ECAP sensing for high frequency neural stimulation

Abstract

Techniques for implementing adaptive adjustment of parameters of high frequency electrical stimulation using electrically evoked compound action potentials (ECAPs) are disclosed. In one example, a medical device delivers electrical stimulation therapy comprising an electrical stimulation burst to a patient, where the electrical stimulation burst comprises a pulse frequency greater than or equal to 500 hertz. After delivering the electrical stimulation burst, the medical device stops delivery of the high frequency electrical stimulation therapy for a predetermined period of time. During the predetermined period of time, the medical device senses an ECAP from the patient and determines a value of a parameter that at least partially defines the electrical stimulation burst based on the sensed ECAP. In response to the predetermined period of time elapsing, the medical device resumes delivery of the high frequency electrical stimulation in accordance with the determined parameter.

Description

TECHNICAL FIELD

[0001] The present disclosure relates generally to medical treatment, and more particularly to electrical stimulation therapy. BACKGROUND

[0002] Medical devices, including implantable medical devices (IMDs), can be used to treat a variety of medical conditions. For example, medical electrical stimulation devices can deliver electrical stimulation therapy to a patient via external and / or implanted electrodes. The electrical stimulation therapy can include stimulating neural tissue, muscle tissue, the brain, the heart, or other tissue in the patient. In some examples, the electrical stimulation device is implanted entirely within the patient. For example, an implantable electrical stimulation device can include an implantable electrical stimulation generator and one or more implantable leads with electrodes. Alternatively, the electrical stimulation device can include a leadless stimulator. In some cases, the implantable electrodes can be coupled to an external electrical stimulation generator via one or more percutaneous leads or a fully-implanted lead with a percutaneous lead extension.

[0003] Medical electrical stimulators have been proposed for alleviating a variety of symptoms or conditions, such as chronic pain, tremor, Parkinson's disease, depression, epilepsy, migraine headaches, urinary or fecal incontinence, pelvic pain, sexual dysfunction, obesity, and gastroparesis. Electrical stimulators can be configured to deliver electrical stimulation therapy via leads that include electrodes that can be implanted proximate a patient's spinal cord, pelvic nerves, gastrointestinal organs, sacral nerves, peripheral nerves, or within the patient's brain. Stimulation proximate the spinal cord, proximate the sacral nerves, within the brain, and proximate peripheral nerves are commonly referred to as spinal cord stimulation (SCS), sacral neuromodulation (SNM), deep brain stimulation (DBS), and peripheral nerve stimulation (PNS), respectively. SUMMARY

[0004] Generally, the present disclosure describes techniques for implementing adaptive adjustment of parameters defining high frequency electrical stimulation pulses using an electrically evoked compound action potential (ECAP). A sensed feature value of the ECAP can be employed to control titration of the amplitude of a low frequency spinal cord neuromodulation (SCS) system in order to maintain a desired level of paresthesia sensation in the patient. Low frequency stimulation systems generally deliver stimulation pulses at a pulse frequency less than 500 hertz. However, patients using low frequency systems can experience inconsistent or uneven sensations caused by subtle shifts in the distance between the stimulation electrodes and the spinal cord.

[0005] High frequency stimulation generally involves delivering stimulation pulses at a pulse frequency greater than or equal to 500 hertz. High frequency stimulation can employ other mechanisms of action for therapeutic delivery to a patient as compared to low frequency stimulation. ECAP feedback can still be used to control parameters of high frequency stimulation. However, high frequency stimulation pulses can mask ECAP signals, hindering detection of ECAP signals from a target nerve. As such, techniques for controlling low frequency stimulation parameters in conjunction with ECAP feedback can be ineffective for deployment in high frequency stimulation systems.

[0006] The systems, devices, and techniques disclosed herein provide for high frequency stimulation that can also employ ECAPs to adaptively adjust parameters defining pulses of high frequency electrical stimulation (e.g., stimulation at a pulse frequency greater than or equal to 500 hertz). In one example, a medical device delivers high frequency stimulation in the form of a burst of electrical stimulation pulses, and has a pause in high frequency electrical stimulation between each burst. By temporarily pausing high frequency stimulation for a predetermined amount of time, the medical device can sense an ECAP response from a target nerve during this amount of time and without interference from the delivered pulses. In this way, the medical device can use the sensed ECAP to adjust a value of one or more parameters defining high frequency stimulation (e.g., for subsequent pulses). In some examples, the last pulse in a burst is different from the previous pulses in the burst and is configured to elicit a detectable ECAP. Additionally or alternatively, the medical device can deliver low frequency electrical stimulation during the pause in high frequency stimulation. One or more pulses of the low frequency stimulation can elicit a detectable ECAP signal and / or maintain therapeutic efficacy for the patient during the pause.

[0007] Accordingly, by using the techniques described herein, a medical device can pause delivery of high frequency electrical stimulation in order to allow time for the medical device to detect an ECAP signal that can be used to adjust the high frequency electrical stimulation. During pulse delivery, the ECAP signal can not otherwise be detectable because the large amplitude of the delivered pulses from the high frequency electrical stimulation can mask the ECAP signal. Further, a medical device as described herein can deliver low frequency electrical stimulation while pausing high frequency electrical stimulation and sensing an ECAP signal resulting from one or more pulses of the low frequency stimulation, thereby maintaining therapeutic efficacy for the patient while sensing the ECAP. A medical device as described herein can deliver enough pulses for high frequency electrical stimulation while also detecting an ECAP response from the patient during brief pauses in pulse delivery, thereby allowing titration of a value of one or more parameters defining pulses of the high frequency electrical stimulation therapy using sensed values of characteristics of the ECAP.

[0008] In one example, the disclosure describes a method comprising: delivering, by a medical device, electrical stimulation therapy comprising a first electrical stimulation burst to a patient, wherein the first electrical stimulation burst comprises a first pulse frequency greater than or equal to 500 hertz; after delivering the first electrical stimulation burst, stopping, by the medical device, delivery of the electrical stimulation therapy for a predetermined time period; during the predetermined time period, sensing, by the medical device, an evoked compound action potential (ECAP) signal from tissue of the patient; determining, by the medical device and based on a characteristic value of the ECAP signal, a value of at least one parameter that at least partially defines a second electrical stimulation burst, wherein the second electrical stimulation burst comprises a second pulse frequency greater than or equal to 500 hertz; and in response to the predetermined time period having elapsed, delivering the second electrical stimulation burst according to the value of the at least one parameter that at least partially defines the second set of pulses.

[0009] In another example, the disclosure describes a medical device configured to: deliver electrical stimulation therapy comprising a first electrical stimulation burst to a patient, wherein the first electrical stimulation burst comprises a first pulse frequency greater than or equal to 500 hertz; after delivering the first electrical stimulation burst, stop delivery of the electrical stimulation therapy for a predetermined time period; during the predetermined time period, sense an evoked compound action potential (ECAP) signal from tissue of the patient; determine, based on a characteristic value of the ECAP signal, a value of at least one parameter that at least partially defines a second electrical stimulation burst, wherein the second electrical stimulation burst comprises a second pulse frequency greater than or equal to 500 hertz; and in response to the predetermined time period having elapsed, deliver the second electrical stimulation burst according to the value of the at least one parameter that at least partially defines the second set of pulses.

[0010] In another example, the disclosure describes a non-transitory computer- readable medium comprising instructions that, when executed, are configured to cause a processing circuit of an implantable medical device to: control a stimulation generator of the implantable medical device to deliver electrical stimulation therapy comprising a first electrical stimulation burst to a patient, wherein the first electrical stimulation burst comprises a first pulse frequency that is greater than or equal to 500 hertz; after delivering the first electrical stimulation burst, control the stimulation generator to stop delivery of the electrical stimulation therapy for a predetermined time period; during the predetermined time period, sense an evoked compound action potential (ECAP) signal from tissue of the patient; determine a value of at least one parameter at least partially defining a second electrical stimulation burst based on a characteristic value of the ECAP signal, wherein the second electrical stimulation burst comprises a second pulse frequency that is greater than or equal to 500 hertz; and in response to the predetermined time period elapsing, control the stimulation generator to deliver the second electrical stimulation burst according to the value of the at least one parameter at least partially defining the second set of pulses.

[0011] 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. BRIEF DESCRIPTION OF DRAWINGS

[0012] Figure 1 FIG. 1 is a schematic diagram illustrating an example implantable stimulation system including a pair of implantable stimulation electrode arrays carried by an implantable lead.

[0013] Figure 2 FIG. 2 is a functional block diagram illustrating example components of an IMD, such as the IMD shown in FIG. 1. Figure 1 FIG. 3 is a functional block diagram illustrating example components of an external programmer, such as the external programmer shown in FIG. 1.

[0014] Figure 3 FIG. 4 is a functional block diagram illustrating example components of an external programmer and an IMD, such as the external programmer and the IMD shown in FIG. 1. Figure 1 FIG. 5 is a graph illustrating example electrical stimulation bursts in accordance with the techniques of this disclosure.

[0015] Figure 4A , 4B FIGS. 5A, 5B, and 5C are graphs illustrating example electrical stimulation bursts in accordance with the techniques of this disclosure.

[0016] Figure 5 FIG. 6 is a graph illustrating example electrical stimulation bursts and a signal sensed from a patient’s response in accordance with the techniques of this disclosure.

[0017] Figure 6 FIG. 7 is a flowchart illustrating operations in accordance with the techniques of this disclosure.

[0018] In all of the drawings and descriptions, like reference numerals refer to like elements. DETAILED DESCRIPTION

[0019] The present disclosure includes systems, devices, and methods related to adjusting electrical stimulation parameter values that define high frequency electrical stimulation delivered to a patient. In a therapy or intervention type of application, a patient can receive electrical stimulation therapy to alleviate a variety of symptoms or conditions. In some cases, a physician or clinician can manually adjust electrical stimulation parameters based on patient feedback, such as a patient’s perception of a reduction in pain levels or any changes in symptoms. However, patient feedback can be inconsistent over time and is also subjective. In this way, it can be difficult to determine the most appropriate stimulation parameters to alleviate a patient’s symptoms or conditions and provide improved system performance (e.g., efficient energy utilization and targeted therapy delivery).

[0020] In the past, spinal cord stimulation (SCS) by patients consisted of low frequency periodic electrical pulses delivered to the patient’s dorsal column for the purpose of inducing paresthesia. As described herein, “low frequency electrical stimulation” refers to electrical stimulation that includes a pulse frequency of less than 500 hertz, which can typically result in paresthesia in a patient. The paresthesia is used to mask pain experienced in a particular region of the body, such as the lower back or legs. The sensory signal, in this case periodic electrical pulses from a spinal cord stimulator or the pain signal itself, is relayed to the brain via the dorsal column of the spinal cord. The dorsal column is composed of multiple sensory fiber types, generally classified by fiber thickness and their associated signal propagation velocity. The very thick (13-20 pm) Aa fibers have an action potential propagation velocity of approximately 100 m / s and are associated with proprioception. The thick diameter (6-12 pm) Ab fibers are heavily myelinated with an action potential propagation velocity of close to 60 m / s. Paresthesia achieved with SCS is believed to result from modulation of Ab fibers. The thinner diameter (2-5 pm), myelinated Ad fibers have an action potential propagation velocity of approximately 10 m / s. The unmyelinated C fibers (0.2 pm - 1.5 pm) transmit signals at 2 m / s. Both Ad and C fibers are responsible for transmitting pain signals to the brain, with Ad and C fibers contributing to sharp and burning pain characteristics, respectively.

[0021] There are many factors that can affect signal propagation along the spinal cord. Examples include certain chemical factors, disease states, or the presence or absence of electrical stimulation. In some cases, it is desirable to adjust a therapeutic intervention to a patient based on measured spinal cord signal propagation characteristics. One approach for handling these factors, which can vary over time, includes detecting ECAP signals. In various examples, electrical stimulation is applied to a patient’s spinal cord at a particular location, and the resulting ECAPs can be detected and recorded. Sensing and measurement of these ECAP signals is not limited to the spinal cord, and can also be recorded in other locations besides the spinal cord, such as in peripheral nerves, or for example, from within the brain.

[0022] In view of these factors, other parameters for delivering SCS therapy different from historically applied SCS therapy can provide efficacy in the treatment of a particular patient. For example, high frequency SCS systems deliver stimulation with a much faster pulse frequency than traditional SCS therapy provided at, for example, 50 hertz. As described herein, "high frequency electrical stimulation" refers to electrical stimulation that includes a pulse frequency greater than or equal to 500 hertz. A determined advantage of applying high frequency electrical stimulation therapy is that patients have reported a reduction or elimination of pain sensation and without the associated paresthesia typically experienced when using low frequency SCS therapy. However, at least one disadvantage of these high frequency pulses is that the electrical pulse trains delivered to the patient at high frequencies can mask any ECAP signals. Thus, when a medical device is delivering high frequency electrical stimulation to a patient, the medical device can not be able to detect ECAPs, thereby hindering the medical device's use of ECAP responses to control titration of values of one or more parameters defining the pulses of the high frequency electrical stimulation.

