 100 dB of hearing loss.

At least one measurement difference value is then determined, step305, for at least one electrode contact204that is currently located at a given insertion depth into the patient cochlea205based on comparing current stimulus response data for the at least one electrode contact to prior stimulus response data for at least one prior electrode contact previously located at the given insertion depth. Basically, difference values might typically be determined for each electrode contact for which there were one or more other electrode contacts previously at the same location.

More specifically, when the electrode array203has been inserted up to the point of two of the electrode contacts E1and E2being within the cochlea205(FIG.4C), response measurement recordings from the second electrode contact E2when it was just inserted are compared with the recordings from the first electrode contact E1at the time when it was just introduced into the cochlea205. Then when the electrode array203is inserted up to the point of three electrode contacts E1, E2and E3being within the cochlea205(FIG.4D), then response measurement recordings from the third electrode contact E3after it was just inserted are compared with the recordings from the second electrode contact E2when it was just inserted and from the first electrode contact E1when it was just inserted. At the same time, the response measurement recordings from the second electrode contact E2at its current location are compared to the response measurement recordings from the first electrode contact E1when it was at the same location. And so on.

When at least one measurement difference value exceeds a defined difference value threshold, step306, then a potential trauma response is identified and the insertion is paused, step309. In specific embodiments, the insertion controller201program instructions may determine multiple measurement difference values for multiple different electrode contacts204currently located at various different given insertion depths within the cochlea205, and then identify a potential trauma response when any of the measurement difference values exceeds the defined difference value. When at least one measurement difference value does not exceed the defined difference value threshold at step306, then, if the insertion is complete, step307, and stops. Otherwise, if the insertion is not complete at step307, insertion of the electrode array203continues until the next contact204enters the cochlea205, repeating from step303.

For example,FIG.5shows examples of response signal measurements recorded at the advancing electrode contacts204over time. Usually the signal amplitude tends to generally increase up to some inflection point, after which it generally decreases until insertion of the electrode array203is completed. This depends on the specific stimulus frequency that is used. Such expected signal behaviour would be indicative of no potential trauma and no hearing loss. However, potential trauma and hearing loss may be observed when the amplitudes of the evoked response signals decrease at a given location in the cochlea205. In the examples shown inFIG.5, this can be seen in the signals beginning at time4where the signal amplitudes are uniformly lower at all the measurement locations by up to 30%. At this stage of electrode insertion, the surgeon is needed to be notified of the potential trauma.

After pausing the insertion at step309for a short period because of a potential trauma, then it may be useful to proceed as shown inFIG.3Bby measuring and recording the stimulus response again for each inserted contact204at its current location, step310, and then determining measurement difference values between each inserted electrode contact204for which there are response measurements of a previous electrode contact204to occupy the same location, step311, and then determining again if a potential trauma response is identified, step312. It may be that the response measurements return to normal values after pausing, in which case, the insertion of the electrode array203again continues until the next contact204enters the cochlea205, repeating from step303.

If a potential trauma response is still present at step312, then the surgeon may take steps to try to resolve the problem; for example, maneuvering the array203, step313, for example, by partially rotating the array203and/or partially withdrawing the array203. Then the stimulus response is measured and recorded again for each inserted contact204at its current location, step314, and the measurement difference values are determined between each inserted electrode contact204for which there are response measurements of a previous electrode contact204to occupy the same location, step315, and then determining again if a potential trauma response is identified, step316. If the response measurements return to normal values (no potential trauma identified) after maneuvering the electrode array203, then the insertion of the electrode array203again continues until the next contact204enters the cochlea205, repeating from step303. If there still is a potential trauma present at step316after maneuvering the electrode array203, then the process ends (insertion complete, step307) and the surgeon decides whether to withdraw the array without completing the surgery or to complete the insertion procedure notwithstanding the trauma that is created.

The program instructions executed by the insertion controller201may be configured to propose which part of the electrode array203creates the greatest portion of the insertion force. Then the electrode array can be maneuvered to lower this insertion force as much as possible.

