Transient overstimulation management based on ecap

Abstract

Therapy can be determined using evoked compound action potentials (ECAPs). For example, a medical device includes stimulation generation circuitry and processing circuitry. The processing circuitry is configured to determine whether a characteristic of a first ECAP is greater than a threshold ECAP characteristic value. Based on the characteristic of the first ECAP being greater than the threshold ECAP characteristic value, the processing circuitry is configured to decrease a parameter of a first set of pulses delivered by the stimulation generation circuitry after the first ECAP. Additionally, the processing circuitry is configured to determine whether a characteristic of a second ECAP is less than the threshold ECAP characteristic value, and based on the characteristic of the second ECAP being less than the threshold ECAP characteristic value, increase a parameter of a second set of pulses delivered by the stimulation generation circuitry after the second ECAP.

Description

TECHNICAL FIELD

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

[0002] Medical devices can be external or implanted, and can be used to deliver electrical stimulation therapy to a patient via various tissue sites to treat a variety of symptoms or conditions, such as chronic pain, tremor, Parkinson's disease, epilepsy, urinary or fecal incontinence, sexual dysfunction, obesity, or gastroparesis. Medical devices can deliver electrical stimulation therapy via one or more leads that include electrodes located proximate to a target site associated with the brain, the spinal cord, the pelvic nerves, peripheral nerves, or the gastrointestinal tract of a patient. Stimulation proximate to the spinal cord, proximate to the sacral nerve, within the brain, and proximate to peripheral nerves are commonly referred to as spinal cord stimulation (SCS), sacral neuromodulation (SNM), deep brain stimulation (DBS), and peripheral nerve stimulation (PNS), respectively.

[0003] An evoked compound action potential (ECAP) is a synchronous firing of a population of neurons that occurs in response to a stimulus, including in some cases electrical stimulation, applied by a medical device. The ECAP can be detectable because it is an event separate from the stimulus itself, and the ECAP can reveal characteristics of the effect of the stimulus on the nerve fibers. Electrical stimulation can be delivered by a medical device to a patient in the form of a train of electrical pulses, and parameters of the electrical pulses can include frequency, amplitude, pulse width, and pulse shape. The parameters of the electrical pulses can be changed in response to sensory input, such as an ECAP sensed in response to a train of electrical pulses. Such a change can affect a patient’s perception of the electrical pulses, or affect a lack of such perception. SUMMARY

[0004] In general, systems, devices, and techniques are described for controlling electrical stimulation based on at least one stimulation threshold. More specifically, the techniques of the present disclosure can enable a medical device to control an electrical stimulation level based on sensing a plurality of evoked compound action potentials (ECAPs). For example, the medical device can decrease an intensity of stimulation pulses in response to a characteristic of a detected ECAP signal exceeding a threshold ECAP value, and subsequently increase the intensity of the stimulation pulses after a characteristic of a later ECAP signal falls back below the threshold ECAP value. The medical device can decrease the intensity from a predetermined intensity (e.g., a predetermined amplitude value), and increase the intensity back to the predetermined intensity, as programmed for the delivered pulses. This process can be referred to as a semi-closed loop technique, as the medical device can be configured only to adjust a stimulation parameter to a value below a predetermined value (rather than also being configured to increase the stimulation parameter above the predetermined value). For example, such a decrease in the intensity of the stimulation pulses can reduce an undesirable effect of the stimulation caused by patient movement.

[0005] In some examples, a medical device can deliver electrical stimulation therapy to a target tissue (e.g., a nerve fiber) of a patient, the electrical stimulation therapy including a plurality of stimulation pulses, where some or all of the stimulation pulses are therapy pulses that contribute to a therapeutic effect on the patient. Additionally, the medical device can be configured to detect ECAPs in response to the electrical stimulation therapy. The ECAPs can be indicative of an effect of the electrical stimulation therapy on the patient. For example, characteristics of the detected ECAPs, such as ECAP amplitude, ECAP detection rate, or ECAP length, can reveal whether the patient is able to perceive the electrical stimulation therapy or whether the patient is experiencing discomfort from the electrical stimulation therapy. The stimulation pulses can include control pulses that are delivered to the target tissue of the patient. The control pulses are stimulation pulses that elicit detectable ECAPs that the medical device can use as feedback for adjusting subsequent stimulation pulses. The control pulses can or can not contribute to a therapeutic effect on the patient. In some examples, in addition to the control pulses, the stimulation pulses can also include notification pulses. The notification pulses can be configured to contribute to a therapeutic effect on the patient and can have one or more stimulation parameters selected based on detected ECAPs elicited by one or more control pulses. The notification pulses and the control pulses can be collectively referred to herein as “stimulation pulses.”

[0006] In one example, a medical device comprises: stimulation generation circuitry configured to deliver electrical stimulation to a patient, wherein the electrical stimulation comprises a plurality of pulses; sensing circuitry configured to detect a plurality of evoked compound action potentials (ECAPs) elicited by respective ones of the plurality of pulses; and processing circuitry configured to: determine that a first value of a characteristic of a first ECAP is greater than a threshold ECAP characteristic value; in response to determining that the first value of the characteristic of the first ECAP is greater than the threshold ECAP characteristic value, decrease a parameter of a first set of pulses deliverable by the stimulation generation circuitry at least partially after the first ECAP from a predetermined value; determine that a second value of the characteristic of a second ECAP elicited after the first ECAP is less than the threshold ECAP characteristic value; and in response to determining that the second value of the characteristic of the second ECAP is less than the threshold ECAP characteristic value, increase the parameter of a second set of pulses deliverable by the stimulation generation circuitry at least partially after the second ECAP to the predetermined value.

[0007] In another example, a method includes: delivering, by stimulation generation circuitry of a medical device, electrical stimulation to a patient, wherein the electrical stimulation includes a plurality of pulses; detecting, by sensing circuitry of the medical device, a plurality of evoked compound action potentials (ECAPs) elicited by respective ones of the plurality of pulses; determining, by processing circuitry, that a first value of a characteristic of a first ECAP is greater than a threshold ECAP characteristic value; in response to determining that the first value of the characteristic of the first ECAP is greater than the threshold ECAP characteristic value, decreasing, by the processing circuitry, a parameter of a first set of pulses deliverable by the stimulation generation circuitry at least partially after the first ECAP from a predetermined value; determining, by the processing circuitry, that a second value of the characteristic of a second ECAP elicited after the first ECAP is less than the threshold ECAP characteristic value; and in response to determining that the second value of the characteristic of the second ECAP is less than the threshold ECAP characteristic value, increasing, by the processing circuitry, the parameter of a second set of pulses deliverable by the stimulation generation circuitry at least partially after the second ECAP to the predetermined value.

[0008] In another example, a computer-readable medium includes instructions that, when executed, cause processing circuitry to: control stimulation generation circuitry of a medical device to deliver electrical stimulation to a patient, wherein the electrical stimulation includes a plurality of pulses; control sensing circuitry of the medical device to detect a plurality of evoked compound action potentials (ECAPs) elicited by respective ones of the plurality of pulses; determine that a first value of a characteristic of a first ECAP is greater than a threshold ECAP characteristic value; in response to determining that the first value of the characteristic of the first ECAP is greater than the threshold ECAP characteristic value, decrease a parameter of a first set of pulses deliverable by the stimulation generation circuitry at least partially after the first ECAP from a predetermined value; determine that a second value of the characteristic of a second ECAP elicited after the first ECAP is less than the threshold ECAP characteristic value; and in response to determining that the second value of the characteristic of the second ECAP is less than the threshold ECAP characteristic value, increase the parameter of a second set of pulses deliverable by the stimulation generation circuitry at least partially after the second ECAP to the predetermined value.

[0009] SUMMARY The summary is intended to provide an overview of the subject matter described in the disclosure. It is not intended to provide an exclusive or exhaustive explanation. Further details of one or more examples are set forth in the detailed description and in the accompanying drawings. BRIEF DESCRIPTION OF DRAWINGS

[0010] Figure 1is a conceptual diagram illustrating an example system according to one or more techniques of this disclosure, including an implantable medical device (IMD) configured to deliver spinal cord stimulation (SCS) therapy, and an external programmer.

[0011] Figure 2 is a block diagram illustrating an example configuration of components of an IMD according to one or more techniques of this disclosure.

[0012] Figure 3 is a block diagram illustrating an example configuration of components of an example external programmer according to one or more techniques of this disclosure.

[0013] Figure 4 is a graph of example evoked compound action potentials (ECAPs) for respective stimulation pulses sensed according to one or more techniques of this disclosure.

[0014] Figure 5A is a timing diagram illustrating one example of an electrical stimulation pulse and a corresponding sensed ECAP according to one or more techniques of this disclosure.

[0015] Figure 5B is a timing diagram illustrating one example of an electrical stimulation pulse and a corresponding sensed ECAP according to one or more techniques of this disclosure.

[0016] Figure 6 is a timing diagram illustrating another example of an electrical stimulation pulse and a corresponding ECAP according to one or more techniques of this disclosure.

[0017] Figure 7 is a timing diagram illustrating another example of an electrical stimulation pulse and a corresponding ECAP according to one or more techniques of this disclosure.

[0018] Figure 8 is a timing diagram illustrating another example of an electrical stimulation pulse and a corresponding sensed ECAP according to one or more techniques of this disclosure.

[0019] Figure 9 is a flow diagram illustrating example operations for controlling stimulation based on one or more sensed ECAPs according to one or more techniques of this disclosure.

[0020] Figure 10 illustrates a voltage / current / time graph plotting control pulse current amplitude, therapy pulse current amplitude, ECAP voltage amplitude, and second ECAP voltage amplitude as a function of time according to one or more techniques of this disclosure.

[0021] Figure 11is a flowchart showing exemplary operations for controlling stimulation based on one or more sensed ECAPs in accordance with one or more techniques of this disclosure.

[0022] Figure 12 Voltage / current / time graphs are shown that plot control pulse current amplitude, therapy pulse current amplitude, ECAP voltage amplitude, and second ECAP voltage amplitude as a function of time in accordance with one or more techniques of this disclosure. DETAILED DESCRIPTION

[0023] This disclosure describes examples of medical devices, systems, and techniques for automatically adjusting electrical stimulation therapy delivered to a patient based on one or more characteristics of an evoked compound action potential (ECAP) received by the medical device in response to (in some examples) stimulation pulses delivered by the medical device. The electrical stimulation therapy is typically delivered to a target tissue (e.g., one or more nerves or muscles) of the patient via two or more electrodes. Parameters of the electrical stimulation therapy (e.g., electrode combination, voltage or current amplitude, pulse width, pulse frequency, etc.) are selected by a clinician and / or the patient to provide relief from various symptoms, such as pain, muscle disorders, etc.

[0024] However, when the patient moves, the distance between the electrodes and the target tissue changes. Changes in posture or patient activity can cause the electrodes to move closer to or further away from the target nerve. Lead migration over time can also change this distance between the electrodes and the target tissue. In some examples, transient patient conditions, such as coughing, sneezing, laughing, a Valsalva maneuver, leg lifting, neck movement, or deep breathing, can temporarily cause the stimulation electrodes of the medical device to move closer to the target tissue of the patient, thereby intermittently changing the patient’s perception of the electrical stimulation therapy.

[0025] Because neural recruitment is a function of stimulation intensity as well as the distance between the target tissue and the electrodes, the electrodes moving closer to the target tissue can cause the patient’s perception to increase (e.g., possible discomfort, undesirable sensation, or painful sensation), while the electrodes moving further away from the target tissue can cause the efficacy of the therapy to the patient to decrease. For example, if the stimulation remains consistent and the stimulation electrodes move closer to the target tissue, the patient can perceive the stimulation as being more intense, more uncomfortable, or even more painful. Conversely, when the electrodes move further away from the target tissue, consistent stimulation can result in a decrease in the intensity of the stimulation perceived by the patient, which can decrease the effectiveness of the therapy to the patient. Discomfort or pain caused by transient patient conditions can be referred to herein as “transient overstimulation.” Accordingly, in some examples, it can be beneficial to adjust stimulation parameters in response to patient movement or other conditions that can cause transient overstimulation.

[0026] ECAPs can be evoked by a stimulation pulse delivered to a nerve fiber of a patient. After evocation, the ECAP can travel down the nerve fiber away from the initial stimulation. In some cases, the sensing circuitry of the medical device can detect this ECAP. Characteristics of the detected ECAP signal can indicate that the distance between the electrode and the target tissue is changing. However, in some examples, the duration of the initial stimulation pulse can be long enough that a responsive ECAP is occluded by the initial stimulation pulse itself. In other words, the initial stimulation pulse can evoke an ECAP that reaches the sensing electrode before the stimulation pulse itself terminates. Thus, in some such examples, the medical device can not be able to detect the ECAP because the stimulation pulse generally has a large amplitude and can obscure or otherwise interfere with the ECAP signal.

[0027] The techniques of this disclosure can provide one or more advantages. For example, a medical device can adjust stimulation pulses in order to prevent transient overstimulation from occurring in a patient. In some examples, the medical device can monitor a characteristic of an ECAP sensed by the sensing circuitry of the medical device in response to a stimulation pulse delivered by the medical device. If a value of the characteristic of the first ECAP exceeds a threshold ECAP characteristic value, the medical device can decrement (or reduce) a parameter of a subsequent stimulation pulse. By decrementing the stimulation pulse, the medical device can reduce the probability that the patient experiences transient overstimulation. Additionally, the medical device can continue to monitor ECAPs received by the sensing circuitry after the first ECAP. If a value of the characteristic of a second ECAP is below the threshold ECAP characteristic value, the medical device can increment the parameter of a subsequent stimulation pulse, eventually returning the stimulation pulse to the value of the parameter of the stimulation pulse delivered prior to the first ECAP. In this way, one or more techniques of this disclosure can enable a medical device to temporarily adjust one or more parameters of a stimulation pulse to a value below a predetermined value (e.g., the programmed value of those pulses) in order to prevent transient overstimulation, and subsequently return the stimulation pulse to a previous level after the risk of the patient experiencing transient overstimulation subsides. This process can be referred to as a semi-closed loop technique because the medical device can be configured to only adjust the stimulation parameter to a value below a predetermined value (rather than also being configured to increase the stimulation parameter above the predetermined value).

[0028] To facilitate sensing of ECAPs, a medical device delivering pulses as part of therapy (e.g., notification pulses) can also deliver a plurality of control pulses designed to improve the ability to detect ECAPs. For example, control pulses can be shorter in duration than control pulses to reduce or eliminate signal artifacts caused by control pulses when ECAPs are received at a sensing electrode. In particular embodiments, control pulses are short enough that the pulses end before all or most of an ECAP signal reaches the sensing electrode. In this way, a medical device can interleave a plurality of control pulses with at least some of a plurality of notification pulses. For example, a medical device can deliver a notification pulse for a period of time before delivering a control pulse and sensing a corresponding ECAP, if any. The medical device can then resume delivery of notification pulses for another period of time. In some examples, a pulse duration of control pulses is less than a pulse duration of notification pulses, and the pulse duration of control pulses is short enough that the medical device can sense a separate ECAP for each control pulse. In some examples, control pulses can provide therapy to a patient.

[0029] As described herein, transient patient movement can cause the distance between an electrode and a target tissue to temporarily change during the respective transient patient movement. Such transient patient movement can include one or more quick movements of about a second or less. During such transient movement, the distance between the electrode and the target tissue can change and affect the patient’s perception of electrical stimulation therapy delivered by the medical device. If the stimulation pulses are constant and the electrode moves closer to the target tissue, the patient can experience a greater or enhanced “sensation” or perception from the therapy. This enhanced sensation can be perceived as discomfort or pain (e.g., transient overstimulation) in response to the electrode moving closer to the target tissue. ECAPs are a measure of neural recruitment because each ECAP signal represents a superposition of potentials generated in response to an electrical stimulus (e.g., a stimulation pulse) firing of axons. Changes in characteristics of an ECAP signal (e.g., the amplitude of a portion of the signal) occur as a function of the number of axons that have been activated by stimulation pulses that have been delivered.

[0030] As described herein, the system can monitor changes in a characteristic of the ECAP signal and adjust one or more stimulation parameters of one or more stimulation pulses (e.g., control pulses or notification pulses) that are to be subsequently delivered to the patient based on the changes in the characteristic of the ECAP signal. For example, the system can decrease the intensity of the stimulation pulses (e.g., decrease the current amplitude, pulse width, and / or frequency) in response to detecting an increase in the amplitude of the ECAP signal. In this way, the system can responsively manage the stimulation pulses in response to changes in one or more characteristics of the ECAP signal that are representative of transient patient movement. In particular, based on the sensed one or more characteristics of the ECAP, the system can adjust one or more parameters that at least partially define the stimulation pulses. In certain embodiments, it can be beneficial to alleviate chronic pain in a patient while avoiding inducing transient side effects such as discomfort, pain, or paresthesia. Using paresthesia as an example, some patients can prefer to maintain a therapeutic level of treatment that is sub-perceptually delivered to the patient. Other patients can prefer a therapeutic level that generates a desired level of paresthesia for the patient. In either case, it can be desirable to prevent the patient from feeling discomfort or pain from a transient condition of increased stimulation levels at the nerve, which can be caused by a decrease in the distance between the nerve and the electrode. Thus, the system can utilize the ECAP as feedback to limit undesirable increases in stimulation pulse intensity received at the nerve, which can be perceived by the patient as a change (or presence) of paresthesia, discomfort, pain, or other sensation.

[0031] Because the ECAP can provide an indication of the patient’s perception of the electrical stimulation therapy, the techniques of the present disclosure can enable the medical device to decrease one or more parameters of the stimulation pulses delivered to the target tissue in response to the first ECAP exceeding the threshold ECAP characteristic value. By decreasing the one or more parameters of the notification pulses, the medical device can prevent the patient from experiencing transient overstimulation. Subsequently, if the medical device determines that the sensed ECAP has later dropped below the threshold ECAP characteristic value, the medical device can restore the stimulation pulses to the parameter values set prior to the medical device decreasing the one or more parameters of the stimulation pulses in response to exceeding the threshold ECAP characteristic value.

[0032] In some examples, the medical device can deliver stimulation pulses to include control pulses and notification pulses. After a stimulation pulse delivered first depolarizes a nerve, a neural pulse that can be detected as an ECAP signal travels quickly along the nerve fiber. Thus, if a stimulation pulse delivered by a first electrode has a pulse width that is too long, a different electrode configured to sense ECAPs can sense that stimulation pulse itself as an artifact that obscures a lower amplitude ECAP signal. However, the ECAP signal loses fidelity as the potential propagates from the electrical stimulation because different nerve fibers propagate the potential at different speeds. Thus, sensing the ECAP at a location distal from the stimulation electrode can avoid artifacts caused by stimulation pulses with long pulse widths, but the ECAP signal can lose the fidelity needed to detect changes in the ECAP signal that occur when the electrode to target tissue distance changes. In other words, the system can not be able to identify ECAPs from stimulation pulses configured to provide therapy to the patient at any distance from the stimulation electrode. Thus, the medical device can employ control pulses configured to elicit detectable ECAPs and notification pulses that can or can not contribute to the therapeutic effect of the patient.

