Patent Application
20150320550
A variety of implantable devices can be used to augment or replace natural biological functions. For example, cochlear implant systems can be used to provide a sense of hearing to deaf or severely hard of hearing patients. Cochlear implant systems typically include an external portion and an implantable portion. The implantable portion includes an electrode array that is inserted into the cochlea.
The accompanying drawings illustrate various examples of the principles described herein and are a part of the specification. The illustrated examples are merely examples and do not limit the scope of the claims.
Throughout the drawings, identical reference numbers designate similar, but not necessarily identical, elements.
The implanted portion of a cochlear prosthesis includes an electrode array that is inserted into the cochlea. The insertion of the electrode array into the cochlea places an array of electrodes proximal to the tonotopically arranged nerves in the modiolus of the cochlea. Monitoring the interaction between the electrode array and cochlea during insertion can provide valuable information about insertion forces and the biological function of the cochlea.
In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the present systems and methods. It will be apparent, however, to one skilled in the art that the present apparatus, systems and methods may be practiced without these specific details. Reference in the specification to “an example” or similar language means that a particular feature, structure, or characteristic described in connection with the example is included in at least that one example, but not necessarily in other examples.
The external portion (102) of the cochlear implant system (100) can include a Behind-The-Ear (BTE) unit (175), which contains the sound processor and has a microphone (170), a cable (177), and a transmitter (180). The microphone (170) picks up sound from the environment and converts it into electrical impulses. The sound processor within the BTE unit (175) selectively filters and manipulates the electrical impulses and sends the processed electrical signals through the cable (177) to the transmitter (180). The transmitter (180) receives the processed electrical signals from the processor (175) and transmits them to the implanted antenna assembly (187) by electromagnetic transmission.
The internal implanted portion (200) of the cochlear implant includes an electrode array (195) that is surgically placed within the patient's cochlea. Unlike hearing aids, the cochlear implant (100) does not amplify sound, but works by directly stimulating any functioning auditory nerve cells inside the cochlea (150) with electrical impulses representing the ambient acoustic sound. This bypasses the defective cochlear hair cells that normally transduce acoustic energy into electrical energy. The implanted portion (200) of the cochlear implant system is shown in
A typical human cochlea includes approximately two and a half helical turns of its various constituent channels around the modiolus (330). The modiolus (330) is a conical shaped central axis in the cochlea. The modiolus is formed from spongy bone and has the spiral ganglion located inside of it. The spiral ganglion is a group of nerve cells that detect and transmit a representation of sound from the cochlea to the brain. In a properly functioning cochlea, the dendrites of the spiral ganglion make synaptic contact with the base of hair cells in the organ of Corti. The dendrites are connected to axons of the spiral ganglion. The axons are bundled together to form the auditory portion of the eighth cranial nerve. The hair cells trigger action potentials in the dendrites in response to sound waves passing through the cochlea. These action potentials pass through the spiral ganglion to the brain. To compensate for absent or malfunctioning hair cells, the cochlear lead (190) directly stimulates the spiral ganglion in the modiolus. This bypasses the defective hair cells and/or nerve endings in the organ of Corti.
The cochlear lead (190) includes a flexible body (345) and an electrode array (195) at the distal end of the flexible body. A number of medial electrodes (365) are arranged along one side of the flexible body (345). This array of medial electrodes terminates near the tip (342) of the flexible body (345). Conductors (355) pass through the flexible body to connect to each of electrodes (365). The flexible body may include a number of additional features, such a lumen (352). A stylet can be inserted into the lumen (352) to stabilize and control the electrode array during insertion.
The electrode array (195) is inserted into one of the scalae, typically the scala tympani (320), to bring the individual medial electrodes (365) into close proximity with the tonotopically organized spiral ganglion nerves in the modiolus. Specifically, the electrode array (195) coils around the modiolus of the cochlea with the side of the electrode array that contains the array of medial electrodes on the same side as the modiolus. By placing the array of medial electrodes in proximity with the spiral ganglion, voltages applied by the electrodes can selectively trigger the generation of electrical impulses within the spiral ganglion.
Current electrode leads are not designed to monitor and evaluate the electrophysiologic parameters of the cochlea during electrode insertion. The monitoring of electrophysiologic parameters of during insertion can be useful in preserving residual hearing. Additionally, it may be useful as a tool during automated insertions, particularly for “guided” electrodes.
