Abstract:
This invention comprises a totally implantable Eustachian tube activation device which is intended for patients suffering from Eustachian Tube Dysfunction ailment. The device electrically stimulates the muscles activating the Eustachian tube to perform the opening maneuver of the Eustachian tube valve to aerate the middle ear cavity. The unit is hermetically sealed in a suitable biocompatible container and implanted in a suitable location in close proximity to Eustachian tube. The frequency of the stimulation of the implant may be fixed or can be altered depending on the condition of the patient.

Description:
FIELD 
     The present invention relates to category of surgical instruments devices or methods for transferring non-mechanical form of energy to the body. More specifically, the present invention relates to sub-category of “arrangements in connection with implantation of stimulators”. The apparatus is designed to stimulate muscles controlling the Eustachian Tube electrically and intended to be implanted in humans and animals suffering from medical condition of “Eustachian Tube Dysfunction” or related ailments. 
     BACKGROUND 
     The Eustachian tube is a hollow tube that originates in the back of the nose and connects the nasal cavity to the middle ear space. The middle ear space is the hollowed out portion of the skull bone that contains the hearing mechanism, which is covered by eardrum on one side and cochlea on the other side. The Eustachian Tube provides ventilation, drainage and protection of mid ear against reflux, microorganisms, excessive sound pressure and pressure changes in pharynx. In adults, the Eustachian tube is approximately 35 mm long and approximately 3 mm in diameter. The first part of the Eustachian tube is supported by cartilage and the last part that is close to the middle ear space is located inside the bone structure. The lining tissue of the Eustachian tube is similar to tissue that covers the nasal cavity and responds to external stimulants just as nasal tissue does. 
     The main function of the Eustachian tube is to provide ventilation to the middle ear space, ensuring that its pressure remains at slightly negative but close to ambient air pressure. Another function of the Eustachian tube is to drain secretions and debris from the middle ear space. Several small muscles located in the back of the throat and palate control the opening and closing action of the tube. Typical muscular actions like swallowing and yawning cause contractions of these muscles and activate Eustachian tube function time to time to achieve its pressure regulation function. 
     Eustachian tube is normally closed most of the time to prevent contaminants contained in the nasal cavity to reach the middle ear space cavity. Disorders of ET are basically either “dilatory” type (failure to open adequately) or “patulous” type (failure to maintain tube closed at rest). Dysfunction of an Eustachian tube makes the tube always open and this condition is called a “patulous” Eustachian tube. Patients with “patulous” dysfunctional Eustachian tube suffer from frequent, chronic ear infections. A more common form of the Eustachian tube dysfunction causes partial or complete blockage of the Eustachian tube which cause sensations of popping, clicking, and ear fullness as well as moderate to severe ear pain associated with the condition. 
     Many people suffer from Eustachian Tube (ET) dysfunction and this condition affects quality of their life. There have been many different attempts over the history to solve the problem of ET dysfunction. Most devices developed are in the form of tubes or similar inserts which are inserted into Eustachian tube to keep it open and provide ventilation. Patents and applications; WO 2009/001358, WO 2006/049131, US patent US 2009/0099573, WO 2005/082303, U.S. Pat. No. 4,015,607 can be cited in this category which more or less achieve the purpose using this method. U.S. Pat. No. 4,888,017 proposes a different approach by providing an inflatable gadget to open the Eustachian tube momentarily by patient applying pressure manually to activate the device which forces open the ET tube. Another remedy used by surgeons to rectify Eustachian tube dysfunction ailment is to fix a grommet on the eardrum of the patient to provide ventilation for the middle ear cavity. These methods mentioned above have some complications. Most patients report that insert devices used for keeping Eustachian tube open simply do not remain in place for long time and provide solution only for a limited time. Grommets (rings) placed on ear drums also tend to fall after several weeks. Additionally, keeping the ET tube always open solves one problem but causes secondary problems by providing an open path for liquid and external contaminants to flood the mid ear cavity. 