[0033] In these examples, the medical device is configured to deliver a plurality of notification pulses configured to provide therapy to the patient and a plurality of control pulses that can or can not contribute to the therapy. At least some of the control pulses can elicit detectable ECAP signals whose primary purpose is not to provide therapy to the patient. The control pulses can be interleaved with the delivery of the notification pulses. For example, the medical device can alternate delivering notification pulses and control pulses such that a control pulse is delivered between successive notification pulses and an ECAP signal is sensed. In some examples, a plurality of control pulses are delivered between the delivery of successive notification pulses and respective ECAP signals are sensed. In some examples, a plurality of notification pulses will be delivered between successive control pulses. In any case, the notification pulses can be delivered according to a selected predetermined pulse frequency such that the notification pulses can produce a therapeutic result for the patient. One or more control pulses are then delivered within one or more time windows between successive notification pulses delivered according to the predetermined pulse frequency and respective ECAP signals are sensed. In this way, the medical device can deliver notification pulses from the medical device without interruption while sensing ECAPs from control pulses delivered during times when notification pulses are not being delivered. In other examples described herein, ECAPs are sensed by the medical device in response to notification pulses delivered by the medical device and control pulses are not used to elicit ECAPs.

[0034] According to examples described herein, a medical device can be configured to deliver stimulation pulses, including a combination of control pulses or a plurality of control pulses and a plurality of notification pulses. In some cases, the plurality of control pulses can be therapeutic and contribute to therapy received by the patient. In other examples, the plurality of control pulses can be non-therapeutic and do not contribute to therapy received by the patient. In other words, a control pulse configured to elicit a detectable ECAP can or can not contribute to alleviating a patient condition or a symptom of a patient condition. In contrast to control pulses, notification pulses can not elicit a detectable ECAP, or the system can not utilize ECAPs from notification pulses as feedback to control therapy. Thus, the medical device or other component associated with the medical device can instead determine values of one or more stimulation parameters that at least partially define notification pulses based on ECAP signals elicited from control pulses. In this way, notification pulses can be informed by ECAPs elicited from control pulses. The medical device or other component associated with the medical device can determine values of one or more stimulation parameters that at least partially define control pulses based on ECAP signals elicited from previous control pulses.

[0035] Although electrical stimulation is generally described herein in the form of electrical stimulation pulses, in other examples electrical stimulation can be delivered in non-pulsed forms. For example, electrical stimulation can be delivered as a signal having various waveform shapes, frequencies, and amplitudes. Thus, electrical stimulation in non-pulsed signal forms can be a continuous signal, which can have a sinusoidal waveform or other continuous waveform.

[0036] Figure 1 is a conceptual diagram illustrating an example system 100 according to one or more techniques of the present disclosure, including an implantable medical device (IMD) 110 configured to deliver spinal cord stimulation (SCS) therapy, and an external programmer 150. Although the techniques described in the present disclosure are generally applicable to a variety of medical devices including external devices and IMDs, for illustrative purposes, the application of such techniques to IMDs, and more specifically, to implantable electrical stimulators (e.g., neurostimulators) will be described. More specifically, for illustrative purposes, the present disclosure will refer to implantable SCS systems, but without limitation thereto, other types of medical devices or other therapeutic applications of medical devices.

[0037] As shown in Figure 1 System 100 includes IMD 110, leads 130A and 130B, and external programmer 150, which are shown in conjunction with a patient 105, who is typically a human patient. In Figure 1In this example, IMD 110 is an implantable electrical stimulator configured to generate and deliver electrical stimulation therapy to patient 105 via one or more electrodes of leads 130A and / or 130B (collectively, "leads 130"), for example, to relieve chronic pain or other symptoms. In other examples, IMD 110 may be coupled to a single lead carrying multiple electrodes, or more than two leads each carrying multiple electrodes. As part of the stimulation pulses delivering the electrical stimulation therapy, IMD 110 may be configured to generate and deliver control pulses configured to trigger an ECAP signal. In some examples, the control pulses may provide therapy. In other examples, IMD 110 may deliver notification pulses that aid in the treatment of the patient but do not trigger a detectable ECAP. IMD 110 may be a long-term electrical stimulator that remains implanted in patient 105 for weeks, months, or even years. In other examples, IMD 110 may be a temporary or experimental stimulator used to screen or evaluate the efficacy of electrical stimulation for long-term treatment. In one example, IMD 110 is implanted in patient 105, while in another example, IMD 110 is an external device coupled to a percutaneously implanted lead. In some examples, IMD 110 uses one or more leads, while in other examples, IMD 110 is leadless.

[0038] IMD 110 can be made of components sufficient to mount IMD 110 (e.g., Figure 2 The component shown may be constructed from any polymer, metal, or composite material housed within the patient 105. In this example, the IMD 110 may be constructed with a biocompatible shell, such as titanium or stainless steel, or a polymeric material (such as silicone, polyurethane, or liquid crystal polymer), and surgically implanted into a site near the pelvis, abdomen, or buttocks of the patient 105. In other examples, the IMD 110 may be implanted in other suitable sites within the patient 105, depending on, for example, the target site within the patient 105 for delivering electrical stimulation therapy. The outer shell of the IMD 110 may be constructed to provide a hermetically sealed component, such as a rechargeable or non-rechargeable power source. Furthermore, in some examples, the outer shell of the IMD 110 is selected from materials that facilitate the reception of energy to charge a rechargeable power source.

[0039] The electrical stimulation energy can be, for example, pulses based on a constant current or constant voltage, delivered from the IMD 110 to one or more target tissue sites in the patient 105 via one or more electrodes (not shown) of the implanted lead 130. Figure 1In this example, the leads 130 carry electrodes disposed adjacent to target tissue of the spinal cord 120. One or more of the electrodes can be disposed at a distal tip of the lead 130 and / or other locations along the middle of the lead. The leads 130 can be implanted and coupled to the IMD 110. The electrodes can transfer electrical stimulation generated by an electrical stimulation generator in the IMD 110 to tissue of the patient 105. Although the leads 130 can each be a single lead, the leads 130 can include lead extensions or other segments that can facilitate implantation or positioning of the leads 130. In some other examples, the IMD 110 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. Further, in some other examples, the system 100 can include one lead or more than two leads, each coupled to the IMD 110 and directed to similar or different target tissue sites.

[0040] The electrodes of the leads 130 can be electrode pads on a paddle lead, circular (e.g., ring) electrodes encircling a lead body, conformal electrodes, cuff electrodes, segmented electrodes (e.g., electrodes disposed at different circumferential locations around a lead rather than a continuous ring electrode), any combination thereof (e.g., ring electrodes and segmented electrodes), or any other type of electrode capable of forming monopolar, bipolar, or multipolar electrode combinations for therapy. For purposes of illustration, ring electrodes disposed at different axial locations of a distal end of the leads 130 will be described.

[0041] The deployment of electrodes via leads 130 is described for purposes of illustration, but electrode arrays can be deployed in different ways. For example, a housing associated with a leadless stimulator can carry electrode arrays, e.g., rows and / or columns (or other patterns), to which a shift operation 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 examples, the electrode arrays include electrode segments arranged at respective locations around a circumference of a lead, e.g., in the form of one or more segmented rings around a circumference of a cylindrical lead. In other examples, one or more of the leads 130 are linear leads having 8 ring electrodes along an axial length of the lead. In another example, the electrodes are segmented rings arranged in a linear fashion at a circumference of the lead along an axial length of the lead.

[0042] Stimulation parameters of a therapy stimulation program that define stimulation pulses of electrical stimulation therapy delivered by IMD 110 through electrodes of lead 130 can include information identifying which electrodes have been selected to deliver stimulation according to the stimulation program, the polarity of the selected electrodes (i.e., the electrode combination used for the program), and the voltage or current amplitude, pulse frequency, pulse width, pulse shape of the stimulation delivered by the electrodes. These stimulation parameters of the stimulation pulses (e.g., control pulses and / or notification pulses) are typically predetermined parameter values that are determined prior to delivery of the stimulation pulses (e.g., according to the stimulation program settings). In some examples, however, the system 100 automatically changes one or more parameter values based on one or more factors or based on user input.

[0043] The ECAP test stimulation programs can define stimulation parameter values that define control pulses delivered by IMD 110 through at least some of the electrodes of lead 130. These stimulation parameter values can include information identifying which electrodes have been selected to deliver control pulses, the polarity of the selected electrodes (i.e., the electrode combination used for the program), and the voltage or current amplitude, pulse frequency, pulse width, and pulse shape of the stimulation delivered by the electrodes. The stimulation signals (e.g., one or more stimulation pulses or a continuous stimulation waveform) defined by the parameters of each ECAP test stimulation program are configured to evoke a compound action potential from the nerve. In some examples, the ECAP test stimulation programs define when control pulses are delivered to the patient based on the frequency and / or pulse width of the notification pulses when the notification pulses are also delivered. In some examples, the stimulation defined by each ECAP test stimulation program is not intended to provide therapy to the patient or contribute to therapy of the patient. In other examples, the stimulation defined by each ECAP test stimulation program can contribute to therapy when the control pulses elicit a detectable ECAP signal and contribute to therapy. In this way, the ECAP test stimulation programs can define stimulation parameters that are the same or similar to the stimulation parameters of the therapy stimulation program.

[0044] Although Figure 1 While the system 100 is described as being involved in SCS therapy, e.g., for treating pain, in other examples, the system 100 can be configured to treat any other condition that can benefit from electrical stimulation therapy. For example, the system 100 can be used to treat tremor, Parkinson's disease, epilepsy, pelvic floor abnormalities (e.g., urinary incontinence or other bladder dysfunction, fecal incontinence, pelvic pain, intestinal dysfunction, or sexual dysfunction), obesity, gastroparesis, or psychiatric disorders (e.g., depression, mania, obsessive-compulsive disorder, anxiety, etc.). In this way, the system 100 can be configured to provide therapy in the form of deep brain stimulation (DBS), peripheral nerve stimulation (PNS), peripheral nerve field stimulation (PNFS), cortical stimulation (CS), pelvic floor stimulation, gastrointestinal stimulation, or any other stimulation therapy capable of treating a condition of the patient 105.

[0045] In some examples, the lead 130 includes one or more sensors configured to allow the IMD 110 to monitor one or more parameters of the patient 105, such as patient activity, pressure, temperature, or other characteristics. One or more sensors can be provided in addition to or in lieu of therapy delivery by the lead 130.

[0046] The IMD 110 is configured to deliver electrical stimulation therapy to the patient 105 through selected combinations of electrodes carried by one or two leads 130, either alone or in combination with electrodes carried or defined by the external housing of the IMD 110. The target tissue for electrical stimulation therapy can be any tissue affected by electrical stimulation, which can be in the form of electrical stimulation pulses or continuous waveforms. In some examples, the target tissue includes a nerve, smooth muscle, or skeletal muscle. In Figure 1 In the illustrated example, the target tissue is tissue proximate to the spinal cord 120, such as within the intrathecal space or epidural space of the spinal cord 120, or in some examples, an adjacent nerve branching from the spinal cord 120. The lead 130 can be introduced into the spinal cord 120 via any suitable region, such as the thoracic, cervical, or lumbar regions. For example, stimulating the spinal cord 120 can prevent pain signals from traveling through the spinal cord 120 and to the brain of the patient 105. The patient 105 can perceive the interruption of the pain signals as a reduction in pain, and thus as an effective therapeutic outcome. In other examples, stimulating the spinal cord 120 can produce paresthesia, which can reduce the patient's 105 perception of pain, and thus provide an effective therapeutic outcome.

[0047] The IMD 110 generates and delivers electrical stimulation therapy to the patient 105 according to one or more therapy stimulation programs to a target stimulation site within the patient 105 via electrodes of the lead 130 to the patient 105. A therapy stimulation program defines values for one or more parameters that define an aspect of therapy delivered by the IMD 110 according to the program. For example, a therapy stimulation program that controls the IMD 110 to deliver stimulation in the form of pulses can define values for voltage or current pulse amplitude, pulse width, and pulse rate (e.g., pulse frequency) of the stimulation pulses delivered by the IMD 110 according to the program.

[0048] In some examples in which an ECAP signal cannot be detected from the type of pulses intended to be delivered to provide therapy to the patient, control pulses and notification pulses can be delivered. For example, the IMD 110 is configured to deliver control stimulation to the patient 105 via a combination of electrodes of the lead 130, either alone or in combination with electrodes carried or defined by the outer housing of the IMD 110. The tissue targeted by the control stimulation can be the same tissue targeted by the electrical stimulation therapy, but the IMD 110 can deliver the control stimulation pulses via the same, at least some of the same, or different electrodes. Because the control stimulation pulses are delivered in an interleaved manner with the notification pulses, the clinician and / or user can select any desired electrode combination for the notification pulses. Similar to the electrical stimulation therapy, the control stimulation can be in the form of electrical stimulation pulses or continuous waveforms. In one example, each control stimulation pulse can include a balanced biphasic square pulse that employs an active recharge phase. However, in other examples, the control stimulation pulses can include a monophasic pulse followed by a passive recharge phase. In other examples, the control pulses can include an unbalanced biphasic portion and a passive recharge portion. Although not required, the biphasic control pulses can include an interphase interval between the positive and negative phases to facilitate the propagation of neural pulses in response to the first phase of the biphasic pulse. The control stimulation can be delivered without interrupting the delivery of the electrical stimulation notification pulses, such as during a window between consecutive notification pulses. The control pulses can elicit an ECAP signal from the tissue, and the IMD 110 can sense the ECAP signal via two or more electrodes on the lead 130. In the case of control stimulation pulses applied to the spinal cord 120, the signal can be sensed by the IMD 110 from the spinal cord 120.

[0049] The IMD 110 can deliver control stimulation to the target stimulation site in the patient 105 via electrodes of the lead 130 in accordance with one or more ECAP test stimulation programs. The one or more ECAP test stimulation programs can be stored in a storage device of the IMD 110. Each ECAP test program of the one or more ECAP test stimulation programs includes values for one or more parameters that define an aspect of the control stimulation delivered by the IMD 110 in accordance with the program, such as current or voltage amplitude, pulse width, pulse frequency, electrode combination, and in some examples, timing based on the notification pulses to be delivered to the patient 105. In some examples, the IMD 110 delivers control stimulation to the patient 105 in accordance with multiple ECAP test stimulation programs.

[0050] A user, such as a clinician or patient 105, can interact with a user interface of an external programmer 150 to program the IMD 110. Programming of the IMD 110 generally can refer to the generation and transfer of commands, programs, or other information to control the operation of the IMD 110. In this way, the IMD 110 can receive transmitted commands and programs from the external programmer 150 to control electrical stimulation therapy (e.g., informed pulses) and control stimulation (e.g., control pulses). For example, the external programmer 150 can transmit therapy stimulation programs, ECAP test stimulation programs, stimulation parameter adjustments, therapy stimulation program selections, ECAP test program selections, user inputs, or other information to control the operation of the IMD 110, e.g., through wireless telemetry or a wired connection. As described herein, stimulation delivered to a patient can include control pulses, and in some examples, stimulation can include control pulses and informed pulses.

[0051] In some cases, if the external programmer 150 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 150 is primarily intended for use by a patient, it can be characterized as a patient programmer. A patient programmer generally can be accessible to the patient 105 and, in many cases, can be a portable device that can accompany the patient 105 at all times in the patient’s daily life. For example, the patient programmer can receive input from the patient 105 when the patient wishes to terminate or change electrical stimulation therapy. Generally, a physician or clinician programmer can support selection and generation of programs by a clinician for use by the IMD 110, while a patient programmer can support adjustment and selection of such programs by a patient during routine use. In other examples, the external programmer 150 can include or be part of an external charging device that recharges a power source of the IMD 110. In this way, a user can use one device or multiple devices to program and charge the IMD 110.

[0052] As described herein, information can be transmitted between the external programmer 150 and the IMD 110. Accordingly, the IMD 110 and the external programmer 150 can communicate via wireless communication using any techniques known in the art. Examples of communication techniques can include, for example, radiofrequency (RF) telemetry and inductive coupling, although other techniques are also contemplated. In some examples, the external programmer 150 includes a communication head that can be placed proximate to the IMD 110 implant site adjacent to the patient’s body to improve the quality or security of communication between the IMD 110 and the external programmer 150. Communication between the external programmer 150 and the IMD 110 can occur during or separate from power transmission.

[0053] In some examples, IMD 110 delivers electrical stimulation therapy to a target tissue site of the spinal cord 120 of patient 105 via electrodes (not shown) on lead 130 in accordance with a plurality of therapy stimulation programs in response to commands from external programmer 150. In some examples, IMD 110 makes modifications to the therapy stimulation programs as the therapy needs of patient 105 evolve over time. For example, modifications to the therapy stimulation programs can result in adjustments to at least one parameter of the plurality of informed pulses. When patient 105 receives the same therapy for a long period of time, the efficacy of the therapy can decrease. In some cases, the parameters of the plurality of informed pulses can be updated automatically.

[0054] In the present disclosure, the efficacy of electrical stimulation therapy can be indicated by one or more features of action potentials (e.g., the amplitude of one or more peaks or the amplitude between one or more peaks, or the area under the curve of one or more peaks) induced by stimulation pulses delivered by IMD 110 (i.e., features of ECAP signals). Electrical stimulation therapy delivered by lead 130 of IMD 110 can cause neurons within the target tissue to induce a compound action potential that travels up and down the target tissue, eventually reaching a sensing electrode of IMD 110. In addition, control stimulation can also elicit at least one ECAP, and the ECAP in response to control stimulation can also be a proxy for therapy efficacy. The amount of action potentials induced (e.g., the number of action potential signals propagated by neurons) can be based on various parameters of the electrical stimulation pulses, such as amplitude, pulse width, frequency, pulse shape (e.g., the rate of change of the voltage and / or current amplitude of the pulse at the onset and / or offset of the pulse), etc. The rate of change can define the rate of change of the voltage and / or current amplitude of the pulse at the onset and / or offset of each pulse or phase within a pulse. For example, a very high rate of change indicates a steep or even near-vertical edge of the pulse, while a low rate of change indicates a longer ramp up (or ramp down) of the pulse amplitude. In some examples, these parameters contribute to the strength of the electrical stimulation. In addition, the features (e.g., amplitude) of the ECAP signals can vary based on the distance between the stimulation electrode and the nerves affected by the electric field produced by the delivered control stimulation pulses.

[0055] In one example, each therapy pulse can have a pulse width greater than about 300 ps (in some examples such as between about 300 ps and 1000 ps (i.e., 1 millisecond)). At these pulse widths, IMD 110 can be insufficient to detect the ECAP signal because the therapy pulse is also detected as an artifact that obscures the ECAP signal. If the ECAP is not sufficiently recorded, the ECAP that reaches IMD 110 cannot be compared to a target ECAP characteristic (e.g., a target ECAP amplitude), and the electrical stimulation therapy cannot be altered in response to the responsive ECAP. When the informing pulses have these longer pulse widths, IMD 110 is able to deliver control stimulation in the form of control pulses. The control pulses can have a pulse width less than about 300 ps, such as a biphasic pulse with each phase having a duration of about 100 ps. Because the control pulses can have a shorter pulse width than the informing pulses, the ECAP signal can be sensed and identified after each control pulse and used to inform IMD 110 of any changes that should be made to the informing pulses (and in some examples, the control pulses). Generally, the term“pulse width” refers to the total duration of each phase of a single pulse, and the interphase interval as appropriate. A single pulse includes, in some examples, a single phase (i.e., a monophasic pulse), or in other examples, two or more phases (e.g., a biphasic pulse or a triphasic pulse). The pulse width defines a time period that begins with the start time of the first phase of the pulse and ends with the end time of the last phase of the pulse (e.g., a biphasic pulse with a positive phase that lasts 100 ps, a negative phase that lasts 100 ps, and an interphase interval that lasts 30 ps defines a pulse width of 230 ps). In another example, a control pulse can include a positive phase that lasts 90 ps, a negative phase that lasts 90 ps, and an interphase interval that lasts 30 ps to define a pulse width of 210 ps. In another example, a control pulse can include a positive phase that lasts 120 ps, a negative phase that lasts 120 ps, and an interphase interval that lasts 30 ps to define a pulse width of 270 ps.

