Range of motion detection and analysis for spinal cord stimulation devices

Abstract

A method for determining a state of a patient with an implanted neurostimulator comprises receiving acceleration data of the patient, determining a body movability score of the patient, based at least in part on the acceleration data, and determining a physiological patient state based at least partly on the BMS.

Description

[0001] RANGE OF MOTION DETECTION AND ANALYSIS FOR SPINAL CORD

[0002] STIMULATION DEVICES

[0003] The present invention relates to methods for determining a state of a patient with an implanted neurostimulator, NS, and to respective implantable NSs and computer programs.

[0004] The field of pain management would benefit significantly from the availability of an objective, physiologic marker of pain (as contrasted with purely subjective measurements or assessments). In the state of the art, several physiologic variables have previously been measured for this purpose, such as change in heart rate and skin conductance. In general, however, these markers have not been seen to correlate adequately enough with pain to warrant their use as a reliable surrogate measure of pain.

[0005] A patient’s health state is often assessed clinically to determine how much the patient is impeded by pain: Standardized physical functioning and performance tests for determining an aspect of a patient’s health state exist and have been used for pain measurements. Some examples for such typical tests are a forward-reach test for chronic back pain patients, a timed “Up & Go” test for osteoarthritis patients, and a grip strength test for rheumatoid arthritis patients. The forward reach test may assess functional balance of the patient. The test may measure how far a person is able to reach forward beyond the length of their arms without losing their balance. The timed “Up & Go” test may, e.g., comprise measuring how long it takes the patient to complete a series of tasks, e.g.: standing up from a chair, walking a predetermined distance (e.g., three meters), turning around and sitting down again. The grip strength test may comprise measuring the force applied by a patient squeezing a dynamometer as tightly as possible. In general, these performance tests have been seen to predict self-reported pain only nominally. Presently, the evaluation is limited to in-clinic exams conducted by the physician, and quantitative progress is rarely documented, which results in a lack of comparability and reproducibility. Further, current clinical measures of such parameters are largely behavioral and difficult to assess objectively.

[0006] As a result, there is still a need for improving methods for determining a state of a patient with an NS as well as implantable NSs and computer programs.

[0007] The above need is at least partly met by the aspects as described herein.

[0008] According to a first aspect of the invention, a method for determining a state of a patient with an implanted NS is provided. The method comprises receiving acceleration data of the patient, determining a body movability score, BMS, of the patient, based at least in part on the acceleration data, and determining a physiological patient state based at least partly on the BMS.

[0009] The present invention is based in part on the understanding that one of the more objective indicators of a physiological patient state (e.g., of a patient suffering from back pain), although indirect, is body movability (in many cases specifically movability of the spine). In detail, for patients with chronic back pain, spinal flexion and extension, rotation, and / or lateral motion may be a reliable and accurate indicator. Patients suffering from severe pain may be hindered in just these movements. Based thereon, the present invention finds a reproducible and objective way for determining a physiological patient state of a patient with an implanted NS. This may increase the accuracy and efficiency of workflows involved in NS patient monitoring and their treatment, e.g., via electrical stimulation provided by the NS. This may improve the overall patient health state and patient satisfaction with the NS. Such workflows may not rely on subjective and potentially misleading patient-reported feedback.

[0010] In detail, the received acceleration data may be acquired by one or more accelerometers of the patient. The one or more accelerometers may, e.g., comprise an implanted accelerometer and / or a wearable accelerometer. Typically, the involved one or more accelerometers may each measure the gravitational acceleration and / or further accelerations along one or more axes, preferably three axes, more preferably three orthogonal axes. The acceleration data may, e.g., comprise the acceleration values measured along the one or more axes (and / or a value proportional to the acceleration values measured along the one or more axes) at a certain time. Thus, the acceleration data may comprise a time stamp indicative of the time at which the acceleration data have been acquired / measured.

[0011] The sensor (e.g., an accelerometer) providing the acceleration data may, e.g., measure the strength of the gravitational field along three axes and provide the as-acquired measures as (one-, two-, or three-dimensional) acceleration data, e.g., in the form of a three-dimensional vector. When these three axes are orthogonal, the measures are linearly independent which is a common choice to facilitate data processing etc. The acceleration data may, e.g., comprise values from a single measurement by an accelerometer and / or values from a plurality of (e.g., consecutive) measurements of the accelerometer which may reduce the effects of potential non-representative outliers, and / or a mean value thereof.

[0012] The NS may, e.g., comprise a brain stimulator, a vagus nerve stimulator (VNS), a deep brain stimulator (DBS), a responsive neurostimulator (RNS), a sacral nerve stimulator (SNS), a transcranial magnetic stimulator (TMS), a cochlear implant, a peripheral nerve stimulator (PNS), a retinal implant, and / or a spinal cord stimulator (SCS).

[0013] The BMS may, e.g., represent a measure that indicates how far, well, often, and / or frequently the patient may move via posture changes. Such movements may, e.g., comprise spinal flexion, extension, rotation, and / or lateral motion. A patient with a good physiological patient state (e.g., suffering from no to little (chronic) pain) may execute movements with ease, over a wide movement range, often, and / or frequently during their daily life and / or in specific sessions comprising specific body movement tasks. For example, they may bend forwards by more than 45° relative to a perfectly upright posture. In contrast, a less healthy patient (e.g., suffering from (chronic) pain) may avoid such movements during their daily life and / or struggle to reach such wide bending angles (e.g., restricted to less than 45° relative to a perfectly upright posture) when instructed to do so in sessions of specific body movement tasks, e.g., as described herein. Movements may, e.g., be parametrized in terms of the acceleration data described herein. In the above example, the BMS may, e.g., comprise a count how often the patient has bent in either direction by more than 45°, or the patient’s maximum forward bending angle. The inventors of the present invention found that the BMS is thus a suitable indicator for the physiological patient state of the patient.

