HK1235725B - System and method for functional electrical stimulation - Google Patents

Description

Systems and methods for functional electrical stimulation

Technical Field

The present invention relates to the field of functional electrical stimulation (FES) devices, and in particular, to FES devices and methods for treating foot drop disorder.

Background Art

Drop foot, also known as foot drop, refers to the inability or difficulty to move the ankle and toes upward while walking. In other words, drop foot means difficulty lifting the front of the foot. It is not a disease in itself: it is often evidence of an underlying neurological disorder (stroke, spinal cord injury, cerebral palsy or peripheral nerve damage). Depending on the severity of drop foot, the effects range from unaesthetic walking and increased energy expenditure to an increased risk of falls or even complete inability to walk. Drop foot can be temporary or permanent.

Drop foot is the result of the interruption or severance of the communication path between the brain, motor nerves and leg muscles. The actual reason for drop foot is that the spinal cord brain does not operate as it should due to the central input of pathway lesions, changes and the incoming signals of changes. Traditionally, drop foot treatment equipment is limited to the adjustment equipment that prevents the dragging of the toes. Ankle foot orthosis (AFO) plays a role by limiting the speed of plantar flexion during the weight-bearing reaction (foot hitting the ground) and prevents the foot from dropping (drop foot) during the swing phase of gait. This prevents the toes of the foot from contacting with the floor and reduces the risk of stumbling. AFO usually extends from the end of the metatarsal head just to the end of the fibular head.

In recent years, functional electrical stimulation (FES) devices have become common for treating foot drop. FES devices activate motor neurons or reflex pathways by electrically stimulating nerve fibers. For example, international patent application WO2011/079866A1 discloses a device for externally activating paralyzed body parts by stimulating peripheral nerves or muscles, the device comprising a soft garment with multiple pad electrodes on one side and an activation device on the other side. In the case of foot drop, the use of an FES device enables the patient to periodically lift their foot (toes) as part of a near-natural gait cycle.

Nowadays, both percutaneous systems and implantable systems are available. Typically, percutaneous FES systems are used for both rehabilitation and as orthotics, while implantable FES systems are only corrective. If percutaneous FES treatment can not reach a satisfactory level of rehabilitation and the function of loss is successfully reconstructed using a surface FES orthosis, then the patient is considered to be a good candidate for the implantation of an FES system. The shortcomings and surgical risks of the possible problems associated with long-term implantation and the long-term changes caused by stimulation (for example, the irreversible adverse effects on neural tissue or the physical failure of the electrodes requiring an invasive correction process) make people tend to prefer surface devices rather than implants.

An advantage of systems based on surface electrodes is that they can be used in the early stages after a stroke as an add-on treatment. There is growing evidence that electrical stimulation contributes to better recovery and has long-term effects. This is because electrical stimulation not only elevates the foot during swing, it also activates many afferent fibers and provides strong input to the central nervous system. Clinical studies have shown that combining FES with exercise significantly increases the residual effects of treatment compared to exercise-based therapy alone.

U.S. patent application US2007/0112394A1 describes a functional electrical stimulation orthosis for providing functional electrical stimulation to a user's limb segments. A product implemented based on this disclosure is the NESS, owned by Bioness, which can be lightweight, installed slightly below the knee and designed to be easy to put on and take off. It has three main parts: a remote controller using wireless communication, a gait sensor, and a leg cuff. Stimulation pulses are delivered to the skin via commercial self-adhesive electrodes and timing is generated by a pressure heel switch. A trained clinician completes the initial adjustment of electrode positioning and stimulation parameters, while the user controls some parameters via a remote control unit.

U.S. patent applications US5643332A and US5814093A describe a functional electrical stimulator. A product implemented based on such disclosures is the WalkAide foot drop stimulator owned by Innovative Neurotronics. It is a battery-operated single-channel electrical stimulator that utilizes a tilt sensor to control the activation and deactivation of stimulation during normal gait. It includes an integrated single-channel electrical stimulator, two electrodes, and electrode leads. WalkAide can effectively combat foot drop by generating dorsiflexion of the ankle joint during the swing phase of gait. The device is attached to the leg, slightly below the knee, near the head of the fibula. The user can adjust the intensity.

The device shown in US5643332A measures only the orientation of the lower leg, not the orientation of the foot. Therefore, it cannot control the position of the foot. It is limited to modifying the on/off timing of the stimulation, but not other stimulation parameters: the system adjusts only the timing of the stimulation (on/off), but not the intensity or any other stimulation parameters that depend on the angle of the lower leg relative to gravity.

In summary, none of the disclosed devices is able to adjust the stimulation electrodes or stimulation parameters in real time so as to obtain optimal movement.

Summary of the Invention

It is therefore an object of the present invention to provide a functional electrical stimulation device and method for correcting foot drop that has the ability to adapt during use so as to optimize its performance.

According to one aspect of the present invention, a functional electrical stimulation system for correcting drop foot is provided, comprising: a device configured to be arranged on a user's partially paretic/affected leg, the device being provided with a plurality of multi-pad electrodes on one side, wherein at least one of the electrodes is configured to provide a stimulation electrical signal at a point on the leg where it is positioned, wherein the corresponding stimulation electrical signal forms a stimulation pattern; and at least one sensor configured to be positioned on the user's partially paretic/affected leg or the corresponding foot during use of the system. In use of the system, the sensor is configured to measure information during movement and emit a sensor signal representing the movement. The system further comprises: a device for calculating a foot trajectory based on the sensor signal, for detecting a gait phase based on the foot trajectory, for evaluating a gait quality based on the foot trajectory, and for modifying the stimulation pattern if the gait quality is below a certain threshold; and a device for selectively activating at least one of the electrodes according to the modified stimulation pattern.

In a preferred embodiment, the device for evaluating gait quality based on the foot trajectory further includes means for loading a predefined trajectory and calculating the deviation of the current step from the predefined trajectory. Furthermore, gait quality is preferably evaluated when the gait is in the following phases: during plantar flexion in the push-off gait phase; and during dorsiflexion in the swing gait phase when the user is leaving the ground.

