Fluid filled microphone balloon to be implanted in the middle ear

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FLUID FILLED MICROPHONE BALLOON
TO BE IMPLANTED IN THE MIDDLE EAR

This application claims the benefit of U.S. Provisional Application Serial No. 60/122,373, filed Mar. 2,1999, which 5 application is incorporated herein by reference.

BACKGROUND OF THE INVENTION

The present invention relates to an implantable microphone system that is useable with cochlear implants or 10 implantable hearing aids, and more particularly to an implantable microphone system that senses motion of the tympanic membrane and transfers such motion to a microphone sensor via a fluid communication channel.

A cochlear implant is an electronic device designed to 15 provide useful hearing and improved communication ability to individuals who are profoundly hearing impaired and unable to achieve speech understanding with hearing aids. Hearing aids (and other types of assistive listening devices) make sounds louder and deliver the amplified sounds to the 20 ear. For individuals with a profound hearing loss, even the most powerful hearing aids may provide little to no benefit.

A profoundly deaf ear is typically one in which the sensory receptors of the inner ear, called hair cells, are damaged or diminished. Making sounds louder or increasing 25 the level of amplification, e.g., through the use of a hearing aid, does not enable such an ear to process sound. In contrast, cochlear implants bypass damaged hair cells and directly stimulate the hearing nerves with electrical current, allowing individuals who are profoundly or totally deaf to 30 receive sound.

In order to better understand how a cochlear implant works, and how the present invention is able to function, it is helpful to have a basic understanding of how the ear 3J normally processes sound. The ear is a remarkable mechanism that consists of three main parts: the outer ear, the middle ear and the inner ear. The outer ear comprises the visible outer portion of the ear and the ear canal. The middle ear includes the eardrum (or tympanic membrane) and three 4Q tiny bones. The inner ear comprises the fluid-filled snailshaped cochlea which contains thousands of tiny hair cells.

When the ear is functioning normally, sound waves travel through the air to the outer ear, which collects the sound and directs it through the ear canal to the middle ear. The sound 45 waves strike the eardrum, or tympanic membrane, and cause it to vibrate. This vibration creates a chain reaction in the three tiny bones in the middle ear. These three tiny bones are medically termed the malleus, incus and stapes, but are also commonly referred to as the "hammer", "anvil" and "stir- 50 rup". Motion of these bones, in turn, generates movement of the oval window, which in turn causes movement of the fluid contained in the cochlea.

The cochlea is lined with thousands of tiny sensory receptors commonly referred to as hair cells. As the fluid in 55 the cochlea begins to move, the hair cells convert these mechanical vibrations into electrical impulses and send these signals to the hearing nerves. The electrical energy generated in the hearing nerves is sent to the brain and interpreted as "sound". 60

In individuals with a profound hearing loss, the hair cells are damaged or depleted. In these cases, electrical impulses cannot be generated normally. Without these electrical impulses, the hearing nerves cannot carry messages to the brain, and even the loudest of sounds may not be heard. 65

Although the hair cells in the cochlea may be damaged, there are usually some surviving hearing nerve fibers. A

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cochlear implant works by bypassing the damaged hair cells and stimulating the surviving hearing nerve fibers with an electrical signal. The stimulated nerve fibers then carry the electrical signals to the brain, where they are interpreted as sound.

Representative cochlear implant devices are described in U.S. Pat. Nos. 4,267,410; 4,428,377; 4,532,930; and 5,603, 726, incorporated herein by reference.

Cochlear implants currently use external microphones placed on the body that pick up sound (sense acoustic pressure waves and convert them to electrical signals) and then transmit the electrical signals to a signal processor for amplification, processing and conversion into an electrical stimulation signal (either current or voltage) that is applied to the surviving acoustic nerves located in the cochlea. Such a microphone is, by design, very sensitive, and in order to be sensitive, is by its nature very fragile. Disadvantageously, the external microphone can be damaged if it becomes wet, is dropped or is exposed to extreme conditions frequently encountered in the external environments. These fragile and sensitive microphones also restrict the user's lifestyle and activities. For example, when a user must wear a microphone, he or she is restricted from participation in swimming and other sports, e.g., contact sports, unless the microphone is removed during such activities. If the microphone is removed, however, the user no longer is able to hear. Moreover, many users also find an external microphone cosmetically objectionable since they appear out of place and mark the user as "needing assistance".

