Patent Description:
Medical devices may be external or implanted, and may be used to deliver electrical stimulation therapy to patients to various tissue sites to treat a variety of symptoms or conditions such as chronic pain, tremor, Parkinson's disease, epilepsy, urinary or fecal incontinence, sexual dysfunction, obesity, or gastroparesis. A medical device may deliver electrical stimulation therapy via one or more leads that include electrodes located proximate to target locations associated with the brain, the spinal cord, pelvic nerves, peripheral nerves, or the gastrointestinal tract of a patient. Hence, electrical stimulation may be used in different therapeutic applications, such as deep brain stimulation (DBS), spinal cord stimulation (SCS), pelvic stimulation, gastric stimulation, or peripheral nerve field stimulation (PNFS).

A clinician may select values for a number of programmable parameters in order to define the electrical stimulation therapy to be delivered by the implantable stimulator to a patient. For example, the clinician may select one or more electrodes, a polarity of each selected electrode, a voltage or current amplitude, a pulse width, and a pulse frequency as stimulation parameters. A set of parameters, such as a set including electrode combination, electrode polarity, amplitude, pulse width and pulse rate, may be referred to as a program in the sense that they define the electrical stimulation therapy to be delivered to the patient. Documents <CIT>, <CIT>, <CIT>, <CIT>, <CIT> and <CIT> relate to neuromodulation systems and methods.

In some examples, the disclosure describes example medical devices, systems, and techniques for automatically adjusting electrical stimulation therapy delivered to a patient to eliminate or reduce the occurrence of evoked action potentials in tissues of the patient. For example, a medical device system may be configured to determine that electrical stimulation therapy being delivered to a patient according to a set of stimulation parameter values evokes an action potential in a tissue of a patient, e.g., by sensing the evoked compound action potentials in tissue of the patient via one or more sensors. Based on the determination, the medical device system may be configured to adjust one or more of the stimulation parameters values defining the electrical stimulation therapy delivered to the patient to identify a set of therapy parameters values that do not evoke action potentials in a tissue of the patient when delivered.

In some examples, to adjust the electrical stimulation therapy, the medical device system may deliver a series of electrical pulses in which the amplitude of the respective pulses is increased, e.g., by ramping up the amplitude value of the respective pulses. The initial stimulation pulse may have an amplitude such that the delivered stimulation is below the activation threshold and does not evoke an action potential in the tissue of a patient. While the series of pulses is delivered to the patient, the medical device system may monitor the patient to determine when an action potential is evoked by a stimulation pulse. The medical device system may then reduce the amplitude the stimulation to a value below the amplitude of the stimulation pulse that first evoked an action potential in the tissue of the patient, e.g., by a predetermined percentage or to the value of one or the preceding stimulation pulses in the series of delivery pulses. The medical device may then resume delivery of the electrical stimulation to the patient according to the adjusted amplitude value. In this manner, the medical device system may maintain the delivery of electrical stimulation to a patient that is below the activation threshold of the tissue such that action potentials are not evoked in the tissue (e.g., except for brief occurrences of evoked compound action potentials that may trigger the parameter adjustment), while also delivering therapy at a relatively high intensity.

In one example, this disclosure describes a method, not under the scope of the present invention, comprising: controlling delivery of an electrical stimulation therapy from an implantable medical device to a patient according to at least one therapy program, wherein the electrical stimulation therapy is configured to provide pain relief to the patient without substantially resulting in paresthesia perceived by the patient; and periodically adjusting the electrical stimulation therapy delivered to the patient in response to detected compound action potentials, wherein the adjustment to the electrical stimulation therapy is configured to eliminate action potentials in tissue of the patient evoked by the delivered electrical stimulation, and wherein the controlling and the adjusting are performed via one or more processors.

In another example, this disclosure describes a method, not under the scope of the present invention, comprising: controlling delivery of an electrical stimulation therapy from an implantable medical device to a patient according to at least one therapy program, wherein the electrical stimulation therapy is configured to provide pain relief to the patient without substantially resulting in paresthesia perceived by the patient; and in response to detecting an electrically-evoked compound action potential, adjusting the electrical stimulation therapy delivered to the patient to eliminate action potentials in tissue of the patient evoked by the delivered electrical stimulation, and wherein the controlling and the adjusting are performed via one or more processors.

In another example, this disclosure describes a method, not under the scope of the present invention, comprising: controlling delivery of an electrical stimulation therapy from an implantable medical device to a patient according to at least one therapy program, wherein the electrical stimulation therapy is configured to provide pain relief to the patient without substantially resulting in paresthesia perceived by the patient; and while detecting an electrically-evoked compound action potential, adjusting at least one parameter of the at least one therapy program defining the electrical stimulation therapy delivered to the patient until the electrically evoked compound action potential is no longer detected, and wherein the controlling and the adjusting are performed via one or more processors.

In another example, this disclosure describes a medical device system comprising: a stimulation generator configured to deliver electrical stimulation to a patient; and a processor configured to control delivery of an electrical stimulation therapy from the stimulation generator to the patient according to at least one therapy program, wherein the electrical stimulation therapy is configured to provide pain relief to the patient without substantially resulting in paresthesia perceived by the patient; and periodically adjust the electrical stimulation therapy delivered to the patient in response to detected compound action potentials, wherein the adjustment to the electrical stimulation therapy is configured to eliminate action potentials in tissue of the patient evoked by the delivered electrical stimulation, and wherein the controlling and the adjusting are performed via one or more processors.

In another example, this disclosure describes a medical device system comprising: a stimulation generator configured to deliver electrical stimulation to a patient; and a processor configured to: control delivery of an electrical stimulation therapy from an implantable medical device to a patient according to at least one therapy program, wherein the electrical stimulation therapy is configured to provide pain relief to the patient without substantially resulting in paresthesia perceived by the patient; and in response to detecting an electrically-evoked compound action potential, adjust the electrical stimulation therapy delivered to the patient to eliminate action potentials in tissue of the patient evoked by the delivered electrical stimulation.

In another example, this disclosure describes a medical device system comprising: a stimulation generator configured to deliver electrical stimulation to a patient; and a processor configured to: control delivery of an electrical stimulation therapy from an implantable medical device to a patient according to at least one therapy program, wherein the electrical stimulation therapy is configured to provide pain relief to the patient without substantially resulting in paresthesia perceived by the patient; and while detecting an electrically-evoked compound action potential, adjust at least one parameter of the at least one therapy program defining the electrical stimulation therapy delivered to the patient until the electrically evoked compound action potential is no longer detected.

In another example, this disclosure describes a medical device system comprising: means for controlling delivery of an electrical stimulation therapy from an implantable medical device to a patient according to at least one therapy program, wherein the electrical stimulation therapy is configured to provide pain relief to the patient without substantially resulting in paresthesia perceived by the patient; and means for periodically adjusting the electrical stimulation therapy delivered to the patient in response to detecting compound action potentials, wherein the adjustment to the electrical stimulation therapy is configured to eliminate action potentials in tissue of the patient evoked by the delivered electrical stimulation, and wherein the controlling and the adjusting are performed via one or more processors.

The details of one or more examples of the techniques of this disclosure are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the techniques will be apparent from the description and drawings, and from the claims.

In some examples, the disclosure describes example medical devices, systems, and techniques for automatically adjusting electrical stimulation therapy delivered to a patient to prevent or reduce the occurrence of evoked action potentials in tissue of the patient. For example, a medical device system may be configured to determine that electrical stimulation therapy being delivered to a patient according to a set of stimulation parameter values evokes an action potential in a tissue of a patient, e.g., by sensing the evoked compound action potentials in a tissue of the patient via one or more sensors. Based on the determination, the medical device system may be configured to adjust one or more of the stimulation parameters values defining the electrical stimulation therapy delivered to the patient to identify a set of therapy parameters values that do not evoke action potentials in a tissue of the patient when delivered.

Implantable medical devices (IMDs) may provide electrical stimulation therapy to treat various diseases or perform pain relief in the patient. In certain situations, the electrical stimulation therapy causes electrical charge to accrue in the tissue of the patient. This build-up of electrical charge may evoke an action potential in the nervous tissue of the patient. The action potential, a short-lasting event in which the electrical membrane potential of a cell rapidly rises and falls, may cause propagation of the electrical stimulation along the spinal cord to the brain, causing unwanted side effects, such as paresthesia or discomfort in the patient. A clinician may manually configure the one or more parameters defining the electrical stimulation therapy in a clinical visit to prevent evoking action potentials. However, over time, impedance changes in the IMD, movement of the leads of the IMD, and/or changes in the position or posture of the patient (among other reasons) may change the effect of the electrical stimulation therapy such that the delivered electrical stimulation therapy undesirably evokes action potentials in the tissue of the patient.

According to some examples of the disclosure, the described systems, devices, and techniques may be employed to prevent delivery of electrical stimulation that evoke actions potentials in a tissue of the patient while still maintaining efficacious therapy. For example, a medical device system may be configured to determine that electrical stimulation therapy being delivered to a patient according to a set of stimulation parameter values evokes an action potential in a tissue of a patient, e.g., by sensing the evoked compound action potentials in a tissue of the patient via one or more sensors. As referred to herein, a compound action potential is a summation of a plurality of individual action potentials, wherein, due to the small magnitude of an individual action potential, the individual action potential may be difficult to accurately measure.

Based on the determination, the medical device system may be configured to adjust one or more of the stimulation parameters values defining the electrical stimulation therapy delivered to the patient to identify a set of therapy parameters values that do not evoke action potentials in a tissue of the patient when delivered.

As described above, in some examples, to adjust the electrical stimulation therapy, the medical device system may deliver a series of electrical pulses in which the amplitude of the respective pulses is increased, e.g., by ramping up the amplitude value of the respective pulses. The initial stimulation pulse may have an amplitude such that the delivered stimulation is below the activation threshold and does not evoke action potential in the tissue of a patient. While the series of pulses is delivered to the patient, the medical device system may monitor the patient to determine when a compound action potential is evoked by a stimulation pulse. The medical device system may then reduce the amplitude the stimulation to a value below the amplitude of the stimulation pulse that first evoked an action potential in the tissue of the patient, e.g., by a predetermined percentage or to the value of one or the preceding stimulation pulses in the series of delivery pulses. The medical device may then resume delivery of the electrical stimulation to the patient according to the adjusted amplitude value. In this manner, the medical device system may maintain the delivery of electrical stimulation to a patient that is below the activation threshold of the tissue such that compound action potentials are not evoked in the tissue (e.g., except for brief occurrences of evoked action potentials that may trigger the parameter adjustment), while also delivering therapy at a relatively high intensity.