[0023] As discussed herein, systems, devices, and methods for adjusting one or more parameters of high frequency electrical stimulation based on detected ECAPs are described. ECAPs can be evoked in response to the application of one or more electrical stimulation pulses defined according to a set of stimulation parameters. Adjusting electrical stimulation parameters based on detected ECAPs can provide more objective information than patient feedback. Moreover, ECAP detection can allow a system to provide closed loop stimulation control. Incorporating ECAPs into the adjustment and / or titration of stimulation parameters can enable a stimulation system to provide stimulation therapy using less energy, improved patient perception of stimulation, more targeted stimulation delivery to desired tissue, and / or improved treatment efficacy compared to techniques that do not incorporate ECAP detection. In some examples, dorsal column stimulation therapy (e.g., a type of spinal cord stimulation) or other electrical stimulation therapy is provided according to a treatment program that defines values of stimulation parameters such as current or voltage amplitude, pulse frequency, pulse width, burst frequency, and / or pulse shape that are selected to provide a level of therapy such as a reduction or elimination of pain experienced by a patient. In some examples, spinal cord stimulation can also include stimulation of dorsal nerve roots. Moreover, stimulation is not limited to stimulation of the spinal cord and can be applied to peripheral nerves or their end organs. Moreover, peripheral stimulators need not be implanted devices and they can also include non-electrical stimulation (e.g., mechanical, thermal).

[0024] The technology, systems, and devices disclosed herein can provide high frequency stimulation that employs ECAP to adaptively adjust parameters defining the high frequency electrical stimulation (e.g., stimulation with a pulse frequency greater than or equal to 500 hertz). In one example, a medical device delivers high frequency stimulation in the form of a train of electrical stimulation pulses, and has a pause in the high frequency electrical stimulation between each train. By temporarily pausing the high frequency stimulation for a predetermined amount of time, the medical device can sense an ECAP response from a target nerve during this amount of time, allowing the medical device to use the sensed ECAP to adjust a value of one or more parameters defining the pulses of the high frequency stimulation. In some examples, the medical device uses a last pulse in the train, which is different from the other pulses in the train and is configured to elicit a detectable ECAP. Additionally or alternatively, the medical device can deliver low frequency electrical stimulation (e.g., one or more pulses) during the pause in the high frequency stimulation in order to elicit an ECAP response and / or maintain therapeutic efficacy in the patient during the pause. Thus, by using the technology described herein, a medical device can be enabled to deliver high frequency electrical stimulation and sense an ECAP response during a pause in the high frequency stimulation, such that the device can use the ECAP signal as feedback to adjust one or more parameters of the high frequency electrical stimulation for subsequent delivery. Without such a pause in the delivery of the high frequency electrical stimulation, the ECAP signal can not be detectable and usable for feedback.

[0025] The detected ECAP can provide more objective information for adjusting the parameter values defining the subsequent high frequency stimulation pulses, as compared to patient feedback. Additionally, the technology set forth herein enables a device to employ ECAP detection as a closed loop control of a system delivering high frequency electrical stimulation. By incorporating detection of the ECAP signal into feedback for adjusting stimulation parameters and / or titration, a medical device can deliver high frequency electrical stimulation that provides more targeted stimulation delivery to a desired tissue, improved therapeutic efficacy, and / or less power consumption as compared to techniques that do not incorporate ECAP detection. An electrical sensing system, such as an electrical sensing system within an implantable medical device, or in electrical communication with such an implantable medical device, can perform the ECAP detection described herein. The sensing system can include one or more electrodes positioned a distance away from a site at which electrical stimulation is applied.

[0026] In some examples, the detection or lack of detection of the presence of an ECAP in response to stimulation provided with a particular set of therapy parameters is used to program the initial stimulation therapy parameters provided to a patient via an implantable medical device. In other examples, the detection of an ECAP in response to stimulation provided with a particular set of therapy parameters can be used to automatically adjust existing stimulation therapy parameters. The presence or absence of an ECAP or a characteristic value of an ECAP in response to a set of stimulation therapy parameters can be used to control programming and adjustment of parameters of high frequency electrical stimulation.

[0027] For example, an IMD (or other medical device) can begin providing stimulation according to an initial set of therapy parameters (e.g., including a relatively high frequency, such as 15 kHz). The IMD detects an ECAP signal generated by one or more nerve fibers as a result of the applied stimulation, and compares a characteristic value of the ECAP signal to a target characteristic value for the ECAP. Based on the comparison result, the IMD can adjust one or more parameters of the stimulation therapy in order to reduce the difference between the characteristic value of the ECAP signal and the target characteristic value for the ECAP. For example, the IMD can reduce the amplitude and / or pulse frequency of the applied stimulation pulses to generate a new set of therapy parameters for subsequent therapy. The IMD can then apply the new stimulation therapy to the patient, sense a resulting ECAP generated as a result of the application of the new therapy, and can further generate a new set of therapy parameters for therapy according to this closed-loop control scheme.

[0028] In some examples, a given stimulation therapy can be applied to a patient, and the resulting ECAP signal is sensed and analyzed to determine whether the patient's response to that same particular set of stimulation parameters has changed. In some examples, the ECAP signal is detected in response to a current stimulation therapy program in a continuous manner. For example, the ECAP signal can be detected every few seconds, every minute, every few minutes, every hour, every day, or every week. In some examples, the medical device can initiate and detect the ECAP signal in response to a change in another sensed physiological parameter. For example, the medical device can pause high frequency stimulation to detect the ECAP signal when there is a change in the patient's activity level or posture that can indicate that the value of one or more parameters of the high frequency stimulation pulses should be changed (e.g., because the electrodes can have moved relative to the target nerve). These changes in the patient's activity level and / or posture can be sensed and / or determined by the same device that is providing stimulation therapy to the patient, or by a device that is not the same device that is providing stimulation therapy to the patient.

[0029] A patient as used herein generally refers to a human patient, but is not limited to a human, and can include an animal. Various references to a "test patient" as used herein can include an animal for receiving a test stimulation pattern and for collecting data related to stimulation testing according to the various techniques described herein.

[0030] Figure 1This is a schematic diagram illustrating an exemplary implantable stimulation system 10, which includes a pair of implantable electrode arrays in the form of stimulation leads 16A and 16B. While the techniques described in this disclosure are generally applicable to a variety of medical devices, including external and implantable medical devices (IMDs), for illustrative purposes, the application of such techniques to IMDs will be described, and more specifically, to implantable electrical stimulators, such as neurostimulators. More specifically, for illustrative purposes, this disclosure relates to implantable spinal cord stimulation (SCS) systems, but is not limited thereto, and also relates to other types of medical devices.

[0031] like Figure 1 As shown, system 10 includes an IMD 14 and an external programmer 20, which are shown in conjunction with patient 12. Figure 1 In the example, the IMD 14 is an implantable electrical stimulator configured for spinal cord stimulation (SCS), for example, to relieve chronic pain or other symptoms. Similarly, although... Figure 1 An implantable medical device is shown, but other embodiments may include an external stimulator, such as a lead with a percutaneous implantation or an implantable lead with a percutaneous lead extension. Stimulation energy is delivered from the IMD 14 to the spinal cord 18 of the patient 12 via one or more electrodes disposed on implantable leads 16A and 16B (collectively, “leads 16”). In some applications, such as spinal cord stimulation (SCS) for the treatment of chronic pain, adjacent implantable leads 16 may have longitudinal axes that are substantially parallel to each other.

[0032] although Figure 1 While involving SCS treatment, system 10 may alternatively target any other condition that may benefit from stimulation therapy. For example, system 10 may be used to deliver stimulation to one or more tissues to treat tremor, Parkinson's disease, epilepsy, urinary or fecal incontinence, sexual dysfunction, obesity, or gastroparesis. In this manner, system 10 may be configured to provide treatment using deep brain stimulation (DBS), pelvic floor stimulation, gastric stimulation, or any other form of stimulation therapy. Furthermore, patient 12 is typically a human patient.

[0033] Each of the leads 16 may include electrodes, and parameters of the procedure for controlling the delivery of stimulation therapy via the IMD 14 may include information identifying which electrodes have been selected to deliver stimulation according to the stimulation procedure, the polarity of the selected electrodes (i.e., the electrode configuration for the procedure), and the voltage or current amplitude, pulse rate, and pulse width of the stimulation delivered by the electrodes. For illustrative purposes, the delivery of stimulation pulses will be described. However, stimulation may be delivered in other forms, such as continuous waveforms. Procedures for controlling the delivery of other treatments via the IMD 14 may include other parameters, such as the dose, rate, etc., for drug delivery.

[0034] exist Figure 1In the illustrated example, the lead 16 carries one or more electrodes positioned adjacent to a target tissue of the spinal cord. The one or more electrodes can be disposed at a distal tip of the lead 16 and / or at other locations along the middle of the lead. The lead 16 can be implanted and coupled to the IMD 14. Alternatively, as noted above, the lead 16 can be implanted and coupled to an external stimulator, such as through a percutaneous port. In some cases, the external stimulator can be a trial or screening stimulation used in a temporary fashion to assess potential efficacy to help consider chronic implantation for the patient. In further embodiments, the IMD 14 can be a leadless stimulator having one or more electrode arrays disposed on a housing of the stimulator rather than leads extending from the housing.

[0035] Stimulation can be delivered via a selected combination of electrodes carried in one or both of the leads 16, such as in a bipolar, unipolar, or multipolar combination. The target tissue can be any tissue affected by electrical stimulation energy, such as electrical stimulation pulses or waveforms. Such tissues include nerves, smooth muscle, and skeletal muscle. In the illustrated example, the target tissue is the spinal cord 18. For example, stimulating the spinal cord 18 can prevent pain signals from traveling through the spinal cord and to the brain of the patient. The patient 12 can perceive the interruption of the pain signals as a reduction in pain and thus as an effective therapeutic outcome. Figure 1

[0036] The deployment of electrodes via leads 16 is described for illustrative purposes, but electrode arrays can be deployed in different ways. For example, a housing associated with a leadless stimulator can carry electrode arrays, such as rows and / or columns (or other patterns), to which multiplexing operations can be applied. Such electrodes can be arranged as surface electrodes, ring electrodes, or protrusions. As another alternative, the electrode arrays can be formed by rows and / or columns of electrodes on one or more paddle leads. In some embodiments, the electrode arrays can include electrode segments that can be arranged at respective locations around a perimeter of a lead, such as in the form of one or more segmented rings around a circumference of a cylindrical lead. Other electrode and lead configurations can be suitable for use with the present disclosure so long as they enable the IMD 14 to electrically stimulate and sense from a target tissue.

[0037] In the illustrated example, the lead 16 carries one or more electrodes positioned adjacent to a target tissue of the spinal cord. The one or more electrodes can be disposed at a distal tip of the lead 16 and / or at other locations along the middle of the lead. The lead 16 can be implanted and coupled to the IMD 14. Alternatively, as noted above, the lead 16 can be implanted and coupled to an external stimulator, such as through a percutaneous port. In some cases, the external stimulator can be a trial or screening stimulation used in a temporary fashion to assess potential efficacy to help consider chronic implantation for the patient. In further embodiments, the IMD 14 can be a leadless stimulator having one or more electrode arrays disposed on a housing of the stimulator rather than leads extending from the housing. Figure 1 ​In the example of treating pain, the stimulation energy is delivered by IMD 14 to the spinal cord 18 to reduce the amount of pain perceived by patient 12. As described above, IMD 14 can be used with a variety of different pain therapies, such as peripheral nerve stimulation (PNS), peripheral nerve field stimulation (PNFS), DBS, cortical stimulation (CS), sacral neuromodulation (SNM), pelvic floor stimulation, gastric stimulation, etc. The electrical stimulation delivered by IMD 14 can take the form of electrical stimulation pulses or continuous stimulation waveforms, and can be characterized by a controlled voltage level or a controlled current level, as well as a pulse width and a pulse rate (i.e., pulse frequency) in the case of stimulation pulses.

[0038] In some examples, IMD 14 can deliver stimulation therapy according to one or more programs. A program defines one or more parameters that define an aspect of therapy delivered by IMD 14 according to the program. For example, a program that controls IMD 14 to deliver stimulation in the form of pulses can define the voltage or current pulse amplitude, pulse width, and pulse rate of the stimulation pulses delivered by IMD 14 according to the program. The program can also define the electrode combination used to deliver the stimulation pulses, including electrode polarity. Further, therapy can be delivered according to multiple programs, where the multiple programs are contained within each of multiple groups.

