Abstract:
A system and method of neural stimulation is disclosed, comprising the steps of electrically connecting at least one electrode to a first tissue, applying a stimulus to the at least one electrode, observing a response of a second tissue, identifying an electrode position on the first tissue wherein a desired response occurs on the second tissue when the stimulus is applied to the at least one electrode, and fixing the at least one electrode in place at the identified electrode position.

Description:
[0001]    This application claims the benefit of U.S. Patent Application Nos. 60/978,519 and 61/017,614 and 61/136,102, filed on Oct. 9, 2007 and Dec. 29, 2007 and Aug. 12, 2008 respectively, which are herein incorporated by reference in their entirety. 
       STATEMENT OF RELATED APPLICATION 
       [0002]    This application is related to International Patent Application [Docket No. 069737-5005-WO], which also claims the benefit of U.S. Patent Application Nos. 60/978,519 and 61/017,614 and 61/136,102. 
     
    
     FIELD OF THE INVENTION 
       [0003]    The present invention relates to a system and method for adjusting neural stimulation of a target tissue, such as a nerve, muscle, or organ. 
       BACKGROUND OF INVENTION 
       [0004]    Neural stimulation is useful in treating various acute and chronic medical conditions, including pain, arthritis, sleep apnea, seizure, incontinence, and migraines, which are physiological conditions affecting millions of people worldwide. Current treatment options range from drug intervention, non-invasive approaches such as the continuous positive air pressure (CPAP) machine for sleep apnea, to invasive surgical procedures. In many instances, patient acceptance and therapy compliance are well below desired levels, rendering current treatments ineffective as long-term solutions. 
         [0005]    Implants are a promising alternative treatment. For example, vagus nerve stimulation is thought to affect some of its connections to areas in the brain prone to seizure activity. Sacral nerve stimulation is an FDA-approved electronic stimulation therapy for reducing urge incontinence. Stimulation of peripheral nerves may help treat arthritis pain. As another example, pharyngeal dilation via hypoglossal nerve (XII) stimulation has been shown to be an effective treatment method for obstructive sleep apnea (OSA). The nerves are stimulated using an implanted electrode. In particular, the medial XII nerve branch (i.e., genioglossus), has demonstrated significant reductions in upper airway airflow resistance (i.e., increased pharyngeal caliber). 
         [0006]    While electrical stimulation of nerves has been experimentally shown to remove or ameliorate certain conditions, e.g., obstructions in the upper airway in the case of sleep apnea, current implementation methods typically require accurate and selective stimulation of a target tissue. Therefore, a need exists for a system and method for identifying an optimal location on a target tissue, e.g., a muscle or nerve, and placing an implant electrode at such location to achieve optimal stimulation of such target tissue. 
       SUMMARY OF INVENTION 
       [0007]    The present invention includes a system and method for adjusting neural stimulation of a target, such as a nerve, muscle, or organ. In an embodiment of the invention, the method includes electrically connecting at least one electrode to a first tissue, applying a stimulus to the at least one electrode, observing a response of a second tissue, identifying an electrode position on the first tissue wherein a desired response occurs on the second tissue when the stimulus is applied to the at least one electrode, and fixing the at least one electrode in place at the identified electrode position. In certain embodiments, the stimulus applicator is disposable. 
         [0008]    The stimulus can be a voltage signal, a current signal, and can be preprogrammed. In certain embodiments, the voltage or current signal is a controlled voltage or a controlled current signal. In other embodiments, an estimated minimum stimulus is calculated, and in yet another embodiment a stimulus profile is generated. The stimulated tissue may be selected from the group consisting of nerve tissue, muscle tissue, and organ tissue. Examples of a desired stimulus response include a change in airway patency, at least partial blockage of a neural impulse, and the initiation of at least one neural impulse. A response can be directly or indirectly observed, either visually or with instrumentation. 
         [0009]    In another embodiment of the invention, a neural stimulation system includes at least one electrode electrically connected to a first tissue, means for applying a stimulus to the at least one electrode, means for observing a response of a second tissue, means for identifying an electrode position on the first tissue wherein a desired response occurs on the second tissue when the stimulus is applied to the at least one electrode, and means for fixing the at least one electrode in place at the identified electrode position. 