In some examples, the adjustment of the therapy parameters by the medical device system, as described herein, may be initiated based on a trigger other than that of directly sensing evoked compound action potentials in the tissue of a patient. In some examples, a medical device system may be programmed to periodically perform such an adjustment, e.g., on a daily or weekly basis. In some examples, the adjustment may be triggered by the determination that the patient has transitioned from one posture to another and/or occupies a particular posture (e.g., a posture that is likely to result in the delivered electrical stimulation therapy evoking actin potential in the tissue of the patient). In another example, the adjustment may be triggered based on the receipt of input from the patient indicating that he/she is experiencing paresthesia or another effect indicating that the delivered therapy is an evoked action potential in the tissue of the patient. In other examples, the adjustment is performed in response to a signal received from a sensor, such as an accelerometer, a pressure sensor, a bending sensor, a sensor configured to detect a posture of the patient, or a sensor configured to detect a respiratory function of patient. In yet another example, the adjustment is performed in response to a signal indicating an electrically-evoked compound action potential (eCAP) of the tissue of the patient.

In some examples, the system monitors a tissue of the patient for an action potential evoked by the delivery of the electrical stimulation therapy. Upon detecting the evoked compound action potential, the system may suspend delivery of the electrical stimulation therapy for an amount of time. Alternatively, or additionally, the system may reduce the amplitude of the electrical stimulation therapy prior to resuming the delivery of therapy to determine a set of electrical stimulation parameters that do not evoke a compound action potential. Alternatively, or additionally, the suspended therapy may be resumed based on patient or other use input, e.g., received patient input. The suspension of therapy may be initiated based on another one of the example triggers described herein other than that of directly sensing compound action potentials evoked by the delivery electrical stimulation therapy.

In some examples, following the time period over which the therapy delivery is suspended, the system may perform titration of one or more parameters defining the electrical stimulation therapy delivered to the patient to adjust the electrical stimulation therapy such that the electrical stimulation provides efficacious therapy to the patient (e.g., by providing pain relief) while remaining substantially below a threshold that evokes a compound action potential in the tissue of the patient (e.g., an amplitude having a magnitude <NUM>%, <NUM>%, <NUM>%, or <NUM>% below a threshold amplitude that evokes a compound action potential). Generally speaking, the lower the amplitude, the less risk of evoking compound action potentials in the tissue of patient <NUM> and the less power consumption by IMD <NUM>.

As used herein, titration of one or more electrical stimulation therapy parameter(s) may refer to the gradual adjustment of one or more electrical stimulation therapy parameters to determine a primary set of electrical stimulation therapy parameters for subsequent delivery. In some examples, this gradual adjustment is an incremental or decremental adjustment, such as with a step function. In other examples, the gradual adjustment is continuous adjustment that is a substantially smooth increase or decrease in the value of the parameter. In one example of titration, a system selects a plurality of different values for an electrical stimulation therapy parameter, such as a current amplitude or a voltage amplitude, and the system delivers electrical stimulation according to the each of the values for the electrical stimulation therapy parameter. The system determines the response of the patient to the electrical stimulation described by each of the values for the electrical stimulation parameter. In some examples, the system gradually increases the value for the electrical stimulation parameter. In other examples, the system gradually decreases the value for the electrical stimulation parameter. In yet further examples, the system selects randomized, non-ordered values for the electrical stimulation parameter. In this fashion, the system may test a plurality of different values to select a primary set of electrical stimulation therapy parameters for subsequent delivery to the patient. In some examples, a clinician may titrate, or instruct the system to titrate, one or more electrical stimulation therapy parameters to determine a primary set of electrical stimulation therapy parameters that describe an electrical stimulation therapy that has the greatest efficacy in treating one or more diseases of the patient, evokes the fewest side effects in the patient, or satisfies other criteria for the delivery of electrical stimulation therapy. In other examples, the system titrates one or more electrical stimulation therapy parameters to determine a primary set of electrical stimulation therapy parameters that describe an electrical stimulation therapy that does not evoke a compound action potential in the patient but effectively treats pain of the patient.

Example techniques of the disclosure may allow a medical device system to detect an evoked compound action potential occurring in a tissue of a patient during delivery of an electrical stimulation therapy, and in response to the detected compound action potential, adjust one or more parameters of a plurality of electrical stimulation therapy programs. Such an IMD system may allow a clinician to quickly configure a system for delivering electrical stimulation therapy to provide pain relief without paresthesia. For example, an IMD system as described herein may automatically titrate or adjust one or more parameters defining the electrical stimulation therapy during an initial or subsequent programming session to identify one or more sets of therapy parameter values (also referred to as a therapy program) without the need for patient feedback. Furthermore, because an IMD system as described herein provides for automatic titration of the one or more parameters, the IMD system may periodically perform such titration at home or at the request of a patient without the involvement of the clinician.

<FIG> is a conceptual diagram illustrating example system <NUM> that includes implantable medical device (IMD) <NUM> configured to deliver electrical stimulation therapy to patient <NUM>. In the example shown in <FIG>, IMD <NUM> is configured to deliver SCS therapy according to the techniques of the disclosure. Although the techniques described in this disclosure are generally applicable to a variety of medical devices including external and implantable medical devices (IMDs), application of such techniques to IMDs and, more particularly, implantable electrical stimulators (e.g., neurostimulators) will be described for purposes of illustration. More particularly, the disclosure will refer to an implantable spinal cord stimulation (SCS) system for purposes of illustration, but without limitation as to other types of medical devices or other therapeutic applications of medical devices.

As shown in <FIG>, system <NUM> includes an IMD <NUM>, leads 16A, 16B, and external programmer <NUM> shown in conjunction with a patient <NUM>, who is ordinarily a human patient. In the example of <FIG>, IMD <NUM> is an implantable electrical stimulator that is configured to generate and deliver electrical stimulation therapy to patient <NUM> via electrodes of leads 16A, 16B, e.g., for relief of chronic pain or other symptoms. IMD <NUM> may be a chronic electrical stimulator that remains implanted within patient <NUM> for weeks, months, or even years. In other examples, IMD <NUM> may be a temporary, or trial, stimulator used to screen or evaluate the efficacy of electrical stimulation for chronic therapy. In one example, IMD <NUM> is implanted within patient <NUM>, while in another example, IMD <NUM> is an external device coupled to percutaneously implanted leads. In some examples, IMD uses one or more leads, while in other examples, IMD <NUM> is leadless.

IMD <NUM> may be constructed of any polymer, metal, or composite material sufficient to house the components of IMD <NUM> (e.g., components illustrated in <FIG>) within patient <NUM>. In this example, IMD <NUM> may be constructed with a biocompatible housing, such as titanium or stainless steel, or a polymeric material such as silicone, polyurethane, or a liquid crystal polymer, and surgically implanted at a site in patient <NUM> near the pelvis, abdomen, or buttocks. In other examples, IMD <NUM> may be implanted within other suitable sites within patient <NUM>, which may depend, for example, on the target site within patient <NUM> for the delivery of electrical stimulation therapy. The outer housing of IMD <NUM> may be configured to provide a hermetic seal for components, such as a rechargeable or non-rechargeable power source. In addition, in some examples, the outer housing of IMD <NUM> may be selected from a material that facilitates receiving energy to charge the rechargeable power source.

Electrical stimulation energy, which may be constant current or constant voltage based pulses, for example, is delivered from IMD <NUM> to one or more target tissue sites of patient <NUM> via one or more electrodes (not shown) of implantable leads 16A and 16B (collectively "leads <NUM>"). In the example of <FIG>, leads <NUM> carry electrodes that are placed adjacent to the target tissue of spinal cord <NUM>. One or more of the electrodes may be disposed at a distal tip of a lead <NUM> and/or at other positions at intermediate points along the lead. Leads <NUM> may be implanted and coupled to IMD <NUM>. The electrodes may transfer electrical stimulation generated by an electrical stimulation generator in IMD <NUM> to tissue of patient <NUM>. Although leads <NUM> may each be a single lead, lead <NUM> may include a lead extension or other segments that may aid in implantation or positioning of lead <NUM>. In some other examples, IMD <NUM> may be a leadless stimulator with one or more arrays of electrodes arranged on a housing of the stimulator rather than leads that extend from the housing. In addition, in some other examples, system <NUM> may include one lead or more than two leads, each coupled to IMD <NUM> and directed to similar or different target tissue sites.

The electrodes of leads <NUM> may be electrode pads on a paddle lead, circular (e.g., ring) electrodes surrounding the body of the lead, conformable electrodes, cuff electrodes, segmented electrodes (e.g., electrodes disposed at different circumferential positions around the lead instead of a continuous ring electrode), or any other type of electrodes capable of forming unipolar, bipolar or multipolar electrode combinations for therapy. Ring electrodes arranged at different axial positions at the distal ends of lead <NUM> will be described for purposes of illustration.

The deployment of electrodes via leads <NUM> is described for purposes of illustration, but arrays of electrodes may be deployed in different ways. For example, a housing associated with a leadless stimulator may carry arrays of electrodes, e.g., rows and/or columns (or other patterns), to which shifting operations may be applied. Such electrodes may be arranged as surface electrodes, ring electrodes, or protrusions. As a further alternative, electrode arrays may be formed by rows and/or columns of electrodes on one or more paddle leads. In some examples, electrode arrays may include electrode segments, which may be arranged at respective positions around a periphery of a lead, e.g., arranged in the form of one or more segmented rings around a circumference of a cylindrical lead.

The therapy parameters for a therapy program (also referred to herein as a set of electrical stimulation parameter values) that controls delivery of stimulation therapy by IMD <NUM> through the electrodes of leads <NUM> may include information identifying which electrodes have been selected for delivery of stimulation according to a stimulation program, the polarities of the selected electrodes, i.e., the electrode combination for the program, and voltage or current amplitude, pulse rate, and pulse width of stimulation delivered by the electrodes. Delivery of stimulation pulses will be described for purposes of illustration.

Although <FIG> is directed to SCS therapy, e.g., used to treat pain, in other examples system <NUM> may be configured to treat any other condition that may benefit from electrical stimulation therapy. For example, system <NUM> may be used to treat tremor, Parkinson's disease, epilepsy, a pelvic floor disorder (e.g., urinary incontinence or other bladder dysfunction, fecal incontinence, pelvic pain, bowel dysfunction, or sexual dysfunction), obesity, gastroparesis, or psychiatric disorders (e.g., depression, mania, obsessive compulsive disorder, anxiety disorders, and the like). In this manner, system <NUM> may be configured to provide therapy taking the form of deep brain stimulation (DBS), peripheral nerve stimulation (PNS), peripheral nerve field stimulation (PNFS), cortical stimulation (CS), pelvic floor stimulation, gastrointestinal stimulation, or any other stimulation therapy capable of treating a condition of patient <NUM>.