[0014] For example, the physiological patient state may comprise a class from a predetermined list of at least two classes. In the most rudimentary example, the list of classes may only comprise a first class (e.g., indicating a sufficiently healthy physiological patient state) and a second class (e.g., indicating an unhealthy physiological patient state), wherein the second class may be seen as an indicator for adjusting the patient therapy, e.g., as described herein. In further, more advanced, examples there may be more than two classes to choose from. E.g., there may be a plurality of classes indicating an unhealthy physiological patient state, e.g., indicating impeded body movability in terms of movement range, duration, frequency, direction, and / or time during the day, etc. For example, a physiological patient state may indicate that a first patient moves frequently enough throughout the day but only within a reduced range (e.g., measured in terms of small bending angles of the spine). For a second patient, on the other hand, a physiological patient state may be determined that indicates that they move at a reduced movement frequency throughout the day but when they move, their body movement range (e.g., measured in terms of small bending angles of the spine) is at a healthy level. Herein, a physiological patient state characterized as “healthy” may indicate that no medical intervention and / or adjustment of the currently delivered therapy (e.g., directed at treating (chronic) pain) may be required. Vice versa, a physiological patient state characterized as “unhealthy” may indicate that a medical intervention and / or adjustment of the currently delivered therapy (e.g., directed at treating (chronic) pain) may be required.

[0015] In one example, the acceleration data, the BMS, and the physiological patient state may relate to one another as follows: The acceleration data may allow deriving a forward and / or sideward bending angle of the patient at multiple times. Tracking the patient throughout the day and / or during test sessions, wherein the patient executes predetermined movements, may allow to determine, e.g., the maximum forward bending angle of the patient. In this example, the BMS may be said maximum forward bending angle of the patient. Thus, the BMS can be determined based on the acceleration data. The determining of the physiological patient state may, e.g., be done as follows: Patients with a maximum forward bending angle between 0° and 30° may be categorized in a first physiological patient state (“bad” or “poor”). Patients with a maximum forward bending angle between 30° and 60° may be categorized in a second physiological patient state (“medium”). Patients with a maximum forward bending angle of 60° or more may be categorized in a third physiological patient state (“good”). In other examples, there may be less or more distinct physiological patient states for categorizing the patient.

[0016] In some examples, the acceleration data may comprise first acceleration data measured by a first accelerometer and second acceleration data measured by a second accelerometer. Optionally, determining the BMS may be based on a first location of the first accelerometer and a second location of the second accelerometer, in some examples. The first and / or second accelerometer on the anchor and / or lead may communicate its data back to the NS via wired or wireless communication. Wired connections could be made if the accelerometer is part of the lead. Or a wireless transceiver could be used that is powered by some means (e.g. power transmitted via the lead).

[0017] In essence, acceleration data from two or more accelerometers allow more profound insights into the patient’s body movement, wherein the body movements may in particular relate to internal patient body movements and / or posture changes. This may, e.g., comprise core movements like spinal flexion and extension, rotation, and / or lateral motion. Using more than one accelerometer may, e.g., increase data fidelity, accuracy of movement analysis, and / or pose as a redundant embodiment that may allow reducing the effect of erroneous measurements and / or statistical outliers.

[0018] Utilizing two or more accelerometers allows to accurately monitor body-internal posture changes like bending and / or rotating movements. E.g., when one accelerometer is located near the patient’s hip it may remain stationary when the patient bends backwards, forwards, and / or to either side. A second exemplary accelerometer, e.g., located near the patient’s shoulder blade, may rotate with the patient’s body when they bend backwards, forwards, and / or to either side. Thus, the combined information from the first and second acceleration data from the first and second accelerometer, respectively, provide more detailed insights into the body movements of the patient. As in this example, it may, e.g., be advantageous to locate the plurality of accelerometers along the axis of interest, e.g., for a patient with (chronic) back pain on two locations on the axis of the spine.

[0019] As one can see in this example, information on the first location of the first accelerometer and the second location of the second accelerometer may help to correctly parametrize, process, and / or interpret the respective first and second acceleration data and / or the differences therebetween.

[0020] In some examples, determining the BMS may be based at least partly on comparing the first acceleration data, the second acceleration data, the BMS, and / or a predetermined threshold.

[0021] This may provide a more accurate, reliable, and / or reproducible determining of the physiological patient state of a patient with an implanted NS. In detail, the comparing may allow to identify statistical outliers, erroneous measurements (e.g., of acceleration data), etc.

[0022] For example, comparing the first and second acceleration data may, as described herein, allow to understand the underlying body movement in more detail. Comparing the acceleration data with the current BMS may, e.g., allow to understand whether the latest acceleration data lie within an expected range or not. Comparing the BMS, the acceleration data, and / or parts thereof with one or more respective predetermined thresholds may allow for a classification of the BMS, the acceleration data, and / or parts thereof. In this example, the predetermined threshold may, e.g., indicate a maximum or minimum value for a healthy or unhealthy range for the respective parameter.

[0023] For example, the NS may comprise a pulse generator, PG, and a lead comprising an electrode. Optionally, the first accelerometer may be mounted to the lead and / or the second accelerometer may be mounted to the PG.

[0024] It may be particularly advantageous to provide the NS with its own one or more accelerometers for the following reasons: The method described herein may be of particular interest for patients with, e.g., chronic pain. As the implantation of an NS (e.g., an SCS) is typically prescribed in just these patients, the accelerometers may provide the exact information required for said patients, e.g., according to the method described herein. Thus, only one implantation procedure may be required instead of two (as, e.g., in examples, wherein the NS and the one or more accelerometers may be implanted separately from one another). This may reduce surgery-associated health risks for the patient and / or save time and costs. Further, the accelerometers may be controlled and / or provided with electricity by the respective means of the NS, e.g., by connecting them to the PG of the NS. Thereby, the accelerometers may be implanted into the patient in a space- and work-efficient manner.