There have been a number of published concepts for implantable microphones which can be used with implantable hearing aids and cochlear implants. In such concepts, it is common to attempt to utilize the acoustic characteristics of the human ear to improve sound quality and obtain some directionality. The general concept in these proposals is based on the common idea of implanting some type of acoustic sensor in the inner ear cavity and to couple it mechanically to the acoustic chain.

The most popular approach discussed in the art to mechanically couple an acoustic sensor to the acoustic chain is to clamp the driving element to the malleus, incus or stapes. Disadvantageously, this approach suffers from several drawbacks: (1) the complexity of placement of the clamping elements, (2) the long-term stability of the clamp and clamping elements, (3) a degradation of performance due to ingrowth of tissue into the middle ear, and (4) potential damage to the malleus, incus or stapes bones.

It thus is evident that improvements are needed in the way users of a cochlear implant, or other hearing aid systems, sense or hear sounds, and more particularly, it is evident that improvements are needed in the implantable microphones used with such systems.

BRIEF SUMMARY OF THE INVENTION

The present invention addresses the above and other needs by providing an implantable microphone system, usable with a cochlear implant system or other hearing aid prosthesis. Such microphone system detects sound pressure waves (acoustic waves) sensed at the tympanic membrane of a patient through a fluid communication channel established between the middle-ear side of the tympanic membrane and an implantable microphone capsule. The implantable microphone capsule includes first and second compartments separated by a flexible diaphragm. The second compartment is in fluid communication with a thin-walled balloon positioned in contact with the tympanic membrane within the middle 3

ear. The first compartment includes a microphone sensor, adapted to transduce mechanical motion to an electrical signal. Such microphone sensor is mechanically coupled through a mechanical linkage to the flexible diaphragm. The microphone sensor, in turn, is electrically connected to the 5 cochlear implant system or other hearing aid prosthesis.

In accordance with one aspect of the invention, fluid communication is established between the thin-walled balloon within the middle ear (which is in contact with a middle-ear component, such as the middle ear side of the 1° tympanic membrane, or the stapes) and the flexible diaphragm within the microphone capsule via a flexible tube. A suitable fluid, such as a natural saline solution, is injected into the balloon, tube and second compartment within the microphone capsule via an injection port formed in the wall 15 of the microphone capsule and fluid compartment. Such injection port comprises a penetratable seal, e.g., penetratable by a hypodermic needle. In addition to allowing a suitable volume of fluid to be injected into the fluid communication link, such injection port also allows air or other 20 gases to be vented therefrom.

In operation, vibrations (physical movement) of the tympanic membrane, or other middle ear components, caused by sound pressure waves sensed through the outer ear canal, are coupled through the fluid communication system to the 25 flexible diaphragm within the microphone capsule. Movement of the flexible diaphragm, in turn, is sensed by the microphone sensor and transduced to an electrical signal which is forwarded to the hearing aid prosthesis, e.g., a cochlear implant system. 30

It is thus an object of the present invention to provide an implantable microphone system usable with an implantable cochlear stimulation system.

It is a feature of the invention to provide an implantable 3J microphone system that allows sound waves, collected through the patient's outer ear, to be sensed and converted to electrical signals representative of the sensed sound, which electrical signals may then be processed in accordance with a suitable speech processing strategy and con- 4Q verted to stimulation signals adapted to stimulate the patient's auditory nerve through an electrode array implanted within the patient's cochlea.