In some examples, lead <NUM> may include one or more sensors configured to allow IMD <NUM> to monitor one or more parameters of patient <NUM>. The one or more sensors may be provided in addition to, or in place of, therapy delivery by lead <NUM>.

IMD <NUM> is configured to deliver electrical stimulation therapy to patient <NUM> via selected combinations of electrodes carried by one or both of leads <NUM>, alone or in combination with an electrode carried by or defined by an outer housing of IMD <NUM>. The target tissue for the electrical stimulation therapy may be any tissue affected by electrical stimulation, which may be in the form of electrical stimulation pulses or continuous waveforms. In some examples, the target tissue includes nerves, smooth muscle or skeletal muscle. In the example illustrated by <FIG>, the target tissue is tissue proximate spinal cord <NUM>, such as within an intrathecal space or epidural space of spinal cord <NUM>, or, in some examples, adjacent nerves that branch off of spinal cord <NUM>. Leads <NUM> may be introduced into spinal cord <NUM> in via any suitable region, such as the thoracic, cervical or lumbar regions. Stimulation of spinal cord <NUM> may, for example, prevent pain signals from traveling through spinal cord <NUM> and to the brain of patient <NUM>. Patient <NUM> may perceive the interruption of pain signals as a reduction in pain and, therefore, efficacious therapy results.

IMD <NUM> generates and delivers electrical stimulation therapy to a target stimulation site within patient <NUM> via the electrodes of leads <NUM> to patient <NUM> according to one or more therapy programs. A therapy program defines values for one or more parameters that define an aspect of the therapy delivered by IMD <NUM> according to that program. For example, a therapy program that controls delivery of stimulation by IMD <NUM> in the form of pulses may define values for voltage or current pulse amplitude, pulse width, and pulse rate for stimulation pulses delivered by IMD <NUM> according to that program.

Moreover, in some examples, IMD <NUM> delivers electrical stimulation therapy to patient <NUM> according to multiple therapy programs, which may be stored as a therapy program group. For example, as described below, in some examples, IMD <NUM> may deliver different pulses of electrical stimulation signal via respective electrode combinations, and each of the electrode combinations may be associated with a respective therapy program. The therapy programs may be stored as a group, such that when IMD <NUM> generates and delivers electrical stimulation therapy via a selected group, IMD <NUM> delivers electrical stimulation signal via two or more therapy programs.

A user, such as a clinician or patient <NUM>, may interact with a user interface of an external programmer <NUM> to program IMD <NUM>. Programming of IMD <NUM> may refer generally to the generation and transfer of commands, programs, or other information to control the operation of IMD <NUM>. In this manner, IMD <NUM> may receive the transferred commands and programs from programmer <NUM> to control stimulation therapy. For example, external programmer <NUM> may transmit therapy programs, stimulation parameter adjustments, therapy program selections, therapy program group selections, user input, or other information to control the operation of IMD <NUM>, e.g., by wireless telemetry or wired connection.

In some cases, external programmer <NUM> may be characterized as a physician or clinician programmer if it is primarily intended for use by a physician or clinician. In other cases, external programmer <NUM> may be characterized as a patient programmer if it is primarily intended for use by a patient. A patient programmer may be generally accessible to patient <NUM> and, in many cases, may be a portable device that may accompany patient <NUM> throughout the patient's daily routine. For example, a patient programmer may receive input from patient <NUM> when the patient wishes to terminate or change stimulation therapy. In general, a physician or clinician programmer may support selection and generation of programs by a clinician for use by IMD <NUM>, whereas a patient programmer may support adjustment and selection of such programs by a patient during ordinary use. In other examples, external programmer <NUM> may be included, or part of, an external charging device that recharges a power source of IMD <NUM>. In this manner, a user may program and charge IMD <NUM> using one device, or multiple devices.

As described herein, information may be transmitted between external programmer <NUM> and IMD <NUM>. Therefore, IMD <NUM> and programmer <NUM> may communicate via wireless communication using any techniques known in the art. Examples of communication techniques may include, for example, radiofrequency (RF) telemetry and inductive coupling, but other techniques are also contemplated. In some examples, programmer <NUM> may include a communication head that may be placed proximate to the patient's body near the IMD <NUM> implant site in order to improve the quality or security of communication between IMD <NUM> and programmer <NUM>. Communication between programmer <NUM> and IMD <NUM> may occur during power transmission or separate from power transmission.

In some examples, IMD <NUM>, in response to commands from external programmer <NUM>, delivers electrical stimulation therapy according to a plurality of electrical stimulation therapy programs to a target tissue site of the spinal column <NUM> of patient <NUM> via electrodes (not depicted) on leads <NUM>. In some examples, IMD <NUM>, in response to commands from external programmer <NUM>, titrates one or more parameters defining the plurality of electrical stimulation therapy programs, for example, a voltage amplitude (for voltage controlled devices), a current amplitude (for current-controlled devices), a pulse width, or a pulse frequency, to deliver electrical stimulation of gradually increasing strength. As described further below, the titration may be used to identify a set of therapy parameter values for an electrical stimulation therapy that does not evoke action potentials in the tissue of a patient when delivered but that also provides for efficacious treatment of patient pain.

In some examples, the target tissue is a tissue of the spinal column <NUM> of patient <NUM>. As one example, the target tissue may be a tissue of a dorsal column of the spinal column <NUM> of patient <NUM>. In other examples, the target tissue is a nerve tissue of patient <NUM> or a muscle tissue of patient <NUM>.

During delivery of electrical stimulation therapy defined by one or more electrical stimulation programs, IMD <NUM>, via the electrodes interposed on leads <NUM>, senses target tissue site of the spinal column <NUM> of patient <NUM> to measure the electrical activity of the target tissue site. IMD <NUM> senses when electrical stimulation therapy defined by the one or more electrical stimulation programs evokes a compound action potential in the target tissue site of patient <NUM>. In some examples, IMD <NUM> receives a signal indicative of the compound action potential from one or more sensors internal or external to patient <NUM>. Such an example signal may include a signal indicating an electrically-evoked compound action potential (eCAP) of the tissue of the patient <NUM>. Examples of the one or more sensors include one or more sensors configured to measure an compound action potential of the patient <NUM>, or a side effect indicative of a compound action potential. For example, the one or more sensors may be an accelerometer, a pressure sensor, a bending sensor, a sensor configured to detect a posture of patient <NUM>, or a sensor configured to detect a respiratory function of patient <NUM>. However, in other examples, external programmer <NUM> receives a signal indicating a compound action potential in the target tissue of patient <NUM> and transmits a notification to IMD <NUM>.

In response to sensing an evoked compound action potential, IMD <NUM> adjusts at least one electrical stimulation therapy program of the plurality of electrical stimulation therapy programs. For example, IMD <NUM> selects a value for the one or more parameters defining the electrical stimulation therapy such that delivery of the electrical stimulation therapy does not evoke a compound action potential in the patient. As another example, IMD <NUM> halts delivery of the electrical stimulation therapy. In yet another example, IMD <NUM> selects a different electrical stimulation therapy program of the plurality of electrical stimulation therapy programs for defining the delivery of electrical stimulation therapy to patient <NUM>.

In some examples, a patient or clinician uses external programmer <NUM> to instruct IMD <NUM> to perform titration or other adjustment to the one or more parameters defined by an electrical stimulation therapy programs to calibrate the electrical stimulation therapy delivered by IMD <NUM>. For example, a clinician, via external programmer <NUM>, may perform such a titration to configure IMD <NUM> for delivery of therapy in an outpatient or post-implantation setting. Similarly, patient <NUM> may require an adjustment of the parameters describing the electrical stimulation therapy programs, i.e., because patient <NUM> is experiencing side effects of the electrical stimulation therapy. In this example, patient <NUM>, via external programmer <NUM>, performs such a titration to reconfigure IMD <NUM> for delivery of therapy. In another example, during subsequent use by patient <NUM>, IMD <NUM> periodically monitors the target tissue site of patient <NUM> for an evoked compound action potential and adjusts the plurality of electrical stimulation therapy programs defining the electrical stimulation therapy in response to the evoked compound action potential. Such an evoked compound action potential may arise over time due to impedance changes in the IMD <NUM>, movement of the leads of the IMD, and changes in the position of IMD <NUM>, and indicate a need for recalibration of the electrical stimulation therapy delivered by IMD <NUM>.

In response to determining that an evoked compound action potential occurs, IMD <NUM> suspends delivery of the electrical stimulation therapy to stop the compound action potential. After suspending delivery of the electrical stimulation therapy for a predetermined amount of time, IMD <NUM> resumes delivery of the electrical stimulation therapy. For example, evoked action potentials in patient <NUM> may result in significant but transient side effects, such as paresthesia, respiratory distress (i.e., coughing), or falling. Instead of attempting to determine a new amplitude for the electrical stimulation while the transient side effects are occurring, IMD <NUM> suspends therapy to allow the transient side effects to dissipate and resumes therapy after the transient side effects have subsided. In some examples, if after several attempts to resume delivery of electrical stimulation fail (i.e., because compound action potentials are detected or because the side effects are still present), IMD <NUM> may determine that the side effects are a new steady state for patient <NUM> given the present amplitude of electrical stimulation therapy. Accordingly, IMD <NUM> may perform titration, as described below, of one or more parameters describing the electrical stimulation therapy to determine an electrical stimulation that, when delivered according to a new set of electrical stimulation parameters, does not evoke an action potential in the tissue of patient <NUM>.

In another example, after the predetermined amount of time, IMD <NUM>, via electrodes of leads <NUM>, delivers electrical stimulation therapy according to one or more reduced parameters, such as a reduced amplitude. IMD <NUM> senses, via electrodes of leads <NUM>, an electrical parameter of the target tissue site of patient <NUM> to determine whether the electrical stimulation therapy according to the one or more reduced parameters continues to evoke a compound action potential. Upon determining that the target tissue site no longer exhibits a compound action potential, IMD <NUM> resumes delivery of the electrical stimulation therapy according to the one or more reduced parameters. Upon determining that the target tissue site continues to exhibit a compound action potential, IMD <NUM> suspends the electrical stimulation therapy for another unit of the predetermined amount of time. Typically, the predetermined amount of time is in the order of minutes, e.g., approximately <NUM> minute, approximately <NUM> minutes, approximately <NUM> minutes, etc..