[0025] The one or more leads of the NS may comprise one or more electrodes. The lead may typically be configured to be placed near the nerve to be stimulated. For example, the leads of an SCS may be configured to be implanted into the patient and / or placed in the epidural space between the spinal cord and the vertebrae, allowing for electrical stimulation of the spinal cord via the one or more electrodes. The one or more electrodes may, e.g., be located along the lead body and / or the lead may comprise paddles (i.e., flattened areal portions of the lead, typically, e.g., at the distal end of the lead) comprising the one or more electrodes. The electrodes may comprise, e.g., cylindrical surfaces (e.g., surrounding the lead body) and / or areal surfaces (e.g., on the lead paddle and / or the lad body). The lead may, e.g., comprise an elongated shape and / or be flexible such as to allow following, e.g., the vertebral canal (e.g., both during implantation and during the patient’s daily life, wherein the vertebral canal may be bent in any direction).

[0026] The NS may be configured to provide neurostimulation to the patient, e.g., via the one or more electrodes. Therein, the neurostimulation may be characterized by a neurostimulation amplitude, a frequency, and / or a stimulation pattern.

[0027] In some examples, one or more of the leads of the NS may comprise one or more anchors for anchoring the lead to the patient’s body. The first accelerometer may be mounted to the lead via the anchor.

[0028] Generally, (lateral) migration of the lead (e.g., induced by patient movements) poses a serious complication of the therapy delivered by an NS. Securing the lead via anchors, e.g., by midline anchoring or anchoring near the proximal end of the lead may allow to keep the lead, and thus its electrodes, in their designated location relative to the patient and specifically the neural stimulation sites.

[0029] The anchors provide stable anchoring points, as per their function. Thus, when an accelerometer is mounted to an anchor, it may remain essentially stationary within the patient. When the accelerometer remains at its designated location, e.g., the determining of the BMS may (in some examples based on the location of the accelerometer, as described herein) may be conducted with an improved reliability, accuracy, and reproducibility.

[0030] In detail, one or more of the leads of the NS may comprise different or the same number of anchors in the same or in different positions along the length of the lead. The anchors may, e.g., fixedly attached to a portion of the patient’s body, e.g., by means of a clamp, stable, screw, adhesive, and / or insertion of the anchor in a mechanically locked way.

[0031] For example, the BMS may comprise a bending angle relative to a default posture of the patient, wherein optionally the BMS may comprise a bending direction associated with the bending angle. For example, the BMS may comprise a (maximum) forward bending angle of a patient, a count, how often (e.g., per day), a patient bends forward by a certain minimum bending angle, etc.

[0032] In some examples, the BMS may, e.g., comprise a measure for the bending angles (in all directions - forward, backward, left, and right) the patient may execute during their daily life and / or in specific sessions described herein. These bending angles may span an angular range which may, e.g., be expressed through one or more values of the BMS. E.g., the angular range may describe a cone (as illustrated, e.g., in Fig. 2B) in which the patient’s upper body may be positioned during the patient’s body movements. The BMS may in some examples comprise the (average) opening angle of said cone. In other examples, the BMS may e.g., comprise said angular range divided by a predetermined angular range for a healthy (hypothetical) reference patient or said angular range divided by the full spherical angle 4K.

[0033] In some examples, the BMS may comprise and / or be based on a motion duration, a motion frequency, a range of motion maximum, a motion count, a parameter of the electrical stimulation, and / or a pain measure. Further, one or more accelerometers may be also used to track activity levels.

[0034] This may allow for a more sophisticated determination of the BMS and, based thereon, the physiological patient state, which in turn may be more meaningful as they account for more details on the patient movements (e.g., motion duration, motion frequency, range of motion maximum, motion count), how the patient feels (e.g., pain measure) and / or the therapy delivered to the patient by the NS (e.g., parameter of the electrical stimulation).

[0035] For example, the BMS may weight a range of motion maximum, e.g., a maximum forward bending angle differently depending on whether neurostimulation was delivered at the time of the respective movement or not. While a high maximum forward bending angle may indicate a particularly good physiological patient state when no or only moderate neurostimulation was being delivered at that time, it may not (or less) do so when neurostimulation with a high amplitude and / or frequency was being delivered at that time. The same may account analogously for the other parameters. E.g., there may be a first BMS for times when neurostimulation is delivered to the patient and a second BMS for times when no neurostimulation is delivered to the patient. E.g., the difference between said first and second BMS may indicate how strongly the patient depends on the neurostimulation and / or if the neurostimulation is efficient (e.g., for a large difference between the first and second BMS) or not (e.g., for a small or no difference between the first and second BMS).

[0036] The method may in some examples further comprise repeatedly receiving the acceleration data, repeatedly determining the BMS, and repeatedly determining the physiological patient state, preferably at a predetermined frequency of more than 0.01 Hz, 0.1 Hz or 1 Hz. Further, sampling rate of more than 100 per second may be useful to characterize range of motion (ROM) but leave it flexible for more rudimentary sampling.

[0037] The repetition of the at least one step of the method may allow for continuous (remote) patient monitoring at a rate that that is sufficiently high to recognize changes in the patient’s health, e.g., parametrized by the physiological patient state - potentially much earlier than via in-person appointments of the patient with an attending health professional which, for time and cost reasons can only be conducted at a significantly lower rate. At the same time, the rate may be low enough to keep energy consumption of the involved devices (e.g., the accelerometer and / or, optionally, the NS coupled to the accelerometer) sufficiently low to guarantee a long battery lifetime of said device(s). In total, this may provide a cheap and efficient way to implement remote patient monitoring of this parameter(s).