         [0010]    In still another embodiment of the invention, a computer program product comprises a computer readable medium having stored thereon computer executable instructions that, when executed on a computer, causes the computer to perform a method of neural stimulation, including the steps of applying a stimulus to at least one electrode electrically connected to a first tissue, observing a response of a second tissue, and identifying an electrode position on the first tissue wherein a desired response occurs on the second tissue when the stimulus is applied to the at least one electrode. 
         [0011]    In another embodiment of the invention, a neural stimulation system includes at least one electrode electrically connected to a first tissue, a gross adjustment stimulator coupled to and delivering a stimulus to the at least one electrode, a stimulus measurement subsystem in communication with the gross adjustment stimulator and having at least one sensor, the at least one sensor measuring a response of a second tissue, and a programming subsystem in communication with the stimulus measurement subsystem, the programming subsystem collecting data from the group consisting of stimulus data and tissue response data. 
         [0012]    It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. In the drawings: 
           [0014]      FIG. 1  illustrates an exemplary embodiment of a gross adjustment stimulation system; 
           [0015]      FIG. 2  illustrates an exemplary embodiment of an initial gross adjustment method; and 
           [0016]      FIG. 3  illustrates an exemplary embodiment of a post-surgical adjustment method. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0017]    The present invention relates to a gross adjustment stimulation system and methods for adjusting stimulation electrode placement for treating various acute and chronic medical conditions. Conditions treatable with implants include, but are not limited to, arthritis, sleep apnea, seizure, incontinence, and migraine. The exemplary conditions may be treated using, for example, the methods and systems disclosed in U.S. patent application Ser. Nos. 11/707,104 and 11/707,053, both filed Feb. 16, 2007, and herein incorporated by reference in their entireties. Other exemplary methods and systems are described below. 
         [0018]    I. Electrical Stimulation and Neural Recruitment 
         [0019]    Electrical stimulation has been successfully applied to activate both peripheral sensory and motor nerves, as well as the sensory and motor nerves making up the central nervous system, (e.g., the spinal cord and the brain). Generally, electrical stimulation used to cause activation in a nerve follows several simple rules, which are described below. 
         [0020]    (a) Nerves closest to an activating cathodal contact are activated (recruited) before their more distant neighbors; 
         [0021]    (b) Nerves with greater fiber diameters are recruited before nerves with narrow fibers; and 
         [0022]    (c) Nerve recruitment is directly proportional to the amount of current delivered. 
         [0023]    Nerves may be electrically stimulated, or recruited, using electrical stimulation pulses of current. Nerves with the lowest threshold axon fibers are recruited first and preferentially. Excitation of the nerve axons by electrical stimulation occurs when nerves close to a stimulating electrode contact have activation thresholds low enough to be excited by the electrode and are depolarized above their threshold membrane voltage. 
         [0024]    One of the major contributors to this activation threshold is nerve diameter. Due to the electrical cable properties of the nerve, large diameter nerve fibers have a lower excitation threshold than do smaller diameter fibers, and thus are more easily excited. Nerve fibers are more likely to be recruited by an electrical stimulation pulse if they are close to the activating electrode and are of larger diameter than other fibers. 
         [0025]    Motor nerve excitation is typically performed at very slow stimulation rates or frequencies because of the problem of overdriving the motor units activated, and because the relatively long time constants of muscle activation reduces the need for high frequency stimulation. With every pulse of stimulation delivered to a motor nerve there is a corresponding contraction of the motor units excited. This contraction is controlled by the physical and electrochemical properties of the muscle motor unit and has a much longer time constant than the excitation of the nerve that activates it. One pulse delivered to the motor unit results in a twitch, while bursts of pulses or multiple pulses at the proper frequency produce a fused contraction with little pulsatile characteristics. Depending upon the muscle group, this fusion or tetanic frequency can be as low as approximately 15 Hz for large muscles or as high as approximately 80 to 100 Hz for smaller muscles. Compared to sensory nerve applications, such as cochlear implant stimulation where stimulation frequencies can be many thousands of Hz, motor nerve stimulation is very slow. 
         [0026]    Since the frequencies for motor nerve excitation are quite low, multiple electrodes can be multiplexed to single pulse generators. While only one contact is active at a time, multiple muscle groups are essentially driven at the same time using an interlaced stimulation pattern. Since the muscle dynamics are so slow compared to the nerve, the contractions produced appear simultaneous and smooth. 