After the predetermined amount of time, IMD <NUM> delivers electrical stimulation according to one or more parameters having further reduced magnitudes, and again determines whether the electrical stimulation according to one or more parameters having further reduced magnitudes continues to evoke a compound action potential. Upon determining that no such compound action potential is evoked, IMD <NUM> gradually increases the magnitude of the one or more parameters, delivers electrical stimulation according to the one or more parameters, and determines a point at which the electrical stimulation evokes a compound action potential to determine a threshold at which the magnitude of the one or more parameters defining the electrical stimulation therapy evokes a compound action potential. At this point, IMD <NUM> may reduce the magnitude of the one or more parameters by a percentage or ratio substantially below the magnitude of the one or more parameters that evokes a compound action potential. For example, the percentage or value may be <NUM>%, <NUM>%, <NUM>%, or <NUM>% of the magnitude of the one or more parameters that evoked the compound action potential, etc. IMD <NUM> delivers electrical stimulation therapy according to one or more parameters substantially below the threshold that evokes a compound action potential in the patient.

As described herein, in some examples, upon resuming the delivery of electrical stimulation therapy, IMD <NUM> may titrate or otherwise adjust one or more electrical stimulation parameters of the previously suspended therapy to identify a set of therapy parameters that do not evoke compound action potentials in the tissue of the patient while maintaining efficacious therapy.

In some examples, upon detecting an evoked compound action potential, IMD <NUM> automatically performs titration of one or more parameters defining the electrical stimulation therapy delivered to the patient to adjust the electrical stimulation therapy such that the electrical stimulation provides adequate therapy to the patient while remaining below a threshold that evokes a compound action potential in the tissue of the patient. In other words, upon detecting the evoked compound action potential, IMD <NUM> automatically titrates one or more parameters defining the plurality of electrical stimulation therapy programs, for example, a voltage amplitude (for voltage controlled devices), a current amplitude (for current-controlled devices), a pulse width, or a pulse frequency, to gradually reduce the magnitude of the one or more parameters defining the plurality of electrical stimulation therapy programs. Upon determining a value for the one or more parameters describing the electrical stimulation therapy that does not evoke a compound action potential in patient <NUM>, IMD <NUM> selects that value for the one or more parameters and resumes delivery of the electrical stimulation therapy according to the new parameter set.

In the example of <FIG>, IMD <NUM> described as performing a plurality of processing and computing functions. However, external programmer <NUM> instead may perform one, several, or all of these functions. In this alternative example, IMD <NUM> functions to relay sensed signals to external programmer <NUM> for analysis, and external programmer <NUM> transmits instructions to IMD <NUM> to adjust the one or more parameters defining the electrical stimulation therapy. For example, IMD <NUM> may relay the sensed signal indicative of an evoked compound action potential to external programmer <NUM>. In response to the signal, external programmer <NUM> may instruct IMD <NUM> to halt delivery of electrical stimulation, select another electrical stimulation program of the plurality of electrical stimulation programs that defines the electrical stimulation therapy delivered to patient <NUM>, or adjust one or more parameters defines the electrical stimulation therapy delivered to patient <NUM>.

Accordingly, some examples of the disclosure allow a system <NUM> including an IMD <NUM> to detect an evoked compound action potential occurring in a tissue of a patient <NUM>, and in response to the detected action potential, adjust one or more parameters defining the electrical stimulation therapy. System <NUM> may allow a clinician to quickly configure a system for delivering electrical stimulation therapy to provide pain relief without paresthesia. For example, a system <NUM> as described herein may automatically titrate or otherwise adjust one or more parameters defining the electrical stimulation therapy during configuration without the need for feedback from patient <NUM>. Furthermore, because system <NUM> as described herein provides for automatic titration of the one or more parameters, system <NUM> may periodically perform such titration at home or at the request of patient <NUM> without the involvement of the clinician.

<FIG> is a block diagram of the example IMD <NUM> of <FIG>. In the example shown in <FIG>, IMD <NUM> includes processor <NUM>, memory <NUM>, stimulation generator <NUM>, sensing module <NUM>, telemetry module <NUM>, sensor <NUM>, and power source <NUM>. Each of these modules may be or include electrical circuitry configured to perform the functions attributed to each respective module. For example, processor <NUM> may include processing circuitry, stimulation generator <NUM> may include switch circuitry, sensing module <NUM> may include sensing circuitry, and telemetry module <NUM> may include telemetry circuitry. Memory <NUM> may include any volatile or non-volatile media, such as a random access memory (RAM), read only memory (ROM), non-volatile RAM (NVRAM), electrically erasable programmable ROM (EEPROM), flash memory, and the like. Memory <NUM> may store computer-readable instructions that, when executed by processor <NUM>, cause IMD <NUM> to perform various functions. Memory <NUM> may be a storage device or other non-transitory medium.

In the example shown in <FIG>, memory <NUM> stores therapy programs <NUM> and sense electrode combinations and associated stimulation electrode combinations <NUM> in separate memories within memory <NUM> or separate areas within memory <NUM>. Each stored therapy program <NUM> defines a particular set of electrical stimulation parameters (e.g., a therapy parameter set), such as a stimulation electrode combination, electrode polarity, current or voltage amplitude, pulse width, and pulse rate. In some examples, individual therapy programs may be stored as a therapy group, which defines a set of therapy programs with which stimulation may be generated. The stimulation signals defined by the therapy programs of the therapy group include stimulation pulses that may be delivered together on an overlapping or non-overlapping (e.g., time-interleaved) basis.

Accordingly, in some examples, stimulation generator <NUM> generates electrical stimulation signals in accordance with the electrical stimulation parameters noted above. Other ranges of therapy parameter values may also be useful, and may depend on the target stimulation site within patient <NUM>. While stimulation pulses are described, stimulation signals may be of any form, such as continuous-time signals (e.g., sine waves) or the like.

Processor <NUM> may include any one or more of a microprocessor, a controller, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field-programmable gate array (FPGA), discrete logic circuitry, or any other processing circuitry configured to provide the functions attributed to processor <NUM> herein may be embodied as firmware, hardware, software or any combination thereof. Processor <NUM> controls stimulation generator <NUM> according to therapy programs <NUM> stored in memory <NUM> to apply particular stimulation parameter values specified by one or more of programs, such as amplitude, pulse width, and pulse rate.

In the example shown in <FIG>, the set of electrodes <NUM> includes electrodes 116A, 116B, 116C, and 116D, and the set of electrodes <NUM> includes electrodes 118A, 118B, 118C, and 118D. Processor <NUM> also controls stimulation generator <NUM> to generate and apply the stimulation signals to selected combinations of electrodes <NUM>, <NUM>. In some examples, stimulation generator <NUM> includes a switch module that couples stimulation signals to selected conductors within leads <NUM>, which, in turn, deliver the stimulation signals across selected electrodes <NUM>, <NUM>. Such a switch module ma y be a switch array, switch matrix, multiplexer, or any other type of switching module configured to selectively couple stimulation energy to selected electrodes <NUM>, <NUM> and to selectively sense bioelectrical neural signals of spine <NUM> with selected electrodes <NUM>, <NUM>.

In other examples, however, stimulation generator <NUM> does not include a switch module. In these examples, stimulation generator <NUM> comprises a plurality of pairs of voltage sources, current sources, voltage sinks, or current sinks connected to each of electrodes <NUM>, <NUM> such that each pair of electrodes has a unique signal generator. In other words, in these examples, each of electrodes <NUM>, <NUM> is independently controlled via its own signal generator (e.g., via a combination of a regulated voltage source and sink or regulated current source and sink), as opposed to switching signals between electrodes <NUM>, <NUM>.

Stimulation generator <NUM> may be a single channel or multi-channel stimulation generator. In particular, stimulation generator <NUM> may be capable of delivering a single stimulation pulse or multiple stimulation pulses at a given time via a single electrode combination or multiple stimulation pulses at a given time via multiple electrode combinations. In some examples, however, stimulation generator <NUM> may be configured to deliver multiple channels on a time-interleaved basis. For example, a switch module of stimulation generator <NUM> may serve to time divide the output of stimulation generator <NUM> across different electrode combinations at different times to deliver multiple programs or channels of stimulation energy to patient <NUM>. In another example, the stimulation generator <NUM> may control the independent sources or sinks on a time-interleaved bases.

Electrodes <NUM>, <NUM> on respective leads <NUM> may be constructed of a variety of different designs. For example, one or both of leads <NUM> may include two or more electrodes at each longitudinal location along the length of the lead, such as multiple electrodes at different perimeter locations around the perimeter of the lead at each of the locations A, B, C, and D. On one example, the electrodes may be electrically coupled to switch module <NUM> via respective wires that are straight or coiled within the housing the lead and run to a connector at the proximal end of the lead. In another example, each of the electrodes of the lead may be electrodes deposited on a thin film. The thin film may include an electrically conductive trace for each electrode that runs the length of the thin film to a proximal end connector. The thin film may then be wrapped (e.g., a helical wrap) around an internal member to form the lead <NUM>. These and other constructions may be used to create a lead with a complex electrode geometry.

Although sensing module <NUM> is incorporated into a common housing with stimulation generator <NUM> and processor <NUM> in <FIG>, in other examples, sensing module <NUM> may be in a separate housing from IMD <NUM> and may communicate with processor <NUM> via wired or wireless communication techniques. Example bioelectrical signals include, but are not limited to, a signal generated from local field potentials within one or more regions of spine <NUM>.

Sensor <NUM> may include one or more sensing elements that sense values of a respective patient parameter. For example, sensor <NUM> may include one or more accelerometers, optical sensors, chemical sensors, temperature sensors, pressure sensors, or any other types of sensors. Sensor <NUM> may output patient parameter values that may be used as feedback to control delivery of therapy. IMD <NUM> may include additional sensors within the housing of IMD <NUM> and/or coupled via one of leads <NUM> or other leads. In addition, IMD <NUM> may receive sensor signals wirelessly from remote sensors via telemetry module <NUM>, for example. In some examples, one or more of these remote sensors may be external to patient (e.g., carried on the external surface of the skin, attached to clothing, or otherwise positioned external to the patient).

Telemetry module <NUM> supports wireless communication between IMD <NUM> and an external programmer <NUM> or another computing device under the control of processor <NUM>. Processor <NUM> of IMD <NUM> may receive, as updates to programs, values for various stimulation parameters such as amplitude and electrode combination, from programmer <NUM> via telemetry module <NUM>. The updates to the therapy programs may be stored within therapy programs <NUM> portion of memory <NUM>. Telemetry module <NUM> in IMD <NUM>, as well as telemetry modules in other devices and systems described herein, such as programmer <NUM>, may accomplish communication by radiofrequency (RF) communication techniques. In addition, telemetry module <NUM> may communicate with external medical device programmer <NUM> via proximal inductive interaction of IMD <NUM> with programmer <NUM>. Accordingly, telemetry module <NUM> may send information to external programmer <NUM> on a continuous basis, at periodic intervals, or upon request from IMD <NUM> or programmer <NUM>.