Tip elements are not found on any conventional cochlear electrode array. As discussed above, the medial electrodes on conventional electrode arrays are designed to be placed to stimulate the ganglion cells that are adjacent in the modiolar direction to the electrode array. A tip element offers the potential to measure normal auditory potentials during insertion and provides for novel stimulation paradigms. Specifically, the tip elements may be used to stimulate firing of the dendrites connected to the base of hair cells. This can provide a measurement of extent of damage to the hair cells. Consequently, the tip element may direct its stimulation to a different location within the cochlea than the linear array of medial electrodes along one side of the flexible body. Further, the tip element may be used to evaluate the function of portions of the cochlea that the electrode array has not yet passed through. This can be performed by directing stimulation out of the tip of the electrode toward areas in front of the electrode array. Further, the stimulation maybe primarily directed in directions that do not intersect with the modiolus. A variety of tip element designs are described below.
The return path for electricity produced by the various tip electrodes may be an implant ground or an electrode in the linear array. Additionally or alternatively, a split electrode may operate as a differential pair, with a first tip electrode being electrified and a second tip electrode acting as an electrical ground.
The tip electrode(s) can be formed in a variety of ways, including the electrode formation processes described in U.S. Pat. No. 4,686,765 to Byers et al. and U.S. Pat. No. 4,819,647 to Byers et al., which are incorporated by reference herein in their entireties. For example, U.S. Pat. No. 4,819,647 in column 5, line 40 through column 7, line 5 describes an illustrative technique for forming an electrode by forming a ball electrode, swaging the ball electrode into a desired shape, and optionally coating the electrode.
As discussed above, the cochlea is configured to detect high frequency tones near the base and progressively lower frequencies near the apex. In some implementations, the tip electrodes could be used after the insertion is complete to provide additional low frequency content to the cochlea, either as an analog signal or an amplitude modulated pulse string.
In general, a cochlear electrode array with tip elements includes a flexible body and an array of electrodes disposed along a longitudinal surface of the flexible body. A tip element is disposed at a distal end of the flexible body. The tip element lies on a distal surface of the flexible body and is configured to stimulate nerves proximate to the distal end of the flexible body during insertion of the cochlear electrode array into the cochlea. The tip element may include one or more of: at least one conductive electrode (such as a platinum tip electrode), a split electrode, a ball electrode, an optical fiber with a first end terminating at the distal end of the flexible body, and combinations thereof. Where the tip element includes an optical fiber, the optical fiber may be an infrared optical fiber that is transparent at wavelengths greater than 1.5 microns. The tip element may also include various optical components such as a fixed or steerable lens, such as shown in
Tip elements could be included in a variety of cochlear electrodes. For example, the tip elements could be included in a precurved electrode, such as modiolar hugging electrodes, or in electrodes that are substantially straight, such electrode that are designed for lateral placement within the cochlea.
The illustrative system shown in
Only the distal portion of the insertion tool (735) that engages with the electrode array (195) is shown in this diagram. The insertion tool (735) may be any of a variety of tools, including standard manual surgical implements, specialty manual surgical tools that are specifically adapted for insertion of a cochlear implant, or surgical tools that are at least partially automated. Examples of surgical tools that are at least partially automated include surgical tools that are held and manipulated by the surgeon's hand but provide haptic feedback and/or limited amount of automated motion. For example, actuators in the surgical tool may compensate for a hand shake, provide motion that is not easily performed by hand, or automatically advance the electrode into the cochlea. In other examples, the actuator may be fully automatic. Actuators can provide a number of advantages, including sensitivity, accuracy, speed and control that are outside of the capabilities of the human hand. In this example, a cross section of the insertion tool (735) shows three actuators (740).