[0056] As described, the example techniques for adjusting the stimulation parameter values of the notification pulses are based on comparing measured ECAP signal characteristic values to target ECAP characteristic values. During the delivery of the control stimulation pulses defined by one or more ECAP test stimulation programs, the IMD 110 senses tissue potentials of the spinal cord 120 of the patient 105 via two or more electrodes implanted on the lead 130 to measure electrical activity of the tissue. The IMD 110 senses an ECAP from the target tissue of the patient 105, for example, using electrodes and associated sensing circuitry on one or more leads 130. In some examples, the IMD 110 receives a signal indicative of an ECAP from one or more sensors (e.g., one or more electrodes and circuitry) internal or external to the patient 105. Such example signals can include a signal indicative of an ECAP of tissue of the patient 105. Examples of the one or more sensors include one or more sensors configured to measure a compound action potential of the patient 105 or a physiological effect indicative of a compound action potential. For example, to measure a physiological effect indicative of a compound action potential, the one or more sensors can be an accelerometer, a pressure sensor, a flex sensor, a sensor configured to detect a posture of the patient 105, or a sensor configured to detect a respiratory function of the patient 105. In this way, although the ECAP can indicate a change in posture or other patient movement, other sensors can also detect similar changes in posture or movement using modalities separate from the ECAP. In other examples, however, the external programmer 150 receives a signal indicative of a compound action potential in the target tissue of the patient 105 and sends a notification to the IMD 110.

[0057] In the example techniques described in this disclosure, the control stimulation parameters and the target ECAP characteristic values can be initially set at a clinic, but can also be set and / or adjusted by the patient 105 at home. Once the target ECAP characteristic values are set, the example techniques allow for automatic adjustment of the therapy stimulation parameters to maintain a consistent volume of neural activation and a consistent perception of therapy for the patient as the distance of the electrodes to the neurons changes. Being able to change the stimulation parameter values can also allow for therapy to have long-term efficacy and be able to maintain a consistent stimulation intensity (e.g., as indicated by the ECAP) by comparing the measured ECAP values to the target ECAP characteristic values. The IMD 110 can perform these changes without intervention by a physician or the patient 105.

[0058] In some examples, the system varies the target ECAP characteristic value over a period of time. The system can be programmed to vary the target ECAP characteristic in order to adjust the intensity of the informed pulses to provide a varying sensation to the patient (e.g., to increase or decrease the volume of neural activation). In one example, the system can be programmed to oscillate the target ECAP characteristic value between a maximum target ECAP characteristic value and a minimum target ECAP characteristic value at a predetermined frequency to provide a sensation to the patient that can be perceived as a wave or other sensation that can provide therapeutic relief to the patient. The maximum target ECAP characteristic value, the minimum target ECAP characteristic value, and the predetermined frequency can be stored in a storage device of the IMD 110 and can be updated in response to a signal from the external programmer 150 (e.g., a user request to change the values stored in the storage device of the IMD 110). In other examples, the target ECAP characteristic value can be programmed to steadily increase or steadily decrease to a baseline target ECAP characteristic value over a period of time. In other examples, the external programmer 150 can program the target ECAP characteristic value to automatically vary over time according to other predetermined functions or patterns. In other words, the target ECAP characteristic value can be programmed to vary incrementally by a predetermined amount or a predetermined percentage that is selected according to a predetermined function (e.g., a sinusoidal function, a ramp function, an exponential function, a logarithmic function, etc.). The increment of the target ECAP characteristic value change can vary for every particular number of pulses or particular units of time. Although the system can vary the target ECAP characteristic value, the system can still use the received ECAP signal to adjust one or more parameter values of the informed pulses and / or the control pulses in order to meet the target ECAP characteristic value.

[0059] In some examples, IMD 110 includes stimulation generation circuitry configured to deliver electrical stimulation therapy to the patient, where the electrical stimulation therapy includes a plurality of notification pulses. Additionally, the stimulation generation circuitry of IMD 110 can be configured to deliver a plurality of control pulses, where the plurality of control pulses are interleaved with at least some of the plurality of notification pulses. In some examples, IMD 110 includes sensing circuitry configured to detect a plurality of ECAPs, where the sensing circuitry is configured to detect each of the plurality of ECAPs after a control pulse of the plurality of control pulses and before a subsequent therapy pulse of the plurality of notification pulses. Even though IMD 110 can receive the plurality of ECAPs based on IMD 110 delivering the plurality of control pulses (e.g., the plurality of control pulses can evoke the plurality of ECAPs received by IMD 110), the plurality of ECAPs can be indicative of the efficacy of the plurality of notification pulses. In other words, although in some cases the plurality of ECAPs can not be evoked by the plurality of notification pulses themselves, the plurality of ECAPs can still reveal one or more characteristics of the plurality of notification pulses, or one or more effects of the plurality of notification pulses on patient 105. In some examples, IMD 110 delivers the plurality of notification pulses above a perception threshold, where patient 105 is able to perceive the plurality of notification pulses delivered above the perception threshold. In other examples, IMD 110 delivers the plurality of notification pulses below a perception threshold, where patient 105 is unable to perceive the plurality of notification pulses delivered below the perception threshold.

[0060] IMD 110 can include processing circuitry configured to process the plurality of ECAPs received by the sensing circuitry of IMD 110, in some examples. For example, the processing circuitry of IMD 110 is configured to determine whether a parameter of a first ECAP is greater than a threshold parameter value. The processing circuitry can monitor a characteristic value of each of the plurality of ECAPs, and the first ECAP can be the first of the plurality of ECAPs recorded by IMD 110 that exceeds the threshold characteristic value. In some examples, the characteristic monitored by IMD 110 can be an ECAP amplitude. In some examples, the ECAP amplitude can be given by a voltage difference between the Nl ECAP peak and the P2 ECAP peak. More description of the Nl ECAP peak, N2 ECAP peak, and other ECAP peaks can be found in the description below. In other examples, IMD 110 can monitor another characteristic or more than one characteristic of the plurality of ECAPs, such as a current amplitude, a slope, a slew rate, an ECAP frequency, an ECAP duration, or any combination thereof. Figure 4 In some examples where the characteristic includes an ECAP amplitude, the threshold ECAP characteristic value can be selected from a range of about 3 microvolts (pV) to about 300 pV.

[0061] If the processing circuitry of IMD 110 determines that a characteristic of the first ECAP is greater than the threshold ECAP characteristic value, the processing circuitry can decrement (or reduce) a parameter of a set of informed pulses delivered by the stimulation generation circuitry after the first ECAP. In some examples, to decrement the parameter of the set of informed pulses, IMD 110 can decrease the current amplitude value for each therapy pulse of each consecutive therapy pulse of the set of informed pulses. In other examples, to decrement the parameter of the set of informed pulses, IMD 110 can decrease the magnitude of a parameter other than current (e.g., voltage). As multiple ECAPs can indicate some effect of therapy delivered by IMD 110 on patient 105, IMD 110 can decrement the parameter of the set of informed pulses to improve therapy delivered to patient 105. In some cases, an ECAP received by IMD 110 exceeding the threshold ECAP characteristic value can indicate to IMD 110 that one or more of leads 130 has moved closer to a target tissue of patient 105 (e.g., spinal cord 120). In these cases, if therapy delivered to spinal cord 120 is maintained at a current level, patient 105 can experience momentary overstimulation because the distance between leads 130 and the target tissue of patient 105 is a factor in determining the effect of electrical stimulation therapy on patient 105. Thus, decrementing the first set of informed pulses based on determining that the first ECAP exceeds the threshold ECAP characteristic value can prevent patient 105 from experiencing momentary overstimulation due to electrical stimulation therapy delivered by IMD 110.

[0062] After determining that the first ECAP exceeds the threshold ECAP characteristic value, the processing circuitry of IMD 110 can continue to monitor for multiple ECAPs detected by the sensing circuitry. In some examples, the processing circuitry of IMD 110 can identify a second ECAP occurring after the first ECAP, where a characteristic of the second ECAP is less than the threshold ECAP characteristic value. In some cases, the second ECAP can be a leading ECAP occurring after the first ECAP that includes a characteristic value that is less than the threshold ECAP characteristic value. In other words, each ECAP occurring between the first ECAP and the second ECAP can include a characteristic value that is greater than or equal to the threshold ECAP characteristic value. In this way, because IMD 110 can decrement informed pulses delivered to patient 105 between the first ECAP and the second ECAP, the risk of patient 105 experiencing momentary overstimulation during a time period extending between receiving the first ECAP and receiving the second ECAP is reduced. Based on the characteristic of the second ECAP being less than the threshold ECAP characteristic value, the processing circuitry of IMD 110 can increment a parameter of a second set of informed pulses delivered by the stimulation generation circuitry after the second ECAP.

[0063] Figure 2 This is a block diagram illustrating an exemplary configuration of components of an IMD 200 according to one or more technologies disclosed herein. The IMD 200 may be... Figure 1 An example of IMD 110. In Figure 2 In the example shown, IMD 200 includes a stimulus generation circuit system 202, a switching circuit system 204, a sensing circuit system 206, a telemetry circuit system 208, a processing circuit system 210, a storage device 212, a sensor 222, and a power source 224.

[0064] exist Figure 2 In the example shown, storage device 212 stores therapeutic stimulation program 214 and ECAP test stimulation program 216 in a separate memory or a separate area within storage device 212. Storage device 212 also stores threshold 218 and stimulation adjustment mode 220. Each stored therapeutic stimulation program in therapeutic stimulation program 214 defines values ​​for a set of electrical stimulation parameters (e.g., a set of stimulation parameters), such as stimulation electrode combination, electrode polarity, current or voltage amplitude, pulse width, pulse rate, and pulse shape. Each stored ECAP test stimulation program 216 defines values ​​for a set of electrical stimulation parameters (e.g., a set of control stimulation parameters), such as stimulation electrode combination, electrode polarity, current or voltage amplitude, pulse width, pulse rate, and pulse shape. ECAP test stimulation program 216 may also have additional information, such as instructions on when to deliver control pulses based on the pulse width and / or frequency of the notification pulse defined in therapeutic stimulation program 214. In examples where control pulses are provided to the patient without notification pulses, a separate ECAP test stimulation program may not be necessary. Conversely, ECAP testing stimulation procedures that only include control pulses can be limited to the same control pulses as the corresponding treatment stimulation procedures that include control pulses.

[0065] Accordingly, in some examples, the stimulation generation circuitry 202 generates the electrical stimulation signals in accordance with the electrical stimulation parameters described above. Other ranges of stimulation parameter values can also be useful, and can depend on the target stimulation site within the patient 105. While stimulation pulses are described, the stimulation signals can be in any form, such as continuous-time signals (e.g., sinusoids), etc. The switching circuitry 204 can include one or more switch arrays, one or more multiplexers, one or more switches (e.g., a switch matrix or other collection of switches), or other circuitry configured to direct the stimulation signals from the stimulation generation circuitry 202 to one or more of the electrodes 232, 234, or to direct the sensed signals from one or more of the electrodes 232, 234 to the sensing circuitry 206. In other examples, the stimulation generation circuitry 202 and / or the sensing circuitry 206 can include sensing circuitry to direct signals to and / or from one or more of the electrodes 232, 234, which can or can not include the switching circuitry 204.

[0066] The sensing circuitry 206 monitors signals from any combination of the electrodes 232, 234. In some examples, the sensing circuitry 206 includes one or more amplifiers, filters, and analog-to-digital converters. The sensing circuitry 206 can be used to sense physiological signals, such as ECAPs. In some examples, the sensing circuitry 206 detects ECAPs from a particular combination of the electrodes 232, 234. In some cases, the particular combination of electrodes used to sense ECAPs includes different electrodes than a set of electrodes 232, 234 used to deliver stimulation pulses. Alternatively, in other cases, the particular combination of electrodes used to sense ECAPs includes at least one of the same electrodes as a set of electrodes used to deliver stimulation pulses to the patient 105. The sensing circuitry 206 can provide the signals to the analog-to-digital converters for conversion to digital signals for processing, analysis, storage, or output by the processing circuitry 210.

[0067] Under the control of the processing circuitry 210, the telemetry circuitry 208 enables communication between the IMD 200 and an external programmer (e.g., an external programmer 104 of FIG. 1). In some examples, the telemetry circuitry 208 includes inductive coupling. In other examples, the telemetry circuitry 208 includes a wireless communication circuitry, such as a Bluetooth or Bluetooth Low Energy radio. Figure 2wireless communication between IMD 200 and another computing device (not shown). As an update to the program, processing circuitry 210 of IMD 200 can receive values for various stimulation parameters, such as amplitude and electrode combination, from external programmer via telemetry circuitry 208. Updates to therapy stimulation programs 214 and ECAP test stimulation programs 216 can be stored within storage device 212. Telemetry circuitry 208 in IMD 200, as well as telemetry circuits in other devices and systems described herein, such as an external programmer, can enable communication by radio frequency (RF) communication techniques. Additionally, telemetry circuitry 208 can communicate with an external medical device programmer (not shown) via proximal inductive interaction of IMD 200 with the external medical device programmer. The external programmer can be Figure 2 Figure 1 one example of external programmer 150 of

[0068] Thus, telemetry circuitry 208 can transmit information to the external programmer either continuously, at periodic intervals, or upon request from IMD 110 or the external programmer.

[0069] Processing circuitry 210 can include one or more of a microprocessor, a controller, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field-programmable gate array (FPGA), discrete logic circuitry, or any other processing circuitry configured to provide the functions attributed to processing circuitry 210 herein can be embodied as firmware, hardware, software or any combination thereof. Processing circuitry 210 controls stimulation generation circuitry 202 to generate stimulation signals according to therapy stimulation programs 214 and ECAP test stimulation programs 216 stored in storage device 212 to apply stimulation parameter values specified by one or more programs, such as amplitude, pulse width, pulse rate, and pulse shape of each stimulation signal. Figure 2 ​In the illustrated example, the set of electrodes 232 includes electrodes 232A, 232B, 232C, and 232D, and the set of electrodes 234 includes electrodes 234A, 234B, 234C, and 234D. In other examples, a single lead can include all eight electrodes 232 and 234 along a single axial length of the lead. The processing circuitry 210 also controls the stimulation generation circuitry 202 to generate and apply stimulation signals to selected combinations of electrodes 232, 234. In some examples, the stimulation generation circuitry 202 includes switching circuitry (in addition to, or instead of, the switching circuitry 204) that can couple stimulation signals to selected conductors within the lead 230, which in turn deliver the stimulation signals through selected electrodes 232, 234. Such switching circuitry can be a switch array, a switch matrix, a multiplexer, or any other type of switching circuitry configured to selectively couple stimulation energy to selected electrodes 232, 234 and to selectively sense bioelectrical nerve signals of the spinal cord of a patient (not shown) with selected electrodes 232, 234. Figure 2

[0070] In other examples, however, the stimulation generation circuitry 202 does not include switching circuitry, and the switching circuitry 204 is not connected between the stimulation generation circuitry 202 and the electrodes 232, 234. In these examples, the stimulation generation circuitry 202 includes multiple pairs of voltage sources, current sources, voltage sinks, or current sinks connected to each of the electrodes 232, 234, such that each pair of electrodes has a unique signal circuit. In other words, in these examples, each of the electrodes 232, 234 is independently controlled via its own signal circuit (e.g., via a combination of a regulated voltage source and sink or a regulated current source and sink), as opposed to a switched signal between the electrodes 232, 234.

[0071] ​The electrodes 232, 234 on the respective lead 230 can be constructed from a variety of different designs. For example, one or both of the leads 230 can include one or more electrodes at each longitudinal location along the length of the lead, such as one electrode at different peripheral locations around the lead perimeter at each of locations A, B, C, and D. In one example, the electrodes can be electrically coupled to the stimulation generation circuitry 202 via respective conductive wires within the lead housing that are straight or coiled and extend to a connector at the proximal end of the lead, e.g., via switching circuitry 204 and / or switching circuitry of the stimulation generation circuitry 202. In another example, each of the electrodes of the lead can be an electrode deposited on a thin film. The thin film can include a conductive trace for each electrode that extends along the length of the thin film to a proximal end connector. The thin film can then be wrapped (e.g., spiral wrapped) around an inner member to form the lead 230. These and other constructions can be used to form leads with complex electrode geometries.

[0072] While the sensing circuitry 206 is incorporated into a common housing with the stimulation generation circuitry 202 and the processing circuitry 210 in Figure 2 other examples, the sensing circuitry 206 can be located in a housing separate from the IMD 200 and can communicate with the processing circuitry 210 via wired or wireless communication techniques.

[0073] In some examples, one or more of the electrodes 232 and 234 are adapted to sense ECAPs. For example, the electrodes 232 and 234 can sense a voltage amplitude of a portion of the ECAP signal, where the sensed voltage amplitude is a characteristic of the ECAP signal.

[0074] The storage 212 can be configured to store information within the IMD 200 during operation. The storage 212 can include a computer- readable storage medium or computer-readable storage device. In some examples, the storage 212 includes one or more of a short-term memory or a long-term memory. The storage 212 can include, for example, random access memory (RAM), dynamic random access memory (DRAM), static random access memory (SRAM), magnetic discs, optical discs, flash memory, or forms of electrical programmable memory (EPROM) or electrically erasable programmable memory (EEPROM). In some examples, the storage 212 is used to store data indicative of instructions executed by the processing circuitry 210. As discussed above, the storage 212 is configured to store the therapy stimulation program 214, the ECAP test stimulation program 216, the threshold 218, and the stimulation adjustment mode 220.

[0075] In some examples, the stimulation generation circuitry 202 can be configured to deliver electrical stimulation therapy to the patient 105. In some cases, the electrical stimulation therapy can include a plurality of notification pulses. Additionally, the stimulation generation circuitry 202 can be configured to deliver a plurality of control pulses, where the plurality of control pulses are interleaved with at least some of the plurality of notification pulses. The stimulation generation circuitry can deliver the plurality of notification pulses and the plurality of control pulses to a target tissue (e.g., the spinal cord 120) of the patient 105 via the electrodes 232, 234 of the lead 230. By delivering such notification pulses and control pulses, the stimulation generation circuitry 202 can evoke responsive ECAPs in the target tissue that propagate through the target tissue before returning to the electrodes 232, 234. In some examples, different combinations of the electrodes 232, 234 can sense the responsive ECAPs compared to the combinations of the electrodes 232, 234 that deliver the notification pulses and the combinations of the electrodes 232, 234 that deliver the control pulses. The sensing circuitry 206 can be configured to detect the responsive ECAPs via the electrodes 232, 234 and the lead 230. In other examples, the stimulation generation circuitry 202 can be configured to deliver the plurality of control pulses without any notification pulses when the control pulses also provide a therapeutic effect to the patient.

[0076] In some cases, the processing circuitry 210 can direct the sensing circuitry 206 to continuously monitor for ECAPs. In other cases, the processing circuitry 210 can direct the sensing circuitry 206 to monitor for ECAPs based on signals from the sensor 222. For example, the processing circuitry 210 can activate the sensing circuitry 206 based on an activity level of the patient 105 exceeding an activity level threshold (e.g., an accelerometer signal of the sensor 222 rising above a threshold). In some examples, activating and deactivating the sensing circuitry 206 can extend a battery life of the power source 224.