The means for selectively activating at least one of the electrodes according to a modified stimulation pattern comprises multiplexing means for discrete activation or deactivation of the electrodes and for adjusting at least one of the following parameters associated with each electrode: pulse amplitude, pulse width, and time delay between consecutive electrode activations.

In a preferred embodiment, the system includes an article of apparel to which the device is attached.

Preferably, the sensor comprises means for obtaining the orientation of the sensor itself based on the moment of the support gait during which the sensor is stationary. More preferably, the means for obtaining the orientation of the sensor itself comprises a plurality of accelerometers and a plurality of gyroscopes.

In a particular embodiment, means for calculating the foot trajectory from the sensor signal, for detecting the gait phase from the foot trajectory, for assessing the gait quality from the foot trajectory, and for modifying the stimulation pattern if the gait quality is below a certain threshold are at least partially located in the sensor.

In another specific embodiment, the means for calculating the foot trajectory based on the sensor signals, for detecting the gait phase based on the foot trajectory, for evaluating the gait quality based on the foot trajectory, and for modifying the stimulation pattern if the gait quality is below a certain threshold are at least partially located in a housing positioned on the partially paretic/affected leg of the user.

In a particular embodiment, the system comprises means for wirelessly transmitting data obtained at the sensor, pre-processed or processed, to a processing device arranged at a different location.

In another aspect of the present invention, a method for correcting drop foot based on functional electrical stimulation is provided. The method comprises: applying a stimulation pattern to a user's partially paretic/affected leg with the aid of a plurality of multi-pad electrodes, each of the plurality of multi-pad electrodes being configured to provide a stimulating electrical signal at a point on the leg where the electrode is positioned; measuring information during movement and emitting a sensor signal representative of the movement; calculating a foot trajectory based on the sensor signal; detecting a gait phase based on the foot trajectory; assessing gait quality based on the foot trajectory; modifying the stimulation pattern if the gait quality is below a certain threshold; and selectively activating at least one of the electrodes based on the modified stimulation pattern.

In a preferred embodiment, gait phase detection includes detecting an end of a swing start point and an end of a swing, wherein the end of the swing start point is determined as half of the maximum velocity during the swing phase, and wherein the end of the swing is a heel strike, which corresponds to a crossover point from a positive angular velocity to a negative value.

Preferably, the gait quality assessment further comprises loading a predefined trajectory and calculating the deviation of the current step from the predefined trajectory.

Preferably, gait quality is assessed when the gait is in the following phases: during plantar flexion in the push-off gait phase; and in dorsiflexion in the swing gait phase as the user is moving the foot off the ground.

Modification of the stimulation pattern preferably comprises discrete activation or deactivation of electrodes and adjustment of at least one of the following parameters associated with each electrode: pulse amplitude, pulse width, and time delay between consecutive electrode activations.

In another aspect of the present invention, there is provided use of the aforementioned system in the treatment of foot drop.

In a final aspect of the present invention, there is provided a computer program product comprising computer program instructions/code for performing the aforementioned method.

Additional advantages and features of the present invention will become apparent from the following detailed description and will be particularly pointed out in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to complete the description and provide a better understanding of the present invention, a set of drawings is provided. The drawings form an integral part of the description and illustrate embodiments of the present invention, which should not be interpreted as limiting the scope of the present invention but merely as examples of how the present invention may be implemented. The drawings include the following figures:

FIG1 shows a system 1 for correcting foot drop according to an embodiment of the present invention.

Figure 2 shows an exemplary device with an integrated stimulator and array electrodes according to the present invention. The device has a layer of multi-pad electrodes configured to contact the skin and a layer of activation points.

FIG3 illustrates the use of the multi-pad stimulation system during walking.

FIG4 illustrates a flow chart showing a method for assisting walking associated with the system of the present invention.

FIG5 illustrates a flow chart showing modifications to a stimulation pattern.

FIG6 illustrates a flow chart showing a method for P-factor calculation.

Figure 7 shows different gait phases of a walking user and the stimulation schemes associated with the different gait phases. It also shows the gait trajectory generated by the inventive optimization process.

FIG8 illustrates an exemplary pattern of stimulation pulses delivered via multi-pad electrodes.

FIG9 illustrates the calculation of the deviation of the measured trajectory relative to the predefined trajectory during DfOS.

FIG10 shows the “a priori” P0 factor for dorsiflexion.

FIG. 11 illustrates a modified algorithm for a stimulation pattern, where a stimulation pattern is used to define the electrical stimulation to be applied to an electrode array.

DETAILED DESCRIPTION

In this document, the term "include" and its derivatives (such as "comprises", etc.) should be understood in a non-exclusive sense, that is, these terms should not be interpreted as excluding the possibility that the described and defined may include additional elements, steps, etc.

In the context of the present invention, the term "approximately" and its cognate terms (e.g., "approximately" etc.) should be understood to indicate values that are very close to those accompanying the preceding term. That is, deviations within reasonable limits from the exact value should be accepted, as those skilled in the art will understand that deviations from the indicated value are inevitable due to measurement inaccuracies. The above also applies to the terms "about," "around," "close to," and "substantially."

The following description is given for the purpose of describing the general principles of the present invention only and should not be understood in a limiting sense. The following embodiments of the present invention will be described by way of example with reference to the above-mentioned drawings, which show devices and results according to the present invention.