         [0027]    Multiple contact systems also allow the activation to be shared by groups of motor units within the same pool to avoid such problems as muscle fatigue, a common problem in electrically stimulated muscle. Multiple contact systems can also co-activate multiple muscle groups to achieve a desired muscle response. In activating the muscles of the hand or forearm, for instance, several contacts may be activated at the same time by delivering interlaced pulses to first one contact and then another, to activate two or more muscle groups that when added result in a force vector in the desired direction. 
         [0028]    Even with a multiplexed multiple contact system however, the electrodes still tend to activate the nerve fibers closest to the electrode. In that sense, they are not selective, and are constrained to activate only those neurons that are closest to the contact. To compensate for this inability to truly selectively activate the optimal pool of neurons, some stimulation systems depend upon sensors to apply stimulation at optimal times so that the desired response may still be achieved. In order to activate a selected pool of neurons located somewhere between two contacts, but that represent the only pool of neurons desired, it is desirable to use a stimulator that can deliver coincident independently controlled stimulation pulses, rather than a stimulator delivering multiplexed sequential pulses. 
         [0029]    With a stimulator that delivers coincident stimulation pulses, the system can simultaneously deliver currents to each contact. In certain embodiments, these currents are independently controlled. The system can control these currents so that they are at sub-threshold levels (i.e., below the nerve&#39;s recruitment level) for the fibers adjacent to the contact. While the fields around each contact are below the nerve&#39;s recruitment or threshold level, the fields can combine with fields from other concurrently energized electrodes to create pulses strong enough to activate a desired nerve. Thus, nerve populations that do not lie directly under a stimulation electrode contact can be preferentially and selectively activated. Since the nerves can be selectively activated, sensors are not needed to help time the stimulation delivery to achieve the desired results. 
         [0030]    With selective stimulation and a multiple independent current source system and site specific multiple contact electrodes design, in combination with patient specific stimulus programming, only those portions of the nerve fiber or fibers responsible for non-timing dependent activation are recruited and activated, providing the opportunity for a successful open-loop stimulation application. If desired, sensors can be used to improve stimulus timing and delivery. The sensors can be used in a closed-loop system, a triggered open loop, an open loop system, or some combination of the three. 
       A. Sample Conditions Treatable With Implants 
       [0031]    The methods and systems used in conjunction with the present invention can be used to treat a number of conditions by stimulating nerves associated with treating a condition. Stimulation can be such that the stimulus is transmitted by a nerve by activating excitatory pathways, or stimulation can be such that nerve transmission in a nerve is blocked by activating inhibitory pathways. In an exemplary embodiment, the nerve is the sacral nerve. In another embodiment, the nerve is the Vagus nerve. In yet another embodiment, the nerve is a peripheral nerve. Alternatively, the target tissue can be a muscle, including muscles from the head and neck, the torso, the upper limbs and the lower limbs. The target tissue can also be an organ of the body, for example, kidney, liver, lung, brain, skin, ovaries, intestines, arteries and veins, lymph nodes, bones, or joints. 
       B. Exemplary Embodiment 
     Obstructive Sleep Apnea 
       [0032]    The HGN is composed of multiple nerve fibers, each of which controls one or more tongue muscles. In certain treatments, the selected HGN nerve fibers are stimulated in order to cause movement of selected tongue muscles. The invention below describes a gross adjustment stimulation system and method of placing electrodes on a target tissue to produce a desired stimulus response. 
         [0033]    II. Gross Adjustment Stimulation System 
         [0034]      FIG. 1  shows an exemplary embodiment of a gross adjustment stimulation system  100 . The system has at least one electrode  110 , a gross adjustment stimulator  120 , a stimulus measurement subsystem  130 , and a programming subsystem  140 . Each is described below. 
         [0035]    A. Gross Adjustment Stimulator 
         [0036]    In the exemplary embodiment shown in  FIG. 1 , the gross adjustment stimulator  120  is configured to produce the stimulus that will be sent to at least one implanted electrode  110 . The gross adjustment stimulator  120  stimulates the implanted electrode  110  in a manner equivalent to the device to be implanted (e.g., an implantable pulse generator). As described herein, an electrode  110  may be a single electrode, multiple electrodes, or at least one electrode array. Examples of electrodes and gross adjustment stimulators include, but are not limited to, the electrodes and implantable pulse generators described in U.S. Patent Application Nos. 60/978,519 and 61/017,614 and 61/136,102, filed on Oct. 9, 2007 and Dec. 29, 2007 and Aug. 12, 2008 respectively, which are incorporated by reference herein in their entirety. 