     Patents like WO 01/43653 and WO 2008/079476 provides alternative techniques of surgical manipulation of ET tube by laser and radio frequency techniques to remedy the problem of Eustachian Tube Dysfunction related complications. Overall, many humans as well as animals are afflicted with ET dysfunction problem. 
     The present invention attempts to solve the problem with a different mechanism which activates muscles of the ET. The muscles surrounding the ET tube activate the opening/closing action of the ET valve. As R. Leuwer writes in an article titled “Mechanics of Eustachian tube” published in “Chronic Otitis Media. Pathogenesis-Oriented Therapeutic Management”, pp 129-134 edited by B. Ars (2008 Kugler Publications), Eustachian tube has a complex muscular compliance which involves influence of tensor veli palatine muscle, levator veli palatine muscle and medial pterygoid muscle. Most researchers agree that tensor veli palatini and levator veli palatine are primary activators of the Eustachian tube whereas medial pterygoid muscle has secondary influence on function of the ET by changing the position of the ET and the veli muscles mentioned above. 
     In 1979, Cantekin et. al reported in an article published in Ann Otol Rhinol Laryngol. 1979 January-February; 88(1 Pt 1):40-51 that they have conducted a series of experiments with Rhesus monkey and observed that Eustachian Tube (ET) tube action is initiated by muscles surrounding the ET tube. This, indeed has proven that Eustachian tube is not a simple tube and its function can be controlled by a series of coordinated activation of the surrounding muscles. 
     SUMMARY 
     The approach of the present invention is to fix the problem that underlies the Eustachian tube dysfunction problem by way of stimulating muscles through an electronic transplant by injecting current to the involved muscles or nerves controlling the muscles. Eustachian tube is not a simple tube that connects the nasal cavity to the middle ear cavity, it is actually a tubular valve which opens time to time to equalize the pressure inside the mid ear cavity. The ET tube is normally rests in closed state and only opens temporarily for a short time (about 1 sec.) to execute its function. The opening action of the ET tube is achieved by two muscles located on different sides of the ET tube. These two tubal muscles are the Levator Veli Palatini Muscle (LVPM) and the Tensor Veli Palatini muscle (TVPM). Among the two, Tensor Veli Palatini (TVPM) is the main tubal dilator which performs the Eustachian tube function. However LVPM and TVPM function together for a successful opening action of ET. Some researchers also claim that medial pterygoid muscle also plays a role indirectly by making affect of the palatini muscles more effective. Coordinated action of these muscles is necessary for successful opening and closing of the Eustachian Tube which results in aeration and pressure equalization of the mid ear cavity. 
     The present invention is contemplated as a self contained unit with electrodes, power source, electronics and microcontroller in a suitable package to be transplanted in a suitable location in close proximity to the Levator Veli Palatini (LVPM) and the Tensor Veli Palatini muscles (TVPM) of the Eustachian Tube. Microcontroller and the associated electronics of the present invention send an orchestrated series of pulses to the said muscles through electrodes to achieve the desired action of the ET tube. 
     Normally in healthy subjects, the ET aeration action is done time to time through actions like yawning and swallowing. The present invention is contemplated to have different scenarios with different frequencies of muscular stimulation to be selected by the ENT specialist depending on the condition of the patient. An external adjustment unit with wireless connectivity is contemplated to be used for selecting suitable scenario, important parameters and relaying this information to the implanted unit wirelessly. 
     In healthy subjects, the pressure inside the inner ear is maintained slightly negative than the ambient pressure through the action of Eustachian tube. The present invention is contemplated to achieve the same through activation of the ET tube from time to time. How frequent this action needs to be done may depend on the individual patient and may be different for different patients. To achieve this adaptability, the present invention accommodates sensor inputs as well as adaptable frequency plans. In one embodiment, a suitable pressure sensor may be used to sense the inner ear pressure and activate the stimulation action when the pressure is above or below certain limits. In another embodiment, a tilt sensor may be used to initiate stimulation sequence as the patient tilts his or her head. Yet in another embodiment, the stimulation action can be purely time based and do not depend on sensor inputs. As an example of time based activation, the stimulation action can be repeated once every 2 minutes. The present invention is designed to be activated by different scenarios to find the best fit for the patient. 