[0077] In some examples, processing circuitry 210 determines whether a characteristic of the first ECAP is greater than a threshold ECAP characteristic value. The threshold ECAP characteristic value can be stored in storage device 212 as part of threshold values 218. In some examples, the characteristic of the first ECAP is a voltage amplitude of the first ECAP. In some such examples, the threshold ECAP characteristic value is selected from a range of about 10 microvolts (pV) to about 20 pV. In other examples, processing circuitry 210 determines whether another characteristic of the first ECAP (e.g., ECAP current amplitude, ECAP slew rate, area under the ECAP, ECAP slope, or ECAP duration) is greater than a threshold ECAP characteristic value. Threshold values 218 can include a threshold ECAP characteristic value corresponding to each of a set of characteristics that sensing circuitry 206 and processing circuitry 210 are configured to measure in ECAPs in response to stimulation pulses delivered by IMD 200. In this way, processing circuitry 210 can determine electrical stimulation therapy based on one or more of the set of characteristics.

[0078] If processing circuitry 210 determines that the characteristic of the first ECAP is greater than the threshold ECAP characteristic value, processing circuitry 210 is configured to activate a decrementing mode, thereby changing at least one parameter of each therapy pulse in a set of informed pulses delivered by IMD 200 after sensing circuitry 206 senses the first ECAP. Additionally, while the decrementing mode is activated, processing circuitry 210 can change at least one parameter of each control pulse in a set of control pulses delivered by IMD 200 after sensing circuitry 206 senses the first ECAP. In some examples, the at least one parameter of informed pulses and the at least one parameter of control pulses adjusted by processing circuitry 210 during the decrementing mode includes a stimulation current amplitude. In some such examples, during the decrementing mode, processing circuitry 210 decreases a current amplitude of each successive stimulation pulse (e.g., each therapy pulse and each control pulse) delivered by IMD 200. In other examples, the at least one parameter of stimulation pulses adjusted by processing circuitry 210 during the decrementing mode includes any combination of current amplitude, voltage amplitude, slew rate, pulse shape, pulse frequency, or pulse duration.

[0079] In Figure 2In the illustrated example, a decrementing pattern is stored in storage 212 as part of the stimulation adjustment pattern 220. The decrementing pattern can include a list of instructions that enable the processing circuitry 210 to adjust a parameter of the stimulation pulses according to a function. In some examples, when the decrementing pattern is activated, the processing circuitry 210 decreases the parameter (e.g., current) of each successive therapy pulse and each successive control pulse according to a linear function. In other examples, when the decrementing pattern is activated, the processing circuitry 210 decreases the parameter (e.g., current) of each successive therapy pulse and each successive control pulse according to an exponential function, a logarithmic function, or a piecewise function. While the decrementing pattern is activated, the sensing circuitry 206 can continue to monitor responsive ECAPs. In turn, the sensing circuitry 206 can detect ECAPs in response to the control pulses delivered by the IMD 200.

[0080] Throughout the decrementing pattern, the processing circuitry can monitor ECAPs in response to the stimulation pulses. The processing circuitry 210 can determine whether a characteristic of a second ECAP is less than the threshold ECAP characteristic value. In some cases, the second ECAP can be a leading ECAP that occurs after a first ECAP that is less than the threshold ECAP characteristic value. In other words, each ECAP recorded by the sensing circuitry 206 between the first ECAP and the second ECAP is greater than or equal to the threshold ECAP characteristic value. Based on the characteristic of the second ECAP being less than the threshold ECAP characteristic value, the processing circuitry 210 can deactivate the decrementing pattern and activate an incrementing pattern, thereby changing at least one parameter of each therapy pulse in a set of notification pulses delivered by the IMD 200 after the sensing circuitry 206 senses the second ECAP. Additionally, while the incrementing pattern is activated, the processing circuitry 210 can change at least one parameter of each control pulse in a set of control pulses delivered by the IMD 200 after the sensing circuitry 206 senses the second ECAP.

[0081] In some examples, the at least one parameter of the notification pulses and the at least one parameter of the control pulses adjusted by the processing circuitry 210 during the incrementing pattern includes a stimulation current amplitude. In some such examples, during the incrementing pattern, the processing circuitry 210 increases the current amplitude of each successive stimulation pulse (e.g., each therapy pulse and each control pulse) delivered by the IMD 200. In other examples, the at least one parameter of the stimulation pulses adjusted by the processing circuitry 210 during the incrementing pattern includes any combination of a current amplitude, a voltage amplitude, a slew rate, a pulse shape, a pulse frequency, or a pulse duration.

[0082] In Figure 2In the illustrated example, the incrementing mode is stored in storage 212 as part of the stimulation adjustment mode 220. The incrementing mode can include a list of instructions that enable the processing circuitry 210 to adjust the parameters of the stimulation pulses according to a function. In some examples, when the incrementing mode is activated, the processing circuitry 210 increases the parameters (e.g., current) of each successive therapy pulse and each successive control pulse according to a linear function. In other examples, when the incrementing mode is activated, the processing circuitry 210 increases the parameters (e.g., current) of each successive therapy pulse and each successive control pulse according to a non-linear function, such as an exponential function, a logarithmic function, or a piecewise function. While the incrementing mode is activated, the sensing circuitry 206 can continue to monitor the responsive ECAPs. In turn, the sensing circuitry 206 can detect ECAPs in response to the control pulses delivered by the IMD 200.

[0083] The processing circuitry 210 can complete the incrementing mode such that the one or more parameters of the stimulation pulses return to the baseline parameter values of the stimulation pulses delivered prior to the processing circuitry 210 activating the decrementing mode (e.g., prior to the sensing circuitry 206 detecting the first ECAP). By first decrementing and then incrementing the stimulation pulses in response to the ECAPs exceeding the threshold ECAP characteristic value, the processing circuitry 210 can prevent the patient 105 from experiencing transient overstimulation or reduce the severity of the transient overstimulation experienced by the patient 105.

[0084] Although in some examples the sensing circuitry 206 senses ECAPs occurring in response to control pulses delivered according to the ECAP test stimulation program 216, in other examples the sensing circuitry 206 senses ECAPs occurring in response to notification pulses delivered according to the therapy stimulation program 214. The techniques of the present disclosure can enable the IMD 200 to switch between the decrementing mode and the incrementing mode using any combination of ECAPs corresponding to notification pulses and ECAPs corresponding to control pulses.

[0085] The sensors 222 can include one or more sensing elements that sense values of respective patient parameters. As described above, the electrodes 232 and 234 can be electrodes that sense characteristic values of ECAPs. The sensors 222 can include one or more accelerometers, optical sensors, chemical sensors, temperature sensors, pressure sensors, or any other type of sensor. The sensors 222 can output patient parameter values that can be used as feedback to control therapy delivery. For example, the sensors 222 can indicate patient activity, and the processing circuitry 210 can increase the frequency of control pulses and ECAP sensing in response to detecting increased patient activity. In one example, the processing circuitry 210 can initiate control pulses and corresponding ECAP sensing in response to a signal from the sensors 222 indicating that patient activity has exceeded an activity threshold. Conversely, the processing circuitry 210 can decrease the frequency of control pulses and ECAP sensing in response to detecting decreased patient activity. For example, in response to the sensors 222 no longer indicating that sensed patient activity exceeds a threshold, the processing circuitry 210 can suspend or stop delivering control pulses and ECAP sensing. In this way, the processing circuitry 210 can dynamically deliver control pulses and sense ECAP signals based on patient activity to reduce power consumption of the system when the distance of the electrodes to the neurons is unlikely to change, and to increase the system’s responsiveness to changes in ECAPs when the distance of the electrodes to the neurons is likely to change. The IMD 200 can include additional sensors within the housing of the IMD 200 and / or coupled via one or other leads of the lead 130. Further, for example, the IMD 200 can receive sensor signals wirelessly from remote sensors via the telemetry circuitry 208. In some examples, one or more of these remote sensors can be located outside the patient’s body (e.g., carried on an external surface of the skin, attached to clothing, or otherwise positioned outside the patient 105’s body). In some examples, the signals from the sensors 222 indicate a position or body state (e.g., sleeping, awake, sitting, standing, etc.), and the processing circuitry 210 can select a target ECAP characteristic value according to the indicated position or body state.

[0086] The power source 224 is configured to deliver operating power to the components of the IMD 200. The power source 224 can include a battery and power generation circuitry to produce the operating power. In some examples, the battery is rechargeable to allow longer operation periods. In some examples, recharging is accomplished through proximal inductive interaction between an external charger and an inductive charging coil within the IMD 200. The power source 224 can include any one or more of a variety of different battery types such as nickel cadmium, and lithium ion.

[0087] Figure 3is a block diagram illustrating an example configuration of components of an external programmer 300 that demonstrates one or more techniques in accordance with the present disclosure. The external programmer 300 can be an example of the external programmer 150 of Figure 1 Although the external programmer 300 can generally be described as a handheld device, the external programmer 300 can be a larger portable device or a more fixed device. Moreover, in other examples, the external programmer 300 can be included as part of or include the functionality of an external charging device. As Figure 3 illustrated, the external programmer 300 can include processing circuitry 352, a storage device 354, a user interface 356, telemetry circuitry 358, and a power source 360. The storage device 354 can store instructions that, when executed by the processing circuitry 352, cause the processing circuitry 352 and the external programmer 300 to provide the functionality attributed to the external programmer 300 throughout the present disclosure. Each of these components, circuitry, or modules can include circuitry configured to perform some or all of the functions described herein. For example, the processing circuitry 352 can include processing circuitry configured to perform the processes discussed with respect to the processing circuitry 352.

[0088] Generally, the external programmer 300 includes any suitable hardware arrangement that, alone or in combination with software and / or firmware, performs the techniques attributed to the external programmer 300, as well as the processing circuitry 352, the user interface 356, and the telemetry circuitry 358 of the external programmer 300. In various examples, the external programmer 300 can include one or more processors, such as one or more microprocessors, DSPs, ASICs, FPGAs, or any other equivalent integrated or discrete logic circuitry, as well as any combinations of such components. In various examples, the external programmer 300 can also include a storage device 354, such as RAM, ROM, PROM, EPROM, EEPROM, flash memory, hard disks, CD-ROMs, including executable instructions for causing one or more processors to perform the actions attributed to the instructions. Moreover, although the processing circuitry 352 and the telemetry circuitry 358 are described as separate modules, in some examples, the processing circuitry 352 and the telemetry circuitry 358 are functionally integrated. In some examples, the processing circuitry 352 and the telemetry circuitry 358 correspond to respective hardware units, such as ASICs, DSPs, FPGAs, or other hardware units.

[0089] The storage device 354 (e.g., a memory device) can store instructions that, when executed by the processing circuitry 352, cause the processing circuitry 352 and the external programmer 300 to provide the functionality ascribed to the external programmer 300 throughout this disclosure. For example, the storage device 354 can include instructions that cause the processing circuitry 352 to obtain a parameter set from memory, select a spatial electrode movement pattern, or receive a user input and send a corresponding command to the IMD 200, or instructions for any other functionality. Further, the storage device 354 can include a plurality of programs, where each program includes a parameter set defining a stimulation pulse, such as a control pulse and / or an informative pulse. The storage device 354 can also store data received from a medical device (e.g., the IMD 110). For example, the storage device 354 can store ECAP-related data recorded at a sensing module of the medical device, and the storage device 354 can also store data from one or more sensors of the medical device.

[0090] The user interface 356 can include buttons or a keypad, lights, a speaker for voice commands, a display such as a liquid crystal (LCD) display, a light emitting diode (LED) display, or an organic light emitting diode (OLED) display. In some examples, the display includes a touchscreen. The user interface 356 can be configured to display any information related to the delivery of electrical stimulation, a recognized patient behavior, a sensed patient parameter value, a patient behavior criterion, or any other such information. The user interface 356 can also receive user input via the user interface 356. The input can be in the form of, for example, pressing a button on a keypad or selecting an icon from a touchscreen. The input can request that electrical stimulation be started or stopped, the input can request a new spatial electrode movement pattern or a change to an existing spatial electrode movement pattern, or the input can request some other change to the delivery of electrical stimulation.

[0091] The telemetry circuitry 358 can support wireless communication between the medical device and the external programmer 300 under the control of the processing circuitry 352. The telemetry circuitry 358 can also be configured to communicate with another computing device via wireless communication techniques, or directly with a further computing device through a wired connection. In some examples, the telemetry circuitry 358 provides wireless communication via an RF or near-field inductive medium. In some examples, the telemetry circuitry 358 includes an antenna that can take on multiple forms, such as an internal antenna or an external antenna.

[0092] Examples of local wireless communication techniques that can be employed to facilitate communication between the external programmer 300 and the IMD 110 include Radio frequency communications of the set of norms or other standard or proprietary telemetry protocols. In this way, other external devices can be able to communicate with external programmer 300 without needing to establish a secure wireless connection. As described herein, telemetry circuitry 358 can be configured to transmit spatial electrode movement patterns or other stimulation parameter values to IMD 110 to deliver electrical stimulation therapy.

[0093] In some examples, the selection of the stimulation parameter or therapy stimulation program is transmitted to the medical device for delivery to the patient (e.g., patient 105). In other examples, the therapy can include a medication, an activity, or other instruction that patient 105 must perform themselves or that a caregiver performs for patient 105. In some examples, external programmer 300 provides a visual, audible, and / or tactile notification indicating that there is a new instruction. In some examples, external programmer 300 requires receipt of user input to confirm that the instruction has been completed. Figure 1

[0094] According to the techniques of this disclosure, user interface 356 of external programmer 300 receives an indication from a clinician instructing a processor of the medical device to update one or more therapy stimulation programs or to update one or more ECAP test stimulation programs. Updating the therapy stimulation programs and the ECAP test stimulation programs can include changing one or more parameters of the stimulation pulses delivered by the medical device according to the program, such as the amplitude, pulse width, frequency, and pulse shape of the informed pulses and / or the control pulses. User interface 356 can also receive instructions from the clinician to command any electrical stimulation, including the control pulses and / or the informed pulses, to start or stop.

[0095] Power source 360 is configured to deliver operating power to the components of external programmer 300. Power source 360 can include a battery and power generation circuitry to produce the operating power. In some examples, the battery is rechargeable to allow for long-term operation. Recharging can be accomplished through electrical coupling of the power source 360 to a cradle or plug that is connected to an alternating current (AC) outlet. Additionally, recharging can be accomplished through proximal inductive interaction between an external charger and an inductive charging coil within external programmer 300. In other examples, a traditional battery (e.g., nickel cadmium or lithium ion) can be used. Further, external programmer 300 can be directly coupled to an alternating current outlet for operation.

[0096] Figure 3 The architecture of external programmer 300 shown in FIG. 3 is shown by way of example. The techniques set forth in this disclosure can be implemented in Figure 3 example external programmer 300 and other types of systems not specifically described herein. Nothing in this disclosure should be interpreted as a limitation on the generality of the techniques presented in this disclosure or a limitation on the examples of external programmer 300 presented in this disclosure. Figure 3 The example architecture shown in FIG. 3. ​

[0097] Figure 4 is a graph 402 of exemplary evoked compound action potentials (ECAPs) sensed for respective stimulation pulses in accordance with one or more techniques of this disclosure. As shown, graph 402 illustrates an exemplary ECAP signal 404 (dashed line) and an ECAP signal 406 (solid line). In some examples, each of ECAP signals 404 and 406 is sensed from a control pulse delivered from a protected cathode, where the control pulse is a biphasic pulse that includes an interphase gap between each positive and negative phase of the pulse. In some such examples, the protected cathode includes a stimulation electrode located at an end of an 8 electrode lead (e.g., lead 130 of FIG. 1), while two sense electrodes are disposed at another end of the 8 electrode lead. ECAP signal 404 demonstrates a voltage amplitude sensed as a result of a sub-detection threshold stimulation pulse or a stimulation pulse that results in an undetectable ECAP. A peak 408 of ECAP signal 404 is detected, which represents an artifact of the delivered control pulse. However, no propagating signal is detected following the artifact in ECAP signal 404 because the control pulse is a sub-detection stimulation threshold. Figure 4 Figure 1

[0098] ​​Compared to ECAP signal 404, ECAP signal 406 represents the voltage amplitude detected from an over-detection stimulation threshold control pulse. ECAP signal 406 is detected to have a peak 408, which represents an artifact of the delivered control pulse. Following peak 408, ECAP signal 406 also includes peaks PI, Nl, and P2, which are three representative peaks representing propagating action potentials from the ECAP. An exemplary duration of the artifact and peaks PI, Nl, and P2 is about 1 millisecond (ms). When ECAP signal 406 is detected, different features of the ECAP can be identified. For example, a feature of the ECAP can be the amplitude between Nl and P2. This Nl-P2 amplitude can be easily detected even if the artifact is projected onto the relatively larger signal PI, and the Nl-P2 amplitude can be minimally affected by electronic drift in the signal. In other examples, a feature of the ECAP used to control a subsequent control pulse and / or informed pulse can be the amplitude of PI, Nl, or P2 relative to a neutral or zero voltage. In some examples, a feature of the ECAP used to control a subsequent control pulse or informed pulse is the sum of two or more of peaks PI, Nl, or P2. In other examples, a feature of ECAP signal 406 can be the area under one or more of peaks PI, Nl, and / or P2. In other examples, a feature of the ECAP can be a ratio of one of peaks PI, Nl, or P2 to another of these peaks. In some examples, a feature of the ECAP is the slope between two points in the ECAP signal, such as the slope between Nl and P2. In other examples, a feature of the ECAP can be the time between two points of the ECAP, such as the time between Nl and P2. The time between the delivery of a stimulation pulse and one point in the ECAP signal can be referred to as the latency of the ECAP, and can be indicative of the type of fiber captured by the stimulation pulse (e.g., control pulse). ECAP signals with lower latency (i.e., smaller latency values) are indicative of a higher percentage of neural fibers with faster signal propagation, while ECAP signals with higher latency (i.e., larger latency values) are indicative of a higher percentage of neural fibers with slower signal propagation. Latency can also refer to the time between detecting an electrical feature at one electrode and then detecting the electrical feature again at a different electrode. This time (or latency) is inversely proportional to the conduction velocity of the neural fiber. In other examples, other features of the ECAP signal can be used.

[0099] As long as the amplitude of the control pulse is greater than a threshold, the amplitude of the ECAP signal increases with the increase of the pulse amplitude, causing nerve depolarization and signal propagation. The target ECAP characteristic (e.g., target ECAP amplitude) can be determined based on the ECAP signal detected from the control pulse when determining effective treatment delivery of the notification pulse to the patient 105. Therefore, the ECAP signal represents the distance between the stimulating electrode and the nerve appropriate for the stimulation parameter values ​​of the notification pulse delivered at that time. Thus, the IMD 110 can attempt to modify the treatment pulse parameter values ​​using detected changes in the measured ECAP characteristic values ​​and maintain the target ECAP characteristic value during treatment pulse delivery.

[0100] Figure 5A This is a timing diagram 500A illustrating an example of an electrical stimulation pulse according to one or more techniques of this disclosure and the corresponding sensed ECAP. For convenience, refer to... Figure 2 IMD 200 pairs Figure 5A The following description is provided. As shown in the figure, timing diagram 500A includes a first channel 502, multiple control pulses 504A-504N (collectively referred to as "control pulses 504"), a second channel 506, multiple corresponding ECAPs 508A-508N (collectively referred to as "ECAP 508"), and multiple stimulus interference signals 509A-509N (collectively referred to as "stimulus interference signals 509"). Figure 5A In the example, IMD 200 can deliver treatment using a control pulse instead of a notification pulse or without a notification pulse.