[0039] During treatment of patient 12 using IMD 14, movement of patient 12 between different postural states can affect the ability of IMD 14 to deliver a consistent, effective or optimally perceived therapy. For example, when patient 12 bends over, lead 16 can migrate toward IMD 14, causing displacement of the electrodes and possibly disrupting the delivery of effective therapy. The stimulation energy delivered to the target tissue can be reduced due to electrode movement, resulting in decreased efficacy in alleviating symptoms such as pain. As another example, when patient 12 lies down, lead 16 can be compressed toward spinal cord 18. This compression can cause an increase in the amount of stimulation energy delivered to the target tissue. In this case, the amplitude of the stimulation therapy can be reduced to avoid causing additional pain or unusual sensations to patient 12, which can be perceived as an undesirable side effect that detracts from overall efficacy.

[0040] In addition, a change in posture state can present a change in symptoms or symptom levels (e.g., pain levels). Due to the change in posture and / or the change in activity level associated with the patient's posture state, a decrease in efficacy can occur due to an increase or decrease in the coupling of the stimulation energy to the target tissue. To avoid or reduce the possible disruption of effective therapy due to a change in posture state, IMD 14 can include a posture state module that detects the posture state of patient 12 and causes IMD 14 to automatically detect ECAP signals in response to changes in the posture state. Based on the detected ECAP signals, IMD 14 determines whether adjustments to stimulation parameters are recommended or otherwise appropriate. For example, the posture state module can include a posture state sensor, such as an accelerometer, that detects when patient 12 is lying down, standing, or otherwise changing posture. In some examples, instead of or in addition to the patient's posture, the posture state detected by the posture state sensor can also include an activity level.

[0041] The posture state module can include, for example, one or more accelerometers that detect when patient 12 assumes a posture state that can be appropriate for reducing the stimulation amplitude, e.g., when patient 12 is lying down. In some examples, the IMD can automatically reduce the stimulation amplitude so that patient 12 does not have to do so manually. The IMD can then detect ECAP signals in response to the adjusted stimulation parameters to determine whether the adjustment was effective. In other examples, the IMD can detect ECAP signals in response to the stimulation when a change in posture is detected prior to making an adjustment to the stimulation parameters. IMD 14 can analyze the detected ECAP signals to determine one or more characteristic values of the ECAP signals (e.g., the amplitude of one or more peaks of the detected ECAP or the area under the curve of one or more peaks of the ECAP) and then determine an appropriate adjustment to one or more values of the stimulation parameters. Exemplary posture states can include "upright," "upright and active," "lying down," etc.

[0042] As will be described in greater detail below, in some examples, IMD 14 can be configured to automatically adjust the stimulation amplitude upon detecting that patient 12 has changed position. In some examples, in response to detection of a change in position, IMD 14 determines an appropriate adjustment to the stimulation parameters. In some examples, the determination can include detecting an ECAP signal based on the current stimulation parameters and making an adjustment to one or more stimulation parameters based on a determined characteristic value of the detected ECAP signal. In other examples, IMD 14 can select a new set of stimulation parameters stored in memory based on a previously detected ECAP for the same position.

[0043] In some examples, the stimulation parameters can be configured to change at a rate suitable to prevent adverse effects, e.g., effects caused by compression of the lead 16 toward the spinal cord 18 when the patient 12 lies down. In some examples, the IMD 14 can be configured to reduce the stimulation amplitude to a first predetermined lower amplitude value substantially immediately upon detection by the IMD 14 that the patient 12 has lain down. The IMD 14 can then evaluate the appropriateness of the new stimulation amplitude based on the ECAP and make further adjustments as needed. In other examples, the IMD 14 can be configured to detect an ECAP signal to the stimulation upon detection that the patient 12 has lain down. Based on the detected ECAP signal, the IMD 14 can adjust one or more stimulation parameters until the desired characteristics of the detected ECAP signal are achieved.

[0044] In response to the posture state indication of the posture state module, the IMD 14 can change the program set, program, stimulation amplitude, pulse width, pulse rate, and / or one or more other parameters, sets, or programs to maintain therapeutic efficacy. For example, when the patient lies down, the IMD 14 can automatically reduce the stimulation amplitude so that the patient 12 does not need to manually reduce the stimulation amplitude. The amount of the automatic reduction can be determined based at least in part on characteristic values of the detected ECAP signal in the new posture state. In some cases, the IMD 14 can communicate with the external programmer 20 to give proposed stimulation changes in response to a change in posture state, e.g., from a first posture state to a second posture state, and receive approval or rejection of the changes from a user, such as the patient 12 or a clinician, before automatically applying the therapeutic changes. In some examples, posture state detection can also be used to provide notifications, such as providing a notification to a caregiver via a wireless link that the patient can have experienced a fall.

[0045] In some examples, the IMD 14 can periodically detect ECAPs generated in response to the current stimulation parameters and adjust the current stimulation parameters if there is a significant change, i.e., greater than a predetermined threshold change, in the characteristic values of the detected ECAP signal relative to target ECAP characteristic values. For example, the IMD 14 can detect and analyze ECAPs every hour, every day, every week, or every month. In some examples, the IMD 14 can initiate a cycle of ECAP signal detection and analysis if a predetermined amount of time has passed since the last ECAP detection. The IMD 14 can reset this time in response to detecting an ECAP signal. In some examples, the IMD 14 can adjust the rate of ECAP detection based on the posture of the patient 12 or in response to a change in the posture of the patient 12. For example, in response to detecting that the patient 12 has changed posture, the IMD 14 can increase or decrease the rate of detecting ECAPs.

[0046] A user, such as a clinician or patient 12, can interact with a user interface of external programmer 20 to program IMD 14. The user interface can include output devices for presenting information and input devices for receiving user input. Programming of IMD 14 generally can refer to the generation and transfer of commands, programs, or other information to control the operation of IMD 14. For example, external programmer 20 can transmit programs, parameter adjustments, program selections, group selections, or other information to control the operation of IMD 14, such as by wireless telemetry. For example, external programmer 20 can transmit parameter adjustments to support therapy changes caused by changes in the posture of patient 12. As another example, a user can select a program or a group of programs. As such, a program can be characterized by electrode combination, electrode polarity, voltage or current amplitude, pulse width, pulse rate, and / or duration. A group of programs can be characterized by multiple programs delivered simultaneously or in an interleaved or round-robin fashion.

[0047] During delivery of stimulation therapy, patient 12 can make a patient therapy adjustment, i.e., an input via an input device of a user interface of a programmer, to one or more parameters of therapy to customize therapy after patient 12 moves to a different posture state or in anticipation of a next posture state. As described in greater detail below, IMD 14 can detect ECAPs in response to the therapy adjustment. In some examples, the detected ECAPs in response to the adjusted therapy can be stored as indicative of effective therapy for a particular patient state. If the same patient state is detected again, IMD 14 can automatically adjust one or more stimulation parameters to achieve an ECAP feature value corresponding to the stored target ECAP feature value. In examples where IMD 14 is in a recording mode to store all patient therapy adjustments associated with a particular patient state, IMD 14 can implement a method to ensure that a patient therapy adjustment is associated with the correct patient state that patient 12 intended when making the therapy adjustment. Patient 12 can assume the patient state multiple times such that there are multiple instances of the sensed patient state. For example, the patient state can be a posture or activity level. In some examples, each time patient 12 assumes a posture state, the patient can enter one or more therapy adjustments.

[0048] In some cases, if the external programmer 20 is primarily intended for use by a physician or clinician, it can be characterized as a physician or clinician programmer. In other cases, if the external programmer 20 is primarily intended for use by the patient, e.g., for entering patient input to specify patient adjustments to one or more therapy parameters, it can be characterized as a patient programmer. A patient programmer is typically accessible to the patient 12 and, in many cases, can be a portable device that can accompany the patient at all times in the patient's daily life. Typically, a physician or clinician programmer can support selection and generation of programs by a clinician for use by the stimulator 14, while a patient programmer can support adjustment and selection of such programs by the patient manually or via other user input media during regular use.

[0049] The IMD 14 can be constructed with a biocompatible housing, such as titanium or stainless steel, or a polymeric material, such as silicone or polyurethane, and implanted in the patient 12 at a site near the pelvis through a surgical procedure. The IMD 14 can also be implanted in the patient 12 at a location that is least noticeable to the patient 12. Alternatively, the IMD 14 can be external, with percutaneously implanted leads. For SCS, the IMD 14 can be located in the lower abdomen, lower back, upper buttocks, or other location to secure the IMD 14. The leads 16 can be tunneled through tissue from the IMD 14 to a target tissue adjacent to the spinal cord 18 for stimulation delivery.

[0050] At the distal end of the lead 16 is one or more electrodes that deliver electrical stimulation from the lead to the tissue. The electrodes can be electrode pads on a paddle lead, round (e.g., ring) electrodes that surround the body of the lead 16, conformable electrodes, cuff electrodes, segmented electrodes (e.g., partial ring electrodes positioned at different circumferential locations around the circumference of the lead), or any other type of electrode capable of forming monopolar, bipolar, or multipolar electrode configurations for therapy. The electrodes can pierce or be attached directly to the tissue itself. Typically, for purposes of illustration, ring electrodes arranged at different axial locations at the distal end of the lead 16 will be described.

[0051] The titration of the amplitude of the low frequency SCS system is controlled using one or more characteristic values of the ECAP in order to maintain even paresthesia sensation in the patient 12. Low frequency stimulation generally includes stimulation pulses with a pulse frequency less than 500 hertz. However, patients using low frequency stimulation can experience inconsistent or uneven sensation caused by slight misalignment of the stimulation electrodes relative to the spinal cord. High frequency stimulation generally includes stimulation pulses with a pulse frequency greater than or equal to 500 hertz. High frequency stimulation can potentially employ other mechanisms of action such that the patient can experience a reduction in pain rather than paresthesia (or with lower levels of paresthesia). High frequency stimulation efficacy can also change with patient movement. However, high frequency stimulation pulses can occur too frequently such that the presence of these delivered pulses masks the ECAP signal, hindering detection of the ECAP signal from the target nerve. Accordingly, techniques for controlling or adjusting high frequency stimulation pulses (and in some examples, low frequency stimulation parameters) in conjunction with ECAP feedback can include pausing high frequency stimulation for a predetermined period of time long enough to detect at least one ECAP signal.

[0052] According to the techniques of this disclosure, the IMD 14 can use ECAPs to adaptively determine (e.g., set or adjust) parameters of high frequency electrical stimulation. In one example, the IMD 14 delivers high frequency stimulation in the form of electrical stimulation pulse trains, and has a pause in high frequency electrical stimulation between each train. By temporarily pausing high frequency stimulation for a predetermined amount of time, the IMD 14 can sense ECAP signals from one or more target nerves of the patient 12 during this amount of time and without interference from high frequency stimulation. Accordingly, the IMD 14 can use the sensed ECAPs to adjust parameters of the high frequency stimulation. In some examples, the IMD 14 delivers a last pulse (e.g., a master pulse) of the train to elicit a detectable ECAP, where the last pulse is different from previous pulses (e.g., primary pulses) within the same train. Additionally or alternatively, the IMD 14 can deliver low frequency electrical stimulation during the pause in high frequency stimulation in order to elicit an ECAP response and / or maintain therapeutic efficacy in the patient during the pause.

[0053] Accordingly, by using the techniques described herein, the IMD 14 can pause delivery of high frequency electrical stimulation in order to allow time for the IMD 14 to detect an ECAP response to the high frequency electrical stimulation that would otherwise be undetectable by other systems that deliver continuous high frequency electrical stimulation. Furthermore, the medical devices as described herein can deliver low frequency electrical stimulation while pausing high frequency electrical stimulation and sensing ECAPs, thereby maintaining therapeutic efficacy in the patient 12 while sensing ECAPs. Accordingly, the medical devices as described herein can avoid one or more high frequency electrical stimulation pulses from masking the ECAP signal of the patient, thereby allowing the sensed ECAPs to be used as a control signal for titrating one or more parameters of the high frequency electrical stimulation therapy.

[0054] Figure 2 This is a functional block diagram showing the various components of the IMD 14. Figure 2 In this example, IMD 14 includes processing circuitry 80, memory 82, switching circuitry 83, stimulation generator 84, posture status module 86, telemetry circuitry 88, power source 90, and sensing circuitry 92. Stimulation generator 84 may form a treatment delivery module. Processing circuitry 83 may control switching circuitry 83, which switches signals to and / or from lead 16 to sensing circuitry 92 and / or stimulation generator 84. Memory 82 may store instructions executed by processing circuitry 80, stimulation treatment data, ECAP characteristic values, posture status information, posture status indications, and any other information regarding treatment or patient 12. Treatment information may be recorded for long-term storage and retrieval by the user, and treatment information may include any data created by or stored in IMD 14. Memory 82 may include a separate memory for storing instructions (including instructions for ECAP analysis), posture status information, treatment adjustment information, previously detected ECAP signals and / or ECAP characteristic values, program history, and any other relevant data or instructions.