     The invention makes it possible to use variety of different sensors for triggering the stimulation action of the muscles and designed to work with or without sensors. Different types of sensors that can be used toward this goal are already known by the people who are skilled in the state of the art. Operation of the invention without any sensors is also possible through strictly time-based activation. 
     The device is a battery-operated one, which may be equipped with long life or rechargeable type batteries. Battery operated implant technology is already very well known by those who are skilled in the state of art and the invention uses the known techniques for embedding, recharging and housing the unit in a biocompatible hermetically sealed container. Charging of batteries can be done through a coil suitable placed under skin. By inductively coupling the coil with an external RF field the batteries can be charged. This technology of charging is being used by many other implants like implant US 2008/0147144 and technology is well known by those who are skilled in this art. 
     The electronics contained in the invention comprises, power circuit, microcontroller, communication unit and signal conditioning unit. Microcontroller executes the program, communicates with the external world, read sensor inputs and generates output signal to activate the ET muscles. There are vast amount of choices for embedded processors with low power consumption and high processing power thanks to increasing amount of mobile smart devices surround us. One such embodiment of the invention may contain commercially available ARM series processors as the choice for the microcontroller. 
     Signal conditioner converts voltage signals to current signals necessary to activate the muscles or the nerves controlling the muscles. Design of signal conditioning circuits for muscle activation is well know by those skilled in the art of electronics design. One such design is published by E. Bruun and E. U. Haxthausen in Electronics Letter, in November 1991, vol. 27, pp. 2172-2174, titled “Current conveyor based EMG amplifier with shutdown control”. 
     External communication of the implant with the external world is provided through a digital communication link. There are excellent low-power consuming chipsets and protocols based on emerging digital standards. ZigBee is such a technology based on IEEE 802.15.4-2003 which is suitable toward this purpose. Another possible choice is Bluetooth technology which can also be used toward the purpose of establishing communication between implant and the external world. These communication technologies are well known by those who are skilled in the art of electronics and computer engineering. One such embodiment of the invention may use ZigBee chipset for communication with the external world. Another embodiment of the invention may use Bluetooth as the selected standard to communicate with the external world which opens the possibility of using Bluetooth equipped mobile phones or computers to be used for communicating with the implant unit. Current state of the art in electronics offers the possibility of integrating most electronics on a single Field Programmable Gate Array (FPGA) chip. One embodiment of the invention may use a single FPGA to integrate microcontroller, Zigbee and signal conditioning on a single FPGA chip. These technologies are well known to those skilled in this art of FPGA design. 
     The signal generated by the implant is delivered to the muscles or muscle nerves through commercially available medical grade wires and electrodes. One such embodiment of the invention may use Teflon coated stainless steel (SS) wire (316LVM, Cooner Wire Co.) or 90% platinum-10% iridium (Wr) wire (Medwire, Sigmund Cohn Corp.) and commercially available implantable electrodes like one in EP 0 408 358. Another embodiment of the invention may use intramuscular electrode made from 7-strain stainless steel insulated by a biocompatible material for fabrication of a suitable electrode. The electrodes that can be used for muscle activation can be intramuscular type which can be implanted inside the muscle, or epymysial type which can be placed on the muscle, or cuff electrode which can be placed over the nerve stem of the muscle, or it can be intraneural electrode which can be placed inside the nerve stem of the muscle. The materials and the techniques are well known by those who are skilled in the art. One possible source for this information is “Neuroprosthetics, Theory and practice” book which is published by World Scientific publishing in 2004 which is edited by Kenneth W. Horch and Gupreet S. Dhillon which is an authoritative book on the subject. 
     The present invention is intended to be placed subcutaneously in close proximity of the Eustachian tube muscles. One possible location is the temporal bone location favored for Cochlear implants or implantable hearing aids. The location and the practice is well known by the surgeons skilled in the art of such procedures. One possible source to this information is a book titled “Cochlear implants” which is published in 2006 by Thieme Medical Publishers. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1 . Location of ET, TVP and LVP muscles with respect endoscopic view of the Eustachian tube in relaxed state where the ET tube is closed. 