It is a further feature of the invention to provide an implantable microphone system that relies upon a fluid 45 communication channel to transfer pressure waves sensed within the middle ear, e.g., at the tympanic membrane or the stapes, to an implantable, yet outside-of-the middle-ear, microphone capsule whereat such pressure waves may be converted to a suitable electrical signal. 50

It is still another feature of the invention to provide such an implantable microphones system wherein motion or movement of a middle ear component, such as the tympanic membrane or the stapes, is sensed through the use of a thin-walled, fluid-filled, balloon placed in contact with the 55 middle ear components, e.g., immediately behind the tympanic membrane, i.e., on the middle-ear side of the tympanic membrane, or in contact with the stapes.

BRIEF DESCRIPTION OF THE DRAWINGS

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The above and other aspects, features and advantages of the present invention will be more apparent from the following more particular description thereof, presented in conjunction with the following drawings wherein:

FIG. 1 schematically illustrates the three main compo- 65 nents of the invention: a microphone capsule 10, a thin-wall balloon system 20, and a coupling fluid 30;

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FIG. 2 is a perspective view of an the implantable microphone made in accordance with the invention;

FIG. 3 anatomically illustrates the positioning of the microphone system when implanted within and near the middle ear;

FIG. 4 schematically depicts one location within the middle ear of a thin walled balloon used as part of the implantable microphone system of the present invention, and further illustrates use of the implantable microphone system with one type of cochlear implant system;

FIG. 5 schematically illustrates an alternative position for the thin walled balloon within the middle ear, and illustrates use of the implantable microphone with another type of cochlear implant system.

Corresponding reference characters indicate corresponding components throughout the several views of the drawings.

DETAILED DESCRIPTION OF THE
INVENTION

The following description is of the best mode presently contemplated for carrying out the invention. This description is not to be taken in a limiting sense, but is made merely for the purpose of describing the general principles of the invention. The scope of the invention should be determined with reference to the claims.

The present invention is directed to an implantable microphone system. Such system will typically be used by a patient or user having a cochlear prosthesis; but could also be used with any type of hearing aid system where a microphone is needed. A schematic representation of the invention is depicted in FIG. 1. As seen in FIG. 1, the invention includes three main components: (1) a microphone capsule 10; (2) a thin-walled balloon system 20 comprising a balloon 21 and connecting tube 22 made from a biocompatible polymer (such as silicone rubber); and (3) a coupling fluid 30, e.g., natural saline.

The microphone capsule 10 has a first compartment 11 and a second compartment 12 separated by a flexible membrane or diaphragm 13. The first compartment 11 is hermetically sealed and includes a microphone sensor 14 coupled by a mechanical link 16 with the flexible diaphragm 13. The microphone sensor 14 may be any suitable sensor known in the art, e.g., a piezoelectric transducer, that converts movement of the flexible diaphragm 13, as sensed through the mechanical link element 16, to an electrical signal. The electrical signal generated by the microphone sensor 14 is delivered through suitable hermetic feedthrough terminals 15 to wire conductors 27 which carry the signal to a suitable speech processor, as explained more fully below in conjunction with FIG. 4.

The second compartment 12 of the microphone capsule 10 has a connecting port 18 that connects with the flexible polymer tube 22. The tube 22, in turn, is joined with the thin-walled, pillow-shaped, balloon 21 that forms part of the balloon system 20.

The balloon system 20 is implantable within the middle ear of the patient. The system 20 includes the pillow-shaped thin-walled balloon 21 with integral flexible connecting tube 22.

The balloon system 20, including the balloon 21 and tube 22, and second compartment 12 are filled with a suitable fluid 30. It is the function of the fluid 30 to transfer pressure waves caused by motion of the patient's tympanic membrane to the flexible diaphragm 13 within the microphone 5

capsule 10. To this end, the tube 22 provides a fluid communication channel between the balloon 21 and the chamber 12 so that pressure waves introduced at the balloon, e.g., caused by flexing or movement of the balloon wall, are transferred to the flexible diaphragm, 12. Thus, the micro- 5 phone sensor 14 within the first chamber 11 of the microphone capsule 10 senses movement of the flexible diaphragm 13, which movement corresponds to movement of the walls of the balloon 21 as sensed through the fluid communication channel, or tube 22. When the balloon 21 is 10 inplanted so that its wall is adjacent to and in contact with the tympanic membrane, then movements of the tympanic membrane are transferred to the balloon walls. As a result, the microphone sensor 14 generates an electrical signal representative of the movement of the tympanic membrane. 15