FIG1 illustrates an FES system 1 for correcting foot drop according to an embodiment of the present invention. The illustrated system 1 includes a garment 2 designed to be placed on the leg of a user suffering from foot drop. In FIG1 , the upper view illustrates the interior of the garment 2, i.e., the portion designed to contact the user's leg. This portion has an electrode (electrode pad) array. The lower view illustrates the exterior of the garment 2, i.e., the visible portion when the user wears the garment 2. Preferably, the garment 2 is placed on the patient's knee, wherein the electrode array is located on the popliteal fossa. A housing 5 is integrated into the garment, preferably, the housing 5 is on the outside of the garment. The housing 5 has a processing device (also referred to as a control device). The processing device, control device, or control unit may be located entirely or partially at the housing 5. The control device may have a stimulation and signal processing unit 6 (also referred to as a stimulator 6 or stimulation device). Alternatively, the stimulation and signal processing unit 6 may be at least partially integrated into a sensor 8 (e.g., in a microprocessor) not shown in FIG1 . Sensor 8 is described later in this specification. The housing 5 is attached to the garment by means of a clamping mechanism, wherein the clamping mechanism connects the control device to the electrode pads and establishes electrical contact with a demultiplexer 7 which distributes the stimulation pulses to the pads. The demultiplexer 7 is preferably located in the housing 5. The demultiplexer 7 is controlled by a processing unit 6 and activates the selection of the pads to be activated depending on the gait quality as will be described later in this document. As shown in FIG1 , the stimulation and signal processing unit 6 and the demultiplexer 7 can be integrated into a single housing 5. That is, the reference numeral 5 is used to refer both to the hardware (housing) and to the software means (control means) included in said hardware. In FIG1 , the attachment mechanism is a clamping mechanism. Alternatively, other well-known attachment mechanisms can be used.

The garment 2 has a device 3 attached to it or integrated therewith, the device 3 having an integrated stimulator and electrode array. As shown in FIG2 , the device 3 is formed by at least one layer. The device 3 has a stimulation layer 31 formed by a plurality of multi-pad electrodes 315 configured to contact the skin. As shown in FIG1 , the device 3 is placed on the inner surface of the garment 2 so that the multi-pad electrodes 315 contact the user's skin during use. The electrodes 315 also have a connector 33 for connecting the electrodes 315 to a demultiplexer 7 comprising an analog switch (e.g., an analog optocoupler).

The garment 2 is made of any skin-friendly material. Non-limiting examples of such materials are soft neoprene, nylon, polyurethane, polyester, polyamide, polypropylene, silicone, cotton, or any other soft and flexible material. All of the mentioned materials can be used as woven structures, non-woven structures, single-use fabric structures, or laminate structures.

The multi-pad electrode 315 is small enough to allow controlled (spatial and temporal) current flow between the anode and cathode. The location of the cathode (the electrode that depolarizes excitable tissue, such as motor nerves) on the body determines which muscle or nerve is activated; in this case, the muscle or nerve is implicitly the muscle or nerve in the foot drop. The anode can be located anywhere on the body and is often referred to as an indifferent electrode. FIG1 shows the anode 4 in an implemented FES system 1. The anode 4 is embedded in or attached to clothing and, when the system is in use, is configured to be placed below the meniscus. This preferred location is determined to minimize interference with movement and sensation generated by the multi-pad electrode. The effective surface area of the anode 4 is preferably larger than that of a single cathode pad 315 to reduce the current density beneath the anode 4, making it less likely that the nerves beneath the anode will be activated. However, using a slightly different implementation of the demultiplexer, any of the electrode pads 315 can be used as either an anode or a cathode, allowing flexibility in selecting both anode and cathode locations. Based on an algorithm described below, layer 31 of multi-pad electrodes 315 acting as cathodes can selectively direct the current needed to depolarize nerves and, therefore, stimulate activation of peripheral nerves. Such selective activation delays fatigue, which is typical of conventional devices for electrical stimulation using surface electrodes. It can also adapt to changes in the position of the stimulated nerve relative to the skin and multi-pad electrodes, which are common due to dynamic changes in limb morphology during gait and also due to slow changes in limb diameter, such as changes in hydration and vascularization or temporary swelling of the limb.

Stimulation and signal processing unit 6 can communicate with external devices including user applications such as smart phones, tablets or PCs through wireless protocols. User applications are optional. User applications can provide instructions and controls for the stimulation process. Through wireless connection, the user or treatment expert can set specific stimulation parameters, initiate stimulation schemes (which run on the stimulator processor) and observe the stimulation execution. The stimulator 6 is responsible for real-time control and transmission of the stimulation based on the control algorithm stored in the stimulator memory and executed in the processing device according to the user's request. Through the stimulator 6, the device can be turned on and off, and some parameters such as overall stimulation intensity can be adjusted. The stimulation demultiplexer 7 is an electronic component designed for effective stimulation pulse manipulation to specify the stimulation area (electrode pad).

In a specific embodiment not shown in FIG2 , multi-pad electrodes 315 can be manually controlled by a user, thereby allowing manual adjustment. In this embodiment, device 3 additionally includes a layer containing sensing pads (also referred to as activation means, activation points, or activation sensors). This additional layer is located on the surface of device 3 opposite the surface on which multi-pad electrodes 315 are located. The activation points are configured to selectively activate/deactivate corresponding electrodes of the multi-pad electrodes. Preferably, manual activation of the electrodes is combined with an external device via wireless communication.

The device 3 can take any shape as long as it includes at least one electrode (cathode). In the absence of a separate anode, the minimum configuration of the device 3 includes at least two electrodes (one anode and one cathode). Figure 2 shows a preferred multi-pad electrode design with a matrix of two rows of electrodes or pads 315, wherein each row of electrodes or pads 315 has eight elements. The optimal response of a single group or multiple groups of pads is evaluated, all activated simultaneously (synchronous case) or in series (one pad after another) in the asynchronous case. In this embodiment, the contacts are rectangular with rounded edges to minimize the so-called edge effect (high current density at the edge of the electrode). Alternatively, any other shape and number of pads can be used. The size and shape of the pads are selected to produce comfortable and selective stimulation. Preferably, the layer 31 with the multi-pad electrodes 315 is integrated into a soft and flexible substrate (garment 2), wherein the substrate is designed in such a way that the system can only be positioned in one possible way, thereby facilitating the use of the system. The garment 2 is manufactured in such a way that it takes into account leg landmarks (knee meniscus) for easy and repeatable repositioning with an acceptable tolerance (approximately ±2 cm). Repositioning errors are compensated by adjusting the stimulation pattern.