[0055] Processing circuitry 80 controls stimulation generator 84 to deliver electrical stimulation via electrode combinations formed by electrodes in one or more electrode arrays. For example, stimulation generator 84 can deliver therapeutic electrical stimulation via electrodes on one or more leads 16 (e.g., electrodes 94A-94D and 96A-86D of corresponding leads 16A and 16B), for example as stimulation pulses or continuous waveforms. Components described as processing circuitry within IMD 14, external programmer 20, or any other device described in this disclosure may each include one or more processors, individually or in any suitable combination, such as one or more microprocessors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), programmable logic circuits, etc.

[0056] The stimulation generator 84 can include stimulation generation circuitry for generating stimulation pulses or waveforms and switching circuitry for switching stimulation between different electrode combinations, e.g., in response to control by the processing circuitry 80. In particular, the processing circuitry 80 can selectively control the switching circuitry to cause the stimulation generator 84 to deliver electrical stimulation to a selected electrode combination and to shift the electrical stimulation in the first or second direction to a different electrode combination as therapy must be delivered to a different location within the patient 12. In other examples, the stimulation generator 84 can include multiple current sources and sinks to drive more than one electrode combination at a time. For example, each electrode can have its own current source and sink that can be selectively activated so that the electrode can pull or sink a controlled amount of current. The electrode configurations, e.g., electrode combinations and associated electrode polarities, can be represented by data stored in memory locations in the memory 82 of, e.g., the IMD 14. The processing circuitry 80 can access the memory locations to determine the electrode combination and control the stimulation generator 84 to deliver electrical stimulation by the indicated electrode combination. To adjust the electrode combination, amplitude, pulse rate, or pulse width, the processing circuitry 80 can instruct the stimulation generator 84 to make the appropriate changes to therapy according to instructions within the memory 82 and overwrite the memory locations to indicate the changed therapy. In other examples, the processing circuitry 80 can utilize two or more memory locations rather than overwriting a single memory location.

[0057] When stimulation is activated, the processing circuitry 80 can access not only the memory locations that specify the electrode combination, but also other memory locations that specify various stimulation parameters such as voltage or current amplitude, pulse width, and pulse rate. The stimulation generator 84, e.g., under control of the processing circuitry 80, then utilizes the electrode combination and parameters in formulating and delivering electrical stimulation to the patient 12.

[0058] According to examples described herein, the processing circuitry 80 can adjust such stimulation parameters to modify the stimulation therapy delivered by the IMD 14 based on a detected ECAP signal of the patient 12. In some examples, the processing circuitry 80 can detect an ECAP signal of the patient 12 that indicates that modification of the stimulation therapy is appropriate, e.g., according to instructions stored in the memory 82. The processing circuitry 80 can access instructions for modifying the stimulation therapy based on the detected ECAP signal, e.g., by changing from a current stimulation program to a program that results in a desired characteristic value of the ECAP, e.g., a characteristic value that achieves a target ECAP characteristic value.

[0059] According to other examples described herein, such stimulation parameters can be adjusted to modify the stimulation therapy delivered by IMD 14 based on a combination of the detected ECAP signals and the detected posture state. In some examples, processing circuitry 80 can detect ECAP signals of patient 12 via sensing circuitry 92 and detect a posture state of patient 12 via posture state module 86. If a change in ECAP signals has been detected (e.g., a change in an ECAP characteristic value), the detected posture state can be used to help processing circuitry 80 determine an appropriate stimulation program in order to achieve a target ECAP characteristic value. For example, memory 82 can include stimulation programs associated with detected posture states that in the past resulted in a target ECAP characteristic value.

[0060] Processing circuitry 80 accesses stimulation parameters in memory 82, e.g., as programs and program sets. After selecting a particular program set, processing circuitry 80 can control stimulation generator 84 to deliver stimulation according to the programs in the set, e.g., simultaneously or in a time-interleaved fashion. A set can include a single program or multiple programs. As previously described, each program can specify a set of stimulation parameters, such as amplitude, pulse width, and pulse rate. In addition, each program can specify a particular electrode combination for delivering stimulation. Likewise, an electrode combination can specify particular electrodes in a single array or multiple arrays, e.g., particular electrodes on a single lead or between multiple leads. Processing circuitry 80 can also control telemetry circuitry 88 to send and receive information to and from external programmer 20. For example, telemetry circuitry 88 can send information to and receive information from programmer 20.

[0061] In some examples, IMD 14 includes posture state module 86, which allows IMD 14 to sense or detect a current patient posture state, e.g., a posture, activity, or any other static position or motion of patient 12. In Figure 2 In examples, posture state module 86 can include one or more accelerometers, such as a three-axis accelerometer, which is capable of detecting a static orientation or vector in three dimensions. The three-axis accelerometer can be a micro-electromechanical system (MEMS) accelerometer. In other examples, posture state module 86 can alternatively or additionally include one or more gyroscopes, pressure transducers, or other sensors to sense a current posture state assumed by patient 12. The posture state information generated by posture state module 86 and processing circuitry 80 can correspond to an activity and / or posture or total level of physical activity (e.g., an activity count based on footfall sounds) undertaken by patient 12, among others.

[0062] Posture state information from posture state module 86 can be stored in memory 82 for later review by a clinician, for adjustment of therapy, for presentation of posture state indications to patient 12 and / or a clinician, e.g., via a user interface display of external programmer 20, or some combination thereof. For example, processing circuitry 80 can record posture state parameter values or outputs of a 3-axis accelerometer and assign the posture state parameter values to a particular predefined posture indicated by the posture state parameter values. In this way, IMD 14 is able to track how often patient 12 remains in a certain posture state. IMD 14 can also store which set or which program was being used to deliver therapy when patient 12 was in a sensed posture state. Further, processing circuitry 80 can also adjust therapy for a new posture state when posture state module 86 indicates that patient 12 has actually changed postures. In some examples, a change in posture can trigger sensing of an ECAP signal. Based on a sensed ECAP from sensing circuitry 92, processing circuitry 80 can determine appropriate adjustments to one or more current stimulation therapy parameters in order to achieve a target ECAP characteristic value. In some examples, a current characteristic value of an ECAP signal can be compared to a target ECAP characteristic value (e.g., a value of a feature or ECAP signal template) that corresponds to effective therapy.

[0063] The processing circuit 80 can analyze the sensed ECAP signal to determine values of different types of features according to the techniques described herein. For example, the sensed ECAP signal can include a first peak amplitude, a second peak amplitude, and a third peak amplitude representing a propagating action potential from the ECAP. An example duration of each peak is about 1 millisecond (ms). For example, a feature of the ECAP can be an amplitude between the first peak and the second peak. Such an amplitude can be readily detected even in the presence of artifacts or electronic drift in the sensed signal. In other examples, a feature can be an amplitude of one of the first, second, or third peaks relative to a neutral or zero voltage. In some examples, a feature can be a sum of two or more of the first, second, or third peaks. In other examples, a feature can be an area under one or more of the first, second, or third peaks. In other examples, a feature of the ECAP can be a ratio of one of the first, second, or third peaks to another of the peaks. In some examples, a feature of the ECAP can be a slope between two points in the ECAP signal, such as between two of the first, second, or third peaks. In other examples, a feature of the ECAP can be a time between two points of the ECAP, such as between two of the first, second, or third peaks. The time between the time of delivery of a stimulation pulse and one point in the ECAP signal can be referred to as a latency of the ECAP, and can be indicative of the type of fiber captured by the control stimulation pulse. The latency of the ECAP can also be a feature evaluated by the processing circuit 80. ECAP signals with lower latencies (e.g., smaller latency values) are indicative of a higher percentage of neural fibers with faster signal propagation, while ECAP signals with higher latencies (e.g., larger latency values) are indicative of a higher percentage of neural fibers with slower signal propagation. In other examples, other features of the ECAP signal can be used.

[0064] The amplitude of the ECAP signal increases with increasing pulse amplitude as long as the amplitude of the stimulation pulse is greater than a threshold value, causing the nerve to depolarize and propagate the signal. A target ECAP feature (e.g., a target ECAP amplitude) can be determined from the ECAP signal detected from the stimulation pulse to deliver effective therapy to the patient. Thus, the ECAP signal is representative of the distance between the stimulation electrode and the nerve for the stimulation parameter values of the stimulation pulse delivered at the time. Thus, the processing circuit 80 can attempt to use detected changes in the measured ECAP feature values to change the stimulation pulse parameter values and maintain a target ECAP feature value during delivery of the primary and master stimulation pulses.

[0065] Accordingly, IMD 14 can be configured to provide ECAP-responsive stimulation therapy to patient 12. Stimulation adjustments in response to changes in ECAP signals or patient state can be automatic or semi-automatic (requiring patient approval). In many cases, fully automatic adjustments can be desirable, such that IMD 14 can react more quickly to changes in patient state or to changes in therapy efficacy that can not be related to changes in patient state. In some examples, ECAP sensing and analysis can be used to refine stimulation therapy programs selected based on sensed posture.

[0066] Memory 82 can include a definition of each posture state of patient 12. In one example, the definition of each posture state can be shown as a cone in three-dimensional space. Whenever a posture state parameter value (e.g., a vector) from a three-axis accelerometer of posture state module 86 resides within a pre-defined cone or volume, processing circuitry 80 indicates that patient 12 is in the posture state of the cone or volume. In other examples, posture state parameter values from a 3-axis accelerometer can be compared to values in a lookup table or equation to determine the posture state in which patient 12 currently resides. Exemplary techniques for detecting patient posture states include the examples described in U.S. Patent No. 8,708,934, entitled "REORIENTATION OF PATIENT POSTURE STATES FOR POSTURE- RESPONSIVE THERAPY," filed April 30, 2009, and issued April 29, 2014, the entirety of which is incorporated herein by reference.

[0067] Although posture state module 86 is described as containing one 3-axis accelerometer, posture state module 86 can contain multiple single-axis accelerometers, dual-axis accelerometers, 3-axis accelerometers, or some combination thereof. In some examples, the accelerometers or other sensors can be located within or on IMD 14, on one of leads 16 (e.g., at the distal tip or at an intermediate location), on an additional sensor lead located somewhere in patient 12's body, within a separate implanted sensor, or even worn on patient 12. For example, one or more microsensors can be implanted in patient 12's body to wirelessly communicate posture state information to IMD 14. In this way, patient 12 posture state can be determined from multiple activity sensors placed at various locations on or in patient 12's body.

[0068] In some examples, the posture state module 86 can additionally or alternatively be configured to sense one or more physiological parameters of the patient 12. For example, the physiological parameters can include heart rate, electromyography (EMG), electroencephalography (EEG), electrocardiography (ECG), body temperature, respiratory rate, or pH. In some embodiments, the processing circuitry 80 can use these physiological parameters to confirm or reject changes in the sensed posture state that can be caused by vibration, patient travel (e.g., in an airplane, car, or train), or some other false positive of the posture state. In some examples, one or more physiological parameters can be used to determine a patient state other than posture. Further, ECAP sensing and analysis can be used to confirm changes in the relationship between the stimulation source and the stimulation target in the patient 12.

[0069] Adjusting one or more stimulation parameters in response to changes in the sensed ECAPs can allow the IMD 14 to achieve a level of automation in therapy adjustment. Specifically, the IMD 14 can continuously or periodically adjust stimulation therapy parameters in order to maintain a target ECAP characteristic value corresponding to effective therapy. Automatically adjusting stimulation can free the patient 12 from the fixed task of manually adjusting therapy each time the patient 12 changes posture. Automatically adjusting stimulation based on the sensed ECAP signals can also correct for natural drift of the lead 16 regardless of posture state. For example, by detecting the ECAP signals over time, the processing circuitry 80 can determine that the location of the nerve being stimulated has changed over time and automatically adjust therapy according to the changing conditions without needing to receive changes in different patient states from the patient 12 via the programmer 20.

[0070] Further, the IMD 14 can store patient 12 input regarding perceived physiological conditions (e.g., symptoms) that are not detected by any of the implemented sensors. For example, the patient 12 can provide input to the programmer 20 indicating the location of any symptoms the patient perceives and the characteristics of the particular type of symptom. The processing circuitry 80 can associate this physiological condition information with the currently detected posture state, stimulation parameters, and / or time stamp to provide a complete picture of therapy to the patient or clinician at a later time. Such information can be stored in the memory 82 of the IMD 14, the memory of the programmer 20, and / or the memory of some other device.

[0071] Wireless telemetry with an external programmer 20, e.g., a patient programmer or clinician programmer, or another device in IMD 14 can be achieved by RF communication or proximal inductive interaction between IMD 14 and external programmer 20. Telemetry circuitry 88 can send information to and receive information from external programmer 20 in a continuous manner, at periodic intervals, at aperiodic intervals, or on demand by the stimulator or programmer. To support RF communication, telemetry circuitry 88 can include appropriate electronic components, such as amplifiers, filters, mixers, encoders, decoders, and the like.

