Modified implanted drop foot stimulator system with graphical user interface for customised stimulation pulse-width profiles

A modified implanted drop foot stimulator that allows cyclic modulation of the stimulation pulse-width during gait has been developed. Stimulation was on two channels of a four-channel 12 polar cuff electrode. The stimulator allowed modulation of stimulation pulse-width, between 0 and 255μs, on both channels throughout the swing and stance phases of gait. Stimulation was applied between 17 and 40 Hz. The clinician can specify an infinite range of stimulation profiles on a desktop computer, using a user-friendly LabVIEW^TM interface. The desktop program generated a stimulation profile table of 100 values, which was then downloaded to the drop foot stimulator. As each phase of gait imposed different biomechanical demands on the ankle dorsiflexor muscles, different stimulation intensities were desirable, throughout gait, to match these demands. Moreover, as the gait of each person with hemiplegia is unique, the biomechanical demands imposed throughout the gait cycle for each user of a drop foot stimulator are unique. This stimulator architecture allowed the clinician to, specify stimulation intensities individually, at each phase of the gait cycle for each drop foot stimulator user. The stimulator was evaluated on a male hemiplegic subject. It was used to increase the stimulation pulse-width by 150% at 5% of gait cycle prior to heel strike. The system performed well, with the ankle angle at heel strike increasing by 5° owing to this increased pulse-width.     

A system for the delivery of programmable, adaptive stimulation intensity envelopes for drop foot correction applications

We describe the design of an intelligent drop foot stimulator unit for use in conjunction with a commercial neuromuscular electrical nerve stimulation (NMES) unit, the NT2000. The developed micro-controller unit interfaces to a personal computer (PC) and a graphical user interface (GUI) allows the clinician to graphically specify the shape of the stimulation intensity envelope required for a subject undergoing drop foot correction. The developed unit is based on the ADuC812S micro-controller evaluation board from Analog Devices and uses two force sensitive resistor (FSR) based foot-switches to control application of stimulus. The unit has the ability to display to the clinician how the stimulus intensity envelope is being delivered during walking using a data capture capability. The developed system has a built-in algorithm to dynamically adjust the delivery of stimulus to reflect changes both within the gait cycle and from cycle to cycle. Thus, adaptive control of stimulus intensity is achieved.     

Three dimensional inertial sensing of foot movements for automatic tuning of a two-channel implantable drop-foot stimulator

A three dimensional inertial sensing system for measuring foot movements during gait is proposed and tested. It can form the basis for an automated tuning system for a two-channel implantable drop-foot stimulator. The foot orientation and position during the swing phase of gait can be reconstructed on the basis of three-dimensional measurement of acceleration and angular velocity, using initial and final conditions during mid-stance. The foot movements during gait of one stroke person using the implanted two-channel stimulator were evaluated for several combinations of stimulation parameters for both channels. The reconstructed foot movements during gait in this person indicated that the channel stimulating the deep peroneal nerve contributes mainly to dorsiflexion and provides some reduction of inversion seen without stimulation, while the channel activating the superficial peroneal nerve mainly provides additional reduction of inversion. This agrees with anatomical knowledge about the function of the muscles activated by both branches of the peroneal nerve. The inertial sensor method is expected to be useful for the clinical evaluation of foot movements during gait supported by the two-channel drop-foot stimulator. Furthermore, it is expected to be applicable for the automated balancing of the two stimulation channels to ensure optimal support of gait.     

A versatile drop foot stimulator for research applications

Drop Foot Stimulators are used to correct hemiplegic drop foot by synchronising the application of Functional Electrical Stimulation (FES) of the Common Peroneal Nerve (CPN) to the swing phase of the gait cycle. A research Drop Foot Stimulator (DFS) has been developed with a very flexible architecture to enable the investigation of a variety of gait-correction strategies. The portable unit has been carefully designed to optimise functionality while keeping its size and power consumption to a minimum. The device has two channels of stimulation, with all parameters of stimulation for each channel independently programmable. Four analogue and four digital sensor input channels are provided with a wide variety of sensor types possible. A microcontroller core is utilised to enable the implementation of different control algorithms. A PC-based user interface enables easy programming of the system configuration.     

Modular transcutaneous functional electrical stimulation system

A new multipurpose programmable transcutaneous electric stimulator, Compex Motion, was developed to allow users to design various custom-made neuroprostheses, neurological assessment devices, muscle exercise systems, and experimental setups for physiological studies. Compex Motion can generate any arbitrary stimulation sequence, which can be controlled or regulated in real-time using any external sensor or laboratory equipment. Compex Motion originated from the existing Compex 2 electric stimulator, manufactured by a Swiss based company, Compex SA. The Compex Motion stimulator represents a further evolution and expansion of the ETHZ-ParaCare functional electrical stimulation system. This stimulator provides all the advanced functional electrical stimulation (FES) application and control features and can be easily incorporated into any standard rehabilitation program. Compex Motion has successfully been applied as a neuroprosthesis for walking, reaching and grasping in more than 100 stroke and spinal cord injured patients. This system has also been used to strengthen muscles and to investigate muscle properties in able-bodied subjects. Compex Motion is a multipurpose FES system specially designed to promote sharing and exchanging of stimulation protocols, sensors, and user interfaces. To the best of our knowledge an FES system that has similar capabilities does not exist yet.     