[0038] In some examples, the steps of the method may be repeated at the same or different rates. In one exemplary embodiment, the receiving of the acceleration data may be executed at a first rate (e.g., once per hour). This may, e.g., comprise measuring the respective acceleration data once per hour, accordingly. Determining the BMS and / or the physiological patient state may be executed at a second rate (e.g., lower than the first rate like, e.g., once per day). This would allow to base the determining of the BMS and / or the physiological patient state on a plurality of acceleration data: In this example, each BMS might be determined based on the last 24 acceleration data acquired during the day. In another example, the BMS might be determined based on the last 48 acceleration data acquired during the last two days. Thereby, two consecutively determined BMS may be based on partly overlapping acceleration data.

[0039] In some examples, the acceleration data may be received at least in part from an external accelerometer and / or a remote server. Generally, the acceleration data may at least in part be received from and / or acquired by an internal accelerometer (e.g., an accelerometer mounted to the NS), an external accelerometer (e.g., a wearable accelerometer), and / or a remote device (e.g., a remote server, a cloud server, etc., wherein acceleration data acquired by an internal and / or an external device may be stored).

[0040] Receiving acceleration data, determining the BMS, and / or determining the physiological patient state may at least partly be executed by the NS, an external device and / or by both in combination. In one example, the NS may receive the acceleration data from the one or more accelerometers and transmit the acceleration data to an external device, e.g., an external server. The external device may then determine the BMS and / or determine the physiological patient state, e.g., as described herein. In some examples, the external device may then provide the BMS, the physiological patient state, and / or instructions for adjusting the electrical stimulation provided to the patient via the NS to the NS, wherein the instructions may be based at least partly on the BMS and / or the physiological patient state.

[0041] Particularly, there are various options to involve one or more external accelerometers into the method described herein, as exemplarily illustrated for the three following examples:

[0042] In the first example, an external accelerometer may be built into a patient remote of the NS, either independently or in conjunction with an NS-mounted accelerometer, to acquire acceleration data. Acceleration data collection may, e.g., occur when the patient holds the device in a uniform, replicable position, e.g., between the chest and head, and performs a set of uniform, replicable tasks, e.g., according to instructions as described herein. These tasks may, e.g., test forward, lateral, and / or rotational movements. To this end, the patient may hold the device manually and / or use a strap or other accessory to hold the device in a predetermined manner. With this exemplary application, the device is adhered to the end of the limb of interest, the motion of interest may be performed, and the device may be notified (e.g., by pressing a button) when it comes to the point of greatest range of motion. The only change to acceleration data collection may be the requirement of a button press at the point of maximum deflection for each task.

[0043] The second example for an external device may be a dedicated motion sensing input device. Such external device may be used to acquire and / or assess acceleration data. This system may transmit the acceleration data to another external device and / or the NS. The device may, e.g., be used in addition to other approaches described herein, e.g., for additional rehabilitative purposes. An exemplary implementation may comprise follow-up sessions. An attending health professional may guide the session and / or use the same motion sensing input device for multiple patients. This approach may, in some examples, result in a more controlled acceleration data collection than an (implanted) internal accelerometer, as sessions could be guided and provide feedback to the patient. This exemplary embodiment might also be simpler to implement and / or easier to repair or replace in the event of failure.

[0044] In the third example, an external sensor applied as a wearable device, e.g., a wearable pad, may acquire the acceleration data. That data could either be self-contained or paired with acceleration data from a PG-mounted accelerometer. This system could transmit data via telemetry to a patient remote, via a cable to the patient remote, and / or via telemetry to the PG. If the acceleration data acquired by the external accelerometer is to be integrated with PG accelerometer acceleration data, the external device acceleration data could either be sent to the PG to be processed in real-time (e.g., as described herein), and / or uploaded to a remote server (e.g., a cloud server) in parallel with the PG accelerometer acceleration data and / or be processed there. Such external device would also be far simpler to implement and easier to repair or replace in the event of failure than implanted accelerometers. The external device (e.g., a pad) could either be a disposable, one-time-use device or reusable.

[0045] In some examples, determining the physiological patient state may comprise determining the physiological patient state based on acceleration data of the patient acquired at different points in time, e.g., separated by at least 1 min, 10 min, Ih, 6h, 12h, or 24 h.

[0046] This may guarantee that the physiological patient state accounts for at least a certain time period. This allows to determine a physiological patient state that is representative for rather long-term trends than for short-term changes. E.g., this may advantageously reduce the effects of (single) statistical outliers in the acceleration measurements etc.

[0047] The time differences (At) of 1 min, 10 min, Ih, 6h, 12h, or 24 h lie in typical ranges in which the health state of a patient may change. For example, determining the physiological patient state may be based on at least two acceleration data (one at time t and one at time t+At) from times that differ by more than one of these exemplary time differences At. Optionally, the determining may be based on further acceleration data that may have been acquired and / or received before t, between t and t+At or after t+At.

[0048] In some examples, the method may further comprise adjusting the electrical stimulation provided to the patient via the NS based at least partly on the BMS and / or the physiological patient state.

[0049] Typically, adjusting the electrical stimulation may either be done by the patient themselves, e.g., via a patient remote, an app on their mobile device, etc., based on whether they subjectively perceive a sufficient effect of the neurostimulation (e.g., in the example of an SCS: pain relief) or not. Alternatively, this may be done by a health professional, typically based on subjective patient reports. In contrast to these exemplary electrical stimulation adjustments based on subjective observations, adjusting the electrical stimulation based at least partly on the BMS and / or the physiological patient state may pose a more objective way to perform said adjustment in a more profound and reliable way. This may improve the efficiency of the neurostimulation and, as the adjusting may occur automatically, i.e., without the patient and / or the health professional being actively involved, reduce times during which a badly adjusted neurostimulation is delivered to the patient.