The FES system 1 also includes at least one sensor unit 8 preferably arranged on the foot. In an alternative embodiment, the sensor unit 8 is arranged on the user's leg (or calf), preferably on clothing 2. Figure 3 shows two possible implementations of the sensor unit 8. Non-limiting examples of the sensor unit 8 are inertial sensors such as inertial MEMS sensors, accelerometers, and gyroscopes. The sensor unit 8 is preferably an inertial measurement unit (IMU). When using the system, at least one sensor 8 is configured to measure information during movement (walking) and transmit sensor signals representing movement to the stimulation and signal processing unit 6. These signals allow the control device 5 to calculate the foot trajectory and therefore calculate the gait phase when the user walks. The sensor 8 arranged on the user's leg or calf (rather than on the user's foot) allows detection of the trajectory of the foot and leg (or calf). Because the dynamic activation of foot dorsiflexion can be detected at the calf, the signal can be used as a means of measuring gait quality. The sensor 8 is preferably located on the foot, because the data measured by the sensor arranged on the leg or calf usually has poor performance.

FIG3 shows an IMU sensor 8 on a user's foot. Preferably, a 6-degree-of-freedom IMU is used to automatically obtain the orientation of the sensor arranged on the foot without requiring precise instructions on how to position the sensor, wherein the IMU has 3 accelerometers and 3 gyroscopes. To obtain the orientation of the sensor 8, the automated algorithm utilizes the moment of the stance gait during the sensor's rest period. The sensor rest state is determined as the following period: the vector sum of the gyro signals is close to 0, and the vector sum of the accelerometer signals is close to 1g given by gravity. During these periods, the direction of gravity (-z) can be determined. The main direction of the leg during the swing phase determines the sagittal plane (along the x direction). The vector product of x and z determines the direction of foot inversion (y) and eversion (-y). In order to optimize dorsiflexion, the angular velocity around the y axis is analyzed and optimized. For eversion and varus, the angular velocity around the z axis is analyzed and optimized. This same description of the sensor 8 positioned on the foot applies to the sensor 8 positioned on the leg or calf.

The primary method for characterizing foot motion to determine gait phase without knowing the exact position or orientation of sensor 8 is to use the norm (NORM) of the angular velocity vector obtained from the 3-axis gyroscope. The norm of the angular velocity obtained from the gyroscope in the x, y, and z directions is defined as sqrt(x² + y² + z²). This signal is used to determine the gait phase during the gait cycle and is now referred to as the gyro signal.

Fig. 3 illustrates the use of multi-pad stimulation system during walking. As described below, stimulator 6 is configured to receive the signal captured by sensor 8 during walking, for calculating foot trajectory according to sensor signal, detect gait phase according to foot trajectory and modify stimulation pattern. As indicated, a part of control device (particularly at least a portion of the stimulation and signal processing unit 6 of stimulator 6 or stimulation device) can be located at sensor 8 (for example, in a microprocessor) positioned on leg (calf) or foot. Alternatively, stimulator 6 can be located at housing 5 positioned at clothing 2. The main goal of this algorithm is to evaluate the contribution of each stimulation pattern to the foot motion of expectation based only on the foot angular velocity signal on the sagittal plane. Algorithm only performs the modification of stimulation pattern by modifying stimulation pattern and observing foot response (angular velocity) when the stability of patient and the trajectory of foot during walking are endangered. Such period of time that the stimulation pattern of modification can be tested is during stance phase and during swing phase initial and near end, during which foot ground clearance is sufficient and can not cause stumbling or interference to the placement of foot. If the stimulator 6 is in the housing 5, a wireless protocol is used to obtain a signal from the sensor 8 and the signal is transmitted to the stimulator. Preferably, the stimulator and the IMU unit are both equipped with a wireless module. If the stimulator 6 is in the sensor 8, there is no need for wireless transmission of the measurement result. Based on the signal obtained from the sensor 8, control and parameter modification are performed. If the data obtained by the sensor 8 is processed in the microprocessor in the sensor unit 8, the pre-processed or fully processed data can be wirelessly transmitted to the remaining control device in the housing 5. In this way, the amount of the data transmitted can be kept small. The example of such processed data is that the gait phase is determined to be the triggering of other typical events during support, lift-off, swing, heel strike or gait. The actual limb angle relative to the determined x-axis, y-axis, and z-axis can also be calculated.

A stimulation pattern comprises a set of active pads within the multi-pad electrode, wherein each active pad is assigned a suitable stimulation pulse amplitude, frequency, and pulse width. Each stimulation pattern also includes a specific time delay between consecutive pad activations. The system and method for correcting foot drop allows for real-time optimization of the stimulation pattern produced by the multi-layer device 3, and thus improves and maintains the quality of the assisted movement. In other words, the system and method are able to modify the stimulation pattern during walking based on information captured by the sensor 8 positioned on the patient's partially paralyzed (or damaged) leg. This is achieved by a method that implements a fully automated process.

During the use of FES device 1 and the execution of the method for correcting foot drop, the main goal is to produce functional foot movement. However, when meeting the following two conditions, functional foot movement is achieved: when in the push-off gait phase, a strong plantar flexion (ankle extension) (as shown in Figure 7, between reference numerals 71 and 72) for pushing the body forward is produced; and when in the swing phase of gait, a confident dorsiflexion (ankle flexion) (as shown in Figure 7, between reference numerals 73 and 68) for foot ground clearance is produced. However, a functional gait can have been achieved when producing confident dorsiflexion. The goal of the foot drop device and method is to achieve and maintain desired foot movement by using the device. The sensor 8 positioned on the affected foot of the user is used to complete the assessment of the stimulation result. The sensor 8 measures information while the user is walking, and transmits a sensor signal representing movement. Foot trajectory is assessed according to the signal. Foot trajectory is essential for detecting gait phase. Figure 7 represents the different gait phases of the user who is walking.