As further seen in FIG. 1, the microphone capsule 10 further includes an injection port 17 that allows the second chamber 12, as well as the balloon system 20, to be filled with the fluid 30. This injection port 17 also allows air bubbles (or other undesirable gaseous bubbles) to be 20 removed from the chamber 12 and balloon system 20. The injection port 17 may be realized through the use of a suitable semipermeable membrane that seals an opening 28 in the exterior wall of the capsule 10 that defines the second compartment 12. Such membrane may be easily pierced by 25 a sharp instrument, such as a hypodermic needle, for the purpose of injecting the fluid 30 into the fluid system and for removing air bubbles therefrom.

The second compartment 12 of the microphone capsule 10, including the balloon system 20, is made from materials 30 selected to make the system water-tight, i.e., a closed system. Thus, a change of the contents of system occurs only by diffusion to keep in balance with the body fluid(s) when the system is implanted.

In a preferred embodiment, the fluid 30 comprises a natural saline liquid without air bubbles. It is to be understood, however, that other types of fluids may be used, including both liquid and gaseous fluids. Further, a different fluid may be used within the compartment 12 than is used 4Q within the balloon system 20, e.g., a first fluid 30' within the compartment 12, and a second fluid 30" within the balloon system 20, which two fluids are then in contact with each other through a thin membrane separator strategically placed at some point between the two fluid systems, e.g., at the inlet 4J port to the chamber 12.

Turning next to FIG. 2, there is shown is a perspective view of an the implantable microphone system made in accordance with the invention. The microphone system includes the microphone capsule 10 and the balloon system 50 20. The balloon system 20 includes the thin-walled balloon 21 and connecting tube (or fluid communication channel) 22. The microphone capsule 10 includes a system of attachment to surrounding bone (or other) tissue. In the embodiment shown in FIG. 2, such attachment system includes a 55 plurality of barbed pins 26 that protrude out from the capsule 10. These barbed pins or tines 26 are configured to be pushed into pre-drilled holes in the surrounding bone tissue.

Turning next to FIG. 3, the manner of implanting the microphone system will be described. FIG. 3 anatomically 60 illustrates the preferred positioning of the microphone system when implanted within and near the middle ear of a patient. Advantageously, the microphone system may be implanted during a standard cochlear implant placement without any additional preparation. A normal mastoid cavity 65 is formed in conventional manner. As part of this process, the mastoid cavity, when exposed by folding over the facia

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and skin flap, is drilled for placement of a cochlear electrode system 52 within the snail-shaped cochlea 46 of the patient. After insertion of the electrode system 52 into the cochlea 46, and fixation of the cochlear stimulator (not shown in FIG. 3) attached to the electrode system 52, the balloon 21 is placed through the facial recess behind the tympanic membrane 40. Due to is size and flexible nature, the balloon 21 remains in contact with the back of the tympanic membrane (i.e., the side of the tympanic membrane within the middle ear) and is supported at the promontory.

The microphone capsule 10 is placed within the mastoid cavity using a suitable system of attachment. For example, barbed pins 26 may be pushed into pre-drilled holes in the mastoid bone. The microphone output wires 27 (FIG. 1) are then connected to the speech processing system. The connecting tube 22 is laid down within the mastoid cavity. The facia and skin flap are then replaced over the opening and sutured for closure.

Turning next to FIG. 4, the operation of the implantable microphone system will be described in connection with a cochlear implant system. FIG. 4 schematically illustrates one position for the thin walled balloon within the middle ear and shows the use of the implantable microphone with a cochlear implant system. The cochlear implant system depicted in FIG. 4 includes an implantable cochlear stimulator (ICS) 54 coupled to an implantable speech processor (ISP) 56 by way of a coupling wire 58 formed in a loop 59. Other types of coupling between the ISP 56 and the ICS 54 may, of course, also be used. The speech processor, for example, could be an external (non-implanted) speech processor, if desired. Alternatively, the ISP 56 and ICS 54 may be housed within the same package. Various types of fully implantable, and partially implantable, cochlear stimulation systems are described in PCT Publication W099/ 06108, published Feb. 11, 1999, corresponding to PCT Patent Application Ser. No. PCT/US98/15996, which publication is incorporated herein by reference, any of which could be used with the present invention. Indeed, the microphone of the present invention is not limited to a particular type of cochlear stimulation system, but may be used with any type of hearing aid device.