[0072] Power source 90 delivers operating power to the components of IMD 14. Power source 90 can include a small rechargeable or non-rechargeable battery and a power generation circuit to produce the operating power for IMD 14. Recharging can be accomplished through proximal inductive interaction between an external charger and an inductive charging coil within IMD 14. In some embodiments, the power requirements can be small enough to allow IMD 14 to utilize patient motion and implement a kinetic energy scavenge ing device to trickle charge a rechargeable battery. In other embodiments, a traditional battery can be used for a limited period of time. As a further alternative, an external inductive power source can be percutaneously energize IMD 14 when needed or desired.

[0073] Sensing circuitry 92 can be configured to detect an ECAP signal. In other examples, sensing circuitry 92 can be located on lead 16 and can include one or more electrodes in lead 16 in combination with appropriate amplification, filtering, and / or signal processing circuitry. In some examples, sensing circuitry 92 can include additional electrodes on the housing of IMD 14. In some examples, sensing circuitry 92 can be carried by an additional sensor lead located somewhere in patient 12, provided as a stand-alone implantable sensor, or even worn on patient 12. For example, one or more microsensors can be implanted in patient 12 to wirelessly communicate sensed ECAP signals or characteristic values to IMD 14. In this way, ECAP signals can be obtained independent of the location of electrodes that deliver electrical stimulation therapy.

[0074] According to the techniques of this disclosure, IMD 14 can use ECAPs to adaptively adjust parameter values of high frequency electrical stimulation. In one example, processing circuitry 80 controls stimulation generator 84 to generate high frequency stimulation in the form of high frequency stimulation burst trains for delivery to patient 12 by lead 16, with a pause between each train in which high frequency electrical stimulation is not delivered.

[0075] In some examples, each pulse of a pulse train is defined by the same stimulation parameter values. In other examples, the electrical stimulation pulse train includes a plurality of primary electrical stimulation pulses followed by a master electrical stimulation pulse, where the master electrical stimulation pulse is different from the primary electrical stimulation pulses. For example, the primary electrical stimulation pulses can be configured to provide therapy to the patient 12. The master electrical stimulation pulse can be configured to evoke an ECAP response from the tissue of the patient 12 during a pause in high frequency electrical stimulation. The master electrical stimulation pulse can or can not provide some therapeutic effect to the patient 12.

[0076] Exemplary ranges for electrical stimulation parameters are listed below. However, other parameter values are contemplated. While stimulation pulses are described, the stimulation signal can be any of a variety of forms, such as a sinusoid, etc.

[0077] Each electrical stimulation pulse train can be defined at least in part by a number of pulses, a pulse frequency, and a burst frequency. The pulse frequency defines a frequency at which each pulse within a train is delivered to the patient. The burst frequency defines a frequency at which each train of one or more pulses is delivered to the patient. Typically, the pulse frequency is higher than the burst frequency. In some examples, each train of electrical stimulation pulses includes a pulse frequency selected from a range of greater than or equal to 500 hertz and less than or equal to 20 kilohertz. In some examples, each train of electrical stimulation pulses includes a pulse frequency of about 1.2 kilohertz. In some examples, the burst frequency defining the frequency of the pulse trains is selected from a range of about 1 hertz to about 200 hertz. In some examples, the pause between each train is greater than or equal to 1 millisecond.

[0078] In some examples, each pulse in a train includes a pulse amplitude selected from a range of about 1 milliampere to about 25 milliampere. In some examples, each pulse in a train includes a pulse width selected from a range of about 30 microseconds to about 300 microseconds. In some examples, each primary pulse in a train includes a pulse width selected from a range of about 90 microseconds. In some examples, each master pulse in a train includes a pulse width selected from a range of between about 60 microseconds to about 0.5 milliseconds.

[0079] Typically, the number of pulses in a train is a function of the pulse frequency. For example, for a pulse train including a high pulse frequency, the pulse train can include hundreds of pulses or more. As another example, for a pulse train including a low pulse frequency, the pulse train can include only a few pulses. In some examples, each train of pulses can include 2 or more, 5 or more, or 10 or more pulses. In another example, an electrical stimulation train includes 10 electrical stimulation pulses (e.g., 9 primary electrical stimulation pulses and 1 master electrical stimulation pulse).

[0080] In general, the primary electrical stimulation pulses include one or more parameter values that are different from parameter values that define the master electrical stimulation pulses. For example, the master electrical stimulation pulses include one or more of a current amplitude or a pulse width that is greater than the primary electrical stimulation pulses. In some examples, each of the primary electrical stimulation pulses includes a current amplitude of about 0.4 milliamp, and the master electrical stimulation pulse includes a current amplitude of about 1.0 milliamp.

[0081] In some examples, when adjusting one or more parameters of the electrical stimulation therapy, the processing circuit 80 maintains a ratio of a value of one or more parameters of the primary electrical stimulation pulses to a value of one or more parameters of the master electrical stimulation pulses. For example, the processing circuit 80 controls the stimulation generator 84 to generate a burst of multiple primary electrical stimulation pulses followed by a master electrical stimulation pulse. Each of the primary electrical stimulation pulses includes a current amplitude of about 0.4 milliamp, and the master electrical stimulation pulse includes a current amplitude of about 1.0 milliamp (e.g., a ratio of amplitudes of the primary electrical stimulation pulses to the master electrical stimulation pulse is 0.4 milliamp to 1.0 milliamp, or 1 :2.5). The processing circuit 80 can adjust the current amplitude of the burst in accordance with an incremental step in response to the sensed ECAP signal while maintaining the ratio of the primary electrical stimulation pulses to the master electrical stimulation pulse.

[0082] For example, when causing the amplitude of the burst to increase by a step increment of 10%, the processing circuit 80 controls the stimulation generator 84 to increase the current amplitude of the primary electrical stimulation pulses from 0.4 milliamp to about 0.44 milliamp, and to increase the current amplitude of the master electrical stimulation pulse from 1.0 milliamp to about 1.1 milliamp (e.g., a ratio of 1 :2.5). As another example, when causing the amplitude of the burst to decrease by a step decrement of 10%, the processing circuit 80 controls the stimulation generator 84 to decrease the current amplitude of the primary electrical stimulation pulses from 0.4 milliamp to about 0.36 milliamp, and to decrease the current amplitude of the master electrical stimulation pulse from 1.0 milliamp to about 0.9 milliamp (e.g., a ratio of 1 :2.5).

[0083] By temporarily pausing the high frequency stimulation for a predetermined amount of time, the sensing circuit 92 can sense an ECAP signal from the target nerve of the patient 12 during this amount of time and without interference from the high frequency stimulation. Thus, the processing circuit 80 can use the sensed ECAP to adjust a value of one or more parameters of the burst of high frequency electrical stimulation pulses. In some examples, the processing circuit 80 controls the stimulation generator 84 to modify one or more parameters of the last electrical stimulation pulse of the burst to elicit a detectable ECAP.

[0084] Additionally or alternatively, processing circuitry 80 can control stimulation generator 84 to deliver low frequency electrical stimulation during pauses in the high frequency electrical stimulation burst in order to elicit an ECAP response and / or to maintain therapeutic efficacy for patient 12 during the pause. For example, the low frequency electrical stimulation can include a plurality of electrical stimulation pulses delivered at a pulse frequency less than 500 hertz. In some examples, the low frequency electrical stimulation includes a plurality of electrical stimulation pulses delivered at about 50 hertz. In this way, when high frequency stimulation is paused, patient 12 can not experience an interruption in therapy or can experience a lesser interruption during the pause, and sensing circuitry 92 senses an ECAP from tissue of patient 12.

[0085] In some examples, processing circuitry 80 can use a posture of patient 86 sensed via posture state module 86 to adjust a rate at which ECAPs are sensed from patient 12. For example, processing circuitry 80 can control stimulation generator 84 to deliver a first high frequency electrical stimulation burst to patient 12. Each of the first electrical stimulation bursts includes a plurality of primary pulses configured to provide therapy to patient 12. In some examples, processing circuitry 80 can not include a pause in electrical stimulation delivery between the first high frequency electrical stimulation bursts. Periodically and in a time-interleaved manner, processing circuitry 80 can control stimulation generator 84 to deliver a second high frequency electrical stimulation burst to patient 12 followed by a pause in the delivery of high frequency electrical stimulation therapy. The second electrical stimulation burst includes a plurality of primary pulses configured to provide therapy to patient 12 followed by a master pulse configured to evoke an ECAP signal from patient 12. Processing circuitry 80 can control a rate of ECAP sensing from patient 12 by controlling a rate at which the second high frequency electrical stimulation therapy burst is delivered to patient 12. For example, in response to a change in posture of patient 12, processing circuitry 80 can adjust the rate at which the second high frequency electrical stimulation therapy burst is delivered to patient 12.

[0086] For another example, processing circuitry 80 can deliver only the first high frequency electrical stimulation therapy burst to patient 12 while a posture of patient 12 is constant. In response to detecting a change in posture of patient 12, processing circuitry 80 controls stimulation generator 84 to deliver a second high frequency electrical stimulation therapy burst followed by a pause in the delivery of high frequency electrical stimulation therapy in order to evoke an ECAP signal that processing circuitry 80 can use as feedback to adjust a value of one or more parameters of the electrical stimulation therapy to account for the new posture of patient 12. In this way, when the posture of patient 12 is constant, processing circuitry 80 can deliver continuous electrical stimulation to patient 12 including the first high frequency electrical stimulation therapy burst and, in response to detecting a change in posture, use the second high frequency electrical stimulation therapy burst to elicit an ECAP response to adjust one or more parameters of the high frequency electrical stimulation therapy to accommodate a new assumed posture of patient 12.

[0087] Accordingly, using the techniques described herein, processing circuit 80 can pause delivery of high frequency electrical stimulation in order to allow time for stimulation generator 84 to evoke ECAPs and for sensing circuit 92 to sense the ECAP signals. Otherwise, the ECAPs can not be detected by the system delivering, for example, continuous high frequency electrical stimulation. Accordingly, the medical device as described herein can avoid high frequency electrical stimulation from masking the ECAP signals of the patient, thereby allowing the use of sensed features of the ECAPs as control signals for one or more parameters of the high frequency electrical stimulation therapy for titration.

[0088] Figure 3 FIG. 1 is a functional block diagram illustrating various components of an external programmer 20 of IMD 14. As shown in FIG. 1, external programmer 20 is an external device that includes processing circuitry 104, memory 108, telemetry circuitry 110, user interface 106, and power source 112. External programmer 20 can be implemented as a patient programmer or a clinician programmer. Clinician or patient 12 interacts with user interface 106 in order to manually change stimulation parameters of a program, change programs within a group, turn ECAP-responsive stimulation on or off, view therapy information, view patient status information, view posture state indications, or otherwise communicate with IMD 14. Figure 3

[0089] User interface 106 can include a screen and one or more input buttons that allow external programmer 20 to receive input from a user, as in the example of a programmer. Alternatively, user interface 106 can additionally or solely utilize a touchscreen display, as in the example of a clinician programmer. The screen can be a liquid crystal display (LCD), a dot-matrix display, an organic light-emitting diode (OLED) display, a touchscreen, or any other device capable of delivering and / or accepting information. For visible posture state indications, a display screen can be sufficient. For audible and / or tactile posture state indications, programmer 20 can further include one or more audio speakers, a voice synthesizer chip, a piezoelectric buzzer, etc. The input buttons of user interface 106 can include touchpads, increase and decrease buttons, an emergency off button, and other buttons that control stimulation therapy, as described above with respect to programmer 20. Processing circuitry 104 controls user interface 106, retrieves data from and stores data within memory 108. Processing circuitry 104 also controls the transmission of data by telemetry circuitry 110 to IMD 14 or 26. Memory 108 includes operating instructions for processing circuitry 104 and data related to the therapy of patient 12.

[0090] ​The telemetry circuit 110 allows data to be passed to and from the IMD 14. The telemetry circuit 110 can communicate wirelessly with the IMD 14 in real-time, at a scheduled time, or when the telemetry circuit detects the proximity of a programmer. The user interface 106 can then update the information displayed accordingly. Alternatively, the telemetry circuit 110 can communicate with the IMD 14 when the user sends a signal through the user interface 106. To support RF communication, the telemetry circuit 110 can include appropriate electronic components, such as amplifiers, filters, mixers, encoders, decoders, etc. The power source 112 can be a rechargeable battery, such as a lithium ion or nickel metal hydride battery. Other rechargeable or traditional batteries can also be used. In some cases, an external programmer 20 can be used when coupled to an alternating current (AC) outlet (i.e., AC line power), either directly or via an AC / DC adapter.

[0091] In some examples, in addition to programming the IMD 14, the external programmer 20 can be configured to also recharge the IMD 14. Alternatively, a recharging device can be able to communicate with the IMD 14. The recharging device can then pass programming information, data, or any other information described herein to the IMD 14. In this way, the recharging device can act as an intermediary communication device between the external programmer 20 and the IMD 14. In other cases, the programmer can integrate recharging functionality in a combined programming / recharging device. The techniques described herein can be communicated between IMDs 14 by any type of external device that is able to communicate with the IMD 14.