Power source <NUM> delivers operating power to various components of IMD <NUM>. Power source <NUM> may include a small rechargeable or non-rechargeable battery and a power generation circuit to produce the operating power. Recharging may be accomplished through proximal inductive interaction between an external charger and an inductive charging coil within IMD <NUM>. In some examples, power requirements may be small enough to allow IMD <NUM> to utilize patient motion and implement a kinetic energy-scavenging device to trickle charge a rechargeable battery. In other examples, traditional batteries may be used for a limited period of time.

According to the techniques of the disclosure, processor <NUM> of IMD <NUM> receives, via telemetry module <NUM>, instructions to deliver electrical stimulation therapy according to the one or more electrical stimulation therapy programs to a target tissue site of the spinal column <NUM> of patient <NUM> via a plurality of electrode combinations of electrodes <NUM>, <NUM> of leads <NUM> and/or a housing of IMD <NUM>. In some examples, processor <NUM> of IMD <NUM>, in response to commands from external programmer <NUM>, titrates one or more parameters defining the plurality of electrical stimulation therapy programs, for example, a voltage amplitude (for voltage controlled devices), a current amplitude (for current-controlled devices), a pulse width, or a pulse frequency, to deliver electrical stimulation of gradually increasing strength.

In some examples, processor <NUM> of IMD <NUM> controls stimulation generator <NUM> to deliver electrical stimulation therapy according to the one or more electrical stimulation therapy programs to patient <NUM> via a plurality of electrode combinations of electrodes <NUM>, <NUM> of leads <NUM> at a high-frequency, such as a frequency selected from a range of approximately <NUM>,<NUM> Hertz and less than approximately <NUM>,<NUM> Hertz. In other examples, processor <NUM> of IMD <NUM> delivers electrical stimulation therapy according to a plurality of lower-frequency electrical stimulation therapy programs to the patient <NUM> via a plurality of electrode combinations of electrodes <NUM>, <NUM> of leads <NUM> and on a time-interleaved basis to effectively deliver combined, higher-frequency electrical stimulation to a target tissue site. Techniques for delivering such a combined, higher-frequency electrical stimulation to a target tissue site are described in more detail in <CIT>.

In one example, the electrical stimulation signal comprises of one or more electrical pulses (e.g., a pulse train), wherein each pulse has a pulse width in a range of <NUM> microseconds to <NUM> microseconds. In a further example, each pulse has a pulse width of about <NUM> microseconds to about <NUM> microseconds. In one example, the electrical stimulation signal comprises of one or more electrical pulses (e.g., a pulse train), wherein each pulse has a pulse width in a range of <NUM> microseconds to <NUM> microseconds. In one example, the electrical stimulation signal comprises of one or more electrical pulses (e.g., a pulse train), wherein each pulse has a pulse width of approximately <NUM> microseconds. In one example, the electrical stimulation signal comprises of one or more electrical pulses (e.g., a pulse train), wherein each pulse has a pulse width of approximately <NUM> microseconds.

In some examples, IMD <NUM> delivers the pulses of the electrical stimulation signal via different electrode combinations of two or more of electrodes 116A-116D and 118A-118D and a housing of IMD <NUM>. For example, IMD <NUM> may alternate delivery of pulses between two or more different electrode combinations, or may otherwise interleave the pulses using two or more electrode combinations in any suitable order. In one example, each electrode combination comprises at least one electrode functioning as an anode and at least one other electrode functioning as a cathode, and these electrodes are unique to the electrode combination in that the same electrodes are not used in other electrode combinations that are used to delivery time-interleaved stimulation pulses.

In some examples, the electrical stimulation therapy signal may have a frequency range of approximately <NUM>-<NUM> Hertz. However, in other examples, the electrical stimulation therapy has a frequency greater than approximately <NUM> Hertz in some examples, <NUM>,<NUM> Hertz in some examples, greater than <NUM>,<NUM> Hertz in other examples, greater than <NUM>,<NUM> Hertz in other examples, or greater than <NUM>,<NUM> Hertz in still other examples. When higher frequencies are used in a system using electrically-evoked compound action potentials (eCAPs) to determine if compound action potentials are present, it may be necessary to briefly suspend the delivery of electrical stimulation and deliver a single pulse at a lower amplitude (or a burst of pulses having a lower frequency) to detect the presence of eCAP. Additionally, the electrical stimulation therapy signal may have a frequency of less than approximately <NUM>,<NUM> Hertz in some examples, less than <NUM>,<NUM> Hertz in other examples, less than <NUM>,<NUM> Hertz in other examples, less than <NUM>,<NUM> Hertz in other examples, less than <NUM>,<NUM> Hertz in other examples, or less than <NUM> Hertz in still other examples.

During delivery of electrical stimulation therapy according to the one or more electrical stimulation programs, processor <NUM>, via electrodes <NUM>, <NUM> interposed along leads <NUM>, senses the target tissue site of the spinal column <NUM> of patient <NUM> and measures the electrical activity of the target tissue site. For example, electrodes <NUM>, <NUM> may sense an electrically-evoked compound action potential (eCAP) of the tissue of the patient. Upon detecting that the electrical stimulation therapy according to the one or more electrical stimulation programs evokes a compound action potential in the target tissue site of patient <NUM>, processor <NUM> adjusts at least one electrical stimulation therapy program of the plurality of electrical stimulation therapy programs.

In an alternative example, processor <NUM> receives a signal indicative of an evoked compound action potential from one or more sensors internal or external to patient <NUM>. Upon receiving the signal, processor <NUM> adjusts at least one electrical stimulation therapy program of the plurality of electrical stimulation therapy programs. Examples of the one or more sensors include one or more sensors configured to measure a compound action potential of the patient <NUM>, or a side effect indicative of a compound action potential. For example, the one or more sensors may be an accelerometer, a pressure sensor, a bending sensor, a sensor configured to detect a posture of patient <NUM>, or a sensor configured to detect a respiratory function of patient <NUM>. However, in other examples, external programmer <NUM> receives a signal indicating an evoked compound action potential in the target tissue of patient <NUM> and transmits the signal to processor <NUM>. Processor <NUM> receives the signal via telemetry module <NUM>.

As described above, in response to sensing an evoked compound action potential in the target tissue site of patient <NUM>, or in response to receiving a signal indicative of the compound action potential, processor <NUM> adjusts at least one electrical stimulation therapy program of the plurality of electrical stimulation therapy programs. For example, processor <NUM> identifies a value for the one or more parameters defining the electrical stimulation therapy such that delivery of the electrical stimulation therapy does not evoke a compound action potential in the patient, e.g., by titration of the one or more parameters. In another example, processor <NUM> halts delivery of the electrical stimulation therapy according to the electrical stimulation therapy programs. In yet another example, processor <NUM> selects a different electrical stimulation therapy program of a plurality of electrical stimulation therapy programs that describe delivery of electrical stimulation therapy to patient <NUM>.

In some examples, a clinician uses external programmer <NUM> to transmit commands to processor <NUM> instructing processor <NUM> to perform titration of the one or more parameters describing the plurality of electrical stimulation therapy programs so as to calibrate the electrical stimulation therapy delivered by processor <NUM>. For example, a clinician may perform such a titration to configure IMD <NUM> for delivery of therapy in an outpatient or post-implantation setting. In another example, during subsequent use by patient <NUM>, processor <NUM>, via electrodes <NUM>, <NUM>, periodically monitors the target tissue site of patient <NUM> for an evoked compound action potential. In response to sensing an evoked compound action potential, processor <NUM> adjusts the plurality of electrical stimulation therapy programs. Such an evoked compound action potential may arise over time due to impedance changes in leads <NUM> or electrodes <NUM>, <NUM> of IMD <NUM>, movement of the leads <NUM>, or changes in the position of IMD <NUM> or leads <NUM>. Processor <NUM> may determine that the occurrence of such an evoked action potential indicate a need to recalibrate one or more parameters of the electrical stimulation therapy delivered by processor <NUM>. Alternatively, processor <NUM> may receive a signal indicating the occurrence of such an action potential from one or more sensors, as described above.

Upon detecting an evoked compound action potential, or upon receiving a signal indicative of the compound action potential from one or more sensors or external programmer <NUM>, processor <NUM> suspends delivery of the electrical stimulation therapy to suppress the compound action potential, e.g., by suspending delivery of the electrical stimulation therapy for a predetermined amount of time. In one example, after suspending delivery of the electrical stimulation therapy for the predetermined amount of time, processor <NUM> resumes delivery of the electrical stimulation therapy. In another example, after the predetermined amount of time, processor <NUM> controls stimulation generator <NUM> to deliver electrical stimulation at a reduced amplitude. Processor <NUM>, via electrodes <NUM>, <NUM>, senses an electrical parameter of the target tissue site of patient <NUM>. Upon determining that the target tissue site continues to exhibit a compound action potential, processor <NUM> suspends delivery of the electrical stimulation for the predetermined amount of time.

In response to determining that an evoked compound action potential occurs, processor <NUM> suspends delivery of the electrical stimulation therapy to stop the compound action potential. After suspending delivery of the electrical stimulation therapy for a predetermined amount of time, processor <NUM> controls stimulation generator <NUM> to resume delivery of the electrical stimulation therapy. For example, evoked action potentials in patient <NUM> may result in significant but transient side effects, such as paresthesia, respiratory distress (i.e., coughing), or falling. Instead of attempting to determine a new amplitude for the electrical stimulation while the transient side effects are occurring, processor <NUM> suspends therapy to allow the transient side effects to dissipate and resumes therapy after the transient side effects have subsided. In some examples, if after several attempts to resume delivery of electrical stimulation fail (i.e., because compound action potentials are detected or because the side effects are still present), processor <NUM> may determine that the side effects are a new steady state for patient <NUM> given the present amplitude of electrical stimulation therapy. Accordingly, processor <NUM> may control stimulation generator <NUM> to perform titration, as described below, of one or more parameters describing the electrical stimulation therapy to determine an electrical stimulation that, when delivered according to a new set of electrical stimulation parameters, does not evoke an action potential in the tissue of patient <NUM>.