         FIG. 2 . Location of ET, TVP and LVP muscles with respect endoscopic view of the Eustachian tube in muscles contracted state where the ET tube is open. 
         FIG. 3 . The shape of pulses for different muscle groups of Eustachian Tube. 
         FIG. 4 . Block diagram of the system of the implant. 
         FIG. 5 . Nerves, muscles and ganglions involved in Eustachian tube activation. 
     
    
    
     DESCRIPTION 
     The operation of the present invasion invention will now be described with the aid of figures. The invention is intended to electrically stimulate muscles that operate Eustachian tube. Eustachian tube connects nasal cavity to middle ear cavity to provide pressure equalization and protection. Eustachian tube is not a simple pipe but a complex valve actuated by several muscles around it.  FIG. 1  shows the endoscopic view  10  of Eustachian tube in its normally closed state. When the actuator muscles, tensor veli palatini muscle  16 , levator veli palatine muscle  12  and medial pterygoid muscle  11  are in relaxed state, the opening of Eustachian tube  15  is closed and no air exchange between the two cavities takes place. 
       FIG. 2  shows endoscopic view  20  of Eustachian tube with its actuator muscles in activated state. Medial pterygoid muscle  21  contracts and modifies the location of the Eustachian tube, levator veli palatini muscle  22  contracts and rotates the Eustachian tube and finally the tensor veli palatini  26  contracts and opens the opening of the Eustachian tube  25 . 
     The contractions of these muscles occur in a particular sequence for efficient opening of Eustachian tube. The sequence of muscle activation is shown in  FIG. 3 . Medial pterygoid muscle activity is shown in Channel 1 as waveform S 1 . S 1  at low level indicates relaxed muscle state  11  and S 1  at high level indicates contracted muscle state  21 . Channel 2 indicates activity of levator veli palatini muscle. S 2  waveform at high level indicates contracted levator veli palatine muscle state  22 . S 2  at low level indicates relaxed levator veli palatine muscle state  12 . Channel 3 indicates activity of tensor veli palatini muscle. Waveform S 3  indicates actuation of tensor veli palatine muscle. S 3  at high level means contracted tensor veli palatine muscle  26  and S 3  at low level means tensor veli palatine in relaxed state  16 . The Eustachian tube opening activity starts with medial pterygoid muscle (S 1 ) contracting first. After a delay time of D 1 , the levator veli palatini (S 2 ) contracts. After a delay time of D 3 , the tensor veli palatine (S 3 ) contracts and opens the Eustachian tube. During this instant, the ET tube is open and middle ear cavity is aerated. The open state of the Eustachian tube lasts for D 5  amount of time. After expiration of D 5 , the tensor veli palatine (S 3 ) relaxes which is followed by relaxation of the levator veli palatine muscle (S 2 ) after a delay time of D 4 . Finally, after a delay time of D 2 , the medial pterygoid muscle (S 1 ) relaxes and Eustachian tube returns to its normally closed state. 