[0092] Figure 4A 、 4B FIGS. 1-4C are diagrams illustrating example electrical stimulation pulse trains in accordance with the techniques of this disclosure. For convenience, the description with respect to IMD 14 of FIGS. 1-4C is provided with respect to a left ventricular lead 16. Figure 1 and 2 FIGS. 1-4C are diagrams illustrating example electrical stimulation pulse trains in accordance with the techniques of this disclosure. For convenience, the description with respect to IMD 14 of FIGS. 1-4C is provided with respect to a left ventricular lead 16. Figure 4A FIGS. 1-4C are diagrams illustrating example electrical stimulation pulse trains in accordance with the techniques of this disclosure. For convenience, the description with respect to IMD 14 of FIGS. 1-4C is provided with respect to a left ventricular lead 16.

[0093] Figure 4A An example stimulation signal 430 is shown that includes a first pulse train 410A and a second pulse train 410B of high frequency electrical stimulation pulses. Each of the pulse trains 410A, 410B (collectively, “trains 410”) includes a plurality of primary electrical stimulation pulses 400 followed by a main electrical stimulation pulse 408. The stimulation signal 430 can be generated, for example, by the stimulation generator 84 of the IMD 14 of FIGS. 1-4C. Figure 2 An example stimulation signal 430 is shown that includes a first pulse train 410A and a second pulse train 410B of high frequency electrical stimulation pulses. Each of the pulse trains 410A, 410B (collectively, “trains 410”) includes a plurality of primary electrical stimulation pulses 400 followed by a main electrical stimulation pulse 408. The stimulation signal 430 can be generated, for example, by the stimulation generator 84 of the IMD 14 of FIGS. 1-4C.

[0094] The primary electrical stimulation pulses 400 can be configured to provide therapy to the patient 12. In contrast, the master electrical stimulation pulses 408 can be configured to evoke an ECAP response from the tissue of the patient 12, which can be sensed by the IMD 14 during the pause 416 between the two successive trains 410A, 410B of high frequency electrical stimulation pulses. The IMD 14 can use the ECAP evoked by the master electrical stimulation pulses 408 to adjust one or more parameters (e.g., the amplitude or pulse width of the pulses 400, 408) of either or both of the primary electrical stimulation pulses 400 and the master electrical stimulation pulses 408. In some examples, the IMD 14 adjusts both the primary electrical stimulation pulses 400 and the master electrical stimulation pulses 408 in a ratio manner (e.g., to maintain a ratio of one or more parameters of the primary electrical stimulation pulses 400 to one or more parameters of the master electrical stimulation pulses 408).

[0095] The master electrical stimulation pulses 408 are defined by different parameter values than the primary electrical stimulation pulses 400. As shown, the master electrical stimulation pulses 408 have a greater pulse width 414 and a greater pulse amplitude 412 than the pulse width 404 and the pulse amplitude 406 of the primary electrical stimulation pulses 400. Although the pulses 400, 408 forming the train 410A are depicted as having a rectangular morphology, the morphology of the pulses can be triangular, sinusoidal, Gaussian, exponential, ramped, or any morphology or combination thereof for delivering electrical charge to and from the target tissue of the patient 12. Figure 4A The master electrical stimulation pulses 408 are defined by different parameter values than the primary electrical stimulation pulses 400. As shown, the master electrical stimulation pulses 408 have a greater pulse width 414 and a greater pulse amplitude 412 than the pulse width 404 and the pulse amplitude 406 of the primary electrical stimulation pulses 400. Although the pulses 400, 408 forming the train 410A are depicted as having a rectangular morphology, the morphology of the pulses can be triangular, sinusoidal, Gaussian, exponential, ramped, or any morphology or combination thereof for delivering electrical charge to and from the target tissue of the patient 12.

[0096] In some examples, the number of primary electrical stimulation pulses 400 is selected from a range greater than or equal to 2 and less than or equal to 50. In some examples, the number of primary electrical stimulation pulses 400 is 9 followed by a single master electrical stimulation pulse 408.

[0097] The primary pulse interval 402 and the pulse width 404 of the primary electrical stimulation pulses 400 can be fixed or variable. Each of the primary electrical stimulation pulses 400 can have an asymmetric primary pulse width 402 for the anode and cathode phases.

[0098] The stimulation signal 430 further includes a pulse-to-pulse interval 416 (also referred to herein as a“pause”) during which no electrical charge is delivered to the patient 12. The sensing circuit 92 of the IMD 14 can sense the ECAP response of the patient 12 evoked by the master electrical stimulation pulses 408 during the pause interval 416. The use of the pause interval 416 can reduce instances in which the primary electrical stimulation pulses 400 mask and / or interfere with the ECAP response of the patient 12, such that the IMD 14 can use one or more characteristic values of the ECAP response to adjust one or more parameters of either or both of the primary electrical stimulation pulses 400 or the master electrical stimulation pulses 408.

[0099] Figure 4B An exemplary stimulation signal 440 is shown that includes a first pulse train 410A and a second pulse train 410B of high frequency electrical stimulation pulses. Each of the pulse trains 410A, 410B includes a plurality of primary electrical stimulation pulses 400 followed by a main electrical stimulation pulse 408. The pulse trains 410A, 410B can be generated, for example, by the stimulation generator 84 of the IMD 14 of Figure 2 The stimulation signal 440 can be substantially similar to the stimulation signal 430 of Figure 4A However, the stimulation signal 440 further includes an inter-pulse interval 418 during which no electrical charge is delivered to the patient 12. The inter-pulse interval 418 is interposed between the last primary electrical stimulation pulse 400 and the main electrical stimulation pulse 408.

[0100] As described above with respect to the stimulation signal 430 of Figure 4A The sensing circuit 92 of the IMD 14 senses a first ECAP signal of the patient 12 evoked by the main electrical stimulation pulse 408 during the pause interval 416. In addition, the sensing circuit 92 of the IMD 14 senses a second ECAP signal of the patient 12 evoked by the last primary electrical stimulation pulse 400 during the pause interval 418. The use of the pause intervals 416 and 418 can reduce instances in which the primary electrical stimulation pulses 400 mask and / or interfere with the ECAP signals of the patient 12, such that the IMD 14 can use one or more characteristic values of the first and second ECAP signals to control adjustment of one or more parameters of either or both of the primary electrical stimulation pulses 400 or the main electrical stimulation pulse 408.

[0101] In addition, the first ECAP signal for the last primary electrical stimulation pulse 400 can exhibit a different morphology than the second ECAP response for the main electrical stimulation pulse 408. The IMD 14 or a clinician reviewing the first and second ECAP signals can use the difference in morphology between the first ECAP signal and the second ECAP signal to further adjust the value of one or more parameters defining either or both of the primary electrical stimulation pulses 400 or the main electrical stimulation pulse 408.

[0102] Figure 4C An exemplary high frequency stimulation signal 450 and a low frequency stimulation signal 460 are shown. The high frequency stimulation signal 450 includes a high frequency first pulse train 410A and a second pulse train 410B. Each of the trains 410 includes a plurality of primary electrical stimulation pulses 400 followed by a main electrical stimulation pulse 408. The low frequency stimulation signal 460 includes a low frequency pulse train 420 of one or more low frequency electrical stimulation pulses. The stimulation signals 450 and 460 can be generated, for example, by the stimulation generator 84 of the IMD 14 of Figure 2 The stimulation signal 450 can be substantially similar to the stimulation signal 430 of Figure 4A However, the stimulation signal 440 further includes an inter-pulse interval 418 during which no electrical charge is delivered to the patient 12. The inter-pulse interval 418 is interposed between the last primary electrical stimulation pulse 400 and the main electrical stimulation pulse 408.

[0103] As Figure 4C depicted in the example of FIG. 4, during the interval 416, the IMD delivers a train 420 of low frequency electrical stimulation pulses to the patient 12. After the pause 416 has elapsed, the IMD 14 can cease delivery of the train 420 of low frequency electrical stimulation pulses and resume delivery of the train 410B of high frequency electrical stimulation pulses. In some examples, the electrical stimulation pulses 420 include a pulse frequency of less than 500 hertz. In some examples, the electrical stimulation pulses 420 include a pulse frequency of about 50 hertz.

[0104] The train 420 of low frequency electrical stimulation pulses can substantially not mask or substantially not interfere with the ECAP signal sensed from the patient 12. For example, the electrical stimulation pulses 420 can be configured to elicit an ECAP response from the patient 12. Additionally or alternatively, the electrical stimulation pulses 420 can be configured to maintain the therapeutic efficacy of the patient 12 during the pause 416 between the trains 410A and 410B of high frequency electrical stimulation pulses. Thus, by delivering the train 420 of low frequency electrical stimulation pulses during the pause 416 between the trains 410A and 410B of high frequency electrical stimulation pulses, the IMD 14 can avoid causing a therapeutic disruption to the patient 12 during the pause 416 while sensing the ECAP from the tissue of the patient 12.

[0105] Figure 5 is a graph showing an exemplary stimulation train 502 of electrical stimulation pulses and an ECAP signal 504 sensed from a patient in accordance with the techniques of this disclosure. For convenience, the description of the IMD 14 relative to Figure 1 and 2 is described. Figure 5

[0106] High frequency stimulation can employ other mechanisms of action in addition to paresthesia compared to low frequency stimulation. However, the high frequency stimulation effects can change if the electrode location changes relative to the target nerve. Thus, incorporating a feedback control system into a high frequency SCS system can provide a more consistent uniform therapy to the patient. However, high frequency electrical stimulation pulses can mask the ECAP response of the patient. For example, resolving the ECAP signal in the presence of high frequency stimulation is particularly challenging because high frequency stimulation can induce greater stimulation artifacts compared to low frequency stimulation. Stimulation artifacts are non-linear sources of interference that manifest simultaneously with the delivery of the high frequency electrical stimulation pulses. The stimulation artifacts act to impair the ability of a medical device system, such as the IMD 14, to resolve the ECAP signal of the tissue of the patient 12. Thus, a high frequency SCS system can be unable to resolve the ECAP signal in the presence of high frequency stimulation.

[0107] ​According to the techniques of this disclosure, a medical device system temporarily suspends delivery of high frequency electrical stimulation pulses. The suspension in the high frequency electrical stimulation leaves a brief window for the emergence and detection of ECAP signals before the delivery of the next high frequency electrical stimulation pulse. In some examples, the high frequency stimulation is a train comprising two or more stimulation pulses having a pulse frequency greater than or equal to 500 hertz. The train can repeat at a burst frequency of 1 hertz to 200 hertz, with the IMD 14 interposing at least a 1 millisecond pause between the end of a first stimulation train and the beginning of a second stimulation train. Thus, using the techniques disclosed herein, the IMD 14 can titrate the high frequency stimulation using ECAPs without the masking of the ECAPs by the high frequency electrical stimulation pulses.

[0108] As Figure 5 depicted, the processing circuitry 80 controls the stimulation generator 84 to generate a train 502 of electrical stimulation pulses for delivery to the patient 12. In Figure 5 the example, the stimulation generator 84 generates a train 502 of 10 balanced biphasic pulses comprising a pulse frequency of 1,000 hertz, a pulse amplitude of 5.75 milliamps, and a pulse width of 90 microseconds. The processing circuitry 80 controls the stimulation generator 84 to deliver each train 502 every 12 milliseconds (e.g., a burst rate of 83.3 hertz). The processing circuitry 80 controls the stimulation generator 84 to stop the delivery of the high frequency electrical stimulation for a pause interval 506 of 2 milliseconds.

[0109] During the pause interval 506, the sensing circuitry 92 senses a signal from the patient 12 indicative of an ECAP response to the train 502. As Figure 5 shown, during the delivery of the electrical stimulation train 502, the electrical stimulation delivered by the stimulation generator 84 causes noise 510. The noise 510 has a much greater magnitude than the ECAP response of the patient 12 and can make it impossible for the sensing circuitry 92 to detect the ECAP response of the patient 12. By using the pause interval 506, the sensing circuitry 92 is able to sense a clean, artifact-free ECAP response 508 of the patient 12. The pause interval 506 is selected so as to leave sufficient time for the emergence of the ECAP response 508, as otherwise the ECAP response 508 can be undetectable in the presence of the high frequency electrical stimulation. The processing circuitry 80 can then use the ECAP response 508 to adjust one or more parameters of the delivered high frequency electrical stimulation as described above.

[0110] Figure 6 is a flowchart illustrating operations according to the techniques of this disclosure. In particular, Figure 6 the flowchart depicts operations to adjust one or more parameters of an electrical stimulation therapy comprising a train of high frequency electrical stimulation pulses using an ECAP response of a patient. For convenience, the operations are described with reference to the IMD 14 and the processing circuitry 80 of Figure 1 and 2 the IMD 14 and the processing circuitry 80Figure 6 The description is made.