As seen in FIG. 4, sound waves 60 travel through the air to the outer ear 62, which collects the sound and directs it through the ear canal 63 to the middle ear 64. The sound waves 60 strike the eardrum, or tympanic membrane 40, and cause it to vibrate. In a functioning ear, this vibration creates a chain reaction in the three tiny bones in the middle ear, the malleus 42, the incus 43 and the stapes 44. Motion of these bones, in turn, generates movement of the oval window 45, which in turn causes movement of the fluid contained in the cochlea 46, which in turn triggers the hair cells and excites the auditory nerve, as explained previously.

A patient using a cochlear implant system, however, does not have a fully functioning ear. In fact, such patients may not have a functioning middle ear 64, or other defects or disease may prevent sound waves 60 form being transferred to the hair cells in the cochlea.

As seen in FIG. 4, the sound waves 60 are picked up by the eardrum 40, i.e., they cause the tympanic membrane (eardrum) 40 to vibrate as a function of the intensity and frequency of the sound. These vibrations are transferred to the fluid 30 inside of the balloon 21. These vibrations are then carried by the fluid 30, through the tube 22, to the diaphragm 13 within the microphone capsule 10. In this manner, the diaphragm 13 is caused to vibrate as a function of the intensity and frequency of the sound waves 60.

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The vibrations of the diaphragm 13 are detected by the microphone transducer sensor 14 (FIG. 1) within the first compartment 11 of the microphone capsule 10. As explained previously, such detection includes converting the sensed vibrations to electrical signals that are present on micro- 5 phone output wires 27. The wires 27 are connected to the ISP 56, or other suitable processor. The ISP 56 processes the electrical signals in accordance with a selected speech processing strategy and sends control signals, e.g., via the looped coil 59, to the ICS 54. The ICS 54 responds to the 10 control signals by generating appropriate electrical stimuli which is delivered to individual electrode contacts 53 spaced apart on the electrode array 52. These electrical stimuli excite neurons embedded within the modiolar wall of the cochlea 46, causing nerve impulses to be sent through the 15 auditory nerve 47 to the patient's brain, thereby allowing the patient to experience the sensation of hearing based on the sound waves 60 collected in his or her outer ear 62.

Turning next to FIG. 5, there is shown a schematic diagram similar to that shown in FIG. 4, but with the thin 2o walled balloon 21', which forms part of the implantable microphone, being located at a different location within the middle ear 64. Rather than being placed so as to contact the middle-ear side of the tympanic membrane 40 (as shown in FIG. 4), the thin walled balloon 21' shown in FIG. 5 is placed 25 so as to be in contact with the stapes 44. The embodiment of the invention illustrated in FIG. 5 is particularly suited for patients having a functioning middle ear because it allows the tympanic membrane 40, as it vibrates as a result of sensed sound waves, to drive the malleus 42 (which is the 30 normal load driven by the malleus). The malleus 42, in turn, drives or vibrates the incus 43, which drives or vibrates the stapes 44. The stapes, in turn vibrates the thin walled balloon 21', which is a liquid medium (and which thus represents the normal type of load driven by the stapes—a fluid-filled 35 medium). The positioning of the thin-walled balloon 21' shown in FIG. 5 thus represents a better impedance match for the incoming sound waves. That is, for the embodiment shown in FIG. 5, the tympanic membrane 40 will not be unduly damped or restricted from vibrating as it could be 40 when a fluid-filled medium is in contact with it.