     The present invention is designed to activate muscles in this particular sequence. The block diagram of the invention is shown in  FIG. 4 . The electrodes for stimulating muscles are connected to output channels  33 . Output signal conditioner  35  is responsible for generating voltage to current conversion and adjusting amplitude and frequency of the signals that are send to electrodes. Microcontroller  31  is the main processor of the implant and responsible for generating pulse sequences, delay times and deciding when to send the pulse sequences to electrodes. Microcontroller  31 , does this by executing a program embedded in its memory. Waveforms similar to S 1 , S 2 , S 3  shown in  FIG. 3  are sent to electrodes connected individually to output channels  33  to ensure proper sequence of muscle contraction for successful activation of Eustachian tube. Decision about when to send waveforms S 1 , S 2 , S 3  to electrodes is done by microcontroller  31 , either by timing between pulse sequences or by depending on the sensor inputs or by external triggers. As an example to decision by timing, a particular embodiment of invention may send sequence of pulses to open Eustachian tube every 1500 seconds. A real-time clock  34  connected to microcontroller  31  helps to determine delay times as well as different application schedules dependent on time of the day. As an example, a particular embodiment of the invention may apply pulse sequences less frequently at nighttime then daytime. Decision about when to send pulse sequences to electrodes can also be done by sensor inputs. Sensors are connected to input channel  42  and input signals are conditioned by input signal conditioner  30 . A particular embodiment of the invention may use a pressure sensor to detect the pressure inside the middle ear cavity and whenever the pressure exceeds certain threshold level, the microcontroller  31  decides to send pulse sequences to open Eustachian tube. Another particular embodiment of the invention may use tilt sensor to sense the position of the head and decide to activate the Eustachian tube muscles whenever patient bows his/her head. Yet another particular embodiment of the invention may use an electrode connected to a particular muscle to receive the trigger signal. As an example, whenever patient performs a swallow action, an electrode implanted in one of the suitable muscles or nerves involved in swallow action can provide the input signal to initiate the actuation of the Eustachian tube. In this case, the electrode that comes from the muscle or the nerve becomes the input sensor connected to input channel  42 . Yet another way of activation can be through the signal provided by the external communication unit  39 . External communication unit  39 , is an external device which can be used to communicate with the implant  45  through digital or analog communication techniques. External communication unit  39  can be a PDA (personal digital assistant), a smart phone or any device capable of using low-power digital communication standards like ZigBee, Bluetooth, infrared or like. The device  39  can be used to configure the parameters of the program running inside microcontroller  31  as well as sending a signal to trigger the action to initiate Eustachian tube actuation pulse sequence. The communication unit  36  inside the implant uses the antenna  38  to receive the signals from the external communication unit  39 . The communication between external communication unit  39  and internal communication unit  36  is bidirectional. As a result, the external communication unit  39  can also be used for diagnosing, interrogating the implant  45 . As an example, one particular embodiment of the invention may use external communication unit  39  to show the power remaining in its batteries. Power conditioner  37  monitors the power in battery  40 , which supplies power to the implant  45 . The battery  40  can be charged through a coil  38 , which is made up of few turns of medical grade wire placed subcutaneously under the skin of the patient. 
     The activation of the muscles is done using electrodes connected to output channels  33  of implant  45  shown in  FIG. 4 . The connection mechanism to muscles will be described with the aid of  FIG. 5 .  FIG. 5  shows the muscles, the nerves and the ganglions involved in activation of Eustachian tube. Sphenopalatine ganglion  50  is where the nerve stem  52  to levator veli palatini muscle  53  originates. Otic ganglion  54  on the other hand generates the nerve stem  55  for tensor veli palatini muscle, which eventually reaches tensor veli palatini muscle  56 . The nerve stem  58  for medial pterygoid muscle also starts from otic ganglion  54  and eventually reaches medial pterygoid muscle  57 . In one embodiment, activation of these muscles can be done using intramuscular electrodes placed inside muscles  56 ,  57  and  53 . In another embodiment, these muscles can be activated through epymysial (surface) electrodes stapled on the muscles  56 ,  57  and  53 . Yet in another embodiment, the muscles  53 ,  56  and  57  can be activated through cuff electrodes attached to nerve stems  52 ,  55 ,  58 . Yet in another embodiment, the muscles  53 ,  56  and  57  can be activated through intraneural electrodes placed inside nerve stems  52 ,  55  and  58 . The exact selection of the type of electrode for the particular patient needs to be done by a competent neurosurgeon experienced in the art of electrode placement. The type of electrodes to be used for activation of muscles is well known in the state of the art and the electrodes can be manufactured using medical grade wires or purchased commercially. One possible source for this information is “Neuroprosthetics, Theory and practice” book which is published by World Scientific publishing in 2004 which is edited by Kenneth W. Horch and Gupreet S. Dhillon which is an authoritative book on the subject. 
     The present invention is intended to be placed subcutaneously in close proximity of the Eustachian tube muscles. One possible location is the temporal bone location favored for Cochlear implants or implantable hearing aids. The location and the practice is well known by the surgeons skilled in the art of such procedures. One possible source to this information is a book titled “Cochlear implants” which is published in 2006 by Thieme Medical Publishers.