[0111] As Figure 6 In the example depicted in FIG. 6, the processing circuit 80 controls the stimulation generator 84 to deliver electrical stimulation therapy including a first electrical stimulation therapy burst to the patient 12 (602). In some examples, the first electrical stimulation therapy burst includes a pulse frequency greater than or equal to 500 hertz. In some examples, the electrical stimulation burst includes a plurality of primary electrical stimulation pulses followed by a master electrical stimulation pulse. The primary electrical stimulation pulses can be configured to provide therapy to the patient 12. The master electrical stimulation pulse can be configured to evoke an ECAP response from the tissue of the patient 12 during a pause in high frequency electrical stimulation. However, in some examples, the master electrical stimulation pulse can provide some therapeutic benefit to the patient 12.

[0112] After delivering the first electrical stimulation burst, the processing circuit 80 controls the stimulation generator 84 to cease delivery of electrical stimulation therapy for a predetermined time period (604). In some examples, the predetermined time period is greater than or equal to 1 millisecond.

[0113] During the predetermined time period, the sensing circuit 92 senses an ECAP signal from the tissue of the patient 12 (606). Additionally or alternatively, the processing circuit 80 can control the stimulation generator 84 to deliver low frequency electrical stimulation during the predetermined time period in order to elicit an ECAP response while the high frequency electrical stimulation therapy is suspended and / or to maintain therapeutic efficacy in the patient 12. For example, the low frequency electrical stimulation can include a plurality of electrical stimulation pulses delivered at a pulse frequency less than 500 hertz. In some examples, the low frequency electrical stimulation includes a plurality of electrical stimulation pulses delivered at approximately 50 hertz. In this way, the patient 12 can not experience an interruption in therapy during the pause while the sensing circuit 92 senses an ECAP from the tissue of the patient 12. The processing circuit 80 can also determine a characteristic value of the sensed ECAP signal, which the processing circuit 80 can compare to a target ECAP characteristic value.

[0114] The processing circuit 80 determines a value of at least one parameter defining, at least in part, a second electrical stimulation burst based on the characteristic value of the sensed ECAP signal (608). In some examples, the second electrical stimulation therapy burst includes a pulse frequency greater than or equal to 500 hertz. For example, the sensed ECAP signal can indicate a distance of an electrode disposed along the lead 16 from a target nerve of the patient 12. The processing circuit 80 compares the characteristic value of the ECAP signal to a target characteristic value of the ECAP. If the characteristic value of the ECAP signal is greater than the target characteristic value of the ECAP, the ECAP signal can indicate that the electrode disposed along the lead 16 has shifted closer to the target nerve and a corresponding reduction in one or more parameters of the high frequency electrical stimulation pulses, such as amplitude, is needed to maintain a constant level of therapy to the patient 12.

[0115] In contrast, if the characteristic value of the ECAP signal is less than the target characteristic value of the ECAP, the ECAP signal can indicate that the electrode disposed along lead 16 has shifted away from the target nerve and a corresponding increase in one or more parameters of the high frequency electrical stimulation pulses, such as amplitude, is needed to maintain a constant level of therapy to patient 12. Based on the comparison result, processing circuitry 80 determines a value of at least one parameter defining a second electrical stimulation therapy pulse train in order to reduce the difference between the characteristic value of the ECAP signal and the target characteristic value of the ECAP.

[0116] In response to the predetermined period of time elapsing, processing circuitry 80 controls stimulation generator 84 to deliver the second electrical stimulation pulse train in accordance with the value of the at least one parameter (610). Thus, the medical device as described herein can avoid high frequency electrical stimulation masking the ECAP response of patient 12, thereby allowing the use of one or more characteristic values of the sensed ECAP to control titration of one or more parameters of the high frequency electrical stimulation therapy.

[0117] The following embodiments can illustrate one or more aspects of the present disclosure.

[0118] Embodiment 1 : A method comprising: delivering, by a medical device, an electrical stimulation therapy to a patient including a first electrical stimulation pulse train, wherein the first electrical stimulation pulse train includes a first pulse frequency greater than or equal to 500 hertz; stopping, by the medical device, the delivery of the electrical stimulation therapy for a predetermined period of time after delivering the first electrical stimulation pulse train; sensing, by the medical device, an evoked compound action potential (ECAP) signal from tissue of the patient during the predetermined period of time; determining, by the medical device and based on a characteristic value of the ECAP signal, a value of at least one parameter at least partially defining a second electrical stimulation pulse train, wherein the second electrical stimulation pulse train includes a second pulse frequency greater than or equal to 500 hertz; and in response to the predetermined period of time elapsing, delivering the second electrical stimulation pulse train in accordance with the value of the at least one parameter at least partially defining the second set of pulses.

[0119] Example 2: The method of Example 1, wherein the ECAP signal comprises a first ECAP signal, and wherein the method further comprises: after delivering the second electrical stimulation burst, ceasing, by the medical device, delivery of the electrical stimulation therapy for the predetermined time period; during the predetermined time period, sensing, by the medical device, a second ECAP signal from the tissue of the patient; determining, by the medical device and based on a characteristic value of the second ECAP signal, a value of at least one parameter at least partially defining a third electrical stimulation burst, wherein the third electrical stimulation burst comprises a pulse frequency greater than or equal to 500 hertz; and in response to the passage of the predetermined time period, delivering the third electrical stimulation burst according to the value of the at least one parameter at least partially defining the second set of pulses.

[0120] Example 3: The method of any of Examples 1-2, wherein: the first electrical stimulation burst comprises a plurality of primary electrical stimulation pulses followed by a primary electrical stimulation pulse, the plurality of primary electrical stimulation pulses are defined by a primary set of parameters and are configured to contribute to therapy of the patient, and the primary electrical stimulation pulse is defined by a primary set of parameters and is configured to evoke the ECAP signal from the tissue of the patient, wherein a value of the primary set of parameters is different than a value of the primary set of parameters.

[0121] Example 4: The method of Example 3, wherein the primary electrical stimulation pulse of the first burst comprises a current amplitude that is greater than a pulse amplitude of the plurality of primary electrical stimulation pulses of the first burst.

[0122] Example 5: The method of any of Examples 3-4, wherein the plurality of primary electrical stimulation pulses of the first burst is a first primary electrical current amplitude, wherein the primary electrical stimulation pulse of the first burst comprises a first primary electrical current amplitude, wherein the plurality of primary electrical stimulation pulses of the second burst comprises a second primary electrical current amplitude, wherein the primary electrical stimulation pulse of the second burst comprises a second primary electrical current amplitude, and wherein determining the value of the at least one parameter defining the second electrical stimulation burst comprises: determining a value of the second primary electrical current amplitude that is different than a value of the first primary electrical current amplitude; determining a value of the second primary electrical current amplitude that is different than a value of the first primary electrical current amplitude, wherein a ratio of the second primary electrical current amplitude to the second primary electrical current amplitude is the same as a ratio of the first primary electrical current amplitude to the first primary electrical current amplitude.

[0123] Example 6: The method of Example 5, wherein a value of the second primary current amplitude is greater than a value of the first primary current amplitude, wherein a value of the second main current amplitude is greater than a value of the first main current amplitude, and wherein a ratio of the second primary current amplitude to the second main current amplitude is the same as a ratio of the first primary current amplitude to the first main current amplitude.

[0124] Example 7: The method of any one of Examples 5-6, wherein a value of the second primary current amplitude is less than a value of the first primary current amplitude, wherein a value of the second main current amplitude is less than a value of the first main current amplitude, and wherein a ratio of the second primary current amplitude to the second main current amplitude is the same as a ratio of the first primary current amplitude to the first main current amplitude.

[0125] Example 8: The method of any one of Examples 1-7, wherein the method further comprises: delivering, by the medical device, electrical stimulation therapy comprising a third electrical stimulation burst to the patient during the predetermined time period, wherein the third electrical stimulation burst comprises a third pulse frequency less than 500 hertz; and responsive to the predetermined time period elapsing, ceasing delivery of the electrical stimulation therapy comprising the third electrical stimulation burst.

[0126] Example 9: The method of any one of Examples 1-8, further comprising delivering electrical stimulation therapy comprising a plurality of primary electrical stimulation pulses to the patient; detecting, by the medical device, a change in posture of the patient, wherein: delivering the electrical stimulation therapy comprising the first electrical stimulation burst to the patient comprises delivering, responsive to the detected change in posture of the patient, the first electrical stimulation burst comprising a plurality of primary electrical stimulation pulses followed by a main electrical stimulation pulse, the plurality of primary electrical stimulation pulses configured to provide therapy to the patient, and the main electrical stimulation pulse configured to evoke the ECAP signal from the tissue of the patient.

[0127] Example 10: The method of any one of Examples 1-9, wherein the electrical stimulation therapy comprises a burst frequency greater than or equal to 1 hertz and less than or equal to 200 hertz, wherein the burst frequency comprises a frequency at which the first electrical stimulation burst and the second electrical stimulation burst are delivered to the patient.

[0128] Example 11: The method of any one of Examples 1-10, wherein the medical device is an implantable medical device.

[0129] Example 12: A medical device configured to: deliver electrical stimulation therapy comprising a first electrical stimulation burst to a patient, wherein the first electrical stimulation burst comprises a first pulse frequency greater than or equal to 500 hertz; cease delivery of the electrical stimulation therapy for a predetermined time period after delivering the first electrical stimulation burst; sense an evoked compound action potential (ECAP) signal from tissue of the patient during the predetermined time period; determine a value of at least one parameter at least partially defining a second electrical stimulation burst based on a characteristic value of the ECAP signal, wherein the second electrical stimulation burst comprises a second pulse frequency greater than or equal to 500 hertz; and in response to the predetermined time period having elapsed, deliver the second electrical stimulation burst according to the value of the at least one parameter at least partially defining the second set of pulses.

[0130] Example 13: The medical device of Example 12, wherein the ECAP signal comprises a first ECAP signal, and wherein the medical device is further configured to: cease delivery of the electrical stimulation therapy for the predetermined time period after delivering the second electrical stimulation burst; sense a second ECAP signal from the tissue of the patient during the predetermined time period; determine a value of at least one parameter at least partially defining a third electrical stimulation burst based on a characteristic value of the second ECAP signal, wherein the third electrical stimulation burst comprises a pulse frequency greater than or equal to 500 hertz; and in response to the predetermined time period having elapsed, deliver the third electrical stimulation burst according to the value of the at least one parameter at least partially defining the second set of pulses.

[0131] Example 14: The medical device of Example 12, wherein: the first electrical stimulation burst comprises a plurality of primary electrical stimulation pulses followed by a main electrical stimulation pulse, the plurality of primary electrical stimulation pulses are defined by a primary set of parameters and are configured to contribute to therapy of the patient, and the main electrical stimulation pulse is defined by a main set of parameters and is configured to evoke the ECAP signal from the tissue of the patient, wherein the values of the main set of parameters are different from the values of the primary set of parameters.

[0132] Example 15: The medical device of Example 14, wherein the main electrical stimulation pulse of the first burst comprises a current amplitude that is greater than a pulse amplitude of the plurality of primary electrical stimulation pulses of the first burst.

[0133] Example 16: The medical device of any one of examples 14-15, wherein the plurality of primary electrical stimulation pulses of the first train is a first primary electrical current amplitude, wherein the master electrical stimulation pulse of the first train comprises a first master electrical current amplitude, wherein the plurality of primary electrical stimulation pulses of the second train comprises a second primary electrical current amplitude, wherein the master electrical stimulation pulse of the second train comprises a second master electrical current amplitude, and wherein to determine the value of the at least one parameter defining the second electrical stimulation pulse train, the medical device is configured to: determine a value of the second primary electrical current amplitude that is different from a value of the first primary electrical current amplitude; and determine a value of the second master electrical current amplitude that is different from a value of the first master electrical current amplitude, wherein a ratio of the second primary electrical current amplitude to the second master electrical current amplitude is the same as a ratio of the first primary electrical current amplitude to the first master electrical current amplitude.

[0134] Example 17: The medical device of example 16, wherein the value of the second primary electrical current amplitude is greater than the value of the first primary electrical current amplitude, wherein the value of the second master electrical current amplitude is greater than the value of the first master electrical current amplitude, and wherein a ratio of the second primary electrical current amplitude to the second master electrical current amplitude is the same as a ratio of the first primary electrical current amplitude to the first master electrical current amplitude.

[0135] Example 18: The medical device of any one of examples 16-17, wherein the value of the second primary electrical current amplitude is less than the value of the first primary electrical current amplitude, wherein the value of the second master electrical current amplitude is less than the value of the first master electrical current amplitude, and wherein a ratio of the second primary electrical current amplitude to the second master electrical current amplitude is the same as a ratio of the first primary electrical current amplitude to the first master electrical current amplitude.

[0136] Example 19: The medical device of any one of examples 12-18, wherein the medical device is further configured to: during the predetermined time period, deliver electrical stimulation therapy comprising a third electrical stimulation pulse train to the patient, wherein the third electrical stimulation pulse train comprises a third pulse frequency that is less than 500 hertz; and in response to the predetermined time period elapsing, cease delivery of the electrical stimulation therapy comprising the third electrical stimulation pulse train.