In order to produce defined movements, it is necessary to generate individual or coordinated muscle contractions. These muscle contractions are generated by employing different stimulation patterns based on discrete activation (or deactivation) of pads or electrodes 315 within the multi-pad electrode layer 31; selecting the appropriate amplitude and width of the pulses applied to each electrode 315 during stimulation; and selecting the appropriate time delay between consecutive pad (electrode) activations. All possible combinations of the aforementioned parameters for optimally activating the multi-pad electrodes require complex control algorithms. FIG8 shows an example pattern of stimulation pulses provided by the multi-pad electrodes 315, where T is the period of cyclic repetition of pad activation, Tc is the duration of the cathodic pulse, and Ta is the duration of the anodic pulse (charge compensation pulse).

Each foot movement, and particularly dorsiflexion and plantar flexion, is associated with at least one stimulation pattern. The optimal position of the stimulation pad not only changes with different users, but also for the same user, in different stimulation sessions (sessions) and even in a single session, the optimal position of the stimulation pad also can change due to muscle fatigue or due to the change of the distance between the skin electrode interface and the electrode and the stimulated excitable tissue. Therefore, it is necessary that the FES system has the ability to adapt during use. The method associated with the FES system 1 optimizes the stimulation pattern produced by the device 3 based on multiple pads in real time. Therefore, the quality of the assisted motion provided by the system is improved and maintained. In particular, the feedback information obtained by at least one sensor 8 is used. The currently specified stimulation pattern is modified to achieve optimal plantar flexion and optimal dorsiflexion during gait. In a preferred embodiment, the stimulation scheme is designed to have an event-driven state machine based on the state transition of the input from sensors and timers (hardware modules in the processor being positioned in the housing 5 or the sensor unit 8).

Methods used to optimize stimulation patterns:

(1) Processing of gait phase detection in order to initiate specific stimulation patterns, as described with respect to FIG4 ;

(2) tracking foot motion to assess gait quality, as described with respect to FIG6 ; and

(3) Execute a subroutine for stimulation pattern modification that occurs in a specified period or time window, as necessary. This is illustrated in FIG5 .

With respect to (1) processing gait phase detection in order to initiate a specific stimulation pattern, the stimulation pattern is executed cyclically according to the output of the state machine. The inputs to the state machine are: a) the current state (e.g., exiting the gait phase); b) the shape of the sensor signal at the previous n points, where the shape of the signal representing the angular velocity is the curve shown together with the gait cycle in Figure 7, because the digitization of the sensor data is done at discrete time intervals (sampling times), the expression "previous n points" refers to the n samples of the sensor output before the last available sample; and c) the time elapsed since the last detected event, where an event is a term describing a characteristic predefined moment associated with the observation of the foot movement (via sensor 8) in terms of rhythm. These points are chosen because they are associated with gait phase transitions (e.g., an angular velocity exceeding a negative threshold after a rest period is associated with heel-off).

FIG4 is a flow chart illustrating a method associated with the system of the present invention. First (block 401), the stimulation system is initialized. Next (block 402), the stimulation parameters from the previous session are loaded. The stimulation parameters are stimulation patterns for dorsiflexion and plantar flexion. A stimulation pattern includes a set of active pads in a multi-pad electrode having appropriate stimulation pulse amplitude and width for each pad and a time delay between consecutive pad activations. The stimulation protocol can then be initiated or not (block 403). If the decision is made to initiate the stimulation protocol (if "yes"), the phases of acquiring data from the sensor and values from the timer and performing data recording are executed (block 404). The timer is included in a processor in the housing 5 or in the sensor unit 8. The purpose of the timer is to measure the time elapsed since the last detected event to impose time constraints in automated decision making. Next, it is determined which phase the gait cycle is in (block 405). The decision is made using information about the current gait phase, the signal "shape," and the timer value since the last detected event. The process of gait phase detection based on characteristic events is repeated continuously. After this, calculate quality (Q) index (frame 406) of current gait phase.Use the mathematical function of the part of the automation algorithm that runs on the processor of stimulator 6 to calculate quality index.Depend on current gait phase (dorsiflexion or plantar flexion) to calculate the quality index Qd of dorsiflexion or the quality index Qp of plantar flexion, and derive the value of the quality index Qd of dorsiflexion and the quality index Qp of plantar flexion according to the correlation between actual foot track (corresponding angular velocity) and the ideal foot track (corresponding angular velocity) of superposition.If there is (because they are optional), then user command is decoded (frame 407).The user can initiate stimulation, and indication stimulation is painful or stops automation algorithm by manually controlling stimulator 6 or by the user application being installed on phone, flat plate etc.If there is, then this command has high priority and checks this command with each sensor sampling (for example, 1 second～100 times).

Next, it is determined whether there has been a change in the phase of the gait (block 408). If the phase of the gait has not changed (if "no"), the method returns to the stage of acquiring data from the sensors and values from the timer and performing data recording (block 404). If the phase of the gait has changed (if "yes"), it is checked whether the phase needs to be optimized (block 409). If dorsiflexion is the next phase and the Qd of the previous step is below a certain threshold, optimization will be initiated. A similar process is applicable to plantar flexion. The threshold is dynamic and can be adjusted according to the patient's condition.

The quality index Q is a vector and the value of Qd or Qp is derived from Q depending on the gait phase, wherein Qp is derived for plantar flexion and Qd is derived for dorsiflexion. When the processor in the stimulator 6 enters one of the optimization phases (PfOS or DfOS) and the quality index Q during the previous phase (dorsiflexion for DfOS and plantar flexion for PfOS) is higher than a certain threshold, the algorithm will not enter the modification subroutine; On the contrary, it uses the same pattern used during one of the last two steps. If the quality index Q is lower than a certain threshold, the algorithm runs a subroutine (box 412) for modifying the stimulation pattern. For dorsiflexion, based on the Qd factor of the last two steps, it will use a new pattern (boxes 413 and 414) with better Qd. If Qp is higher or lower than the threshold during the previous plantar flexion, it is decided to enter Pf or PfOS.