Inertial Gait Phase Detection for control of a drop foot stimulator: Inertial sensing for gait phase detection

An Inertial Gait Phase Detection system was developed to replace heel switches and footswitches currently being used for the triggering of drop foot stimulators. A series of four algorithms utilising accelerometers and gyroscopes individually and in combination were tested and initial results are shown. Sensors were positioned on the outside of the upper shank. Tests were performed on data gathered from a subject, sufferer of stroke, implanted with a drop foot stimulator and triggered with the current trigger, the heel switch. Data tested includes a variety of activities representing everyday life. Flat surface walking, rough terrain and carpet walking show 100% detection and the ability of the algorithms to ignore non-gait events such as weight shifts. Timing analysis is performed against the current triggering method, the heel switch. After evaluating the heel switch timing against a reference system, namely the Vicon 370 marker and force plates system. Initial results show a close correlation between the current trigger detection and the inertial sensor based triggering algorithms. Algorithms were tested for stairs up and stairs down. Best results are observed for algorithms using gyroscope data. Algorithms were designed using threshold techniques for lowest possible computational load and with least possible sensor components to minimize power requirements and to allow for potential future implantation of sensor system.     

The adaptive drop foot stimulator – Multivariable learning control of foot pitch and roll motion in paretic gait

Many stroke patients suffer from the drop foot syndrome, which is characterized by a limited ability to lift (the lateral and/or medial edge of) the foot and leads to a pathological gait. In this contribution, we consider the treatment of this syndrome via functional electrical stimulation (FES) of the peroneal nerve during the swing phase of the paretic foot. A novel three-electrodes setup allows us to manipulate the recruitment of m. tibialis anterior and m. fibularis longus via two independent FES channels without violating the zero-net-current requirement of FES. We characterize the domain of admissible stimulation intensities that results from the nonlinearities in patients’ stimulation intensity tolerance. To compensate most of the cross-couplings between the FES intensities and the foot motion, we apply a nonlinear controller output mapping. Gait phase transitions as well as foot pitch and roll angles are assessed in realtime by means of an Inertial Measurement Unit (IMU). A decentralized Iterative Learning Control (ILC) scheme is used to adjust the stimulation to the current needs of the individual patient. We evaluate the effectiveness of this approach in experimental trials with drop foot patients walking on a treadmill and on level ground. Starting from conventional stimulation parameters, the controller automatically determines individual stimulation parameters and thus achieves physiological foot pitch and roll angle trajectories within at most two strides.     

Hardware-software co-design of portable functional gastrointestinal stimulator system

In the recent years, functional electrical stimulation has been applied to restore impaired motility in the gastrointestinal tract. Unlike other methods of electrical stimulation of the gut, microprocessor-controlled, sequential electrical stimulation has been shown to induce peristalsis and enhance emptying in acute canine gastric and colonic models. This study aims at completing the development of a portable microprocessor-based functional stimulator system consisting of a microelectronic stimulator, patient-specific computer-based real-time software and a programming interfacing device. The ultimate goals of the design are to ensure that (1) the portable stimulator can be efficiently utilized in chronic animal experiments; and (2) the device can be further miniaturized into an implantable version. The designed portable stimulator generates four channel sequential bipolar rectangular pulse trains with programmable parameters within the stimulation requirements obtained from a previously developed computer model. Real-time simulation of colonic peristalsis and a case-specific stimulation model were implemented using patient-specific computer-based software. A chronic canine case study confirmed the feasibility of this microprocessor-controlled stimulation method for future clinical applications in humans.     

生物反馈结合运动训练对脑卒中足下垂患者踝关节运动能力的影响

目的观察生物反馈对脑卒中足下垂患者踝关节运动功能的康复效果的影响。方法 20例脑卒中足下垂自愿患者,其中男性13例,女性7例;年龄63～67岁。将其随机分为A组(运动训练组)和B组(生物反馈结合运动训练组),每组各10例。使用手法肌力评定(MMT)分级标准的Kendall百分比法,评定胫前肌肌力;用通用量角器测量踝关节活动度;用改良的Ashworth(MAS)量表评定小腿腓肠肌的痉挛程度;用ME 6000型表面肌电仪收集胫前肌和腓肠肌肌电变化。结果通过3个月的康复治疗,与治疗前相比,B组患者胫前肌徒手肌力和均方根肌电值、踝关节活动度均明显增强(P<0.01);与A组相比,B组患者在治疗1个月时,胫前肌徒手肌力、踝关节活动度均增强(P<0.05),胫前肌均方根肌电值明显增大(P<0.01);治疗3个月时,上述指标均增强显著(P<0.01),同时小腿腓肠肌的痉挛程度及均方根肌电值也明显优于A组(P<0.05)。结论 3个月系统的生物反馈结合运动训练,一定程度地提高了脑卒中足下垂患者的踝关节运动功能,而且结合康复运动训练更促进了患者的康复过程。     