         [0037]    In certain embodiments, the gross adjustment stimulator  120  allows the physician, physician&#39;s assistant, or technician (herein generically referred to as a physician) to start and stop stimulation, and interrogate the stimulus measurement subsystem  130  for information on proper function. In certain exemplary embodiments, the gross adjustment stimulator  120  also allows the patient to direct the system to perform these functions. In certain embodiments, the gross adjustment stimulator  120  displays the status of a communication and power link to the stimulator and status of any external controller (not shown) if, for example, the gross adjustment stimulator is used with an IPG (not shown) having an external controller. In certain embodiments, the physician or patient may also choose operating modes for the stimulator, such as a sleep mode for when the patient intends to go to sleep, an exercise mode for when the patient engages in above normal levels of physical activity, and other alternative operating modes that the patient or physician may program. In certain embodiments, the physician or patient may also adjust levels of stimulation using the gross adjustment stimulator  120 . 
         [0038]    In certain exemplary embodiments, the gross adjustment stimulator  120  stimulation is a controlled voltage or controlled current signal, which may be preprogrammed. In certain embodiments, the gross adjustment stimulator  120  is powered and/or controlled by an RF or other wireless signal. In certain embodiments, gross adjustment stimulator  120  sends stimulation in the form of one or more stimulus signals to at least one electrode  110 . In other embodiments, the stimulation could be sent to at least two electrodes  110 , or an array of electrodes  110 . In other embodiments the stimulator sends continuous or near continuous stimulation to the electrode  110  for at least a portion of the implant procedure. Non-limiting examples include one or more pulses, a pulse train, a sinusoid, a constant source signal, or other controlled stimulation forms known to those skilled in the art. Thus, stimulation of the target tissue and its effects on a response tissue can be controlled based on patient needs, and is not limited to a particular waveform. 
         [0039]    In an embodiment of the invention, gross adjustment stimulator  120  may optionally include a crypto block (not shown). A crypto block is useful in coding unique signals for only the desired electrodes  110 , without interfering with other electrodes controlled by another stimulator  120 . Thus, where there are two or more gross adjustment stimulators  120  in the same vicinity, the crypto block creates a unique signal that will interface with only the desired electrode or electrodes  110 . 
         [0040]    In another embodiment, gross adjustment stimulator  120  may also include a data storage unit and/or a recording unit (not shown) to store and/or record data, respectively. The gross adjustment stimulator  120  may also include a computer interface (a wireless link, USB port, serial port, or fire wire, for example) to collect or transfer data to an external system. In certain embodiments, the gross adjustment stimulator  120  is disposable. 
         [0041]    B. Stimulus Measurement Subsystem 
         [0042]    In the exemplary embodiment shown in  FIG. 1 , the stimulus measurement subsystem  130  measures a target tissue&#39;s response to applied stimulus. In certain embodiments, stimulus comes from one or more implanted electrodes  110 , which receive stimulus from the gross adjustment stimulator  120 . Stimulus responses can be measured directly, indirectly, or some combination of the two. Measurements can be taken using sensors integrated with the implant, external to the implant, or some combination of the two. Direct and indirect sensing, and integrated and external sensors are discussed below. 
         [0043]    1. Direct Measurement 
         [0044]    Direct measurement is the measurement of one or more factors directly influencing airway patency. Factors directly influencing airway patency include, but are not limited to, oral cavity size, tongue protrusion or muscle tone, and respiration airflow (i.e. airway airflow). There are many different ways to measure these factors. These factors may be visually measured, or they can be measured using mechanical, electrical, or electromechanical sensors. Oral cavity size, for example, can be measured using acoustic pharyngometry. Tongue protrusion or muscle tone can be measured using, for example, one or more of a proximity sensor, accelerometer, or pressure sensor. The sensors may be in the mouth, ear, neck, or other suitable location known to those skilled in the art. Tongue protrusion or muscle tone may also be measured with a soft tissue imaging device utilizing photography, ultrasonography or other imaging modalities known to those skilled in the art. Still other ways include observation with an endoscope, or applying a fluorescent dye pattern to the tongue surface and illuminating it using an ultraviolet or fluorescent light source. 