[0101] The first channel 502 is a time / voltage (and / or current) plot that indicates a voltage (or current) of at least one of the electrodes 232, 234. In one example, the stimulation electrode of the first channel 502 can be located on a side of the lead opposite the sensing electrode of the second channel 506. The control pulses 504 can be electrical pulses delivered to the patient’s spinal cord through at least one of the electrodes 232, 234, and the control pulses 504 can be balanced biphasic square pulses with an interphase interval. In other words, each of the control pulses 504 is shown with a negative phase and a positive phase separated by an interphase interval. For example, the control pulses 504 can have a negative voltage for an amount of time and an amount of amplitude that is the same as when it has a positive voltage. Note that the negative voltage phase can precede or follow the positive voltage phase. The control pulses 504 can be delivered according to an ECAP test stimulation program 216 stored in the storage device 212 of the IMD 200, and the ECAP test stimulation program 216 can be updated according to user input via an external programmer and / or can be updated according to signals from the sensor 222. In one example, the control pulses 504 can have a pulse width of less than about 300 microseconds (e.g., the total time of the positive phase, negative phase, and interphase interval is less than 300 microseconds). In another example, the control pulses 504 can have a pulse width of about 100 ps for each phase of the biphasic pulse. As Figure 5A As shown, the control pulses 504 can be delivered via the channel 502. The delivery of the control pulses 504 can be delivered through a protected cathode electrode combination of the lead 230. For example, if the lead 230 is a linear 8 electrode lead, the protected cathode combination is the center cathode electrode and the anode electrode immediately adjacent to that cathode electrode.

[0102] The second channel 506 is a time / voltage (and / or current) plot that indicates a voltage (or current) of at least one of the electrodes 232, 234. In one example, the electrode of the second channel 506 can be located on a side of the lead opposite the electrode of the first channel 502. In response to the control pulses 504, ECAPs 508 can be sensed at the electrodes 232, 234 from the patient’s spinal cord. The ECAPs 508 are electrical signals that can propagate along the nerve away from the origin of the control pulses 504. In one example, the ECAPs 508 are sensed by a different electrode than the electrode used to deliver the control pulses 504. As Figure 5A As shown, the ECAPs 508 can be recorded on the second channel 506.

[0103] Stimulus interference signals 509A, 509B, and 509N (e.g., artifacts of the stimulation pulse) can be sensed by lead 230 and can be sensed during the same time period as the delivery of control pulse 504. Because the amplitude and intensity of these interference signals may be greater than ECAP 508, any ECAP arriving at IMD 200 during the occurrence of stimulation interference signal 509 may not be sufficiently sensed by the sensing circuitry system 206 of IMD 200. However, ECAP 508 can be sufficiently sensed by the sensing circuitry system 206 because each ECAP 508, or at least a portion of ECAP 508 used as feedback for control pulse 504, decreases after each control pulse 504 ends. Figure 5A As shown, the stimulus interference signals 509 and ECAP 508 can be recorded on channel 506.

[0104] Figure 5B This is a timing diagram 500B illustrating an example of an electrical stimulation pulse and a corresponding sensed ECAP according to one or more techniques of this disclosure. For convenience, refer to... Figure 2 IMD 200 pairs Figure 5B The following description is provided. As shown in the figure, the timing diagram 500B includes a first channel 510, multiple control pulses 512A-512N (collectively referred to as "control pulses 512"), a second channel 520, multiple notification pulses 524A-524N (collectively referred to as "notification pulses 524") including passive recharge phases 526A-526N (collectively referred to as "passive recharge phases 526"), a third channel 530, multiple corresponding ECAPs 536A-536N (collectively referred to as "ECAPs 536"), and multiple stimulus interference signals 538A-538N (collectively referred to as "stimulus interference signals 538").

[0105] The first channel 510 is a time / voltage (and / or current) plot that indicates the voltage (or current) of at least one of the electrodes 232, 234. In one example, the stimulation electrode of the first channel 510 can be on the opposite side of the lead from the sensing electrode of the third channel 530. The control pulses 512 can be electrical pulses delivered to the patient's spinal cord through at least one of the electrodes 232, 234, and the control pulses 512 can be balanced biphasic square pulses with an interphase interval. In other words, each of the control pulses 512 is shown with a negative phase and a positive phase separated by an interphase interval. For example, the control pulses 512 can have a negative voltage for an amount of time that is the same as an amount of time that it has a positive voltage. Note that the negative voltage phase can precede or follow the positive voltage phase. The control pulses 512 can be delivered according to an ECAP test stimulation program 216 stored in the storage device 212 of the IMD 200, and the ECAP test stimulation program 216 can be updated according to user input via an external programmer and / or can be updated according to signals from the sensor 222. In one example, the control pulses 512 can have a pulse width of less than about 300 microseconds (e.g., the total time of the positive phase, negative phase, and interphase interval is less than 300 microseconds). In another example, the control pulses 512 can have a pulse width of about 100 ps for each phase of the biphasic pulse. As Figure 5B As shown, the control pulses 512 can be delivered via the first channel 510. The delivery of the control pulses 512 can be delivered through a protected cathode electrode combination of the lead 230. For example, if the lead 230 is a linear 8 electrode lead, the protected cathode combination is the center cathode electrode and the anode electrode immediately adjacent to that cathode electrode.

[0106] The second channel 520 is a time / voltage (and / or current) plot that indicates the voltage (or current) of at least one of the electrodes 232, 234 for the notification pulses. In one example, the electrodes of the second channel 520 can partially or completely share common electrodes with the electrodes of the first channel 510 and the electrodes of the third channel 530. The notification pulses 524 can also be delivered by the same lead 230 configured to deliver the control pulses 512. The notification pulses 524 can be interleaved with the control pulses 512 such that both types of pulses are not delivered during overlapping time periods. However, the notification pulses 524 can or can not be delivered by the exact same electrodes as the electrodes that deliver the control pulses 512. The notification pulses 524 can be monophasic pulses with a pulse width greater than about 300 ps and less than about 1000 ps. In fact, the notification pulses 524 can be configured to have a longer pulse width than the control pulses 512. As Figure 5B As shown, the notification pulses 524 can be delivered on the second channel 520.

[0107] The notification pulses 524 can be configured for passive recharging. For example, each therapy pulse 524 can be followed by a passive recharging phase 526 to equalize the charge on the stimulation electrodes. Unlike pulses configured for active recharging, in which the residual charge on the tissue after a stimulation pulse is immediately removed from the tissue by an opposite applied charge, passive recharging allows the tissue to naturally discharge to some reference voltage (e.g., ground or line voltage) after the therapy pulse terminates. In some examples, the electrodes of the medical device can be grounded at the medical device body. In this case, after the therapy pulse 524 terminates, the charge on the tissue surrounding the electrodes can dissipate to the medical device, resulting in a rapid decay of the residual charge at the tissue after the pulse terminates. This rapid decay is demonstrated in the passive recharging phase 526. The passive recharging phase 526 can have a duration other than the pulse width of the preceding therapy pulse 524. In other examples (not shown), the notification pulse 524 can be a biphasic pulse having a positive phase and a negative phase (and, in some examples, an interphase interval between the phases), which can be referred to as a pulse that includes active recharging. The therapy pulse as a biphasic pulse can or can not have a subsequent passive recharging phase. Figure 5B

[0108] The third channel 530 is a time / voltage (and / or current) plot that indicates the voltage (or current) of at least one of the electrodes 232, 234. In one example, the electrode of the third channel 530 can be located on the opposite side of the lead from the electrode of the first channel 510. In response to the control pulses 512, ECAPs 536 can be sensed at the electrodes 232, 234 from the patient’s spinal cord. The ECAPs 536 are electrical signals that can propagate along the nerve away from the origin of the control pulses 512. In one example, the ECAPs 536 are sensed by a different electrode than the electrode used to deliver the control pulses 512. As Figure 5B demonstrated, the ECAPs 536 can be recorded on the third channel 530.

[0109] The stimulation interference signals 538A, 538B, and 538N (e.g., artifacts of the stimulation pulses) can be sensed by the lead 230 and can be sensed during the same time period as the delivery of the control pulses 512 and the notification pulses 524. Because the amplitude and strength of these interference signals can be greater than the ECAPs 536, any ECAPs reaching the IMD 200 can not be sufficiently sensed by the sensing circuitry 206 of the IMD 200 during the occurrence of the stimulation interference signals 538. However, the ECAPs 536 can be sufficiently sensed by the sensing circuitry 206 because each ECAP 536 falls after the end of each control pulse 512 and before the delivery of the next therapy pulse 524. As Figure 5B ​As shown, the stimulus interference signals 538 and ECAP 536 can be recorded on channel 530.

[0110] Figure 6 This is a timing diagram 600 illustrating another example of an electrical stimulation pulse and a corresponding ECAP according to one or more techniques of this disclosure. For convenience, refer to... Figure 2 IMD 200 pairs Figure 6 The following description is provided. As shown in the figure, the timing diagram 600 includes a first channel 610, multiple control pulses 612A-612N (collectively referred to as "control pulses 612"), a second channel 620, multiple notification pulses 624A-624N (collectively referred to as "notification pulses 624") including passive recharge phases 626A-626N (collectively referred to as "passive recharge phases 626"), a third channel 630, multiple corresponding ECAPs 636A-636N (collectively referred to as "ECAP 636"), and multiple stimulus interference signals 638A-638N (collectively referred to as "stimulus interference signals 638"). Figure 6 It can be basically similar to Figure 5B Except for the differences detailed below.

[0111] Two or more control pulses 612 can be delivered during each of multiple time events (e.g., windows), and each time event represents the time between two consecutive notification pulses 624. For example, during each time event, a first control pulse may be followed directly by a first corresponding ECAP, and a second control pulse may be followed directly by a second corresponding ECAP after the end of the first corresponding ECAP. The notification pulse may begin after the second corresponding ECAP. In other examples not shown here, three or more control pulses 612 may be delivered during each of multiple time events, and a corresponding ECAP signal may be sensed.

[0112] Figure 7 This is a timing diagram 700 illustrating another example of an electrical stimulation pulse and a corresponding ECAP according to one or more techniques of this disclosure. For convenience, refer to... Figure 2 IMD 200 pairs Figure 7are described. As shown, the timing diagram 700 includes a first lane 710, a plurality of control pulses 712A-712N (collectively, "control pulses 712"), a second lane 720, a plurality of notification pulses 724A-724N (collectively, "notification pulses 724") including passive recharge phases 726A-726N (collectively, "passive recharge phases 726"), a third lane 730, a plurality of corresponding ECAPs 736A-736N (collectively, "ECAPs 736"), and a plurality of stimulation interference signals 738A-738N (collectively, "stimulation interference signals 738"). Figure 7 may be substantially similar to Figure 5B , except for the differences detailed below.

[0113] In Figure 5B and Figure 6 the previous examples shown, at least one control pulse is delivered and interleaved between each pair of consecutive notification pulses. However, in some examples, a control pulse 712 is not delivered during each time event (or window) of a plurality of time events, where each time event represents a time between two consecutive notification pulses 724. As shown in the example of Figure 7 , a control pulse 712 is not delivered after therapy pulse 724A and before therapy pulse 724B. In other words, consecutive notification pulses 724A and 724B can be delivered without an intervening control pulse. In any case, the notification pulses are delivered according to a predetermined frequency, and the control pulses can be delivered at any time between the notification pulses.

[0114] The control pulses can be administered according to the ECAP test stimulation program 216. The processing circuitry 210 can be configured to update the ECAP test stimulation program according to user input via the telemetry circuitry 208, as well as through signals from the sensors 222. For example, a clinician can operate a patient programmer and send a signal to the telemetry circuitry 208 that includes instructions for updating the ECAP test stimulation program 216. The clinician can set the control stimulation to be in any of the examples shown in FIGS. 5-7, and the clinician can also customize the control stimulation to be in configurations not shown in FIGS. 5-7. The clinician can choose to stop the control stimulation or start the control stimulation at any time. In some examples, detecting that the patient’s posture or activity level has changed will initiate the control stimulation. Further, as described in Figure 7 , in some examples, the control stimulation can provide a therapeutic benefit to the patient and be provided without any additional notification pulses. Figure 7 Figure 5A

[0115] Figure 8 ​​is a timing diagram 800 that illustrates another example of electrical stimulation pulses and corresponding sensed ECAPs in accordance with one or more techniques of this disclosure. For convenience, reference is made to Figure 2 IMD 200 of FIG. 1 to describe Figure 8 As illustrated, timing diagram 800 includes a first channel 810, a plurality of pulse trains 812A-812N (collectively, “pulse trains 812”), a second channel 820, a plurality of sensed artifacts 822A-822N (collectively, “sensed artifacts 822”), a plurality of corresponding ECAPs 824A-824N (collectively, “ECAPs 824”), a plurality of N1 ECAP peaks 826A-826N (collectively, “N1 ECAP peaks 826”), and a plurality of P2 ECAP peaks 828A-828N (collectively, “P2 ECAP peaks 828”).

[0116] First channel 810 is a time / voltage (and / or current) plot that indicates a voltage (or current) of at least one of electrodes 232, 234. In some examples, first channel 810 can represent a voltage of at least one stimulation electrode of electrodes 232, 234 that delivers the plurality of pulse trains 812. In other examples, first channel 810 can represent a voltage of at least one of electrodes 232, 234 that records a signal of second channel 820. Figure 8 In examples, each pulse train of the plurality of pulse trains 812 can include five stimulation pulses (e.g., control pulses and / or informed pulses). Alternatively, in other examples, each pulse train of the plurality of pulse trains 812 can include more than five stimulation pulses or fewer than five stimulation pulses. In one example, the stimulation electrode that delivers the plurality of pulse trains 812 can be located on an opposite side of lead 230 from a sensing electrode that records a signal of second channel 820. The stimulation pulses in pulse trains 812 can be balanced biphasic square pulses with an interphase interval. In other words, each therapy pulse in pulse trains 812 is shown as having a negative phase and a positive phase separated by an interphase interval. For example, each stimulation pulse can have a negative voltage for an amount of time and an amount of amplitude that is the same as an amount of time and an amount of amplitude that it has a positive voltage. Note that the negative voltage phase can precede or follow the positive voltage phase.

[0117] The bursts 812 can be delivered according to a therapy stimulation program 214 stored in the storage device 212 of the IMD 200, and the therapy stimulation program 214 can be updated according to user input via an external programmer and / or can be updated according to signals from the sensors 222. In this way, at least some of the pulses in each of the bursts 812 can contribute to a therapeutic effect for the patient. In one example, each stimulation pulse of the bursts 812 can have a pulse width of less than about 400 microseconds (e.g., the total time of the positive phase, the negative phase, and the interphase interval is less than 400 microseconds). In another example, each therapy pulse of the bursts 812 can have a pulse width of about 150 ps for each phase of a biphasic pulse. In some examples, the frequency of each of the bursts 812 can be greater than 10 Hertz (Hz) and less than 1500 Hz. In one example, the frequency of each burst can be selected from a range of about 500 Hz to about 1500 Hz. In other examples, the frequency of each burst can be selected from a range of about 20 Hz to about 100 Hz. These frequencies can vary based on the number of pulses and the pulse width of each pulse within each burst 812. Additionally, the amount of time required for the detection window of the ECAP 824 can limit the frequency of the bursts 812. As Figure 8 As shown, the bursts 812 can be delivered via the first channel 810. The delivery of the bursts 812 can be delivered through a lead 230 in a protected cathode electrode combination. For example, if the lead 230 is a linear 8 electrode lead, the protected cathode combination is the center cathode electrode and the anode electrode immediately adjacent to the cathode electrode.

[0118] The second channel 820 is a time / voltage (and / or current) plot that indicates the voltage (or current) of at least one of the electrodes 232, 234. In one example, the electrode of the second channel 820 can be located on the opposite side of the lead from the electrode of the first channel 810. In another example, the electrode of the second channel 820 can be located on the same side of the lead as the electrode of the first channel 810. In some examples, the electrode of the second channel 820 can be located on the same side of the lead as the electrode of the first channel 810, but offset from the electrode of the first channel 810. In other examples, the electrode of the second channel 820 can be located on the opposite side of the lead from the electrode of the first channel 810, but offset from the electrode of the first channel 810. Figure 8In this example, the second channel 820 is a sensing channel of the lead 230. In this way, the second channel 820 is configured to record sensed artifacts 822 and ECAPs 824. In some examples, the frequency of the stimulation pulses within each pulse train 812 is high enough such that the second channel 820 cannot sense a fully or almost fully developed ECAP after each stimulation pulse of the pulse train 812. In other words, the duration of time between successive pulse trains 812 can be scheduled to be long enough to allow for detection of a portion or all of an ECAP (e.g., at least a desired portion of an ECAP) in the section channel 820. Thus, after each therapy pulse burst of the pulse train 812, the second channel 820 can sense a respective ECAP of the ECAPs 824. Since in some cases the first channel 810 can not apply any stimulation for a certain period of time after each pulse train (e.g., pulse burst), the second channel 820 can sense the ECAPs 824 including the Nl ECAP peak 826 and the P2 ECAP peak 828 during the period of time after the respective pulse train 812. In some examples, to determine an ECAP amplitude of each ECAP 824, the IMD 200 determines a difference between the amplitude of the respective Nl peak and the respective P2 peak. For example, the IMD 200 can determine that the amplitude of the ECAP 824A is a difference between the amplitude of the Nl peak 826A and the amplitude of the P2 peak 828A. By delivering stimulation pulses as Figure 8 The IMD 200 can deliver high frequency therapy stimulation to the patient 105 while still recording ECAPs that can be used as feedback to determine (e.g., maintain or adjust) subsequent therapy, as illustrated. In some examples, the patient 105 can not perceive the “break” that occurs after each pulse train 812. Rather, in some such examples, the patient 105 can perceive continuous high frequency stimulation even though no stimulation pulses are delivered in the duration of time between subsequent pulse trains.

[0119] In some examples, all of the stimulation pulses within a single burst 812 can be the same (e.g., defined by the same stimulation parameters). In other examples, the last pulse in a burst can be different from the previous pulses in order to improve the resulting ECAP signal elicited and / or to provide a pulse that does not interfere with ECAP detection. For example, the last pulse in each burst (or some bursts) can have one or more different stimulation parameter values, such as a different amplitude, pulse width, pulse shape, or other characteristic. In one example, the last pulse in each burst 812 can have a greater amplitude than the other pulses in the same burst. The last pulse can have a longer or shorter pulse width. In some examples, a shorter pulse width can reduce the likelihood of creating artifacts on the detected ECAP. In any case, the last pulse can have a greater or lesser charge or phase than the other pulses in the same burst, and the last pulse can be referred to as a control pulse. The earlier pulses in the same burst can be referred to as notification pulses because they are informed by the previous control pulse (e.g., the last pulse in the previous burst).