In this implementation, the external surgical unit (702) includes a sensing module (705) and a control module (710). The sensing module (705) is connected to tip elements (745, 750). Additionally, the sensing module (705) may be connected to the linear array of electrodes (365). The sensing module (705) can provide stimulus to the tip elements. For example, the sensing module (705) may provide optical energy of desired wavelengths, intensities, and duration to the optical fiber (750). The sensing module (705) may also supply electrical voltage/current to the tip electrode (745). For example, the sensing module (705) may stimulate nerves by sending a pulse of infrared light down the optical fiber. The optical fiber transmits the light to the target nerve tissue. The nerve tissue is stimulated to produce an action potential which is detected by the tip electrode (745). One or more of the linear electrodes (365) can be used as a ground for this measurement. The sensing module (705) senses the voltage produced by the stimulated nerves.
The sensing module (705) transmits its results to the control module (710). The control module (710) may include a number of sub units. For example, the control module (710) may include an actuator controller (715), a distance estimator (720), a trauma unit (725) and a nerve function unit (730). The actuator controller (715) can be used to provide: input to the mechanical actuators (740), haptic output, audio output, graphical output or any other suitable action. The description of actuators given in
The distance estimator (720) can output any of a number of products based on the input from the sensing module. For example, the distance between the tip of the electrode array and the wall of the cochlea can be measured in a variety of ways. In one example, light pulses are sent down the optical fiber. The light pulses exit the optical fiber and a portion of the light pulses reflect back into the optical fiber. These reflections are detected by the sensor module and the distance module calculates the distance between the tip of the electrode and the cochlear wall. Additionally or alternatively, the distance and/or contact of the electrode array with the cochlea can be measured using electrical capacitance, audio techniques or other suitable methods. This distance information can be used by the control module to provide the desired output/control.
The trauma unit (725) can be used to detect changes in the cochlea that indicate that trauma has occurred during the insertion of the electrode array. For example, the trauma unit may accept the nerve performance data from the sensor module and determine if changes in the function of the cochlea are related to trauma. In other examples, trauma may be detected directly. For example, tissue that has been exposed to trauma may react differently to incident light or electrical stimulation. The control module may use this information to control the actuators to mitigate the trauma.
The nerve function unit (730) may produce a map of the function of the cochlea as the electrode array is inserted. This map may be used for a variety of purposes, including detecting trauma resulting from surgery and determining the best way to use the electrodes to improve the hearing of the patient. For example, if the map shows that the patient has significant residual hearing in a particular range of frequencies, the insertion of the electrode array can be modified to minimize trauma in this region. Additionally, the map may be used as an input during programming of the implanted processor. For example, after the electrode array is in place and the cochlear implant is functional, the processor can be programmed to provide supportive stimulation in frequency ranges where there is still residual hearing and to provide replacement stimulation where residual hearing is minimal.
The sensing nature of the design can also be used to monitor the long term health of regions of the cochlea and the auditory nerve. These measurements could be used to drive (re)programming of the cochlear implant as the function of certain cochlear regions or the auditory nerve itself changes.
In each example described above, the tip elements are in a different plane than the linear array of medial electrodes and are configured to stimulate or sense different portions of the cochlea.
The flexible body (345) is inserted through the scalae timpani along an insertion path (770). As the flexible body (345) is inserted into the ascending spiral of the scalae timpani, the flexible body bends so that the medial electrodes (365) are oriented toward the medial wall (780) along the length of the flexible body. Specifically, the medial electrodes (602) are generally parallel to the medial wall (780) and are the closest part of the flexible body to the medial wall. As discussed above, this places the array of medial electrodes (365) proximal to the spiral ganglion in the modiolus.
In contrast, the tip elements (760) are located at the most distal end of the flexible body (345) and are not solely configured to stimulate the spiral ganglion. Specifically, the tip elements (760) are oriented in a plane that is different than the plane of the array of medial electrodes and are configured to stimulate (or sense) nerve activity in directions other than the medial direction. The tip elements may be oriented to stimulate or sense: the area in front of the electrode array; the organ of Corti (775) (typically 90 degrees up or down from the medial direction); or the outer wall of the cochlea (180 degrees away from the medial wall).
When the tip elements (760) are oriented to sense the area in front of the electrode array they may produce information about any structural blockages that might be in the cochlear channel or the auditory response of the cochlear nerves prior to contact by the electrode array. When the tip elements (760) are oriented to stimulate/sense response by the organ of Corti (775) in locations adjacent to the tip of the electrode array, the tip simulators (760) may be sensing the immediate impact of the electrode array insertion on the function of the cochlea. When negative responses are detected during insertion, the electrode array can be backed out prior to causing irreversible trauma. A different insertion approach can then be taken to advance the electrode array into the cochlea. When the tip elements (760) are configured to sense the outer wall (785) of the cochlea, the tip elements can be used to measure the distance between the tip element and the wall or other parameters. This can be useful in atraumatic insertion of the electrode array and provide feedback to guide electrode array away from the lateral cochlea wall (765).