[0050] In a simple example, the neurostimulation amplitude, frequency, and / or stimulation pattern may be increased and / or varied in a first way when the physiological patient state falls below a first predetermined threshold (wherein, e.g., values of the physiological patient state below said first threshold may indicated a bad health state of the patient and / or an inefficient neurostimulation therapy), the neurostimulation amplitude, frequency, and / or stimulation pattern may be decreased and / or varied in a second way when the physiological patient state exceeds a second predetermined threshold (wherein, e.g., values of the physiological patient state above said second threshold may indicate a very good health state of the patient in which the patient may not require the currently administered therapy and / or an efficient neurostimulation therapy), and the neurostimulation may be kept as it is when the value of the physiological patient state is between the first and second predetermined threshold.

[0051] The method may in some examples further comprise providing the patient with a predetermined instruction for executing at least one patient movement. The instruction may be provided via / on the patient remote.

[0052] By providing the patient with such instructions, the acceleration data may be collected when the patient executes the movements according to the instructions. This may allow for a more targeted acceleration data collection and / or comparing said acceleration data with useful metrics. Metrics (note that a standardized calibration process will be required for accurate use of this invention, but such a calibration process is not the subject of this disclosure) may, e.g., comprise: a maximum daily range of motion achieved, a number of times patient achieved movement range beyond a defined threshold, and / or a maximum time sustained past said threshold, wherein the threshold may be a clinician-set threshold (e.g., expressed in degrees from center axis), an arbitrary threshold, and / or a threshold being a predetermined percentage of the maximum range of motion.

[0053] These instructions may, e.g., be instructions for the patient to perform performance tests, such as, e.g., the loaded forward-reach test for chronic back pain patients, timed “Up & Go” test for osteoarthritis patients, and grip strength for rheumatoid arthritis patients.

[0054] According to a further aspect of the present invention, an implantable NS comprises a PG, at least one lead comprising at least one electrode, a first accelerometer, and an (implanted or implantable) anchor for anchoring the lead to the patient’s body, wherein the first accelerometer is mounted to the lead via the anchor.

[0055] When an accelerometer is mounted to an anchor, it may remain essentially stationary within the patient. When the accelerometer remains at its designated location, e.g., the determining of the BMS may (in some examples based on the location of the accelerometer, as described herein) may be conducted with an improved reliability, accuracy, and reproducibility.

[0056] The implantable NS may in some examples further comprise a second accelerometer (internally) mounted to the PG.

[0057] Utilizing two or more accelerometers may allow accurately monitoring body-internal posture changes like bending and / or rotating movements. The combined information from the first and second acceleration data from the first and second accelerometer, respectively, may provide more detailed insights into the body movements of the patient, as described herein. In some examples, the implantable NS may comprise means for determining the BMS of the patient based at least in part on acceleration data of the first accelerometer, and optionally of the second accelerometer, if present, and / or means for determining a physiological patient state based at least partly on the BMS.

[0058] According to a further aspect of the invention, a computer program comprises instructions for executing the steps of the method as described herein.

[0059] It is noted that all features described herein may be implemented as a corresponding functionality (means) of the NS described herein, as a corresponding step of the methods outlined herein and / or as a corresponding instruction of the computer programs outlined herein. Even if described with reference to an NS, method and / or computer program, the aspects outlined herein may be applied to the respective other of an NS, method and / or computer program.

[0060] Fig. 1A shows a schematic representation of a patient with an implanted spinal cord stimulator and three exemplary rotational axes in an exemplary patient coordinate system.

[0061] Fig. IB shows an exemplary lead placement in the spinal canal of a patient.

[0062] Fig. 1C shows a schematic representation of an exemplary spinal cord stimulator comprising two accelerometers.

[0063] Fig. ID shows a schematic representation of an exemplary lead of a spinal cord stimulator comprising a lead comprising a plurality of electrodes and an accelerometer attached to the lead.

[0064] Fig. 2A shows an accelerometer in four exemplary orientations with respect to the patient coordinate system. Fig. 2B shows a patient performing a forward bending movement and an illustration of the associated accelerometer motion with forward and backward bending.

[0065] Fig. 2C shows a flowchart of an exemplary method for determining a physiological patient state of a patient with an implanted neurostimulator.

[0066] Fig. 3A shows an exemplary spinal cord stimulator comprising two leads each comprising a lead anchor with a long lead offshoot configured to connect the pulse generator of the spinal cord stimulator with the lead anchor.

[0067] Fig. 3B shows an exemplary spinal cord stimulator comprising two leads each comprising a lead anchor with a short lead offshoot configured to connect with the lead anchor as the proximal lead end connects with the pulse generator of the spinal cord stimulator.

[0068] Fig. 3C shows an exemplary lead anchor configured to be in communication with the pulse generator of the spinal cord stimulator via contacts with the lead electrodes.

[0069] Fig. 3D shows from three different angles an exemplary lead anchor configured to be in communication with the pulse generator of the spinal cord stimulator via an antenna.

[0070] Figs. 1A-1D illustrate the general geometry of a typical SCS comprising at least one accelerometer and how such SCS may be used to collect acceleration data of a patient:

[0071] In detail, Fig. 1A shows a schematic representation of a patient 100 with an implanted SCS 110 and three exemplary rotational axes (x, y, z) in an exemplary patient coordinate system, wherein the patient 100 may move relative to the patient coordinate system. Said patient coordinate system is in the example of Fig. 1 A chosen as a cartesian coordinate system with the z-axis along the gravitational force acting on the patient 100. In the exemplary patient orientation of Fig. 1A, the x-axis points along the patient’s direction of view and the y-axis to the patient’s left. As described herein, for patients 100 with chronic back pain, spinal flexion and extension, rotation, and lateral motion may be of particular interest to assess their health state, e.g., relating to the pain they experience. These movements may, e.g., be associated with a rotation about the x-axis (rot-x) by bending to the left and / or the right, rotation about the y-axis (rot-y) by bending forwards and / or backwards, and / or rotation about the z-axis (rot-z) by rotating the upper body about the spine. All these movements may potentially be recorded by an accelerometer of the patient, e.g., of in implanted medical device (like an NS and / or an SCS).