In operation, the embodiment of the invention depicted in FIG. 5 operates essentially the same as that described above in connection with FIG. 4. That is, the sound waves 60 are picked up by the eardrum 40, i.e., they cause the tympanic 45 membrane (eardrum) 40 to vibrate as a function of the intensity and frequency of the sound. These vibrations are transferred through the incus 43 and stapes 44, to the fluid 30 inside of the thin-walled balloon 21'. These vibrations are then carried by the fluid 30, through the tube 22, to the 50 diaphragm 13 within the microphone capsule 10. In this manner, the diaphragm 13 is caused to vibrate as a function of the intensity and frequency of the sound waves 60.

Still with reference to FIG. 5, the vibrations of the diaphragm 13 are detected by the microphone transducer 55 sensor 14 (FIG. 1) within the first compartment 11 of the microphone capsule 10. As explained previously, such detection includes converting the sensed vibrations to electrical signals that are present on microphone output wires 27. The wires 27 are connected to the ISP 56, or other suitable 60 processor. The ISP 56 processes the electrical signals in accordance with a selected speech processing strategy and sends control signals, e.g., via cable 58', to the ICS 54. The ICS 54 responds to the control signals by generating appropriate electrical stimuli that are delivered to individual 65 electrode contacts 53 spaced apart on the electrode array 52. These electrical stimuli excite neurons embedded within the

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modiolar wall of the cochlea 46, causing nerve impulses to be sent through the auditory nerve 47 to the patient's brain, thereby allowing the patient to experience the sensation of hearing based on the sound waves 60 collected in his or her outer ear 62.

A more detailed description of a fully implantable cochlear stimulation system of the type shown in FIGS. 4 and 5 may be found in U.S. patent application Ser. No. 09/404,966, filed Sep. 24, 1999, now U.S. Pat. No. 6,308, 101; or Ser. No. 09/126,615, filed Jul. 31, 1998, now U.S. Pat. No. 6,067,474, both of which applications are incorporated herein by reference.

As described above, it is thus seen that the present invention provides an implantable microphone system usable with an implantable cochlear stimulation system. It is further seen that such system allows sound waves, collected through the patient's outer ear, to be sensed and converted to electrical signals representative of the sensed sound. These electrical signals may then be processed in accordance with a suitable speech processing strategy and converted to stimulation signals adapted to stimulate the patient's auditory nerve through an electrode array implanted within the patient's cochlea.

As further described above, it is seen that the present invention provides an implantable microphone system that utilizes a fluid communication channel to transfer pressure waves sensed within the middle ear, e.g., at the tympanic membrane, or at the stapes, to an implantable, yet outsideof-the middle-ear, microphone capsule. It is within this microphone capsule where the transferred pressure waves are converted to an electrical signal.

Finally, it is seen that the present invention provides an implantable microphone system wherein motion or movement of one or more middle ear components of a patient's middle ear, e.g., movement of the tympanic membrane or movement of the stapes, is sensed through the use of a thin-walled, fluid-filled, balloon system placed in contact with the moving middle ear component, i.e., immediately behind the tympanic membrane, i.e., on the middle-ear side of the tympanic membrane, or in contact with the stapes. Advantageously, such sensing system is reliable, is stable over a long period of time, does not damage the middle ear bones, and does not promote tissue ingrowth within the middle ear.

While the invention herein disclosed has been described by means of specific embodiments and applications thereof, numerous modifications and variations could be made thereto by those skilled in the art without departing from the scope of the invention set forth in the claims.

What is claimed is:

1. An implantable microphone system, usable by a patient having a cochlear prosthesis, comprising:

a microphone capsule having first and second chambers separated by a flexible diaphragm, the second chamber having a first fluid therein;

a microphone sensor within the first chamber that is in mechanical contact with the flexible diaphragm, the microphone sensor comprising a transducer that converts movement of the flexible diaphragm to an electrical signal;

a balloon implantable in the middle ear of the patient, the balloon having a second fluid therein, and having a wall adapted to be coupled with a movable component of the middle ear, wherein movement of the middle ear component causes the balloon wall to also move;

a fluid communication channel coupling the first fluid within the second compartment of the microphone