[0137] Example 20: A non-transitory computer-readable medium comprising instructions that, when executed, are configured to cause a processing circuit of an implantable medical device to: control a stimulation generator of the implantable medical device to deliver electrical stimulation therapy comprising a first electrical stimulation burst to a patient, wherein the first electrical stimulation burst comprises a first pulse frequency that is greater than or equal to 500 hertz; after delivering the first electrical stimulation burst, control the stimulation generator to stop delivery of the electrical stimulation therapy for a predetermined time period; during the predetermined time period, sense an evoked compound action potential (ECAP) signal from tissue of the patient; determine a value of at least one parameter at least partially defining a second electrical stimulation burst based on a characteristic value of the ECAP signal, wherein the second electrical stimulation burst comprises a second pulse frequency that is greater than or equal to 500 hertz; and in response to the predetermined time period elapsing, control the stimulation generator to deliver the second electrical stimulation burst according to the value of the at least one parameter at least partially defining the second set of pulses.

[0138] It should be understood that various aspects disclosed herein can be combined in different combinations than the combinations expressly presented in the description and accompanying drawings. It should also be understood that, depending on the example, certain acts or events of any of the processes described herein can be performed in a different sequence, can be added, modified or omitted (e.g., all described acts or events can not be required, or a desired result can be achieved in only some acts or events). Additionally, the description sometimes uses terms like “implement” or “execute,” to describe the functioning of the devices and methods described herein. It will be appreciated that not all devices or methods for performing the described functions need to perform the described functions in the same manner, or perform all the described functions, to be considered implementing these disclosures. Moreover, the illustrations of the examples described herein are intended to provide a generic understanding of the features of the various aspects. The illustrative features as described herein can be combined or eliminated in order to provide a more concise description of the subject matter.

[0139] In one or more examples, the described techniques can be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, the functions can be stored as one or more instructions or code on a computer-readable medium and executed by a hardware-based processing unit. Computer-readable media can include non-transitory computer-readable media, which corresponds to a tangible medium such as data storage media (e.g., RAM, ROM, EEPROM, flash memory, or any other medium that can be used to

[0140] Instructions can be executed by one or more processors, such as one or more digital signal processors (DSPs), general purpose microprocessors, application specific integrated circuits (ASICs), field programmable logic arrays (FPGAs), or other equivalent integrated or discrete logic circuitry. Accordingly, the term “processor” as used herein can refer to any of the foregoing structure or any other physical structure suitable for implementation of the described techniques. Also, the techniques could be fully implemented in one or more circuits or logic elements.

[0141] Various examples have been described. These and other examples are within the scope of the following claims.

Claims

1. A medical device system, the system comprising: processing circuitry; and memory storing instructions that, when executed by the processing circuitry, cause the medical device system to perform a method comprising: delivering, by a medical device, electrical stimulation therapy comprising a first electrical stimulation burst to a patient, wherein the first electrical stimulation burst comprises a first pulse frequency greater than or equal to 500 hertz; stopping, by the medical device, delivery of the electrical stimulation therapy for a predetermined time period after delivering the first electrical stimulation burst; sensing, by the medical device, an evoked compound action potential (ECAP) signal from tissue of the patient during the predetermined time period; determining, by the medical device and based on a characteristic value of the ECAP signal, a value of at least one parameter that at least partially defines a second electrical stimulation burst, wherein the second electrical stimulation burst comprises a second pulse frequency greater than or equal to 500 hertz; and in response to the predetermined time period having elapsed, delivering the second electrical stimulation burst according to the value of the at least one parameter that at least partially defines the second electrical stimulation burst.

2. The system of claim 1, wherein the ECAP signal comprises a first ECAP signal, and wherein the method further comprises: stopping, by the medical device, delivery of the electrical stimulation therapy for the predetermined time period after delivering the second electrical stimulation burst; sensing, by the medical device, a second ECAP signal from the tissue of the patient during the predetermined time period; determining, by the medical device and based on a characteristic value of the second ECAP signal, a value of at least one parameter that at least partially defines a third electrical stimulation burst, wherein the third electrical stimulation burst comprises a pulse frequency greater than or equal to 500 hertz; and in response to the predetermined time period having elapsed, delivering the third electrical stimulation burst according to the value of the at least one parameter that at least partially defines the second electrical stimulation burst.

3. The system of claim 1, wherein: the first electrical stimulation burst comprises a plurality of primary electrical stimulation pulses followed by a primary electrical stimulation pulse, the plurality of primary electrical stimulation pulses are defined by a primary set of parameters and are configured to contribute to therapy of the patient, and the primary electrical stimulation pulse is defined by a primary set of parameters and is configured to evoke the ECAP signal from the tissue of the patient, wherein a value of the primary set of parameters is different than a value of the primary set of parameters.

4. The system of claim 3, wherein the primary electrical stimulation pulse of the first electrical stimulation burst comprises a current amplitude that is greater than a pulse amplitude of the plurality of primary electrical stimulation pulses of the first electrical stimulation burst.

5. The system of claim 3, wherein the plurality of primary electrical stimulation pulses of the first electrical stimulation burst is a first primary electrical current amplitude, wherein the primary electrical stimulation pulse of the first electrical stimulation burst comprises a first primary electrical current amplitude, wherein the plurality of primary electrical stimulation pulses of the second electrical stimulation burst comprises a second primary electrical current amplitude, wherein the primary electrical stimulation pulse of the second electrical stimulation burst comprises a second primary electrical current amplitude, and wherein the primary electrical stimulation pulse of the third electrical stimulation burst comprises a third primary electrical current amplitude. wherein the primary electrical stimulation pulses of the second electrical stimulation burst comprise a second primary current amplitude, and wherein determining the value of the at least one parameter defining the second electrical stimulation burst comprises: determining a value of the second primary current amplitude that is different from a value of the first primary current amplitude; determining a value of the second primary current amplitude that is different from a value of the first primary current amplitude, wherein a ratio of the second primary current amplitude to the second primary current amplitude is the same as a ratio of the first primary current amplitude to the first primary current amplitude.

6. The system of claim 5, wherein the value of the second primary current amplitude is greater than the value of the first primary current amplitude, wherein the value of the second primary current amplitude is greater than the value of the first primary current amplitude, and wherein a ratio of the second primary current amplitude to the second primary current amplitude is the same as a ratio of the first primary current amplitude to the first primary current amplitude.

7. The system of claim 5, wherein the value of the second primary current amplitude is less than the value of the first primary current amplitude, wherein the value of the second primary current amplitude is less than the value of the first primary current amplitude, and wherein a ratio of the second primary current amplitude to the second primary current amplitude is the same as a ratio of the first primary current amplitude to the first primary current amplitude.

8. The system of claim 1, wherein the method further comprises: delivering, by the medical device, electrical stimulation therapy comprising a third electrical stimulation burst to the patient during the predetermined time period, wherein the third electrical stimulation burst comprises a third pulse frequency that is less than 500 hertz; and in response to the predetermined time period having elapsed, ceasing delivery of the electrical stimulation therapy comprising the third electrical stimulation burst.

9. The system of claim 1, the method further comprising: delivering electrical stimulation therapy comprising a plurality of primary electrical stimulation pulses to the patient; detecting, by the medical device, a change in posture of the patient, wherein: delivering the electrical stimulation therapy comprising the first electrical stimulation burst to the patient comprises delivering, to the patient, the first electrical stimulation burst comprising a plurality of primary electrical stimulation pulses followed by a primary electrical stimulation pulse in response to the detected change in posture of the patient, the plurality of primary electrical stimulation pulses are configured to provide therapy to the patient, and the primary electrical stimulation pulse is configured to evoke the ECAP signal from the tissue of the patient.

10. The system of claim 1, wherein the electrical stimulation therapy comprises a burst frequency that is greater than or equal to 1 hertz and less than or equal to 200 hertz, wherein the burst frequency comprises a frequency at which the first electrical stimulation burst and the second electrical stimulation burst are delivered to the patient.

11. The system of claim 1, wherein the medical device is an implantable medical device.

12. A medical device configured to: deliver electrical stimulation therapy comprising a first electrical stimulation burst to a patient, wherein the first electrical stimulation burst comprises a first pulse frequency that is greater than or equal to 500 hertz; stopping delivery of the electrical stimulation therapy for a predetermined period of time after delivering the first electrical stimulation burst; sensing, during the predetermined period of time, an evoked compound action potential, ECAP, signal from tissue of the patient; determining, based on a characteristic value of the ECAP signal, a value of at least one parameter at least partially defining a second electrical stimulation burst, wherein the second electrical stimulation burst comprises a second pulse frequency greater than or equal to 500 hertz; and in response to the predetermined period of time having elapsed, delivering the second electrical stimulation burst according to the value of the at least one parameter at least partially defining the second electrical stimulation burst.

13. The medical device of claim 12, wherein the ECAP signal comprises a first ECAP signal, and wherein the medical device is further configured to: stop delivery of the electrical stimulation therapy for the predetermined period of time after delivering the second electrical stimulation burst; sensing, during the predetermined period of time, a second ECAP signal from the tissue of the patient; determining, based on a characteristic value of the second ECAP signal, a value of at least one parameter at least partially defining a third electrical stimulation burst, wherein the third electrical stimulation burst comprises a pulse frequency greater than or equal to 500 hertz; and in response to the predetermined period of time having elapsed, delivering the third electrical stimulation burst according to the value of the at least one parameter at least partially defining the second electrical stimulation burst.

14. The medical device of claim 12, wherein: the first electrical stimulation burst comprises a plurality of primary electrical stimulation pulses followed by a master electrical stimulation pulse, the plurality of primary electrical stimulation pulses are defined by a primary set of parameters and are configured to contribute to therapy of the patient, and the master electrical stimulation pulse is defined by a master set of parameters and is configured to evoke the ECAP signal from the tissue of the patient, wherein a value of the master set of parameters is different from a value of the primary set of parameters.

15. The medical device of claim 14, wherein the master electrical stimulation pulse of the first electrical stimulation burst comprises a current amplitude that is greater than a pulse amplitude of the plurality of primary electrical stimulation pulses of the first electrical stimulation burst.

16. The medical device of claim 14, wherein the plurality of primary electrical stimulation pulses of the first electrical stimulation burst is a first primary electrical current amplitude, wherein the master electrical stimulation pulse of the first electrical stimulation burst comprises a first master electrical current amplitude, wherein the plurality of primary electrical stimulation pulses of the second electrical stimulation burst comprises a second primary electrical current amplitude, wherein the master electrical stimulation pulse of the second electrical stimulation burst comprises a second master electrical current amplitude, and wherein to determine the value of the at least one parameter defining the second electrical stimulation burst, the medical device is configured to: determine a value of the second primary electrical current amplitude that is different from a value of the first primary electrical current amplitude; and determine a value of the second master electrical current amplitude that is different from a value of the first master electrical current amplitude, wherein a ratio of the second primary current amplitude to the second main current amplitude is the same as a ratio of the first primary current amplitude to the first main current amplitude.

17. The medical device of claim 16, wherein a value of the second primary current amplitude is greater than a value of the first primary current amplitude, wherein a value of the second main current amplitude is greater than a value of the first main current amplitude, and wherein a ratio of the second primary current amplitude to the second main current amplitude is the same as a ratio of the first primary current amplitude to the first main current amplitude.

18. The medical device of claim 16, wherein a value of the second primary current amplitude is less than a value of the first primary current amplitude, wherein a value of the second main current amplitude is less than a value of the first main current amplitude, and wherein a ratio of the second primary current amplitude to the second main current amplitude is the same as a ratio of the first primary current amplitude to the first main current amplitude.

19. The medical device of claim 12, wherein the medical device is further configured to: during the predetermined time period, deliver electrical stimulation therapy comprising a third electrical stimulation burst to the patient, wherein the third electrical stimulation burst comprises a third pulse frequency that is less than 500 hertz; and in response to the predetermined time period elapsing, cease delivery of the electrical stimulation therapy comprising the third electrical stimulation burst.

20. A non-transitory computer-readable medium comprising instructions that, when executed, are configured to cause a processing circuit of an implantable medical device to: control a stimulus generator of the implantable medical device to deliver electrical stimulation therapy comprising a first electrical stimulation burst to a patient, wherein the first electrical stimulation burst comprises a first pulse frequency that is greater than or equal to 500 hertz; after delivering the first electrical stimulation burst, control the stimulus generator to cease delivery of the electrical stimulation therapy for a predetermined time period; during the predetermined time period, sense an evoked compound action potential (ECAP) signal from tissue of the patient; determine a value of at least one parameter that at least partially defines a second electrical stimulation burst based on a characteristic value of the ECAP signal, wherein the second electrical stimulation burst comprises a second pulse frequency that is greater than or equal to 500 hertz; and in response to the predetermined time period elapsing, control the stimulus generator to deliver the second electrical stimulation burst according to the value of the at least one parameter that at least partially defines the second electrical stimulation burst.

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