         [0045]    Respiration airflow may be measured mechanically, electrically, with electromechanical sensors, or some combination of the above. One way is to use a nasal canula or a thermistor. Other ways include a respiration transducer involving thermocouples, piezo thermal sensors, pressure and differential pressure sensors, or other flow sensors known to those skilled in the art. Respiration airflow may also be measured by a pneumotachograph or a respiratory inductance plethysmograph. These ways are exemplary only, and not limited to what is discussed. Other ways known to those skilled in the art may be used without departing from the scope of the invention. 
         [0046]    2. Indirect Measurement 
         [0047]    Indirect measurement is the measurement of one or more indicators influenced by airway patency. Exemplary indicators include, but are not limited to blood oxygen level, blood pressure, heart rate, torso motion (to sense, for example, relative breathing ease), and snoring. Many different sensors can measure these indirect indictors. Indirect measurements can be made using, for example, peripheral arterial tonometry. In other examples, blood oxygen level may be measured an oxygen sensor, pulse oximetry, an infrared (IR) sensor, or an earlobe monitoring unit. Snoring can be measured using, for example, a differential pressure sensor, a vibration sensor, or a microphone. Snoring can also be detected using a nasal canula. 
         [0048]    3. Sensors 
         [0049]    The ability to sense and measure airway patency, directly or indirectly, increases the ease and accuracy of evaluating patient response to the stimulus patterns. In the exemplary embodiment shown in  FIG. 1 , the sensor or sensors that input data to the stimulus measurement subsystem  130  may be internal to an electrode  110  or array of electrodes  110 , the gross adjustment stimulator  120  or IPG (not shown). In other exemplary embodiments, the sensor or sensors may be external to the electrode  110  or array of electrodes  110 , gross adjustment stimulator  120 , or IPG (not shown). In certain embodiments, at least one internal sensor is a MEMS device, such as a pressure sensor or accelerometer. In another embodiment, at least one internal sensor is an electrical sensor capable of recording a change related to changes in muscle tone. Sensor information (from internal and/or external sensors for example) may be retrieved in real time over a bidirectional link, (an RF or other wireless link known to those skilled in the art, for example) or through use of an interface placed below the surface of the skin. In certain embodiments, the sensors are external to the electrode  110  or IPG, but still internal to the patient. For example, external sensors may be located in the ear, the nasal passage, the throat, or other measurement points known to those skilled in the art. External sensors may also be located external to the patient in, for example, a medical facility, a laboratory, or a patient&#39;s home. 
         [0050]    C. Programming Subsystem 
         [0051]    In the exemplary embodiment of  FIG. 1 , a programming subsystem  140  collects data on the stimulus applied during gross adjustment. The programming subsystem  140  may also contain preprogrammed stimulus data, which may be used to apply stimulus to the at least one electrode  110 . In other embodiments, the programming subsystem  140  collects data on the stimulus response, (tissue response, for example) and in still other exemplary embodiments the programming subsystem collects data on both the applied stimulus and the stimulus response. This data can then be used to program user specific stimulus patterns to open the airway and decrease sleep disordered breathing/obstructive sleep apnea for download to hypoglossal nerve(s) implants. In a certain embodiment, for example, at least one sensor collects data that protruder muscles a, c, and f are not affected by a given stimulus, but flattening muscles b, d, and e are stimulated when nerve fibers x, y, and z are stimulated at a frequency of n Hz. In certain exemplary embodiments, sensor information is stored in a sensor memory (not shown) in the stimulus measurement subsystem  130 . The measured data is passed to or obtained by the programming subsystem  140 , where it is be recorded and correlated with the applied stimulus patterns. 
         [0052]    Sensed information data may also be passed directly to the programming subsystem  140 . Once the data are collected and correlated, the programming subsystem  140  generates a stimulus profile based on the obtained information. The stimulus profile may be downloaded into an IPG (not shown) or gross adjustment stimulator  120 . The signals from these sensors (internal or external) can be correlated by direct observation (by a physician, patient, or other user, for example), or can be digitized and analyzed via software algorithms to create a stimulus profile. This profile can be used to apply a stimulus that generates a desired response in the targeted tissue. In certain embodiments, software in the programming subsystem  140  generates an algorithm to suggest electrode combinations and stimulus levels to elicit the desired stimulus response. 