[0072] Fig. IB shows an exemplary lead placement in the spinal canal of a patient. The spine comprises a spinal canal / vertebral canal wherein the spinal cord is located. Typically, the one or more leads 130 of an SCS are introduced into the spinal canal such that the lead runs parallel and along the spinal cord such that the one or more lead electrodes of each lead may contact the spinal cord to deliver electrical stimulation to the spinal cord of the patient. The configuration of Fig. IB is only one example, and the concept of the present invention may be applied to other lead placements, e.g., targeting other nerves than the spinal cord (e.g., in the stimulation of spinal nerves, deep brain stimulation, etc.).

[0073] Fig. 1C shows a schematic representation of an exemplary SCS 110 comprising two accelerometers 140, 150. The SCS 110 comprises one pulse generator 120, comprising the first accelerometer 140, and a plurality of leads 130, wherein the first lead 131 comprises the second accelerometer 150 and the second lead 132 does not comprise an accelerometer (but may in other embodiments). Thereby, the first accelerometer 140 and the second accelerometer 150 may be spaced apart by a certain distance (i.e., approximately the length of the portion of the first lead 131 between the second accelerometer 150 and the pulse generator 120) when implanted into the patient’s body.

[0074] Fig. ID shows a schematic representation of an exemplary lead 131 of a spinal cord stimulator comprising a plurality of electrodes 133 and an accelerometer 150 attached to the lead 131. In the example of Fig. ID, the lead contacts / electrodes 133 extend around the circumference of the lead 131 and are spaced apart from one another in the longitudinal direction of the lead 131. The accelerometer 150 may be located near the distal end of the lead 131. Thereby, the accelerometer 150 may be advantageously placed as far as possible from the pulse generator (typically at the proximal end of the lead 131, not shown) and its optional accelerometer (also not shown). Thereby, the two accelerometers may provide substantially different acceleration data which may allow for a more profound data base for BMS determination as described herein.

[0075] Fig. 2A shows an accelerometer 140, 150 in four exemplary orientations with respect to the patient coordinate system (indicated by the axes x, y, and z). The accelerometer 140, 150 is represented by a grey cuboid. The orientation of the accelerometer 140, 150 is represented by the three accelerometer axes u, v, and w.

[0076] In the top left panel of Fig. 2A, the faces of the cuboid are parallel to all three axes of the patient coordinate system and the u-axis is parallel to the x-axis, the v-axis is parallel to the y-axis, and the w-axis is parallel to the z-axis. This illustrates a reference orientation of the accelerometer, e.g., when the patient stands perfectly upright. In result, the accelerometer only experiences an acceleration g along its w-axis.

[0077] In the top right panel, the accelerometer 140, 150 is rotated relative to the orientation in the top left panel by an orientation about the y-axis: The v-axis is still parallel to the y-axis, but the u-axis is rotated relative to the x-axis by an angle 0, and the w-axis is rotated relative to the z-axis by an angle cp. Therefore, the accelerometer in this example experiences an acceleration au= g ■ sin(0) along its u-axis, no acceleration along its v-axis, and an acceleration aw= g ■ cos(<p) along its w-axis. This may, e.g., be a situation in which the patient bends forwards or backwards.

[0078] In the bottom left panel, the accelerometer 140, 150 is rotated relative to the orientation in the top left panel by an orientation about the x-axis: The u-axis is still parallel to the x-axis, but the v-axis is rotated relative to the y-axis by an angle y and the w-axis is rotated relative to the z-axis by an angle cp. Therefore, the accelerometer in this example experiences no acceleration along its x-axis, an acceleration av= g ■ sin( >) along its v-axis, and an acceleration aw= g ■ cos(<p) along its w-axis. This may, e.g., be a situation in which the patient bends to the left or to the right. In the bottom right panel, the accelerometer 149, 159 is rotated relative to the orientation in the top left panel: The u-axis rotated relative to the x-axis by an angle 9, the v-axis is rotated relative to the y-axis by an angle y, and the w-axis is rotated relative to the z-axis by an angle cp. In this general example, the three angles may be determined based on the outputs of the accelerometer along its three axes as follows: with 9 as the angle between the horizon (x-y-plane) and the u-axis of the accelerometer, \p as the angle between the horizon and the v-axis of the accelerometer, and cp as the angle between the gravity vector and the w-axis. Notably, in this example, 9 and y may range from -180° to +180° and cp may range only from 0° to 180°.

[0079] As such gravitational accelerometer is not susceptible to rotations about the z-axis (parallel to the gravitational force), another accelerometer may (e.g., additionally) be used to detect, e.g., twisting motion of the spine which may typically be associated with just that rotation: Twisting motion may, e.g., be detected using an inertial measurement unit (IMU) and / or a gyroscope. Said IMU and / or gyroscope may acquire acceleration data which may be received and further processed (e.g., for determining the BMS and / or the physiological patient state at least partly based thereon) as described herein.

[0080] Fig. 2B shows a patient 100 bending forward and an illustration of the associated accelerometer motion with forward and backward bending. In the coordinates of Fig. 2A, the patient standing upright results in (p = 0°, the patient 100 bending forwards as illustrated in Fig. 2B results in —90° < (p < 0°, and the patient 100 bending backwards results in 0° < (p < 20°. These are typical ranges but may be smaller (for patients with a smaller range of motion (ROM)) or larger (for patients with a larger ROM) in other examples. Fig. 2B further illustrates a cone describing the angular range may in which the patient’s upper body may be positioned during the patient’s body movements. The BMS may in some examples comprise the (average) opening angle of said cone. In the example of Fig. 2B, the patient 100 is shown in the furthest forward bend position they may achieve, i.e., the patient’s spine is oriented along the outer face of the cone.