In another example, after the predetermined amount of time, processor <NUM> controls stimulation generator <NUM> to deliver electrical stimulation therapy according to one or more reduced parameters, such as a reduced amplitude. Processor <NUM> senses, via electrodes of leads <NUM>, an electrical parameter of the target tissue site of patient <NUM> to determine whether the electrical stimulation therapy according to the one or more reduced parameters continues to evoke a compound action potential. Upon determining that the target tissue site no longer exhibits a compound action potential, processor <NUM> controls stimulation generator <NUM> to resume delivery of the electrical stimulation therapy according to the one or more reduced parameters. Upon determining that the target tissue site continues to exhibit a compound action potential, processor <NUM> controls stimulation generator <NUM> to suspend the electrical stimulation therapy for another unit of the predetermined amount of time. Typically, the predetermined amount of time is in the order of minutes, e.g., approximately <NUM> minute, approximately <NUM> minutes, approximately <NUM> minutes, etc..

After the predetermined amount of time, processor <NUM> controls stimulation generator <NUM> to deliver electrical stimulation according to one or more parameters having further reduced magnitudes. Again, processor <NUM> determines whether the electrical stimulation according to one or more parameters having further reduced magnitudes continues to evoke a compound action potential. Upon determining that no such compound action potential is evoked, processor <NUM> gradually increases the magnitude of the one or more parameters and controls stimulation generator <NUM> to deliver electrical stimulation according to the gradually increasing one or more parameters. Processor <NUM> determines a point at which the electrical stimulation evokes a compound action potential to determine a threshold at which the magnitude of the one or more parameters defining the electrical stimulation therapy evokes a compound action potential. At this point, processor <NUM> reduces the magnitude of the one or more parameters by a percentage or ratio substantially below the magnitude of the one or more parameters that evokes a compound action potential. For example, the percentage or value may be <NUM>%, <NUM>%, <NUM>%, or <NUM>% of the magnitude of the one or more parameters that evoked the compound action potential, etc. Processor <NUM> controls stimulation generator <NUM> to deliver electrical stimulation therapy according to one or more parameters substantially below the threshold that evokes a compound action potential in the patient.

In other examples, upon detecting an evoked compound action potential, processor <NUM> automatically performs titration of one or more parameters defining the electrical stimulation therapy delivered to the patient to adjust the electrical stimulation therapy such that the electrical stimulation provides adequate therapy to the patient while remaining below a threshold that evokes a compound action potential in the tissue of the patient. In other words, upon detecting the evoked compound action potential, processor <NUM> automatically titrates one or more parameters defining the plurality of electrical stimulation therapy programs, for example, a voltage amplitude (for voltage controlled devices), a current amplitude (for current-controlled devices), a pulse width, or a pulse frequency, to gradually reduce the magnitude of the one or more parameters defining the plurality of electrical stimulation therapy programs. Upon determining a value for the one or more parameters defining the electrical stimulation therapy that does not evoke a compound action potential in patient <NUM>, processor <NUM> selects that value for the one or more parameters and resumes delivery of the electrical stimulation therapy according to the new parameter set.

Although IMD <NUM> is generally described herein as an implantable device, the techniques of this disclosure may also be applicable to external or partially external medical devices in other examples. For example, IMD <NUM> may instead be configured as an external medical device coupled to one or more percutaneous medical leads. The external medical device may be a chronic, temporary, or trial electrical stimulator. In addition, an external electrical stimulator may be used in addition to one or more IMDs <NUM> to deliver electrical stimulation as described herein.

<FIG> is a block diagram of the example external programmer <NUM> of <FIG>. Although programmer <NUM> may generally be described as a hand-held device, programmer <NUM> may be a larger portable device or a more stationary device. In addition, in other examples, programmer <NUM> may be included as part of an external charging device or include the functionality of an external charging device. As illustrated in <FIG>, programmer <NUM> may include a processor <NUM>, memory <NUM>, user interface <NUM>, telemetry module <NUM>, and power source <NUM>. Memory <NUM> may store instructions that, when executed by processor <NUM>, cause processor <NUM> and external programmer <NUM> to provide the functionality ascribed to external programmer <NUM> throughout this disclosure. Each of these components, or modules, may include electrical circuitry that is configured to perform some or all of the functionality described herein. For example, processor <NUM> may include processing circuitry configured to perform the processes discussed with respect to processor <NUM>.

In general, programmer <NUM> comprises any suitable arrangement of hardware, alone or in combination with software and/or firmware, to perform the techniques attributed to programmer <NUM>, and processor <NUM>, user interface <NUM>, and telemetry module <NUM> of programmer <NUM>. In various examples, programmer <NUM> may include one or more processors, such as one or more microprocessors, DSPs, ASICs, FPGAs, or any other equivalent integrated or discrete logic circuitry, as well as any combinations of such components. Programmer <NUM> also, in various examples, may include a memory <NUM>, such as RAM, ROM, PROM, EPROM, EEPROM, flash memory, a hard disk, a CD-ROM, comprising executable instructions for causing the one or more processors to perform the actions attributed to them. Moreover, although processor <NUM> and telemetry module <NUM> are described as separate modules, in some examples, processor <NUM> and telemetry module <NUM> are functionally integrated. In some examples, processor <NUM> and telemetry module <NUM> correspond to individual hardware units, such as ASICs, DSPs, FPGAs, or other hardware units.

Memory <NUM> (e.g., a storage device) may store instructions that, when executed by processor <NUM>, cause processor <NUM> and programmer <NUM> to provide the functionality ascribed to programmer <NUM> throughout this disclosure. For example, memory <NUM> may include instructions that cause processor <NUM> to obtain a parameter set from memory, select a spatial electrode movement pattern, or receive a user input and send a corresponding command to IMD <NUM>, or instructions for any other functionality. In addition, memory <NUM> may include a plurality of programs, where each program includes a parameter set that defines stimulation therapy.

User interface <NUM> may include a button or keypad, lights, a speaker for voice commands, a display, such as a liquid crystal (LCD), light-emitting diode (LED), or organic light-emitting diode (OLED). In some examples the display may be a touch screen. User interface <NUM> may be configured to display any information related to the delivery of stimulation therapy, identified patient behaviors, sensed patient parameter values, patient behavior criteria, or any other such information. User interface <NUM> may also receive user input via user interface <NUM>. The input may be, for example, in the form of pressing a button on a keypad or selecting an icon from a touch screen. The input may request starting or stopping electrical stimulation, the input may request a new spatial electrode movement pattern or a change to an existing spatial electrode movement pattern, of the input may request some other change to the delivery of electrical stimulation.

Processor <NUM> may also control user interface <NUM> to display information related to an anatomical atlas (e.g., an atlas of a reference anatomy) and patient-specific anatomy. For example, user interface <NUM> may display a representation of one or more atlas-defined anatomical structures over a representation (e.g., an image) of the specific patient anatomy. User interface <NUM> may present annotation tools for adjusting the structures of the atlas to the patient anatomy and receive user annotations indicating where the corresponding structures of the patient anatomy are located and/or where the atlas should be moved with respect to the patient anatomy. Processor <NUM> may then adjust the position and/or size of the structures of the atlas to more closely match (e.g., a best fit) to the user annotation. After the atlas has been adjusted, the user may refer to the atlas for locations of certain structures of the patient instead of needing to continually find desired structures based on the image of the patient anatomy.

Telemetry module <NUM> may support wireless communication between IMD <NUM> and programmer <NUM> under the control of processor <NUM>. Telemetry module <NUM> may also be configured to communicate with another computing device via wireless communication techniques, or direct communication through a wired connection. In some examples, telemetry module <NUM> provides wireless communication via an RF or proximal inductive medium. In some examples, telemetry module <NUM> includes an antenna, which may take on a variety of forms, such as an internal or external antenna.

Examples of local wireless communication techniques that may be employed to facilitate communication between programmer <NUM> and IMD <NUM> include RF communication according to the <NUM> or Bluetooth specification sets or other standard or proprietary telemetry protocols. In this manner, other external devices may be capable of communicating with programmer <NUM> without needing to establish a secure wireless connection. As described herein, telemetry module <NUM> may be configured to transmit a spatial electrode movement pattern or other stimulation parameter values to IMD <NUM> for delivery of stimulation therapy.

In some examples, selection of therapy parameters or therapy programs may be transmitted to a medical device (e.g., IMD <NUM>) for delivery to patient <NUM>. In other examples, the therapy may include medication, activities, or other instructions that patient <NUM> must perform themselves or a caregiver perform for patient <NUM>. In some examples, programmer <NUM> may provide visual, audible, and/or tactile notifications that indicate there are new instructions. Programmer <NUM> may require receiving user input acknowledging that the instructions have been completed in some examples.

According to the techniques of the disclosure, processor <NUM> of external programmer <NUM> receives, via user interface <NUM>, input from a clinician causing processor <NUM>, via telemetry module <NUM>, to instruct IMD <NUM> to deliver electrical stimulation therapy according to one or more electrical stimulation therapy programs to a target tissue site of the spinal column <NUM> of patient <NUM> via a plurality of electrodes. In some examples, processor <NUM> of external programmer <NUM> receives, via user interface <NUM>, input from a clinician causing processor <NUM>, via telemetry module <NUM>, to instruct IMD <NUM> to titrate one or more parameters defining the plurality of electrical stimulation therapy programs, for example, a voltage amplitude (for voltage controlled devices), a current amplitude (for current-controlled devices), a pulse width, or a pulse frequency, to deliver electrical stimulation of gradually increasing strength.

During delivery of electrical stimulation therapy according to the one or more electrical stimulation programs, IMD <NUM>, via electrodes interposed along leads <NUM>, senses the target tissue site of the spinal column <NUM> of patient <NUM> and measures the electrical activity of the target tissue site. In one example, processor <NUM> of external programmer <NUM> receives, via telemetry module <NUM>, signals from IMD <NUM> indicating the measured electrical activity. Upon determining that the measured electrical activity indicates that electrical stimulation therapy according to the one or more electrical stimulation programs evokes a compound action potential in the target tissue site of patient <NUM>, processor <NUM>, via telemetry module <NUM>, instructs IMD <NUM> to adjust at least one electrical stimulation therapy program of the plurality of electrical stimulation therapy programs. In some examples, processor <NUM> accomplishes this by issuing, via telemetry module <NUM>, a notification of the sensed evoked compound action potential to IMD <NUM>.

In an alternative example, processor <NUM> receives, from one or more sensors internal or external to patient <NUM>, a signal indicating that electrical stimulation therapy according to the one or more electrical stimulation programs evokes a compound action potential in the target tissue site of patient <NUM>. Upon receiving the signal, processor <NUM>, via telemetry module <NUM>, instructs IMD <NUM> to adjust at least one electrical stimulation therapy program of the plurality of electrical stimulation therapy programs. Such an example signal may include a signal indicating an electrically-evoked compound action potential (eCAP) of the tissue of the patient. Other examples of the signal include a signal received from one or more sensors configured to measure a compound action potential of the patient <NUM>, or a side effect indicative of a compound action potential. For example, the signal may be a signal received from an accelerometer, a pressure sensor, a bending sensor, a sensor configured to detect a posture of patient <NUM>, or a sensor configured to detect a respiratory function of patient <NUM>.