For example, if the amplitude of stimulus response recordings dramatically increases during the insertion at a specific location in the cochlea205, this may suggest that the electrode array is pressing on the basilar membrane or is too close to the inner ear hair cells and related neural structures. Often in such cases the latencies of stimulus responses gets shorter while at the other parts of the cochlea205, the amplitudes of the stimulus responses may actually be lower or remain unchanged. This may suggest that such electrode contacts204are on the lateral wall of the scala tympani and thus potentially causing the increase of insertion electrode forces. In such cases it is advised to stop the insertion, wait, and possibly slightly withdraw the electrode array203by some small portion (e.g., 1 mm or more). The surgeon may then continue with the insertion rotating the electrode array to navigate the trajectory of the electrode array tip, depending on the type of electrode array203.

The evaluating values could be the amplitude of the recording signal. It can be amplitude defined as peak-to-peak amplitude (difference between the global/local maximum and global/local minimum) or the amplitudes related specific stimulating frequency, i.e. if the stimulating signal consists of one frequency, i.e. tone pip of frequency f the evaluated amplitude would be related to frequency f. Another value to evaluate are latencies of the recorded signals. Frequency analysis of the stimulus response signals may be performed to determine what types of responses are being recorded. Here, the signal is represented by phase and amplitude at each particular frequencies of recorded signal. The possible specific stimulus responses may include cochlear microphonics (CM), summating potentials (SM), and/or compound action potentials (CAP). For example, CM amplitude for an electrode array may increase by up to ten times when a given electrode contact is moved from the lateral wall to the vicinity of the basilar membrane closer to the hair cells while still maintaining depth position in the scala tympani without causing any additional hearing loss. In such a case, the latency of the stimulus response often shortens.

Changes in the stimulus responses can be reversible and can be controlled by the insertion force and speed, withdrawing, and rotating the electrode array. For example, optimal insertion forces to preserve residual hearing should be maintained less than 25 mN and should never exceed 40 mN. Other influencing factors for hearing preservation include the geometry of the electrode opening into the cochlea and prevention of blood and bone dust in the cochlea.

The risk of hearing trauma increases with insertion depth into the cochlea. Any potential trauma identified during insertion of the electrode array should be immediately evaluated. One advantage of embodiments of the present invention is that the deeper the electrode array is inserted into the cochlea, the more precisely it can be controlled. As an additional benefit, the insertion depth of the electrode array can be estimated. This also provides a way to evaluate and compare the specific insertion behaviour of various different electrode arrays

Embodiments of the invention may be implemented in part in any conventional computer programming language such as VHDL, SystemC, Verilog, ASM, etc. Alternative embodiments of the invention may be implemented as pre-programmed hardware elements, other related components, or as a combination of hardware and software components. Embodiments also can be implemented in part as a computer program product for use with a computer system. Such implementation may include a series of computer instructions fixed either on a tangible medium, such as a computer readable medium (e.g., a diskette, CD-ROM, ROM, or fixed disk) or transmittable to a computer system, via a modem or other interface device, such as a communications adapter connected to a network over a medium. The medium may be either a tangible medium (e.g., optical or analog communications lines) or a medium implemented with wireless techniques (e.g., microwave, infrared or other transmission techniques). The series of computer instructions embodies all or part of the functionality previously described herein with respect to the system. Those skilled in the art should appreciate that such computer instructions can be written in a number of programming languages for use with many computer architectures or operating systems. Furthermore, such instructions may be stored in any memory device, such as semiconductor, magnetic, optical or other memory devices, and may be transmitted using any communications technology, such as optical, infrared, microwave, or other transmission technologies. It is expected that such a computer program product may be distributed as a removable medium with accompanying printed or electronic documentation (e.g., shrink wrapped software), preloaded with a computer system (e.g., on system ROM or fixed disk), or distributed from a server or electronic bulletin board over the network (e.g., the Internet or World Wide Web). Of course, some embodiments of the invention may be implemented as a combination of both software (e.g., a computer program product) and hardware. Still other embodiments of the invention are implemented as entirely hardware, or entirely software (e.g., a computer program product).

Although various exemplary embodiments of the invention have been disclosed, it should be apparent to those skilled in the art that various changes and modifications can be made which will achieve some of the advantages of the invention without departing from the true scope of the invention.