[0120] The sensed artifacts 822 (e.g., artifacts of the stimulation pulses) can be sensed by the lead 230 and can be sensed during the same time period as the delivery of the burst 812. Because the amplitude and strength of these interfering signals can be greater than the ECAP 824, any ECAP reaching the IMD 200 can not be sufficiently sensed by the sensing circuitry 206 of the IMD 200 during the occurrence of the sensed artifacts 822. However, the ECAP 824 can be sufficiently sensed by the sensing circuitry 206 because each ECAP of the ECAP 824 falls near or after the end of each burst 812 and before the delivery of the subsequent burst 812. As shown, the sensed artifacts 822 and the ECAP 824 can be recorded on the second channel 820. Figure 8

[0121] Figure 9 is a flowchart illustrating exemplary operations for controlling stimulation based on one or more sensed ECAPs in accordance with one or more techniques of this disclosure. For convenience, the operations are described with respect to the IMD 200 of Figure 2 However, the techniques of Figure 9 may be performed by different components of the IMD 200 or by additional or alternative medical devices. Figure 9

[0122] ​​Stimulation generation circuitry 202 of IMD 200 can deliver electrical stimulation therapy to a patient (e.g., patient 105). To control the electrical stimulation therapy, processing circuitry 210 can direct the delivery of at least some stimulation pulses in accordance with therapy stimulation programs 214 of storage 212, where the electrical stimulation therapy can include a plurality of control pulses and / or notification pulses. In some cases, the notification pulses can produce an ECAP that is detectable by IMD 200. However, in other cases, the electrode polarization of the notification pulses can interfere with the sensing of ECAPs in response to the notification pulses. In some examples, to elicit ECAPs that are detectable by IMD 200, stimulation generation circuitry 202 delivers a plurality of control pulses interleaved with at least some of a plurality of notification pulses. Processing circuitry 210 can control the delivery of the control pulses in accordance with ECAP test stimulation programs 216. As the control pulses can be interleaved with the notification pulses, sensing circuitry 206 of IMD 200 can detect a plurality of ECAPs, where sensing circuitry 206 is configured to detect each of the plurality of ECAP signals after a control pulse of the plurality of control pulses and before a subsequent notification pulse of the plurality of notification pulses. In this way, IMD 200 can elicit a plurality of ECAPs in the target tissue by delivering control pulses without notification pulses interfering with IMD 200 sensing the ECAPs.

[0123] As Figure 9 illustrated, processing circuitry 210 directs stimulation generation circuitry 202 to deliver a control pulse (902). Stimulation generation circuitry 202 can deliver the control pulse to the target tissue of patient 105 via any combination of electrodes 232, 234 of lead 230. In some examples, the control pulse can include a balanced biphasic square pulse that employs an active recharge phase. However, in other examples, the control pulse can include a monophasic pulse followed by a passive recharge phase. In other examples, the control pulse can include an unbalanced biphasic portion and a passive recharge portion. Although not required, the biphasic control pulse can include an interphase interval between the positive phase and the negative phase to facilitate propagating a neural pulse in response to the first phase of the biphasic pulse. The control pulse can have a pulse width of less than about 300 ps, such as a biphasic pulse with each phase having a duration of about 100 ps.

[0124] After delivering the control pulse, IMD 200 attempts to detect an ECAP (904). For example, sensing circuitry 206 can monitor signals from any combination of electrodes 232, 234 of lead 230. In some examples, sensing circuitry 206 detects an ECAP from a particular combination of electrodes 232, 234. In some cases, the particular combination of electrodes used to sense the ECAP includes different electrodes than the combination of electrodes 232, 234 used to deliver the stimulation pulse. Alternatively, in other cases, the particular combination of electrodes used to sense the ECAP includes at least one of the same electrodes as the combination of electrodes used to deliver the stimulation pulse to patient 105. In some examples, the particular combination of electrodes used to sense the ECAP can be on an opposite side of lead 230 than the particular combination of electrodes used to deliver the stimulation pulse. IMD 200 can detect an ECAP in response to the control pulse. IMD 200 can measure one or more features of the responsive ECAP, such as an ECAP amplitude, an ECAP duration, a peak-to-peak duration, or any combination thereof. For example, to measure an amplitude of an ECAP, IMD 200 can determine a voltage difference between the Nl ECAP peak and the P2 ECAP peak.

[0125] At block 906, processing circuitry 210 determines whether the ECAP amplitude of the responsive ECAP is greater than the ECAP amplitude threshold. If the ECAP amplitude is greater than the ECAP amplitude threshold (“YES” branch of block 906), processing circuitry 210 activates / continues a decrement mode in IMD 200 (908). For example, if the decrement mode is “on” in IMD 200 when processing circuitry determines that the ECAP amplitude is greater than the ECAP amplitude threshold, processing circuitry 210 maintains IMD 200 in the decrement mode. If the decrement mode is “off’ in IMD 200 when processing circuitry determines that the ECAP amplitude is greater than the ECAP amplitude threshold, processing circuitry 210 activates the decrement mode. In some examples, the decrement mode can be stored in storage 212 as part of stimulation adjustment mode 220. The decrement mode can be a set of instructions that cause IMD 200 to decrease one or more parameter values of each successive notification pulse from a respective predetermined value (e.g., a value determined by a stimulation program) and decrease one or more parameter values of each successive control pulse from a respective predetermined value (e.g., a value determined by a stimulation program). In other words, the parameter values can be decreased from values that IMD 200 would use to define the respective pulses in the absence of the ECAP amplitude exceeding the threshold ECAP amplitude. For example, when the decrement mode is activated, processing circuitry 210 can decrease the current amplitude of each successive notification pulse delivered by IMD 200 and decrease the current amplitude of each successive control pulse delivered by IMD 200. After processing circuitry 210 activates / continues the decrement mode, the example operations can return to block 902 and IMD 200 can deliver another control pulse.

[0126] If the ECAP amplitude is not greater than the ECAP amplitude threshold (“NO” branch of block 906), processing circuitry 210 determines whether the decrement mode is activated in IMD 200 (910). If the decrement mode is activated in IMD 200 (“YES” branch of block 910), processing circuitry 210 deactivates the decrement mode and activates an increment mode in IMD 200 (912). In some examples, the increment mode can be stored in storage 212 as part of stimulation adjustment mode 220. The increment mode can be a set of instructions that cause IMD 200 to increase one or more parameter values of each successive notification pulse and increase one or more parameter values of each successive control pulse. For example, when the increment mode is activated, processing circuitry 210 can increase the current amplitude of each successive notification pulse delivered by IMD 200 and increase the current amplitude of each successive control pulse delivered by IMD 200. After processing circuitry 210 deactivates the decrement mode and activates the increment mode, the example operations can return to block 902 and IMD 200 can deliver another control pulse.

[0127] when Figure 9 When the exemplary operation reaches box 910 and the decrement mode is not activated in IMD 200 (the "No" branch of box 910), the processing circuitry system 210 determines whether the increment mode is activated in IMD 200 (914). If the increment mode is activated in IMD 200 (the "Yes" branch of box 914), the processing circuitry system 210 can complete the increment mode in IMD 200 (916). In some examples, to complete the increment mode, the processing circuitry system 210 may increase the current amplitude of each successive notification pulse delivered by IMD 200 and increase the current amplitude of each successive control pulse delivered by IMD 200 until the pulse amplitude of the stimulation pulse reaches the current amplitude of the stimulation pulse delivered by IMD 200 (e.g., a predetermined value that may be set by the stimulation program selected for treatment) before the decrement mode is activated. In this way, the process may not be referred to as a fully closed-loop system. In other words, IMD 200 can monitor the high end (ECAP amplitude threshold) used to adjust the stimulation pulse, rather than monitoring any low end of the sensed ECAP amplitude. For example, IMD 200 can continue to increase the current amplitude of the continuous notification pulses without any feedback from the sensed ECAP, unless the sensed ECAP value exceeds the ECAP amplitude threshold again. After the processing circuitry system 210 completes the incrementing mode, the exemplary operation can return to block 902, and IMD 200 can deliver another control pulse. When Figure 9 When the exemplary operation reaches box 914 and the incremental mode is not activated in IMD 200 (the "No" branch of box 914), the processing circuitry system 210 maintains the stimulus (918) in IMD 200. Although Figure 9 The description covers both notification pulses and control pulses, but when the IMD 200 delivers only control pulses (e.g., no notification pulses) to the patient for treatment, Figure 9 The technology can also be applied.

[0128] Figure 10 A voltage / current / time graph 1000 according to one or more techniques of this disclosure is shown, which plots the control pulse current amplitude 1002, the notification pulse current amplitude 1004, the ECAP voltage amplitude 1008, and the second ECAP voltage amplitude 1010 as a function of time. Additionally, Figure 10 The threshold ECAP amplitude of 1006 is shown. For convenience, it is relative to... Figure 2 IMD200 Figure 10 To describe. However, Figure 10 The technology can be performed by different components of the IMD 200 or by additional or alternative medical devices.

[0129] The voltage / current / time graph 1000 illustrates the relationship between the sensed ECAP voltage amplitude and the stimulation current amplitudes. For example, the control pulse current amplitude 1002 and the informed pulse current amplitude 1004 are plotted as a function of time along with the ECAP voltage amplitude 1008, thus showing how the stimulation current amplitudes change with respect to the ECAP voltage amplitude. In some examples, the IMD 200 delivers a plurality of control pulses and a plurality of informed pulses at the control pulse current amplitude 1002 and the informed pulse current amplitude 1004, respectively. Initially, the IMD 200 can deliver a first set of control pulses, where the IMD 200 delivers the first set of control pulses at a current amplitude I2. Additionally, the IMD 200 can deliver a set of informed pulses, where the IMD 200 delivers the first set of control pulses at a current amplitude Ii. Ii and I2 can be referred to as predetermined values of the amplitudes of the respective control pulses and informed pulses. The predetermined values can be programmed values or stimulation programs have selected as at least partially defining the otherwise selected values of the stimulation pulses to the patient in the absence of transient conditions (e.g., when the ECAP amplitude is below a threshold ECAP value). The first set of control pulses and the first set of informed pulses can be delivered before time T1. In some examples, Ii is 8 milliamps (mA) and I2 is 4 mA. Although the control pulse current amplitude 1002 is shown as being greater than the informed pulse current amplitude 1004, in other examples, the control pulse current amplitude 1002 can be less than or equal to the informed pulse current amplitude 1004.

[0130] While delivering the first set of control pulses and the first set of informed pulses, the IMD 200 can record the ECAP voltage amplitude 1008. During a dynamic or transient condition occurring within the patient 105, such as a cough, a sneeze, a laugh, a Valsalva maneuver, a leg lift, a neck movement, or a deep breath, the ECAP voltage amplitude 1008 can increase if the control pulse current amplitude 1002 and the informed pulse current amplitude 1004 remain constant. This increase in the ECAP voltage amplitude 1008 can be caused by a decrease in the distance between the electrodes and the nerve. For example, as Figure 10 shown, the ECAP voltage amplitude 1008 can increase before time T1 while the stimulation current amplitudes remain constant. The increased ECAP voltage amplitude 1008 can indicate that the patient 105 is at risk of experiencing transient overstimulation due to the control pulses and informed pulses delivered by the IMD 200. To prevent the patient 105 from experiencing transient overstimulation, the IMD 200 can decrease the control pulse current amplitude 1002 and the informed pulse current amplitude 1004 in response to the ECAP voltage amplitude 1008 exceeding the threshold ECAP amplitude 1006. For example, as Figure 10If IMD 200 senses that the voltage amplitude 1008 of the ECAP meets or exceeds the threshold ECAP amplitude 1006, IMD 200 can enter a decremental mode in which the control pulse current amplitude 1002 and the notification pulse current amplitude 1004 are reduced, as shown at time Tl. In some examples, the threshold ECAP amplitude 1006 is selected from a range of about 3 microvolts (pV) to about 300 pV, or a range of about 10 microvolts (pV) to about 20 pV. For example, the threshold ECAP amplitude 1006 is 15 pV. In other examples, the threshold ECAP amplitude 1006 is less than or equal to 3 pV or greater than or equal to 300 pV.

[0131] IMD 200 can respond relatively quickly to an ECAP voltage amplitude 1008 exceeding the threshold ECAP amplitude 1006. For example, the IMD can be configured to detect an exceeding of the threshold ECAP amplitude within 20 milliseconds (ms). If the IMD 200 delivers control pulses at a frequency of 50 Hz, the time period including delivery of a control pulse and detection of the resulting ECAP signal for a single sample can be 20 ms or less. However, since the ECAP signal can occur within one or two ms of delivery of a control pulse, the IMD 200 can be configured to detect an ECAP signal exceeding the threshold ECAP amplitude in less than 10 ms. For transient conditions, such as a patient coughing or sneezing, these sampling periods will be sufficient to identify an ECAP amplitude exceeding the threshold, as well as a responsive reduction in subsequent pulse amplitudes before the ECAP amplitude would reach a higher level that can be uncomfortable for the patient.

[0132] In some cases, the decremental mode can be stored in the storage device 212 of the IMD 200 as part of the stimulation adjustment mode 220. In Figure 10In the illustrated example, the decrementing mode is performed by the IMD 200 on a second set of control pulses and a second set of notification pulses occurring between time Tl and time T2. In some examples, to perform the decrementing mode, the IMD 200 decreases the control pulse current amplitude 1002 of each control pulse in the second set of control pulses according to a first function with respect to time. In other words, the IMD 200 decreases each successive control pulse in the second set of control pulses in proportion to the amount of time that has elapsed since the previous control pulse. Additionally, during the decrementing mode, the IMD 200 can decrease the notification pulse current amplitude 1004 of each notification pulse of the second set of notification pulses according to a second function with respect to time. Although linear first and second functions are illustrated, in other examples, the first and / or second functions can be non-linear, such as a logarithmic function (e.g., a rate of change that decreases with time), an exponential function (e.g., a rate of change that increases with time), a parabolic function, a step-wise function, a plurality of different functions, etc. During the time period (e.g., time interval T2-Tl) in which the IMD 200 operates in the decrementing mode, the ECAP voltage amplitude 1008 of an ECAP sensed by the IMD 200 can be greater than or equal to the threshold ECAP amplitude 1006.

[0133] In Figure 2 In the illustrated example, the IMD 200 can sense an ECAP at time T2, where the ECAP has an ECAP voltage amplitude 1008 that is less than the threshold ECAP amplitude 1006. In some cases, the ECAP sensed at time T2 can be the first ECAP sensed by the IMD 200 having a lower threshold amplitude since the IMD 200 started the decrementing mode at time Tl. Based on sensing the ECAP at time T2, the IMD 200 can deactivate the decrementing mode and activate the incrementing mode. In some cases, the incrementing mode can be stored in the storage device 212 of the IMD 200 as part of the stimulation adjustment mode 220. The IMD 200 can perform the incrementing mode on a third set of control pulses and a third set of notification pulses occurring between time T2 and time T3. In some examples, to perform the incrementing mode, the IMD 200 increases the control pulse current amplitude 1002 of each control pulse of the third set of control pulses according to a third function with respect to time. In other words, the IMD 200 increases each successive control pulse in the third set of control pulses in proportion to the amount of time that has elapsed since the previous control pulse. Additionally, during the incrementing mode, the IMD 200 can increase the notification pulse current amplitude 1004 of each notification pulse of the third set of notification pulses according to a fourth function with respect to time.

[0134] As Figure 10As shown, IMD 200 is configured to decrease the amplitude at a faster rate than it increases the amplitude after ECAP voltage amplitude 1008 falls below threshold ECAP amplitude 1006. In other examples, the rate of change during the decrementing and incrementing modes can be similar. In other examples, IMD 200 can be configured to increase the amplitude of the notification pulses and control pulses at a faster rate than it decreases the amplitude. In other examples, the rate of change of the pulse amplitudes can be relatively instantaneous (e.g., very fast rates). For example, in response to ECAP voltage amplitude 1008 exceeding threshold ECAP amplitude 1006, IMD 200 can immediately reduce the amplitude of one or both of control pulse current amplitude 1002 or notification pulse current amplitude 1004 to a predetermined or calculated value. Then, in response to ECAP voltage amplitude 1008 falling back below threshold ECAP amplitude 1006, IMD 200 can enter an incrementing mode as described above.

[0135] When control pulse current amplitude 1002 and notification pulse current amplitude 1004 return to current amplitude I2 and current amplitude II, respectively, IMD 200 can deactivate the incrementing mode and deliver stimulation pulses at a constant current amplitude. By decreasing stimulation in response to an ECAP amplitude exceeding a threshold and subsequently increasing stimulation in response to the ECAP amplitude falling below the threshold, IMD 200 can prevent or reduce the severity of transient overstimulation experienced by patient 105, whether that reduction is in terms of length of time experienced, relative intensity, or both.

[0136] Figure 10 The techniques described for IMD 200 delivering both control pulses and notification pulses are described. However, the techniques of Figure 10 may be applied to the case where IMD 200 delivers only control pulses to provide therapy to patient 105. In this way, IMD 200 will similarly enter a decrementing mode or an incrementing mode for control pulse current amplitude 1002 based on the detected ECAP voltage amplitude 1008 without needing to adjust the amplitude or other parameters of any other type of stimulation pulse.

[0137] Figure 11 is a flowchart illustrating exemplary operations for controlling stimulation based on one or more sensed ECAPs in accordance with one or more techniques of this disclosure. Figure 11 Similar to the above Figure 9 , except that Figure 11 A buffer is employed that is defined by an upper threshold and a lower threshold that define when the amplitude value is increased or decreased. For convenience, the upper threshold is referred to as a Figure 2 IMD 200 of Figure 11 is described. However, Figure 11The techniques can be performed by different components of IMD 200 or by additional or alternative medical devices.

[0138] Stimulus generation circuitry 202 of IMD 200 can deliver electrical stimulation therapy to a patient (e.g., patient 105). To control the electrical stimulation therapy, processing circuitry 210 can direct the delivery of at least some stimulation pulses in accordance with therapy stimulation programs 214 of storage 212, where the electrical stimulation therapy can include a plurality of control pulses and / or notification pulses. In some cases, the notification pulses can produce an ECAP that is detectable by IMD 200. However, in other cases, the electrode polarization of the notification pulses can interfere with the sensing of ECAPs in response to the notification pulses. In some examples, to elicit ECAPs that are detectable by IMD 200, stimulus generation circuitry 202 delivers a plurality of control pulses interleaved with at least some of a plurality of notification pulses. Processing circuitry 210 can control the delivery of the control pulses in accordance with ECAP test stimulation programs 216. As the control pulses can be interleaved with the notification pulses, sensing circuitry 206 of IMD 200 can detect a plurality of ECAPs, where sensing circuitry 206 is configured to detect each of the plurality of ECAP signals after a control pulse of the plurality of control pulses and before a subsequent notification pulse of the plurality of notification pulses. In this way, IMD 200 can elicit a plurality of ECAPs in the target tissue by delivering control pulses without notification pulses interfering with IMD 200 sensing the ECAPs.

[0139] As Figure 11 shown, processing circuitry 210 directs stimulus generation circuitry 202 to deliver a control pulse (1102). Stimulus generation circuitry 202 can deliver the control pulse to the target tissue of patient 105 via any combination of electrodes 232, 234 of lead 230. In some examples, the control pulse can include a balanced biphasic square pulse that employs an active recharge phase. However, in other examples, the control pulse can include a monophasic pulse followed by a passive recharge phase. In other examples, the control pulse can include an unbalanced biphasic portion and a passive recharge portion. Although not required, the biphasic control pulse can include an interphase interval between the positive phase and the negative phase to facilitate propagating a neural pulse in response to the first phase of the biphasic pulse. The control pulse can have a pulse width of less than about 300 ps, such as a biphasic pulse with each phase having a duration of about 100 ps.