[0081] In exemplary body movements, the exemplary angles of Table 1 may be detected by the at least one accelerometer:

[0082] Table 1 : exemplary angles for selected body movements

[0083] Fig. 2C shows a flowchart of an exemplary method for determining a physiological patient state of a patient with an implanted NS. In the example of Fig. 2C, the first accelerometer 140 mounted to the PG 120 provides the first acceleration data to the PG 120 and the second accelerometer 150 mounted to the lead 130 provides the second acceleration data to the PG 120. In the exemplary method, all consecutive steps, namely determining the BMS of the patient, based at least in part on the acceleration data, and determining the physiological patient state based at least partly on the BMS are executed within the PG, which in the example of Fig. 2C comprises means for the determining. In other examples, other means (e.g., an external device) may execute at least some of the steps of the method, as described herein.

[0084] In some examples, the NS may comprise an accelerometer in its lead anchor. This case (but also cases in which the accelerometer is attached directly to the lead) requires a suitable electrical connection provided to the accelerometer. Figs. 3A-3D shows some exemplary embodiments in which this connection is achieved in different ways: Figs. 3 A and 3B show exemplary SCS 110 comprising two leads 131, 132 each comprising a lead anchor 160 with a long lead offshoot 133 (in Fig. 3A) and a short lead offshoot 133 (in Fig. 3B) configured to connect the pulse generator 120 of the spinal cord stimulator 110 with the lead anchor 160. The features of the shown SCS 110 may, however, be present in any other NS as described herein. The lead offshoots may comprise an electrical conductor. While the long lead offshoot 133 in Fig. 3A extends essentially in parallel to the second lead 132 between the pulse generator 120 and the anchor 160, the short lead offshoot 133 branches off the second lead 132 near the anchor 160. Either way, the offshoot 133 is configured to (electrically) connect the anchor 160 and the pulse generator 120.

[0085] The embodiment of Fig. 3A thus used a dedicated lead / offshoot 133 that makes electrical contact between the PG 120 and the anchor 160 comprising the accelerometer (not shown). In this embodiment, when using two therapeutic leads 131, 132, one of the lead anchors 160 may have an accelerometer, while the other anchor does not. This configuration may reduce the complexity and cost of the two-anchor set, as only one of a pair of anchors 160 needs a dedicated lead / offshoot 133 for data communication. Alternatively, two anchors 160 containing accelerometers may be used for redundancy or increased accuracy. The additional lead 133 would not be used for therapy delivery, it would be used for powering and communicating with the accelerometer embedded in the anchor 160, allowing this lead to be smaller in diameter.

[0086] In Fig. 3B, a short lead offshoot 133 designed to connect with the lead anchor 160 as the proximal lead end connects with a PG port may allow a sensing system within the anchor 160 to be powered by and communicate directly with the PG 120. The PG port may comprise extra contacts for communication and power to the accelerometer (not shown). The lead offshoot 133 may be configured to fit through an insertion needle bore allowing the use of this NS design with known implantation techniques. This design may further improve anchor stability and longevity, reducing the prevalence of lead shift.

[0087] The anchor 160 of the embodiments of Figs. 3 A and 3B may, e.g., be configured as shown in the embodiment of Fig. 1C or ID and may comprise a port 164 that allows the lead to provide power and communication to it. An exemplary anchor 160 with such port 164 is shown from two directions in the bottom panel of Fig. 3B. The port may be configured to receive the lead offshoot 133.

[0088] Fig. 3C shows an exemplary lead anchor 160 configured to be in communication with the pulse generator of the spinal cord stimulator via contacts with the lead electrodes 133 of the lead 131.

[0089] In general, the lead anchor 160 may present a viable accessory for incorporation into an NS for the purpose of determining the BMS and / or the physiological patient state as described herein. This embodiment of Figs. 1C (and also ID) describes a configuration that reduces size constraints in comparison to embodiments with the accelerometer 150 in the lead 131 (cf., e.g., Fig. ID) Here, the size of the accelerometer 150 is less restricted. The trade-off may be seen in that mounting the accelerometer 150 to the lead anchor 160 increases the difficulty of providing power and / or transmitting the acceleration data, increasing the complexity of requisite changes to the system. Figs. 3C and 3D provide two different solutions to this challenge, as described herein. Additionally, inclusion of electrical components in the anchor 160 may require encasement similar to that of the PG to create a hermetic seal, increasing its physical bulk.

[0090] In Fig. 3C, a scaled representation of an exemplary accelerometer 150 is shown. A setscrew 161 is configured to be screwed through the anchor 160 and secure it to the lead 131. No additional bulk is needed to support the accelerometer 150 itself, but additional material may be added to the (e.g., silicone) body of the anchor 160 to accommodate a communications port (cf. e.g., Fig. 3B) or other supporting hardware. The accelerometer 150 may be powered and communicated to via conductors that run back to the PG which may require additional contacts to support interfacing with the accelerometer 150. In the example of Fig. 3C this may be solved as follows:

[0091] The lead 131 typically comprises a plurality of electrodes 133, two of which in the example of Fig. 3C are used to connect to the accelerometer 150. E.g., an additional electrode pair 133 spaced apart from the stimulating electrodes, e.g., outside the vertebral space may be particularly suitable for this purpose. This design choice would advantageously require no changes to the surgical procedure other than guided anchor placement. In the embodiment of Fig. 3C, the anchor 160 comprises an accelerometer 150 which is connected to two anchor contacts 162 via two wires 151, 152, wherein the anchor contacts 162 each contact an electrode 133 of the lead 131 which electrically connects the accelerometer 150 to the lead 131 and thus the PG (not shown).