The tip elements (760) can be differentiated from the electrodes in a variety of ways. For example, the electrodes (365) are in a linear array when the flexible body are straight and are adjacent to and pointed directly toward the medial wall (780) when the flexible body is inserted into the cochlea. Thus, during and after insertion of the flexible body into the cochlea, a normal vector representing the orientation of the medial electrodes would intersect the modiolus. In contrast, the tip elements will typically be oriented around the circumference of the tip or on a forward face of the tip of the flexible body. A normal vector representing the orientation of tip elements will not typically intersect the modiolus. For example, a normal vector representing the orientation of a given element could be calculated by dividing the exposed surface of the element into sections, determining a normal vector for each section, and then summing the normal vectors to produce a resulting vector.
Further, the electrodes in the array are configured to stimulate the spiral ganglion. In contrast, the tip elements are configured to stimulate/sense areas that are in front of the flexible body, above the flexible body (as shown in
In one example, an optical fiber is used to stimulate nerves in the cochlea (block 820) and then electrical potentials generated by the optically stimulated nerves can be detected by an electrode (block 825). In another example, nerves in the cochlea can be stimulated using a electrode tip element (block 830) and then the electrical potentials generated by the stimulated nerves can be detected by the same or a different tip electrode (block 835).
In yet another example, auditory stimulation may be applied while inserting the electrode (block 840). The auditory stimulation may be produced externally to the ear or internally by a transducer. The transducer may be temporarily placed on or near the cochlea during surgery or may be an integral part of the cochlear electrode. The transducer may produce a wide variety of sound waves with varying pitches and intensities. As the nerves in the cochlea respond to the auditory stimulation, the action potentials produced can be sensed using the tip electrodes.
The descriptions above are related to sensing the function of the cochlea. A variety of other measurements can also be made. For example, the fiber optic may be used to directly or indirectly view portions of the cochlea that are in front of the tip electrode.
After mapping the function of the cochlea (block 850), changes in the function can be detected during insertion (block 855). In some examples, reversible trauma can be detected and the electrode insertion adjusted to maximize the function of the cochlea after the electrode array is implanted (block 860). Additionally or alternatively, the map of the cochlear function can be used to program the cochlear implant after insertion (block 865).
The methods, techniques and systems described above are only examples. Principles incorporated in these methods and systems could be applied in a variety of ways. For example, an electrode array that includes an imaging fiber optic may be implanted in a patient and subsequently require revision surgery to remove the electrode array. The imaging fiber optic may be used to during the revision surgery to image the interior of the cochlea as the electrode array is withdrawn. The imaging information may include images of structures and obstructions within the cochlea. Alterations in the structure of cochlea may have occurred during the period the electrode array was implanted. For example, there may be some tissue growth or alteration of the cochlea in response to the presence of the electrode array, aging of the patient, ongoing disease, or other factors. The imaging of these alterations can provide a number of benefits including better selection and programming of replacement cochlear implant or other diagnostic purposes. Similarly, if the tip element includes electrodes, the electrodes may be used to produce a map of the function of the cochlea as the electrode array is withdrawn. This map may be compared to a map that was produced during insertion to evaluate changes in the function of the cochlea.
In sum, incorporating a tip element or elements into a cochlear electrode array can provide for stimulation and detection of the surroundings of the cochlear electrode array during insertion. This allows for the function of the cochlea to be mapped and adjustments made during the insertion of the array. This can preserve residual hearing of the patient and optimize the results of the cochlear implant.
The preceding description has been presented only to illustrate and describe examples of the principles described. This description is not intended to be exhaustive or to limit these principles to any precise form disclosed. Many modifications and variations are possible in light of the above teaching. The features shown and/or described in connection with one figure may be combined with features shown and/or described in connection with other figures.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US12/72138 | 12/28/2012 | WO | 00 |