[0140] After delivering the control pulse, IMD 200 attempts to detect an ECAP (1104). For example, sensing circuitry 206 can monitor signals from any combination of electrodes 232, 234 of lead 230. In some examples, sensing circuitry 206 detects an ECAP from a particular combination of electrodes 232, 234. In some cases, the particular combination of electrodes used to sense the ECAP includes different electrodes than the combination of electrodes 232, 234 used to deliver the stimulation pulse. Alternatively, in other cases, the particular combination of electrodes used to sense the ECAP includes at least one of the same electrodes as the combination of electrodes used to deliver the stimulation pulse to patient 105. In some examples, the particular combination of electrodes used to sense the ECAP can be on an opposite side of lead 230 than the particular combination of electrodes used to deliver the stimulation pulse. IMD 200 can detect an ECAP in response to the control pulse. IMD 200 can measure one or more features of the responsive ECAP, such as an ECAP amplitude, an ECAP duration, a peak-to-peak duration, or any combination thereof. For example, to measure an amplitude of the ECAP, IMD 200 can determine a voltage difference between the Nl ECAP peak and the P2 ECAP peak.

[0141] At block 1106, processing circuitry 210 determines whether the ECAP amplitude of the responsive ECAP is greater than the ECAP amplitude upper threshold. If the ECAP amplitude is greater than the ECAP amplitude upper threshold (“YES” branch of block 1106), processing circuitry 210 activates / continues a decrement mode in IMD 200 (1108). For example, if the decrement mode is “on” in IMD 200 when processing circuitry determines that the ECAP amplitude is greater than the ECAP amplitude upper threshold, processing circuitry 210 maintains IMD 200 in the decrement mode. If the decrement mode is “off’ in IMD 200 when processing circuitry determines that the ECAP amplitude is greater than the ECAP amplitude upper threshold, processing circuitry 210 activates the decrement mode to decrease the pulse amplitude from the predetermined value programmed for stimulation. In some examples, the decrement mode can be stored in storage 212 as part of stimulation adjustment mode 220. The decrement mode can be a set of instructions that cause IMD 200 to decrease one or more parameter values of each successive notification pulse and decrease one or more parameter values of each successive control pulse. For example, when the decrement mode is activated, processing circuitry 210 can decrease the current amplitude of each successive notification pulse delivered by IMD 200 and decrease the current amplitude of each successive control pulse delivered by IMD 200. After processing circuitry 210 activates / continues the decrement mode, the example operations can return to block 1102 and IMD 200 can deliver another control pulse.

[0142] If the ECAP amplitude is not greater than the ECAP amplitude threshold (the "No" branch of block 1106), the processing circuitry 210 determines whether the ECAP amplitude is less than the ECAP amplitude lower threshold in block 1110. If the ECAP amplitude is less than the ECAP amplitude lower threshold (the "Yes" branch of block 1110), the processing circuitry 210 activates an incrementing mode in the IMD 200 (1112). In some examples, the incrementing mode can be stored in the storage device 212 as part of the stimulation adjustment mode 220. The incrementing mode can be a set of instructions that cause the IMD 200 to increase the one or more parameter values of each successive notification pulse and increase the one or more parameter values of each successive control pulse. For example, when the incrementing mode is activated, the processing circuitry 210 can increase the current amplitude of each successive notification pulse delivered by the IMD 200 and increase the current amplitude of each successive control pulse delivered by the IMD 200. After the processing circuitry 210 activates the incrementing mode, the example operations can return to block 1102 and the IMD 200 can deliver another control pulse. The processing circuitry 210 can continue to increment the pulse amplitude until the pulse amplitude returns to a predetermined value of the amplitude programmed for delivery prior to the ECAP amplitude exceeding the ECAP amplitude upper threshold.

[0143] If the ECAP amplitude is not less than the ECAP amplitude lower threshold (the "No" branch of block 1110), the processing circuitry 1114 maintains the current pulse amplitude used to at least partially define the parameter value. In this way, when the ECAP amplitude is between the ECAP amplitude upper threshold and the ECAP amplitude lower threshold, the processing circuitry 210 does not increase the amplitude value back to the predetermined value or decrease the amplitude. This "cushion" can reduce oscillating amplitude values when the ECAP amplitude is similar to the ECAP amplitude threshold. These oscillating amplitude values can be perceived as uncomfortable or unwanted by the patient. However, once the ECAP amplitude drops below the ECAP amplitude lower threshold, the processing circuitry 210 can return the amplitude value to the predetermined amplitude value intended for therapy.

[0144] In some examples, the ECAP amplitude upper threshold and the ECAP amplitude lower threshold are defined. In other examples, the processing circuitry 210 can define the ECAP amplitude upper threshold and / or the ECAP amplitude lower threshold as a cushion or a deviation from a single defined ECAP threshold. For example, the processing circuitry 210 can define the ECAP amplitude lower threshold based on the ECAP amplitude upper threshold defined by a user or calculated from an initial patient perception threshold and / or discomfort threshold. Although Figure 11 While the amplitude of the notification pulses and control pulses are described, techniques can also be applied when the IMD 200 delivers only control pulses (e.g., no notification pulses) to the patient for therapy, Figure 11 .

[0145] Figure 12 A voltage / current / time graph 1200 is shown that plots control pulse current amplitude 1202, informed pulse current amplitude 1204, and ECAP voltage amplitude 1210 as a function of time in accordance with one or more techniques of this disclosure. Additionally, Figure 12 An upper threshold ECAP amplitude 1206 and a lower threshold ECAP amplitude 1208 are shown. Figure 12 A technique can be similar to Figure 10 but Figure 12 A technique is shown in which two thresholds of ECAP voltage amplitude 1210 are employed to provide a buffer zone that can reduce possible oscillations in pulse amplitude if the ECAP amplitude is oscillating near a single ECAP amplitude threshold. For convenience, the upper threshold ECAP amplitude 1206 is referred to as the upper threshold and the lower threshold ECAP amplitude 1208 is referred to as the lower threshold. Figure 2 The IMD 200 of Figure 10 is described. However, Figure 12 The techniques of

[0146] The voltage / current / time graph 1200 shows the relationship between the sensed ECAP voltage amplitude and the stimulation current amplitude. For example, the control pulse current amplitude 1202 and the informed pulse current amplitude 1204 are plotted as a function of time along with the ECAP voltage amplitude 1210, thus showing how the IMD 200 is configured to change the stimulation current amplitude relative to the detected ECAP voltage amplitude (or some other ECAP characteristic value). In some examples, the IMD 200 delivers a plurality of control pulses and a plurality of informed pulses at the control pulse current amplitude 1202 and the informed pulse current amplitude 1204, respectively. Initially, the IMD 200 can deliver a first set of control pulses, where the IMD 200 delivers the first set of control pulses at a current amplitude I2. Additionally, the IMD 200 can deliver a first set of informed pulses, where the IMD 200 delivers the first set of control pulses at a current amplitude Ii. Ii and I2 can be referred to as predetermined values of the amplitudes of the respective control pulses and informed pulses. The predetermined values can be programmed values or stimulation programs have selected as at least partially defining the otherwise selected values of the stimulation pulses to the patient in the absence of transient conditions (e.g., when the ECAP amplitude is below a threshold ECAP value). The first set of control pulses and the first set of informed pulses can be delivered prior to time Ti. In some examples, Ii is 8 milliamps (mA) and I2 is 4 mA. Although the control pulse current amplitude 1202 is shown as being greater than the informed pulse current amplitude 1204, in other examples, the control pulse current amplitude 1202 can be less than or equal to the informed pulse current amplitude 1204.

[0147] While delivering the first set of control pulses and the first set of informing pulses, IMD 200 can determine an ECAP voltage amplitude 1210 from the respective ECAP signals. During dynamic and transient conditions occurring within patient 105, such as a cough, a sneeze, a laugh, a Valsalva maneuver, a leg lift, a neck movement, or a deep breath, the ECAP voltage amplitude 1210 can increase if the control pulse current amplitude 1202 and the informing pulse current amplitude 1204 remain constant. This increase in the ECAP voltage amplitude 1210 can be caused by a decrease in the distance between the electrodes and the nerve. For example, as Figure 12 As shown at time Tl, the ECAP voltage amplitude 1208 can increase while the stimulation current amplitude remains constant. The increasing ECAP voltage amplitude 1208 can indicate that patient 105 is at risk of experiencing transient overstimulation due to the control pulses and informing pulses delivered by IMD 200. However, IMD 200 can not take any action until the ECAP voltage amplitude 1210 exceeds or is greater than the upper threshold ECAP amplitude 1206. To prevent patient 105 from experiencing transient overstimulation, IMD 200 can decrease the control pulse current amplitude 1202 and the informing pulse current amplitude 1204 in response to the ECAP voltage amplitude 12010 exceeding the upper threshold ECAP amplitude 1206. For example, as Figure 12 As shown at time Tl, if IMD 200 senses that the ECAP voltage amplitude 1210 of the ECAP meets or exceeds the upper threshold ECAP amplitude 1206, IMD 200 can enter a decremental mode in which IMD 200 decreases the control pulse current amplitude 1202 and the informing pulse current amplitude 1204. In some examples, the upper threshold ECAP amplitude 1206 is selected from a range of about 3 microvolts (pV) to about 300 pV, or a range of about 10 microvolts (pV) to about 20 pV. For example, the upper threshold ECAP amplitude 1206 is 15 pV. In other examples, the upper threshold ECAP amplitude 1206 is less than or equal to 3 pV or greater than or equal to 300 pV. In some examples, IMD 200 can determine the upper threshold ECAP amplitude 1206 from a target threshold such that the upper threshold ECAP amplitude 1206 is higher than the target threshold and the lower threshold ECAP amplitude 1208 is lower than the target threshold.

[0148] IMD 200 can respond relatively quickly to ECAP amplitudes 1210 exceeding the upper threshold ECAP amplitude 1206. For example, the IMD can be configured to detect an exceeding of the threshold ECAP amplitude within 20 milliseconds (ms). If the IMD 200 delivers control pulses at a frequency of 50 Hz, the time period including delivery of a control pulse and detection of the resulting ECAP signal for a single sample can be 20 ms or less. However, since the ECAP signal can occur within one or two ms of delivery of a control pulse, the IMD 200 can be configured to detect an ECAP signal exceeding the threshold ECAP amplitude within less than 10 ms. For transient conditions, such as a patient coughing or sneezing, these sampling periods will be sufficient to identify an ECAP amplitude exceeding the threshold, as well as a responsiveness of subsequent pulse amplitudes before the ECAP amplitude will reach a higher level that can be uncomfortable for the patient.

[0149] In some cases, the decremental mode can be stored in the storage device 212 of the IMD 200 as part of the stimulation adjustment mode 220. In Figure 10 In the illustrated example, the decremental mode is performed by the IMD 200 on a second set of control pulses and a second set of notification pulses occurring between time Tl and time T2. In some examples, to perform the decremental mode, the IMD 200 decreases the control pulse current amplitude 1202 of each control pulse of the second set of control pulses according to a first function with respect to time. In other words, the IMD 200 decreases each successive control pulse in the second set of control pulses in proportion to the amount of time that has elapsed since the previous control pulse. Additionally, during the decremental mode, the IMD 200 can decrease the notification pulse current amplitude 1204 of each notification pulse of the second set of notification pulses according to a second function with respect to time. Although linear first and second functions are illustrated, in other examples, the first and / or second functions can be non-linear, such as a logarithmic function (e.g., a rate of change that decreases with time), an exponential function (e.g., a rate of change that increases with time), a parabolic function, a step-wise function, a plurality of different functions, etc. During the time period in which the IMD 200 is operating in the decremental mode (e.g., time interval T2-Tl), the ECAP voltage amplitude 1210 of the ECAP sensed by the IMD 200 can be greater than or equal to the upper threshold ECAP amplitude 1206.

[0150] In Figure 12In the illustrated example, IMD 200 can sense an ECAP at time T2, where the ECAP has an ECAP voltage amplitude 1210 that is less than the upper threshold ECAP amplitude 1206. However, the ECAP voltage amplitude 1210 can still be greater than the lower threshold ECAP amplitude 1208. Within this zone between the upper threshold ECAP amplitude 1206 and the lower threshold ECAP amplitude 1208, IMD 200 can maintain the control pulse current amplitude 1202 and the informed pulse current amplitude 1204 (e.g., between T2 and T3). By not immediately increasing the amplitudes of both the control pulse current amplitude 1202 and the informed pulse current amplitude 1204 in response to the ECAP voltage amplitude 1210 falling below the upper threshold ECAP amplitude 1206, IMD 200 can prevent these pulse amplitudes from increasing again, and only experience another spike in the ECAP voltage amplitude 1210. These subsequent spikes can be perceived by the patient if the patient experiences undesirable fluctuations or oscillations in therapy intensity. The lower threshold ECAP amplitude 1208 can be set to a percentage or an absolute value below the upper threshold ECAP amplitude 1206 or the target threshold. In some examples, the zone between the upper threshold ECAP amplitude 1206 and the lower threshold ECAP amplitude 1208 can have a predetermined amount and / or can be adjustable by the patient or a physician. For example, if the patient is still experiencing oscillations in therapy intensity, the upper threshold ECAP amplitude 1206 and / or the lower threshold ECAP amplitude 1208 can be adjusted to increase the zone.

[0151] At T3, IMD 200 can again detect that the ECAP voltage amplitude 1210 exceeds the upper threshold ECAP amplitude 1206, and responsively decrease the control pulse current amplitude 1202 and the informed pulse current amplitude 1204 even further. At time T4, the ECAP voltage amplitude 1210 falls below the upper threshold ECAP amplitude 1206, but is still greater than the lower threshold ECAP amplitude 1208. Accordingly, between times T4 and T5, IMD 200 can maintain the control pulse current amplitude 1202 and the informed pulse current amplitude 1204. At time T5, IMD 200 determines that the ECAP voltage amplitude 1210 has fallen below and is less than the lower threshold ECAP amplitude 1208. In response to the ECAP voltage amplitude 1210 falling below the lower threshold ECAP amplitude 1208, IMD 200 can begin to increase the control pulse current amplitude 1202 and the informed pulse current amplitude 1204 back to the respective predetermined values II and I2 at time T6. If the ECAP voltage amplitude 1210 again exceeds the upper threshold ECAP amplitude 1206 prior to time T6, IMD 200 will have a decreased control pulse current amplitude 1202 and informed pulse current amplitude 1204, as discussed above with respect to the time period between Tl and T2.

[0152] In other examples, the rate of change of the pulse amplitude can be relatively transient (e.g., very fast rate). For example, in response to the ECAP voltage amplitude 1210 exceeding the upper threshold ECAP amplitude 1206, the IMD 200 can immediately reduce the amplitude of one or both of the control pulse current amplitude 1202 or the informed pulse current amplitude 1204 to a predetermined value or a calculated value. Then, in response to the ECAP voltage amplitude 1210 decreasing back below the lower threshold ECAP amplitude 1208, the IMD 200 can enter the incrementing mode as described above.

[0153] When the control pulse current amplitude 1002 and the informed pulse current amplitude 1004 return to the current amplitude I2 and the current amplitude II (e.g., the predetermined or programmed values for each type of pulse), the IMD 200 can again deactivate the incrementing mode and deliver stimulation pulses at a constant current amplitude. By reducing stimulation in response to the ECAP amplitude exceeding an upper threshold and subsequently increasing stimulation in response to the ECAP amplitude falling below a lower threshold, the IMD 200 can prevent the patient 105 from experiencing transient overstimulation or reduce the severity of transient overstimulation experienced by the patient 105, while also reducing potential oscillations that can occur at a single threshold, whether that reduction is in terms of experienced duration, relative intensity, or both.

[0154] Figure 12 The case is described in which the IMD 200 delivers both control pulses and informed pulses. However, the techniques of Figure 10 may be applied to the case in which only control pulses are delivered to provide therapy to the patient and elicit a detectable ECAP signal. In this way, the IMD 200 would similarly enter a decrementing mode or an incrementing mode for the control pulse current amplitude 1202 based on the detected ECAP voltage amplitude 1210 without needing to adjust the amplitude or other parameters of any other type of stimulation pulse.

[0155] The following examples are illustrative systems, devices, and methods described herein.

[0156] Example 1 : A medical device comprising: stimulation generation circuitry configured to deliver electrical stimulation to a patient, wherein the electrical stimulation comprises a plurality of pulses; sensing circuitry configured to detect a plurality of evoked compound action potentials (ECAPs) elicited by respective pulses of the plurality of pulses; and processing circuitry configured to: determine that a first value of a characteristic of a first ECAP is greater than a threshold ECAP characteristic value; in response to determining that the first value of the characteristic of the first ECAP is greater than the threshold ECAP characteristic value, decrease a parameter of a first set of pulses deliverable by the stimulation generation circuitry at least partially after the first ECAP from a predetermined value; determine that a second value of the characteristic of a second ECAP elicited after the first ECAP is less than the threshold ECAP characteristic value; and in response to determining that the second value of the characteristic of the second ECAP is less than the threshold ECAP characteristic value, increase the parameter of a second set of pulses deliverable by the stimulation generation circuitry at least partially after the second ECAP to the predetermined value.

[0157] Example 2: The medical device of Example 1, wherein the parameter of the first set of pulses comprises an amplitude of the first set of pulses, and wherein to decrease the parameter of the first set of pulses, the processing circuitry is configured to decrement an amplitude value from an amplitude of each pulse of the first set of pulses.

[0158] Example 3: The medical device of Example 2, wherein the amplitude value comprises a first amplitude value, wherein the parameter of the second set of pulses comprises an amplitude of the second set of pulses, and wherein to increase the parameter of the second set of pulses, the processing circuitry is configured to increment the amplitude of each pulse of the second set of pulses by a second amplitude value that is different than the first amplitude value.

[0159] Example 4: The medical device of any of Examples 1-3, wherein the characteristic of the first ECAP comprises an amplitude of the first ECAP, wherein the characteristic of the second ECAP comprises an amplitude of the second ECAP, and wherein the threshold ECAP characteristic value comprises an ECAP amplitude of about 3 microvolts (pV) to about 300 (pV).

[0160] Example 5: The medical device of any of Examples 1-4, wherein processing circuitry is configured to set the predetermined value of the parameter to define, when a sensed ECAP is less than the threshold ECAP characteristic value, some of the plurality of pulses that are below a perceptual threshold that defines an intensity at which the patient is unable to perceive the some of the plurality of pulses.

[0161] Example 6: The medical device of any of examples 1-5, wherein the processing circuitry is configured to: deliver a third set of pulses defined at least in part by the predetermined value prior to detecting the first ECAP and using the stimulation generation circuitry; and increase the parameter of the second set of pulses by increasing the parameter of the second set of pulses to the predetermined value such that a last pulse in the second set of pulses is delivered according to at least the predetermined value.

[0162] Example 7: The medical device of any of examples 1-6, wherein: the plurality of pulses includes a plurality of control pulses and a plurality of notification pulses, the plurality of control pulses are interleaved at least in part with the plurality of notification pulses, the sensing circuitry is configured to detect each ECAP in the plurality of ECAPs after a respective control pulse in the plurality of control pulses and not any notification pulse in the plurality of notification pulses, the parameter includes a first parameter, the first set of pulses includes a first set of control pulses in the plurality of control pulses defined at least in part by the first parameter, and the processing circuitry is configured to: in response to determining that the first value of the feature of the first ECAP is greater than the threshold ECAP feature value, decrease a second parameter that at least in part defines a first set of notification pulses in the plurality of notification pulses deliverable by the stimulation generation circuitry after the first ECAP; and in response to determining that the second value of the feature of the second ECAP is less than the threshold ECAP feature value, increase the second parameter that at least in part defines a second set of notification pulses in the plurality of notification pulses deliverable by the stimulation generation circuitry after the second ECAP.