Regarding (2) tracking of the foot trajectory, this task is performed in order to evaluate the generated movement. Based on a predefined ideal trajectory (angular velocity distribution), the deviation ε of the current step from this predefined trajectory is calculated. This is done by applying a mathematical function to the samples captured from the sensor 8. Taking into account the deviation of each sample from the ideal curve, the function returns a single value that represents the Q factor of the foot movement. The algorithm automatically calculates the gait quality. This is divided into two subcategories: the quality of plantar flexion and the quality of dorsiflexion. If the quality of any of these categories is below a certain threshold, the algorithm initiates a subroutine (3) for stimulation pattern modification with the aim of increasing the quality factor.

FIG11 shows an example of the execution of the algorithm for the modification of the stimulation pattern. For each stimulation pattern (on the left), the P table (pattern probability table, on the right) has the following values: the value represents the probability that activating the corresponding pad in the multi-pad electrode will help to generate the desired foot movement (dorsiflexion or plantar flexion). In fact, the P table includes two tables, Pd and Pt, for dorsiflexion and plantar flexion. P0 is the "a priori" P table. It is the starting point for the modification of the stimulation pattern in the main optimization algorithm. During the optimization phase, the P table is modified based on the stimulation pattern applied and the quality of the movement (Q) generated.

The algorithm for recalculating the P factor converges to a stable state from the initial (a priori) P0 factor table. The initial P0 factor table is based on a statistical analysis of the subjects involved in the functional use of the drop foot stimulation system or the P value of the last use before the system was turned off. Figure 10 shows the "a priori" P0 factor for dorsiflexion. It is a probability graph. This probability graph is drawn using a large number of optimization results during user trials for producing the desired dorsiflexion. Figure 10 provides the preferred pads at the beginning of assisted walking (start of the program). Based on this graph, the algorithm determines which pads will be activated to increase the Qd factor. This reasoning also applies to Qp.

Figure 6 illustrates a flow chart showing a method for P-factor calculation. First (box 601), the calculation of the P-table is initiated. Next (box 602), based on the detected event, it is decided whether to start the optimization phase. If it is decided to start the optimization phase (if "yes"), the initial P0 table (prior) for all pads is loaded from memory (box 603). Next, the vectors of the motion recorded during the last optimization phase are loaded (box 604). Subsequently, a list of pads that were stimulated in the last optimization phase is loaded (box 605). Thereafter, the trajectory of deviation from the ideal trajectory (ε) is calculated (box 606). Then, a quality function is applied to the selected pad (box 607). Next, the P-factor for the selected pad is modified based on the quality function (box 608). Then, the P-table and the deviation trajectory (ε) are saved (box 609) and the algorithm is returned to (box 610).

Referring back to the illustration of the algorithm for modifying the stimulation pattern of FIG. 11 , in which a Qd threshold is defined (e.g., Qd=60), during a first step, a stimulation pattern is derived from the a priori P0 table (as shown in FIG. 11 ). (In this example,) the stimulation pattern is formed by two active pads with predefined initial current amplitudes, each having the maximum value from the P0 table. After dorsiflexion, Qd is calculated based on the deviation of the foot trajectory from the ideal foot motion. Based on the obtained Qd, the next pattern is calculated. The first modification in the pattern is an increase in the stimulation amplitude, which results in stimulation pattern 1 (step 1 in FIG. 11 ). After the end of dorsiflexion, Qd is calculated again. Because the increase in Qd is small compared to the threshold, the value of the active pad in the P0 table is reduced, and the value of the adjacent pad that has not yet been tested is increased. If Qd is still below the Qd threshold, the algorithm for modifying the stimulation pattern is initiated. If the favorable pad from the P0 table remains the same, the current amplitude on the active pad is increased (pattern 3) (step 3 in FIG. 11 ). After dorsiflexion, Qd (block 606) is calculated (block 607 in FIG. 6) based on the deviation of the foot trajectory from the ideal foot motion. If the absolute value of the calculated Qd is low, the P-table is modified (block 608 in FIG. 6) to further reduce the P value of the active pad. When the value in the P-table for the inactive pad becomes greater than that for the active pad, a new pad whose current is set to the lowest threshold is automatically activated. In step 4 of FIG. 11, an increase in Qd is shown, which causes an increase in the P value of the newly activated pad. This also means that the stimulation current on this pad increases, while the current on pads with decreasing P values decreases. Once again, in the final step (step 5 in FIG. 11), Qd is calculated, confirming the increasing trend. The P value of pads that contribute significantly to the increase in Qd also increases, while the P values of other active pads decrease and the P values of untested pads near the preferred pad also increase. This results in greater support for the new inactive pad relative to the active pad with a smaller P value. During the last step (step 5 in FIG. 11 ), the Qd value exceeds the quality threshold, making the final stimulation pattern optimal.

FIG5 is a flow chart illustrating modification of a stimulation pattern. First (block 501), modification of the stimulation pattern is initiated. Next (block 502), the stimulation pattern is loaded from memory. Then, the stimulation amplitude of the pad with the lowest value of P is reduced. Next, the stimulation amplitude of the pad with the highest P value is increased.

The subroutine (3) for modifying the stimulation pattern is executed in predefined time windows (periods) that do not jeopardize the patient's safety. These periods are:

(3.1) For modification of the stimulation pattern regarding plantar flexion (because the quality of plantar flexion is below the threshold): During the push-off phase between heel-off and the swing phase, where a gait event is defined as a point with a local maximum of angular velocity (P maximum 711 in Figure 7). "Heel-off" is defined as the moment in time when the heel is completely lifted from the ground. After the start of stimulation, there is a certain time delay (50 to 100 ms) before the foot movement can be observed. Because the push-off duration is comparable to the muscle reaction delay, the entire push-off is designated as the modification period. If the plantar flexion of the previous step has a Qp factor below the threshold, the modification procedure is initiated.