         [0053]    III. Initial Gross Adjustment 
         [0054]      FIG. 2  illustrates an exemplary embodiment of an initial gross adjustment method  200 . In the exemplary method shown, at least one electrode  110  is placed in an initial position on or near the target tissue at step  210 . The electrode  110  need not be physically connected to or touching the target tissue. The electrode  110  only needs to be close enough to the target tissue to make an electrical connection with the tissue. The target tissue may be a nerve, a muscle, or an organ of a patient&#39;s body. In certain embodiments the target tissue is the hypoglossal nerve. In step  220 , at least one stimulus is applied to at least one electrode  110 . Stimulus may be chosen manually, or it may be preprogrammed. In the exemplary method shown, stimulus is applied by the gross adjustment stimulator  120 , but in other embodiments stimulus can be applied from another source. In certain embodiments, the gross adjustment stimulator  120  is acceptable for use in an operating room environment. Exemplary guidelines for devices acceptable for use in an operating room environment are described in  Draft Guidance for Industry and FDA Staff Radio - Frequency Wireless Technology in Medical Devices , released for comment on Jan. 3, 2007, which is hereby incorporated by reference in its entirety. Stimulators configured for wireless use in an operating room need not operate wirelessly, but can if desired. 
         [0055]    Varying stimulus patterns involving permutations of electrode contacts, delivering stimulus of varying current amplitude, duration, and/or frequency are applied to at least one electrode  110 . In certain embodiments, these varying stimulus patterns are applied under the control of a physician or technician, and may be preprogrammed. These varying stimulus patterns have different effects on the nerve fibers that control tongue position, muscle tone, and size and patency of the retrolingual airway. In order to identify which nerve fibers produce the desired stimulus response in the muscles in the tongue to open the airway, stimulus is applied independently to each targeted nerve fiber population of interest. In certain embodiments, the electrode position, applied stimulus, and stimulus response are recorded to help identify the location of the electrode on the nerve that provides optimal stimulation. 
         [0056]    Different levels of stimulation of the nerve fibers are applied to identify the minimum stimulus required to elicit the appropriate muscle movement required to alleviate the symptoms of the physiological condition. Different levels of stimulation often elicit different responses depending on the muscle responding and depending on the different nerve or nerve fibers to be stimulated. Exemplary stimulation patterns are known in the art, or taught in U.S. patent application Ser. Nos. 11/707,104 and 11/707,053. 
         [0057]    The stimulation applied in step  220  can be in many forms. While stimulation may be applied at high frequencies, lowering the stimulation frequency to the lowest required for a smooth, tetanic, and comfortable contraction, for example, reduces overall power consumption and helps reduce muscle fatigue elicited by electrical stimulation. Stimulation may also be delivered as a single pulse, a burst of pulses, or multiple pulses at one or more frequencies. Each frequency can be as low as approximately 15 Hz for large targeted muscles or as high as approximately 80 to 100 Hz for smaller muscles. In other embodiments, Stimulation frequency is adjustable from a low of 1 Hz to a maximum of 100 Hz. Alternatively, stimulation is multiplexed, and in still other embodiments stimulation is delivered in coincident pulses. Stimulation may be delivered to several contacts (not shown) on an electrode  110 , or stimulation may be sequentially applied by delivering interlaced pulses to one contact and then another, to create multiple electric fields that when added result in a force vector in the desired direction to stimulate the target tissue with the desired stimulation level. 
         [0058]    In step  230 , the physician, physician&#39;s assistant, or technician (herein generically referred to as a physician) checks to see if a desired stimulus response is achieved. This step is performed during or after step  220 . In certain exemplary embodiments, a desired response is a blocking of a neural impulse (for example by activating an inhibitory pathway). In certain other exemplary embodiments, a desired response is a change in airway patency. Changes in airway patency, either directly or indirectly, are observed during or after stimulus is applied. Checking for a desired stimulus response helps determine which combinations of contacts and current patterns are most desirable. Stimulus parameters can then be adjusted according to the severity of the apnea. 
         [0059]    The stimulus response may be measured using the stimulus measurement subsystem  130 , by other electronic means, such as a computer or other instrumentation, or even visual observation. These measurements can be direct or indirect. The stimulus measurement subsystem  130  and measurement means are described elsewhere in this application and are not repeated here. In the exemplary embodiment shown, the gross adjustment stimulator  120  applies stimulus to at least one electrode  110 , and the physician checks to see if a desired stimulus response (e.g., tongue movement changes in airway patency) is achieved  230 . In certain embodiments, this helps determine which combinations of contacts and current patterns are desirable for a patient. In other exemplary embodiments, a desired response is at least partial blockage of a neural impulse, and in other exemplary embodiments a desired response is the initiation of a neural impulse. Stimulus patterns producing a desired response may then be stored in the implant, patient control device, a secure archive, or the programming subsystem  140 . This stimulus may be selected by the physician, or it may be preprogrammed. 