[0163] Example 8: The medical device of any of examples 1-7, wherein the threshold ECAP feature value includes an upper threshold ECAP feature value, and wherein the processing circuitry is configured to: determine that the second value of the feature of the second ECAP evoked after the first ECAP is less than the upper threshold ECAP feature value by determining that the second value of the feature of the second ECAP evoked after the first ECAP is less than a lower threshold ECAP feature value that is lower than the upper threshold ECAP feature; and in response to determining that the second value of the feature of the second ECAP is less than the lower threshold ECAP feature value, increase a parameter that at least in part defines a second set of pulses deliverable by the stimulation generation circuitry after the second ECAP to the predetermined value, wherein the processing circuitry is configured to maintain a value of the parameter in response to determining that the second value of the feature of the sensed ECAP is between the upper threshold ECAP amplitude and the lower threshold ECAP amplitude.

[0164] Example 9: The medical device of any of examples 1-8, wherein the medical device includes an implantable medical device.

[0165] Example 10: A method comprising: delivering, by stimulation generation circuitry of a medical device, electrical stimulation to a patient, wherein the electrical stimulation comprises a plurality of pulses; detecting, by sensing circuitry of the medical device, a plurality of evoked compound action potentials (ECAPs) elicited by respective ones of the plurality of pulses; determining, by processing circuitry, that a first value of a characteristic of a first ECAP is greater than a threshold ECAP characteristic value; in response to determining that the first value of the characteristic of the first ECAP is greater than the threshold ECAP characteristic value, decreasing, by the processing circuitry, a parameter of a first set of pulses deliverable by the stimulation generation circuitry at least partially after the first ECAP from a predetermined value; determining, by the processing circuitry, that a second value of the characteristic of a second ECAP elicited after the first ECAP is less than the threshold ECAP characteristic value; and in response to determining that the second value of the characteristic of the second ECAP is less than the threshold ECAP characteristic value, increasing, by the processing circuitry, the parameter of a second set of pulses deliverable by the stimulation generation circuitry at least partially after the second ECAP to the predetermined value.

[0166] Example 11 : The method of example 10, wherein the parameter of the first set of pulses comprises an amplitude of the first set of pulses, and wherein decreasing the parameter of the first set of pulses comprises decrementing an amplitude value from each pulse of the first set of pulses.

[0167] Example 12: The method of example 11, wherein the amplitude value comprises a first amplitude value, wherein the parameter of the second set of pulses comprises an amplitude of the second set of pulses, and wherein increasing the parameter of the second set of pulses comprises incrementing an amplitude value from each pulse of the second set of pulses that is different than the first amplitude value.

[0168] Example 13: The method of any one of examples 10-12, wherein the characteristic of the first ECAP comprises an amplitude of the first ECAP, wherein the characteristic of the second ECAP comprises an amplitude of the second ECAP, and wherein the threshold ECAP characteristic value comprises an ECAP amplitude of about 3 microvolts (pV) to about 300 (pV).

[0169] Example 14: The method of any one of examples 10-13, further comprising setting the predetermined value of the parameter to define, when a sensed ECAP is less than the threshold ECAP characteristic value, some of the plurality of pulses that are below a perceptual threshold that defines an intensity of the some of the plurality of pulses that the patient is unable to perceive.

[0170] Example 15: The method of any of examples 10-14, wherein the plurality of pulses are delivered by the stimulation generation circuitry above a perception threshold, and wherein the patient is able to perceive the plurality of pulses delivered above the perception threshold.

[0171] Example 16: The method of any of examples 10-15, further comprising: delivering, by the stimulation generation circuitry and prior to detecting the first ECAP, a third set of pulses defined at least in part by the predetermined value; and incrementing the parameter of the second set of pulses by increasing the parameter of the second set of pulses to the predetermined value, such that a last pulse in the second set of pulses is delivered according to at least the predetermined value.

[0172] Example 17: The method of any of examples 10-16, wherein: the plurality of pulses includes a plurality of control pulses and a plurality of notification pulses, the plurality of control pulses are interleaved at least in part with the plurality of notification pulses, the sensing circuitry is configured to detect each ECAP in the plurality of ECAPs after a respective control pulse in the plurality of control pulses but not any notification pulse in the plurality of notification pulses, the parameter includes a first parameter, the first set of pulses includes a first set of control pulses in the plurality of control pulses defined at least in part by the first parameter, and the method further comprises: in response to determining that the first value of the feature of the first ECAP is greater than the threshold ECAP feature value, decreasing a second parameter that at least in part defines a first set of notification pulses in the plurality of notification pulses that are deliverable by the stimulation generation circuitry after the first ECAP; and in response to determining that the second value of the feature of the second ECAP is less than the threshold ECAP feature value, increasing the second parameter that at least in part defines a second set of notification pulses in the plurality of notification pulses that are deliverable by the stimulation generation circuitry after the second ECAP.

[0173] Example 18: The method of any of examples 10-17, wherein the threshold ECAP feature value includes an upper threshold ECAP feature value, and wherein: determining that the second value of the feature of the second ECAP elicited after the first ECAP is less than the upper threshold ECAP feature value includes determining that the second value of the feature of the second ECAP elicited after the first ECAP is less than a lower threshold ECAP feature value that is lower than the upper threshold ECAP feature; and in response to determining that the second value of the feature of the second ECAP is less than the lower threshold ECAP feature value, increasing the parameter that at least in part defines a second set of pulses deliverable by the stimulation generation circuitry after the second ECAP to the predetermined value, wherein the method further comprises maintaining the value of the parameter in response to determining that the second value of the feature of the sensed ECAP is between the upper threshold ECAP amplitude and the lower threshold ECAP amplitude.

[0174] Example 19: The method of any of examples 10-18, wherein the medical device comprises an implantable medical device.

[0175] Example 20: A computer-readable medium comprising instructions that, when executed, cause processing circuitry to: control stimulation generation circuitry of a medical device to deliver electrical stimulation to a patient, wherein the electrical stimulation comprises a plurality of pulses; control sensing circuitry of the medical device to detect a plurality of evoked compound action potentials (ECAPs) elicited by respective pulses of the plurality of pulses; determine that a first value of a characteristic of a first ECAP is greater than a threshold ECAP characteristic value; in response to determining that the first value of the characteristic of the first ECAP is greater than the threshold ECAP characteristic value, decrease a parameter of a first set of pulses deliverable by the stimulation generation circuitry at least partially after the first ECAP from a predetermined value; determine that a second value of the characteristic of a second ECAP elicited after the first ECAP is less than the threshold ECAP characteristic value; and in response to determining that the second value of the characteristic of the second ECAP is less than the threshold ECAP characteristic value, increase the parameter of a second set of pulses deliverable by the stimulation generation circuitry at least partially after the second ECAP to the predetermined value.

[0176] Example 21 : The computer-readable medium of example 20, wherein: the parameter of the first set of pulses comprises an amplitude of the first set of pulses; the instructions that cause the processing circuitry to decrease the parameter of the first set of pulses comprise instructions that cause the processing circuitry to decrement the amplitude of each pulse of the first set of pulses by a first amplitude value; the parameter of the second set of pulses comprises an amplitude of the second set of pulses; and the instructions that cause the processing circuitry to increase the parameter of the second set of pulses comprise instructions that cause the processing circuitry to increment the amplitude of each pulse of the second set of pulses by a second amplitude value that is different than the first amplitude value.

[0177] The techniques described in this disclosure can be implemented, at least in part, in hardware, software, firmware or any combination thereof. For example, various aspects of the techniques can be implemented within one or more processors or processing circuitry, including one or more microprocessors, digital signal processors (DSPs), application specific integrated circuits (ASICs), field programmable gate arrays (FPGAs), or any other equivalent integrated or discrete logic circuitry, as well as any combinations of such

[0178] Such hardware, software, and firmware can be implemented within the same device or within separate devices to support the various operations and functions described in this disclosure. In addition, any of the described units, circuits or components can be implemented together or separately as discrete but interoperable logic devices. Depiction of different features as circuits or units is intended to highlight different functional aspects and does not necessarily imply that such circuits or units must be realized by separate hardware or software components. Rather, functionality associated with one or more circuits or units can be performed by separate hardware or software components, or integrated within common or separate hardware or software components.

[0179] The techniques described in this disclosure can also be embodied or encoded in a computer-readable medium, such as a computer-readable storage medium, containing instructions for causing a programmable processor or other processor to perform the methods described herein, such as when those instructions are executed by the processor. Computer-readable storage media can include random access memory (RAM), read only memory (ROM), programmable read-only memory (PROM), erasable programmable read-only memory (EPROM), electrically erasable programmable read-only memory (EEPROM), flash memory, a hard disk, a compact disc (CD), a floppy disk, a cassette, magnetic tape, magnetic medium, optical medium, or other computer-readable medium that can be used.

Claims

1. A medical device comprising: stimulation generation circuitry configured to deliver electrical stimulation to a patient, wherein the electrical stimulation comprises a plurality of pulses; sensing circuitry configured to detect a plurality of evoked compound action potentials (ECAPs) elicited by respective ones of the plurality of pulses; and processing circuitry configured to: determine that a first value of a characteristic of a first ECAP is greater than a threshold ECAP characteristic value; in response to determining that the first value of the characteristic of the first ECAP is greater than the threshold ECAP characteristic value, decrease a parameter of a first set of pulses delivered by the stimulation generation circuitry at least partially after the first ECAP from a predetermined value; determine that a second value of the characteristic of a second ECAP elicited by delivery of the first set of pulses after the first ECAP is less than the threshold ECAP characteristic value; and in response to determining that the second value of the characteristic of the second ECAP is less than the threshold ECAP characteristic value, increase the parameter of a second set of pulses delivered by the stimulation generation circuitry at least partially after the second ECAP to the predetermined value.

2. The medical device of claim 1, wherein the parameter of the first set of pulses comprises an amplitude of the first set of pulses, and wherein to decrease the parameter of the first set of pulses, the processing circuitry is configured to: decrement an amplitude of each pulse in the first set of pulses by an amplitude value.

3. The medical device of claim 2, wherein the amplitude value comprises a first amplitude value, wherein the parameter of the second set of pulses comprises an amplitude of the second set of pulses, and wherein to increase the parameter of the second set of pulses, the processing circuitry is configured to: increment an amplitude of each pulse in the second set of pulses by a second amplitude value that is different than the first amplitude value.

4. The medical device of claim 1, wherein the characteristic of the first ECAP comprises an amplitude of the first ECAP, wherein the characteristic of the second ECAP comprises an amplitude of the second ECAP, and wherein the threshold ECAP characteristic value comprises an ECAP amplitude of about 3 microvolts (pV) to about 300 microvolts (pV).

5. The medical device of claim 1, wherein processing circuitry is configured to set the predetermined value of the parameter to define ones of the plurality of pulses below a perception threshold that defines an intensity at which the patient is unable to perceive the ones of the plurality of pulses when a sensed ECAP is less than the threshold ECAP characteristic value.

6. The medical device of claim 1, wherein the processing circuitry is configured to: deliver a third set of pulses defined at least in part by the predetermined value prior to detecting the first ECAP and using the stimulation generation circuitry; and increasing the parameter of the second set of pulses by increasing the parameter of the second set of pulses to the predetermined value, such that a last pulse of the second set of pulses is delivered according to at least the predetermined value.

7. The medical device of claim 1, wherein: the plurality of pulses includes a plurality of control pulses and a plurality of notification pulses, the plurality of control pulses being at least partially interleaved with the plurality of notification pulses, the sensing circuitry is configured to detect each of the plurality of ECAPs after a respective control pulse of the plurality of control pulses and not any of the plurality of notification pulses, the parameter includes a first parameter, the first set of pulses includes a first set of control pulses of the plurality of control pulses defined at least in part by the first parameter, and the processing circuitry is configured to: in response to determining that the first value of the feature of the first ECAP is greater than the threshold ECAP feature value, decrease a second parameter that at least partially defines a first set of notification pulses of the plurality of notification pulses deliverable by the stimulus generation circuitry after the first ECAP; and in response to determining that the second value of the feature of the second ECAP is less than the threshold ECAP feature value, increase the second parameter that at least partially defines a second set of notification pulses of the plurality of notification pulses deliverable by the stimulus generation circuitry after the second ECAP.

8. The medical device of claim 1, wherein the threshold ECAP feature value includes an upper threshold ECAP feature value, and wherein the processing circuitry is configured to: determine that the second value of the feature of the second ECAP evoked after the first ECAP is less than the upper threshold ECAP feature value by determining that the second value of the feature of the second ECAP evoked after the first ECAP is less than a lower threshold ECAP feature value that is lower than the upper threshold ECAP feature; and in response to determining that the second value of the feature of the second ECAP is less than the lower threshold ECAP feature value, increase the parameter that at least partially defines a second set of pulses deliverable by the stimulus generation circuitry after the second ECAP to the predetermined value, wherein the processing circuitry is configured to maintain a value of the parameter in response to determining that the second value of the sensed feature of the ECAP is between the upper threshold ECAP amplitude and the lower threshold ECAP amplitude.

9. The medical device of claim 1, wherein the medical device includes an implantable medical device.

10. A medical device, the medical device comprising: processing circuitry; and a storage device storing instructions that, when executed by the processing circuitry, cause the processing circuitry to perform a method, the method comprising: controlling a stimulus generation circuitry to deliver electrical stimulation to a patient, wherein the electrical stimulation includes a plurality of pulses; control sensing circuitry detects a plurality of evoked compound action potentials (ECAPs) elicited by respective ones of the plurality of pulses; determining a first value of a characteristic of a first ECAP is greater than a threshold ECAP characteristic value; in response to determining the first value of the characteristic of the first ECAP is greater than the threshold ECAP characteristic value, decreasing a parameter of a first set of pulses delivered by the stimulation generation circuitry at least partially after the first ECAP from a predetermined value; determining a second value of the characteristic of a second ECAP elicited by delivery of the first set of pulses after the first ECAP is less than the threshold ECAP characteristic value; and in response to determining the second value of the characteristic of the second ECAP is less than the threshold ECAP characteristic value, increasing the parameter of a second set of pulses delivered by the stimulation generation circuitry at least partially after the second ECAP to the predetermined value.

11. The medical device of claim 10, wherein the parameter of the first set of pulses comprises an amplitude of the first set of pulses, and wherein decreasing the parameter of the first set of pulses comprises decrementing an amplitude of each pulse in the first set of pulses by an amplitude value.

12. The medical device of claim 11, wherein the amplitude value comprises a first amplitude value, wherein the parameter of the second set of pulses comprises an amplitude of the second set of pulses, and wherein increasing the parameter of the second set of pulses comprises incrementing the amplitude of each pulse in the second set of pulses by a second amplitude value that is different than the first amplitude value.

13. The medical device of claim 10, wherein the characteristic of the first ECAP comprises an amplitude of the first ECAP, wherein the characteristic of the second ECAP comprises an amplitude of the second ECAP, and wherein the threshold ECAP characteristic value comprises an ECAP amplitude of about 3 microvolts (pV) to about 300 microvolts (pV).

14. The medical device of claim 10, the method further comprising setting the predetermined value of the parameter to define ones of the plurality of pulses below a perception threshold when a sensed ECAP is less than the threshold ECAP characteristic value, the perception threshold defining an intensity of the ones of the plurality of pulses that the patient is unable to perceive.

15. The medical device of claim 10, wherein the plurality of pulses are delivered by the stimulation generation circuitry above a perception threshold, and wherein the patient is able to perceive the plurality of pulses delivered above the perception threshold.

16. The medical device of claim 10, the method further comprising: delivering, by the stimulation generation circuitry and prior to detecting the first ECAP, a third set of pulses defined at least in part by the predetermined value; and incrementing the parameter of the second set of pulses by increasing the parameter of the second set of pulses to the predetermined value such that a last pulse in the second set of pulses is delivered according to at least the predetermined value.

17. The medical device of claim 10, wherein: the plurality of pulses includes a plurality of control pulses and a plurality of notification pulses, the plurality of control pulses being at least partially interleaved with the plurality of notification pulses, the sensing circuitry is configured to detect each of the plurality of ECAPs after a respective control pulse of the plurality of control pulses and not any of the plurality of notification pulses, the parameter includes a first parameter, the first set of pulses includes a first set of control pulses of the plurality of control pulses defined at least in part by the first parameter, and the method further includes: in response to determining that the first value of the feature of the first ECAP is greater than the threshold ECAP feature value, decreasing a second parameter that at least partially defines a first set of notification pulses of the plurality of notification pulses that are deliverable by the stimulation generation circuitry after the first ECAP; and in response to determining that the second value of the feature of the second ECAP is less than the threshold ECAP feature value, increasing the second parameter that at least partially defines a second set of notification pulses of the plurality of notification pulses that are deliverable by the stimulation generation circuitry after the second ECAP.

18. The medical device of claim 10, wherein the threshold ECAP feature value includes an upper threshold ECAP feature value, and wherein: determining that the second value of the feature of the second ECAP evoked after the first ECAP is less than the upper threshold ECAP feature value includes determining that the second value of the feature of the second ECAP evoked after the first ECAP is less than a lower threshold ECAP feature value that is lower than the upper threshold ECAP feature; and in response to determining that the second value of the feature of the second ECAP is less than the lower threshold ECAP feature value, increasing the parameter that at least partially defines a second set of pulses deliverable by the stimulation generation circuitry after the second ECAP to the predetermined value, wherein the method further includes maintaining the value of the parameter in response to determining that the second value of the sensed feature of the ECAP is between the upper threshold ECAP amplitude and the lower threshold ECAP amplitude.

19. The medical device of claim 10, wherein the medical device includes an implantable medical device.

20. A computer-readable medium comprising instructions that, when executed, cause processing circuitry to: control stimulation generation circuitry of a medical device to deliver electrical stimulation to a patient, wherein the electrical stimulation includes a plurality of pulses; control sensing circuitry of the medical device to detect a plurality of evoked compound action potentials (ECAPs) evoked by respective pulses of the plurality of pulses; determine that a first value of a feature of a first ECAP is greater than a threshold ECAP feature value; in response to determining that the first value of the feature of the first ECAP is greater than the threshold ECAP feature value, decrease a parameter that at least partially defines a first set of pulses delivered by the stimulation generation circuitry after the first ECAP from a predetermined value; determining that a second value of a characteristic of a second ECAP elicited by delivery of the first set of pulses after the first ECAP is less than the threshold ECAP characteristic value; and in response to determining that the second value of the characteristic of the second ECAP is less than the threshold ECAP characteristic value, increasing the parameter of a second set of pulses delivered by the stimulation generation circuitry after at least in part the second ECAP to the predetermined value.

21. The computer-readable medium of claim 20, wherein: the parameter of the first set of pulses comprises an amplitude of the first set of pulses; the instructions to cause the processing circuitry to decrease the parameter of the first set of pulses comprise instructions to cause the processing circuitry to decrement the amplitude of each pulse in the first set of pulses by a first amplitude value; the parameter of the second set of pulses comprises an amplitude of the second set of pulses; and the instructions to cause the processing circuitry to increase the parameter of the second set of pulses comprise instructions to cause the processing circuitry to increment the amplitude of each pulse in the second set of pulses by a second amplitude value that is different than the first amplitude value.

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