The point of P maximum can be estimated within a suitable time window after heel-off. If this maximum does not occur within the specified time window, time constraints will force the initiation of dorsiflexion. This phase is illustrated in Figure 7 and is referred to as the period between points 71 and 72 in the figure. The heel-off event is a time point and represents the transition from the stance state and the push-off (plantar flexion) phase, which are continuous (non-instantaneous). A heel-off event is detected when the angular velocity (gyro signal) during (immediately after) the stance state exceeds a threshold of 20% of the maximum negative angular velocity of the previous gait cycle. The algorithm takes the first two steps into account to modify all thresholds. After one of these conditions is met, it is possible to detect the P maximum among n points. N points are the last n samples acquired from sensor 8. Updates to the thresholds and time constraints occur at the end of the gait cycle when the overall maximum is extracted. The main purpose of these constraints is to prevent false detections. Preferably, the updated value is calculated as the median using the last k steps. To reiterate, the processing and determination of the Q and P values can be performed in the processing device of the housing 5 or, when the amount of transmitted data needs to be kept small, in the processing device of the sensor unit 8. In this case, the Q and P values are calculated in the processing device of the sensor unit 8 and wirelessly transmitted to the housing 5.

During this short period between reference numerals 71 and 72 shown in Figure 7, the patient propels himself forward, and if the modification of the stimulation pattern produces unwanted foot motion, it will only affect the kinematic aspects of gait, including speed, symmetry, and rhythm, but will not cause potential instability. The next stage of modification of the stimulation pattern is one related to dorsiflexion (3.2).

(3.2) In order to test the modification of the stimulation pattern with respect to dorsiflexion, a test stimulation pattern is applied during the last phase of the swing phase (starting at the point 74 of 50% of the maximum positive angular velocity of the swing phase and the heel strike 68), where the maximum positive angular velocity is 73. This period is illustrated in Figure 7. During this short part of the swing phase, the patient's foot has passed the point of minimum foot clearance. Based on the stimulation twitches generated by the modification of the stimulation pattern, the algorithm estimates whether the modification of the stimulation pattern is increasing or decreasing the dorsiflexion strength. The muscle twitch is the result of a perturbation of the stimulation pattern. The main purpose of the twitch is to produce a difference between the applied pattern and the modified pattern. The evaluation is based on the actual trajectory shape compared to a predefined target trajectory. In Figure 9, the middle line is the predefined trajectory, while the upper and lower lines represent the trajectories that cause an increase or decrease in Qd.

The stimulation protocol includes the following stimulations which are illustrated in FIG7 for different gait phases during walking. FIG7 also shows the foot trajectories resulting from the inventive optimization process. The stimulations for the entire gait cycle are:

(1) A gradually increasing, increased stimulation for the muscle forces involved in plantar flexion (PfRU). The event for triggering this stimulation phase is based on a time delay after the detection of the heel strike (reference numeral 69 in FIG7 ). It is triggered within a defined time window with fixed start and end times for flatfoot detection. The start time can be 0, and in this case the ramp starts after flatfoot is detected on the ground (gyroscope ~0). The PfRU is time limited and the stimulation is turned off if the heel-off event does not occur within the predefined time window. This stimulation phase occurs approximately when the gait cycle is between its 20% and its 30% (reference numerals 69, 70 in FIG7 ).

The initial stimulation pattern during this stimulation phase is the one previously optimized for plantar flexion. The individual amplitude increases are defined by the ramp time and the final pulse amplitude value, which is defined as the value of the Pf pattern. Similar activation patterns are present in able-bodied individuals during the stance phase of gait.

(2) A stimulation called the Plantar Flexion Optimized State (PfOS) is initiated during the Push-Off gait phase. The event for triggering the PfOS is when the heel initially leaves the ground, wherein the angular velocity of the foot is used to detect the initial departure of the heel from the ground. When the value registered by sensor 8 exceeds a set threshold, the Push-Off phase is detected and the stimulation enters its PfOS phase. This is represented in FIG7 , where it can be seen that the stimulation phase is triggered at the beginning of the Push-Off gait phase (following reference numeral 69 , when the PfRU stimulation phase has ended). This stimulation phase occurs approximately when the gait cycle is between its 30% and its 40% (reference numerals 70 , 71 in FIG7 ).

During this PfOS phase, the stimulation pattern is modified for plantar flexion based on the plantar flexion quality function (Qp). Qp is a derived mathematical function. Taking into account the deviation of each sample from the artificial curve, the function returns a single value representing the Qp factor. It is a predefined function. The effect of the modified stimulation pattern is evaluated using the deviation of the foot trajectory from the reference trajectory. Such deviation is obtained from the information captured by the sensor 8 (Figure 3). The Qp factor is recalculated based on the pattern modification and based on the induced trajectory. If the previous PfOS stimulation produced plantar flexion above a defined quality threshold (this is estimated using the deviation of the foot trajectory from the reference trajectory), the next PfOS stimulation will use the same stimulation pattern (without pattern modification).

(3) Dorsiflexion stimulation occurs during the swing phase of gait (Df). The stimulation pattern during this stimulation phase is the dorsiflexion pattern that was optimized during the previous dorsiflexion optimization state (DfOS) into the subsequent gait cycle, as shown in Figure 7.

Dorsiflexion stimulation is initiated at toe-off (reference numeral 711 in FIG7 ), taking into account the time delay between the onset of stimulation and the induced muscle force. The event for initiating this stimulation (Df) is the local maximum negative angular velocity during the early swing phase. Muscle activation for dorsiflexion occurs between 60% and 90% (100% in the case where DfOS is not necessary) (between reference numerals 72 and 74 in FIG7 ).

(4) At the end of the swing phase, a final stimulation (previous stimulation pattern) is initiated. This final stimulation is called the dorsiflexion optimized state (DfOS). This state is executed if the Qd of the previous step is below a threshold. The event used to trigger this state is defined as 50% of the maximum foot angular velocity.