         [0060]    If a desired stimulus response is not obtained, the physician decides at step  240  whether to apply additional stimulus. If the physician chooses to apply additional stimulus  240 , the physician repeats step  220  with the desired stimulus pattern(s). Alternatively, or in addition to step  240 , the physician decides at step  250  whether electrode repositioning is desirable. If repositioning is chosen, the physician chooses a new position by, for example, shifting at least one electrode  110  along a target tissue, and beginning at step  210 . 
         [0061]    If repositioning is not desired, the physician decides at step  260  whether an acceptable outcome was achieved with the stimulus applied to the electrode in its current position. If so, the physician fixes the electrode in place at step  270 . If not, the physician removes the electrode at step  280 . The electrode may be fixed in place using surgical means, such as sutures, glue, fasteners, or other means known to those skilled in the art. The method may be performed with additional stimulus electrodes  110 , and may be performed with an array of electrodes  110 . The steps need not be performed in the order shown, nor do they all need to be performed. The method is exemplary only, and not limited to what is described. 
         [0062]    IV. Post-Surgical Adjustment 
         [0063]    Post-surgical adjustment may begin once the wound heals. Once the patient and wound have healed, the physician begins implant programming to maximize the nighttime retrolingual or pharyngeal airway. Programming may include a range of stimulation values, a programmable delay between switching the implant on and stimulus commencing, a ramp in stimulus intensity over time, and an automatic shut down after a preset interval. Programming may be downloaded to the implant via a wireless link, both for initial trials and for a final stimulus program for use by the patient, or it may be downloaded in USB, serial, or other connection. Programming parameters may include the full range of stimulation values as well as a programmable delay between switching the implant on and stimulus commencing, a ramp in stimulus intensity over time, and an automatic shut down after a predetermined interval. In other embodiments, the IPG itself may be used to generate the signals and stimulation patterns used during gross adjustment. 
         [0064]      FIG. 3  illustrates an exemplary embodiment of a post-surgical adjustment method  300 . In step  310  of the exemplary method shown, electrode stimulation is applied while the patient is awake and the upper respiratory tract (URT) is open. In step  320 , tongue position is measured in response to the applied stimulus. In an exemplary embodiment, tongue position is measured with a tongue protrusion calibration device. The device is placed at the anterior of the mouth and held in place by the teeth, or lips, or other method. In certain methods, the tongue protrusion device is configured to measure anterior tongue thrust using, for example, a pressure sensor. 
         [0065]    The patient is asked at step  330  to evaluate the relative comfort of the tongue position in response to stimulation. If a desired stimulus response is not obtained, steps  310 - 330  may be repeated with another stimulus. At step  340  the physician evaluates whether a stimulus response is desirable. When a desired stimulus response is obtained (i.e. a stimulus that produces an open airway or change in airway patency without causing discomfort to the patient), the stimulus program is saved at step  350  for later use. Stimulus may be programmed by a physician, a physician&#39;s assistant, a technician, or even the patient. 
         [0066]    Another exemplary post-surgical adjustment method is to record the level of nerve activity present when the tongue has normal daytime tone using, for example, an electroneurogram sensor. Under this approach, the signals from the target tissue (e.g., the hypoglossal nerve) are recorded while the patient is awake. This recording can be during the patient&#39;s normal daytime routine, or it can be done while the patient is in a laboratory or medical facility. This information collected from electroneurogram sensor is used to prepare a stimulus program that mimics the daytime nerve signals to be used during while the patient sleeps to treat obstructive sleep apnea. The use of an electroneurogram sensor is exemplary only. Other sensors known to those skilled in the art could also be used to obtain the information above to create a desired stimulus program without departing from the scope of the invention. 
         [0067]    Yet another approach or exemplary method is to program the HGN implant(s) in a laboratory, using a stimulation protocol that minimizes URT obstruction, snoring, and apneic and or hypopneic events observed in the laboratory, in order to maximize the URT patency. Programming may be downloaded to the implant via the RF link, both for initial trials and for a final stimulus program for use by the patient. 
         [0068]    It will be apparent to those skilled in the art that various modifications and variations can be made in the device of the present invention without departing from the scope of the invention. Thus, it is intended that the present invention cover the modifications and variations of the present invention.