As described above, in response to determining that a compound action potential in the target tissue site of patient <NUM> is present, processor <NUM>, via telemetry module <NUM>, instructs IMD <NUM> to adjust at least one electrical stimulation therapy program of the plurality of electrical stimulation therapy programs. For example, processor <NUM> selects different values for the one or more parameters defining the electrical stimulation therapy such that delivery of the electrical stimulation therapy does not evoke a compound action potential in the patient, and instructs, via telemetry module <NUM>, IMD <NUM> to deliver electrical stimulation therapy according to the selected one or more parameters defining the electrical stimulation therapy. In another example, processor <NUM>, via telemetry module <NUM>, instructs IMD <NUM> to halt delivery of the electrical stimulation therapy. In yet another example, processor <NUM> selects a different electrical stimulation therapy program of the plurality of electrical stimulation therapy programs and instructs, via telemetry module <NUM>, IMD <NUM> to deliver electrical stimulation therapy according to the selected electrical stimulation therapy program.

In some examples, processor <NUM> of external programmer <NUM> receives, via user interface <NUM>, input from a user causing processor <NUM>, via telemetry module <NUM>, to transmit commands to IMD <NUM> instructing IMD <NUM> to perform titration of the one or more parameters describing the plurality of electrical stimulation therapy programs so as to calibrate the electrical stimulation therapy. For example, a clinician may perform such a titration to configure system <NUM> for delivery of therapy in an outpatient or post-implantation setting. In another example,.

In this example, patient <NUM>, via external programmer <NUM>, performs such a titration to reconfigure IMD <NUM> such that emergent side effects are reduced or suppressed. In yet another example, during subsequent use by patient <NUM>, processor <NUM>, via telemetry module <NUM>, receives signals from IMD <NUM> or one or more sensors indicating a physiological parameter of a tissue area of patient <NUM>. Processor <NUM> may determine that such signals indicate the presence of an evoked compound action potential, and thus indicate a need to recalibrate one or more parameters of the electrical stimulation therapy delivered by IMD <NUM>.

Upon determining that the physiological parameter is indicative of an evoked compound action potential, processor <NUM>, via telemetry module <NUM>, transmits instructions to IMD <NUM> to adjust the one or more electrical stimulation therapy programs describing the electrical stimulation therapy, suspend delivery of the electrical stimulation, or perform titration of one or more parameters defining the electrical stimulation therapy as described above.

<FIG> is a flowchart illustrating an example operation for delivering SCS therapy according to the techniques of the disclosure. For ease of description, <FIG> is described with respect to system <NUM> shown in <FIG>.

As depicted in <FIG>, processor <NUM> controls stimulation generator <NUM> to deliver electrical stimulation therapy to a target tissue site of the spinal column <NUM> of patient <NUM> via electrodes <NUM>, <NUM> interposed along leads <NUM>. Processor <NUM> may control the delivery of electrical stimulation therapy according to one or more electrical stimulation therapy programs defining the therapy. In some examples, the electrical stimulation therapy programs are configured to provide pain relief to patient <NUM> without substantially inducing paresthesia or other side effects in patient <NUM>.

During delivery of electrical stimulation therapy to patient <NUM> according to the one or more electrical stimulation programs (<NUM>), processor <NUM> periodically adjusts the electrical stimulation therapy delivered to the patient to prevent action potentials in the tissue of the patient evoked by the delivered electrical stimulation (<NUM>). For example, over time, the delivered stimulation may evoke compound action potentials, e.g., for the reasons described above, even though the therapy did not initially evoke compound action potentials when a clinician initially configured the electrical stimulation system. In some examples, processor <NUM> determines when the delivered electrical stimulation <NUM> evokes a compound action potential and adjusts the stimulation therapy in response to the determination (<NUM>). As described herein, the adjusted therapy does not result in an evoked compound action potential in the tissue during subsequent delivery of the electrical stimulation therapy.

For example, IMD <NUM>, via the electrodes <NUM>, <NUM> interposed on leads <NUM>, senses target tissue site of the spinal column <NUM> of patient <NUM> to measure the electrical activity of the target tissue site. Processor <NUM> determines that the delivered electrical stimulation therapy evokes a compound action potential in the target tissue site of patient <NUM>, and in response, adjusts the electrical stimulation therapy as described above. Processor <NUM> may determine that the compound action potentials are evoked by sensing the compound action potential via electrodes <NUM>, <NUM>, or other sensing device. In other examples, processor <NUM> may receive patient input indicating that the patient is experiencing paresthesia. In response to the receipt of the patient input, processor <NUM> may adjust the electrical stimulation therapy. In some examples, processor <NUM> adjusts the electrical stimulation therapy periodically based on the amount of time since the last adjustment, e.g., on a daily or weekly basis. In some example, processor <NUM> may initiate the adjustment to the therapy based on patient activity. For example, processor <NUM> may determine the patient has transitioned from a prone position to a sitting position, from a prone position to a supine position, from a sitting position to a running position, etc..

In some examples, the one or more sensors are internal or external to patient <NUM>. Such an example signal may include a signal indicating an electrically-evoked compound action potential (eCAP) of the tissue of the patient. Other examples of the signal include a signal received from one or more sensors configured to measure a compound action potential of the patient <NUM>, or a side effect indicative of a compound action potential. For example, IMD may receive a signal from an accelerometer, a pressure sensor, a bending sensor, a sensor configured to detect a posture of patient <NUM>, or a sensor configured to detect a respiratory function of patient <NUM>. Such a sensor, for example, may be configured to detect when patient <NUM> is running, walking, standing, sitting, laying down, prone, supine, and the like (e.g., for a posture sensor), or coughing or suffering respiratory distress in patient <NUM> (e.g., for a sensor configured to detect respiratory function). However, in other examples, external programmer <NUM> receives a signal indicating a compound action potential in the target tissue of patient <NUM> and transmits a notification of a sensed evoked compound action potential to IMD <NUM>.

In response to sensing the evoked compound action potential, IMD <NUM> adjusts at least one electrical stimulation therapy program of the plurality of electrical stimulation therapy programs (<NUM>). In one example, IMD <NUM> selects a value for the one or more parameters defining the electrical stimulation therapy such that delivery of the electrical stimulation therapy does not evoke a compound action potential in the patient. As another example, IMD <NUM> halts delivery of the electrical stimulation therapy. In yet another example, IMD <NUM> selects a different electrical stimulation therapy program of the plurality of electrical stimulation therapy programs describing the delivery of electrical stimulation to patient <NUM>.

<FIG> is a flowchart illustrating an example operation for delivering SCS therapy according to the techniques of the disclosure. For convenience, <FIG> is described with respect to system <NUM> of FIGS. <NUM> to <NUM>.

As depicted in <FIG>, processor <NUM> controls stimulation generator <NUM> to deliver electrical stimulation therapy according to one or more electrical stimulation therapy programs to a target tissue site of the spinal column <NUM> of patient <NUM> via electrodes <NUM>, <NUM> interposed along leads <NUM> (<NUM>), e.g. as described with regard to <FIG>.

During delivery of electrical stimulation therapy to patient <NUM> according to the one or more electrical stimulation programs (<NUM>), processor <NUM> controls delivery of electrical stimulation therapy from IMD <NUM> to patient <NUM> according to at least one therapy program. In some examples, the electrical stimulation therapy is configured to provide pain relief to the patient without substantially resulting in paresthesia perceived by the patient. In other examples, the electrical stimulation therapy is configured to provide pain relief to the patient while causing no paresthesia perceived by the patient.

Processor <NUM> determines that the electrical stimulation therapy evokes a compound action potential in the target tissue of patient <NUM> (<NUM>). For example, over time, the delivered stimulation may evoke compound action potentials, e.g., for the reasons described above, even though the therapy did not initially evoke compound action potentials when a clinician initially configured the electrical stimulation system. In some examples, processor <NUM> senses, via the electrodes <NUM>, <NUM> interposed on leads <NUM>, target tissue site of the spinal column <NUM> of patient <NUM> to measure the electrical activity of the target tissue site. In some examples, processor <NUM> senses an electrically-evoked compound action potential (eCAP) of the tissue of patient <NUM>. In an alternative example, processor <NUM> determines that the electrical stimulation therapy is evoking a compound action potential by monitoring, via one or more sensors, one or more physiological parameters of patient <NUM> (e.g., to determine if the patient is suffering from one or more side effects caused by evoked action potentials, such as coughing or falling). In some examples, the one or more sensors are internal or external to patient <NUM>. For example, the sensor may be an accelerometer, a pressure sensor, a bending sensor, a sensor configured to detect a posture of patient <NUM>, or a sensor configured to detect a respiratory function of patient <NUM>. In yet a further example, processor <NUM> determines that the electrical stimulation therapy is evoking a compound action potential by sensing, via the electrodes <NUM>, <NUM> interposed on leads <NUM>, target tissue site of the spinal column <NUM> of patient <NUM> to measure electrical activity of the target tissue site and by monitoring, via one or more sensors, one or more physiological parameters of patient <NUM>. In a still further example, processor <NUM> determines that the electrical stimulation therapy is evoking a compound action potential based on receiving feedback from patient <NUM> indicating that the patient <NUM> is experiencing side effects, such as paresthesia, due to evoked action potentials.

In response to determining that the electrical stimulation therapy evokes a compound action potential, processor <NUM> adjusts one or more parameters defining the stimulation therapy to eliminate the evoked compound action potentials in the tissue of the patient (<NUM>). As described herein, the adjusted therapy does evoke compound action potential in the tissue during subsequent delivery of the electrical stimulation therapy. In some examples, processor <NUM> reduces the magnitude of the one or more parameters defining the electrical stimulation therapy program (e.g., a current amplitude, a voltage amplitude, a frequency, a pulse width, etc). In one example, processor <NUM> selects a value for the one or more parameters defining the electrical stimulation therapy such that delivery of the electrical stimulation therapy does not evoke a compound action potential in the patient. In the example of a voltage-controlled system where IMD <NUM> gradually increases the voltage amplitude of the plurality of electrical stimulation therapy programs, upon detecting an evoked compound action potential, IMD <NUM> determines that the voltage amplitude is at a magnitude that evokes a compound action potential in patient <NUM>. Accordingly, IMD <NUM> selects a value for this voltage amplitude that is less than the voltage amplitude at the level that evokes the compound action potential in patient <NUM>. In the example of a current-controlled system where IMD <NUM> gradually increases the current amplitude of the plurality of electrical stimulation therapy programs, upon detecting an evoked compound action potential, IMD <NUM> determines that the current amplitude is at a magnitude that evokes a compound action potential in patient <NUM>. Accordingly, IMD <NUM> selects a value for the current amplitude that is less than the current amplitude at the level that evokes the compound action potential in patient <NUM>. Thus, IMD <NUM> continues to deliver electrical stimulation therapy at the new value for the one or more parameters defining the plurality of electrical stimulation therapy programs at a level that does not evoke a compound action potential in patient <NUM>, thereby decreasing the severity of side effects experienced by patient <NUM>.