During this gait phase, the foot has left minimum foot clearance and perturbations of the stimulation pattern will not cause falls due to stumbling. Therefore, during DfOS, the stimulation pattern is modified for dorsiflexion based on the dorsiflexion quality function (Qd). Qd also takes into account inversion and eversion of the foot and is optimized by minimizing both inversion and eversion of the foot. The effect of the modified stimulation pattern is estimated using the deviation of the foot trajectory from the reference trajectory. The Qd factor is recalculated based on the pattern modification and based on the induced trajectory (which is obtained by sensor 8). Figure 9 illustrates the calculation of the deviation (ε) of the trajectory measured during DfOS relative to the predefined trajectory. The process of applying DfOS stimulation can be independent of whether the Q factor drops below a certain threshold, because changes in the gait quality in this later stage of swing do not affect the safety of the gait. Therefore, the optimization of dorsiflexion can be performed at any step. The resulting P table can be continuously optimized, and when Qd drops below a certain threshold, a better stimulation pattern is finally available.

During any of the stimulation phases, if a stable state is detected, the system jumps to a rest (no stimulation) phase.

If one of the phases is not properly identified by a defined event, then the time constraint forces the next phase to occur; in this case, the Modify state has a lower priority than the Df state.

A set of stimulation parameters obtained as a result of the optimization process is defined for each active pad 315 and includes pulse width, pulse amplitude, the shape of the compensation (which indicates the type of stimulation pulse), and the time delay between subsequent activations of the pads. Modifications to the stimulation pattern include: increasing/decreasing stimulation parameters (pulse amplitude, pulse width, and frequency); and changing the set of selected active pads based on the functionality of neighboring pads determined during the optimization process.

In summary, the apparatus and method of the present invention provide important advantages over conventional apparatus and methods. For example, relative to the apparatus disclosed in WO2011/079866A1, the present apparatus and method are capable of calculating the foot trajectory based on sensor signals, detecting the gait phase based on the foot trajectory, evaluating the gait quality based on the foot trajectory, and modifying the stimulation pattern applied to the electrodes if the gait quality is below a certain threshold. Moreover, within the gait cycle, at specific time instances (e.g., the end of the swing phase), a new electrode activation configuration (a different subset of pads) is activated, and the new electrode activation configuration is analyzed using sensor signals with respect to the improved functionality. These new, better activation means are tested using short pulse sequences, and the pulse responses are analyzed. In the event that the gait quality is below a certain threshold, the electrode activation configuration that has shown the best pulse response replaces the previous configuration.

As is apparent from the present disclosure, the system provides a solution to the problem of positioning stimulation electrodes to achieve optimal movement. Furthermore, the system is capable of automatically adjusting stimulation parameters. Furthermore, fatigue can be delayed through asynchronous, decentralized stimulation. Stimulation becomes highly selective, accurately targeting the desired nerves and muscles.

On the other hand, the present invention is obviously not limited to the specific embodiment(s) described herein, but includes any variants (for example, with respect to the choice of materials, dimensions, components, configurations, etc.) that would be considered by a person skilled in the art within the general scope of the invention defined in the claims.

Claims (10)

1. A functional electrical stimulation system (1) for correcting foot drop, comprising: Device (3), configured to be placed on a user's partially paralyzed leg, the device (3) having a plurality of multi-pad electrodes (315) on one side (31), at least one of the electrodes (315) being configured to provide a stimulating electrical signal at a point on the leg corresponding to the at least one electrode, wherein the corresponding stimulating electrical signal forms a stimulation pattern; and At least one sensor (8) is configured to be positioned on the user's partially paralyzed leg or corresponding foot during use of the system (1), wherein the sensor (8) is configured to measure information during movement and emit sensor signals indicating the movement. The system (1) is characterized in that it further includes: means (6) for calculating a foot trajectory based on the sensor signal, for detecting a gait phase based on the foot trajectory, for evaluating gait quality based on the foot trajectory, and for modifying the stimulation pattern if the gait quality is below a certain threshold, wherein the stimulation pattern is modified if the plantar flexion quality is below a certain threshold during the push-out phase, or if the dorsiflexion quality is below a certain threshold during the final phase of the swing phase; and means (7) for selectively activating at least one of the electrodes (315) according to the modified stimulation pattern. 2. The system (1) according to claim 1, wherein the means (6) for evaluating the gait quality based on the foot trajectory further includes means for loading a predefined trajectory and for calculating the deviation (ε) of the current step from the predefined trajectory. 3. The system (1) of claim 2, wherein the gait quality is evaluated when the gait is in the following phases: during plantar flexion in the push-out gait phase; and during dorsiflexion in the swing gait phase when the user is lifting the foot off the ground. 4. The system (1) of claim 1, wherein the means (7) for selectively activating at least one of the electrodes (315) according to the modified stimulation pattern comprises: a multiplexer means for discrete activation or deactivation of the electrodes (325) and for adjusting at least one of the following parameters associated with each electrode: pulse amplitude, pulse width and time delay between successive electrode activations. 5. The system (1) according to claim 1 further includes: clothing (2), wherein the device (3) is attached to the clothing (2). 6. The system (1) according to claim 1, wherein the sensor (8) includes means for obtaining the orientation of the sensor (8) itself based on the moment of the support gait during the period when the sensor (8) is stationary. 7. The system (1) according to claim 6, wherein the means for obtaining the orientation of the sensor (8) itself comprises a plurality of accelerometers and a plurality of gyroscopes. 8. The system (1) according to claim 1, wherein the means (6) for calculating foot trajectory based on the sensor signal, for detecting gait phase based on the foot trajectory, for evaluating gait quality based on the foot trajectory, and for modifying the stimulation pattern if the gait quality is below a certain threshold, is at least partially located in the sensor (8). 9. The system (1) according to claim 1, wherein the means (6) for calculating foot trajectory based on the sensor signal, for detecting gait phase based on the foot trajectory, for evaluating gait quality based on the foot trajectory, and for modifying the stimulation pattern if the gait quality is below a certain threshold, is at least partially located in the housing (5) positioned on the user's leg. 10. The system (1) according to claim 1 further includes means for wirelessly transmitting pre-processed or processed data obtained at the sensor (8) to processing means arranged at different locations.