[0092] To ensure that the electrodes 133 configured to connect to the accelerometer 150 do not unwantedly stimulate tissue of the patient’s body, sealing said contacts may be particularly relevant: A sealable contact along the lead 131 configured to connect with a contact on an anchor surface may allow an accelerometer 150 within the anchor 160 to be powered by and / or communicate directly with the PG in a safe way. This may be implemented by ensuring the body (e.g., made of silicone) of the anchor 160 has a tight fit around the lead 131 and / or may be made at least partly from an insulating material.

[0093] In this example, a switch may be included, e.g., via software, to activate or inactivate the contact in the case that such a lead is used but the accelerometer contact 133 is neither used nor sealed. The accelerometer contact 133 could also be provided to the attending health professional sealed and may be required to be unsealed to be accessed for contacting the accelerometer 150 as described herein.

[0094] Another possibility (not shown) to connect to the accelerometer may be a so-called lead puncture mechanism: A direct electrical contact with the PG, allowing for powering by and communication with the PG, could be formed with an anchor designed such that the fixation method (e.g., turning of the set-screw 161) may simultaneously puncture the lead 131 in a controlled manner, form an electrical contact between internal lead circuitry and / or anchor circuitry, and / or seal around that electrical contact. One way in which contact may be established is by using a pair of conductive wires wound around the lead 131, e.g., in a “stub” shielding the lead. The stub may comprise a pair of wires, coiled around the lead lumen, but inside the outer sheath of the lead body. The two wires may be opposite to each other relative to the longitudinal axis of the lead 131 (i.e.,180° from one another). When the set screw 161 in the anchor 160 is engaged, a pinch mechanism may slice through the outer sheath and make contact with the wires. The pinch mechanism may have an A-frame shape each side of which may be connected to a different polarity in the accelerometer 150 (thus providing power to it).

[0095] Fig. 3D shows from three different angles of an exemplary lead anchor 160 configured to be in communication with the pulse generator of the SCS via an antenna 163. In detail, the communication allows transmitting the acceleration data of the anchor’s 160 accelerometer 150 to, e.g., the PG and / or an external device. A setscrew 161 may be configured to be screwed through the anchor 160 and secure it to the lead 131.

[0096] The embodiment of Fig. 3D may be powered independently and outfitted with telemetric capabilities (e.g., Bluetooth low energy (BLE), Near Field Communication (NFC) and / or passive radio frequency (RF)). These may be embedded in the anchor 160 and be in communication with the PG, e.g., without direct electrical connection (as, e.g., in the embodiment of Fig. 3C). Advantageously, this design choice would not limit the lead anchor location.

[0097] In some examples, there may be sensors in the anchor configured to passively acquire acceleration data and / or other indicators of range of motion without requiring a power source. Such exemplary sensors may communicate with the PG via an isolation transformer built into the lead body (i.e., cochlear implants). This configuration could avoid limiting anchor placement location.

Claims

Claims1. A method for determining a state of a patient ( 100) with an implanted neurostimulator, NS, (110) the method comprising: receiving acceleration data of the patient (100); determining a body movability score, BMS, of the patient (100), based at least in part on the acceleration data; and determining a physiological patient state based at least partly on the BMS.

2. The method of claim 1, wherein the acceleration data comprises first acceleration data measured by a first accelerometer (140) of the patient (100) and second acceleration data measured by a second accelerometer (150) of the patient; wherein optionally determining the BMS is further based on a first location of the first accelerometer (1 0) and a second location of the second accelerometer (150).

3. The method of any of claim 2, wherein determining the BMS is based at least partly on comparing the first acceleration data, the second acceleration data, and / or a predetermined threshold.

4. The method of claim 2 or 3, wherein the NS (110) comprises a pulse generator, PG, (120) and a lead (130) comprising an electrode; wherein optionally the first accelerometer (140) is mounted to the PG (120) and / or wherein the second accelerometer (150) is mounted to the lead (130).

5. The method of any of claims 1-4, wherein the lead (130) comprises an anchor (160) for anchoring the lead (130) to the patient’s body and wherein the second accelerometer (150) is mounted to the lead (130) via the anchor (160).

6. The method of any of claims 1-5, wherein the BMS comprises a bending angle relative to a default posture of the patient (100), wherein optionally the BMS comprises a bending direction associated with the bending angle.

7. The method of any of claims 1-6, wherein the BMS comprises a motion duration, a motion frequency, a range of motion maximum, a motion count, a parameter of the electrical stimulation, and / or a pain measure.

8. The method of any of claims 1-7, further comprising repeatedly receiving the acceleration data, repeatedly determining the BMS, and repeatedly determining the physiological patient state; preferably at a predetermined frequency of more than 0.01 Hz, 0.1 Hz or 1 Hz.

9. The method of any of claims 1-8, wherein the acceleration data is received at least in part from an external accelerometer and / or a remote server.

10. The method of any of claims 1-9, wherein determining the physiological patient state comprises determining the state based on acceleration data of the patient (100) acquired at different points in time, separated by at least 1 min, 10 min, Ih, 6h, 12h, or 24 h.

11. The method of any of claims 1-10, further comprising adjusting the electrical stimulation provided to the patient (100) via the NS (110) based at least partly on the BMS and / or the physiological patient state.

12. The method of any of claims 1-11, further comprising providing the patient (100) with a predetermined instruction for executing at least one patient movement.

13. An implantable neurostimulator, NS, (110) comprising: a pulse generator, PG, (120); a lead (130) comprising an electrode; an accelerometer (150); and an anchor (160) for anchoring the lead (130) to the patient’s body; wherein the accelerometer (150) is mounted to the lead (130) via the anchor (160).

14. The implantable NS (110) of claim 13, further comprising: a further accelerometer (140) mounted to the PG (120).

15. A computer program comprising instructions for executing the steps of the method according to any of claims 1-12.

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