In some examples, the operation depicted in <FIG> is performed by a clinician to configured electrical stimulation therapy delivered by IMD <NUM> in an out-patient or post-implantation setting. In other examples, the operation depicted in <FIG> is performed by patient <NUM> to recalibrate the electrical stimulation therapy delivered by IMD <NUM>. For example, patient <NUM> may experience side effects caused by an evoked compound action potential, and, via external programmer <NUM>, instruct IMD <NUM> to recalibrate the electrical stimulation therapy such that the electrical stimulation therapy does not evoke a compound action potential in patient <NUM>. In still further examples, IMD <NUM> may automatically perform the operation depicted in <FIG> to periodically recalibrate the electrical stimulation therapy such that the electrical stimulation therapy does not evoke a compound action potential in patient <NUM>. Such periodic recalibration may occur on a weekly, monthly, or yearly basis, for example.

<FIG> is a flowchart illustrating an example operation for delivering SCS therapy according to the techniques of the disclosure. For convenience, <FIG> is described with respect to system <NUM> of <FIG>.

As depicted in <FIG>, processor <NUM> controls stimulation generator <NUM> to deliver electrical stimulation therapy according to one or more electrical stimulation therapy programs to a target tissue site of the spinal column <NUM> of patient <NUM> via electrodes <NUM>, <NUM> interposed along leads <NUM> (<NUM>), e.g. as described with regard to <FIG>. During delivery of electrical stimulation therapy to patient <NUM> according to the one or more electrical stimulation programs (<NUM>), processor <NUM> determines when the delivered electrical stimulation <NUM> evokes a compound action potential and adjusts the stimulation therapy in response to the determination (<NUM>), e.g., as described with regard to <FIG>.

In response to detecting an evoked compound action potential, IMD <NUM> reduces the magnitude of the amplitude of the electrical stimulation therapy program to a default or preprogrammed magnitude and resumes delivery of electrical stimulation therapy (<NUM>). For example, IMD <NUM> may reduce the amplitude by <NUM>%, <NUM>%, or <NUM>% of its previous value (e.g., such that the amplitude is <NUM>%, <NUM>%, <NUM>% of its previous magnitude). In other examples, IMD <NUM> may reduce the amplitude by a predetermined amount. In still further examples, IMD <NUM> may reduce one or more parameters in addition to, or as an alternative to, reducing the amplitude. For example, for a current-controlled system, IMD <NUM> reduces the current amplitude to a default or preprogrammed magnitude. Similarly, in an example of a voltage-controlled system, IMD <NUM> reduces the voltage amplitude to a default magnitude. In some examples, prior to resuming the delivery of the electrical stimulation therapy at the reduced amplitude, IMD <NUM> waits for a predetermined amount of time, and during this time, IMD <NUM> does not deliver therapy to patient <NUM>. Typically, the predetermined amount of time is in the order of minutes, e.g., approximately <NUM> minute, approximately <NUM> minutes, approximately <NUM> minutes, etc..

IMD <NUM>, via one or more sensors, determines whether electrical stimulation therapy according to an electrical stimulation therapy program at the default magnitude, still evokes a compound action potential in the tissue of patient <NUM> (<NUM>). In some examples, processor <NUM> of IMD <NUM> controls delivery electrical stimulation therapy according to the reduced amplitude for a limited duration, such as by delivering a single pulse of the electrical stimulation. In another example, IMD <NUM>, via electrodes <NUM>, <NUM>, determines whether the electrical stimulation causes an electrical parameter of the target tissue site of patient <NUM> to be greater than a predetermined threshold correlated to a likelihood of evoking compound action potentials in the tissue site of patient <NUM>. In other words, IMD <NUM> may sense an electrical parameter of the target tissue site of patient <NUM>, such as one of a voltage or a current. IMD <NUM> may determine whether the electrical parameter is greater than the predetermined threshold. In some examples, the predetermined threshold is a magnitude of the electrical parameter a value that is slightly less than the electrical energy required to evoke a compound action potential in the target tissue of patient <NUM> (e.g., <NUM>% less, <NUM>% less, <NUM>% less, etc.).

If IMD <NUM> determines that the electrical stimulation evokes a compound action potential (e.g., "YES" block of <NUM>), IMD <NUM> further reduces the magnitude of the electrical stimulation therapy program and returns to step <NUM>. For example, if IMD <NUM> determines that electrical stimulation therapy according to an amplitude that is <NUM>% of a previous maximum amplitude evokes a compound action potential, IMD <NUM> may deliver electrical stimulation therapy according to an amplitude that is <NUM>% of a previous maximum amplitude and determine whether this electrical stimulation therapy evokes a compound action potential. This cycle is repeated until IMD <NUM> determines that the magnitude of the electrical stimulation therapy program does not evoke a compound action potential in the tissue of patient <NUM> (e.g. "NO" block of <NUM>). For example, if IMD determines that electrical stimulation therapy according to the amplitude that is <NUM>% of the previous maximum amplitude still evokes a compound action potential, IMD <NUM> may deliver electrical stimulation therapy according to an amplitude that is <NUM>% of the previous maximum amplitude and determine whether this electrical stimulation therapy evokes a compound action potential. While the example of <FIG> is described with respect to adjustment of the stimulation amplitude, in other examples, other stimulation parameters, such as pulse width or pulse frequency, may be adjusted.

At this point, IMD <NUM> slightly increases the magnitude of the electrical stimulation therapy program (<NUM>) and determines, via the one or more sensors, whether the electrical stimulation therapy program evokes a compound action potential in the tissue of patient <NUM> (<NUM>). As described above, in some examples, this gradual adjustment is an incremental or decremental adjustment, such as with a step function. In other examples, the gradual adjustment is continuous adjustment that is a substantially smooth increase or decrease in the value of the parameter. If the magnitude of the electrical stimulation therapy program does not evoke a compound action potential in the tissue of patient <NUM> (e.g. "NO" block of <NUM>), then IMD returns to step <NUM> and slightly increases the magnitude of the electrical stimulation therapy program (<NUM>). This cycle continues until IMD <NUM> determines that the magnitude of the electrical stimulation therapy program does evoke a compound action potential in the tissue of patient <NUM> (e.g. "YES" block of <NUM>).

By titrating the electrical stimulation therapy in the above-described manner, IMD <NUM> may determine the highest value for the one or more parameters defining the electrical stimulation therapy that does not evoke a compound action potential. For example, IMD <NUM> may determine a maximum or relatively large current amplitude (for a current-controlled system) or a maximum or relatively large voltage amplitude (for a voltage-controlled system) that does not evoke a compound action potential in the target tissue site of patient <NUM>. Accordingly, IMD <NUM> selects a value for the one or more parameters defining the electrical stimulation therapy that does not evoke a compound action potential (<NUM>) and resumes delivery of the electrical stimulation therapy according to the highest value for the one or more parameters (<NUM>). As one example, IMD <NUM> may determine a new amplitude for the electrical stimulation therapy by applying a ratio (e.g., from <NUM> to <NUM>) or a percentage (e.g., from <NUM>% to <NUM>%) to the previous amplitude of the electrical stimulation therapy to select an amplitude for the electrical stimulation therapy that is substantially below a threshold amplitude that evokes a compound action potential. In some examples, the ratio or percentage is a ratio or percentage of a first electrical stimulation amplitude that evoked a compound action potential. In other examples, the ratio or percentage is a ratio or percentage of a previous electrical stimulation amplitude that did not evoke a compound action potential. Generally, the ratio or percentage is different for each patient. In some examples, the patient provides feedback via external programmer <NUM> to adjust the value of the ratio or percentage to prevent sensations of paresthesia during subsequent electrical stimulation therapy as the electrical stimulation therapy changes over time.

<FIG> is a flowchart illustrating an example operation for delivering SCS therapy according to the techniques of the disclosure. For convenience, <FIG> is described with respect to <FIG> and <FIG>. The operations of <FIG> are substantially similar to the operations described above with respect to <FIG>.

In response to receiving a signal indicative of a compound action potential, IMD <NUM> suspends delivery of electrical stimulation therapy (<NUM>). IMD <NUM> waits for a predetermined amount of time, and during this time, IMD <NUM> does not deliver therapy to patient <NUM> (<NUM>). In some examples, the predetermined amount of time is in the order of seconds or minutes, e.g., approximately <NUM> second, approximately <NUM> seconds, approximately <NUM> seconds, approximately <NUM> minute, approximately <NUM> minutes, approximately <NUM> minutes, etc. After the predetermined amount of time has elapsed, IMD <NUM> resumes delivery of the electrical stimulation therapy (<NUM>). In some examples, IMD <NUM> resumes delivery of the electrical stimulation therapy according to the same electrical stimulation parameter set. In other examples, IMD <NUM> adjusts one or more parameters defining the electrical stimulation therapy, in a manner similar to that described above, prior to resuming delivery of the electrical stimulation therapy.

Claim 1:
A medical device system comprising:
a stimulation generator configured to deliver electrical stimulation to a patient;
one or more sensors configured to sense compound action potentials in a tissue of the patient evoked by the electrical stimulation therapy; and
a processor configured to:
control delivery of an electrical stimulation therapy from the stimulation generator to the patient according to at least one therapy program, wherein the electrical stimulation therapy is configured to provide pain relief to the patient without substantially resulting in paresthesia perceived by the patient;
determining, using the one or more sensors, that an evoked compound action potential occurs and suspending delivery of the electrical stimulation therapy for a predetermined amount of time;
resume delivery of the electrical stimulation therapy after the predetermined amount of time; and
periodically adjust one or more stimulation parameters of the electrical stimulation therapy delivered to the patient in response to further detected compound action potentials after expiration of the predetermined time period and after resuming delivery of the electrical stimulation therapy, wherein the adjustment to the one or more stimulation parameters of the electrical stimulation therapy is configured to eliminate action potentials in tissue of the patient evoked by the delivered electrical stimulation.