A microcontroller system for investigating the catch effect: functional electrical stimulation of the common peroneal nerve

Correction of drop foot in hemiplegic gait is achieved by electrical stimulation of the common peroneal nerve with a series of pulses at a fixed frequency. However, during normal gait, the electromyographic signals from the tibialis anterior muscle indicate that muscle force is not constant but varies during the swing phase. The application of double pulses for the correction of drop foot may enhance the gait by generating greater torque at the ankle and thereby increase the efficiency of the stimulation with reduced fatigue. A flexible controller has been designed around the Odstock Drop Foot Stimulator to deliver different profiles of pulses implementing doublets and optimum series. A peripheral interface controller (PIC) microcontroller with some external circuits has been designed and tested to accommodate six profiles. Preliminary results of the measurements from a normal subject seated in a multi-moment chair (an isometric torque measurement device) indicate that profiles containing doublets and optimum spaced pulses look favourable for clinical use.     

The Internal Human Conditioning System: a multipurpose programmable biomedical system

A proposed general-purpose implantable biomedical system is described. This Internal Human Conditioning System (IHCS) is capable of measuring biomedical data of various kinds on a number of independent input channels. The number and specifications of these channels are software selectable by means of a low-power microprocessor. The system is also equipped with different programmable stimulation devices. These stimulators can deliver a programmable waveform in order to stimulate a specific muscle or to carry out an impedance measurement. The on-board eight bit microprocessor is used for communication with the outside world, by means of a serial link. The processor used is the 68HC11 from Motorola. By extensive use of the processor's 'sleep' mode and by switching off all unnecessary electronics, the amount of power consumed is drastically reduced. At present, a two-channel input chip and a programmable stimulator chip have been developed so that a complete system can be produced. For the sake of illustration, some realized and possible future applications are discussed.     

Estimation of the kinetic-optimized stimulus intensity envelope for drop foot gait rehabilitation

The purpose of present study is to estimate the optimal stimulus intensity envelope for drop foot rehabilitation based on a kinetic perspective. The voluntary and electric-stimulated elicited dorsiflexion torque responses of 11 healthy subjects were measured. During dorsiflexion, we recorded the tibialis anterior (TA) electromyography (EMG) or the stimulation intensity at four angles of the ankle joint. From these measurements, we derived two approximate equations that estimate dorsiflexion produced by either voluntary contraction or by electrical stimulation using a sigmoid function and a stepwise-regression analysis. We then tested the predictive capability of the model using Pearson correlation. Both equations indicated high correlation coefficients. Finally, we derived a relation between the TA EMG amplitude and stimulation intensity. From the obtained equation, we determined the optimal stimulus amplitude. We assume that the derived stimulus intensity envelope, calculated from EMG amplitude and angle of ankle joint, satisfies kinetic demand.     

Estimation of the kinetic-optimized stimulus intensity envelope for drop foot gait rehabilitation

The purpose of present study is to estimate the optimal stimulus intensity envelope for drop foot rehabilitation based on a kinetic perspective. The voluntary and electric-stimulated elicited dorsiflexion torque responses of 11 healthy subjects were measured. During dorsiflexion, we recorded the tibialis anterior (TA) electromyography (EMG) or the stimulation intensity at four angles of the ankle joint. From these measurements, we derived two approximate equations that estimate dorsiflexion produced by either voluntary contraction or by electrical stimulation using a sigmoid function and a stepwise-regression analysis. We then tested the predictive capability of the model using Pearson correlation. Both equations indicated high correlation coefficients. Finally, we derived a relation between the TA EMG amplitude and stimulation intensity. From the obtained equation, we determined the optimal stimulus amplitude. We assume that the derived stimulus intensity envelope, calculated from EMG amplitude and angle of ankle joint, satisfies kinetic demand.     

The application of a use case/task based approach in the development of software for a portable neuromuscular stimulator device

This paper describes the use of a use case/task based method in the development of a portable neuromuscular stimulator device. The developed unit allows a variety of stimulus delivery algorithms to be incorporated dependent on the patient's requirements. The developed system consists of a stimulator unit, stimulator firmware, external sensors, a programmer unit, two stimulation channels and electrodes. A clinician specifies a suitable algorithm for a particular patient and then selects the relevant stimulus parameters for that algorithm using the programmer unit. The stimulator unit's architecture supports the addition of future algorithms. The device was developed in accordance with the European Medical Devices Directive 93/42/EEC resulting in the need for a well-defined development lifecycle during the design and development of the neuromuscular stimulator. This development lifecycle must place emphasis on the need to identify potential hazards. Therefore, the adoption of a use case/task driven approach as one of the strategies in eliciting the requirements, both functional and non-functional and specification stages of the development lifecycle resulted in a more rigid hazard/risk analysis leading ultimately to a more robust final system. A comprehensive review of the literature has revealed that use cases have been in use in other contexts but not so in a biomedical context. Therefore, this is a novel strategy to the development of a device in this field. A brief background on the historical development of drop foot stimulators shall be presented thereby displaying the benefits of the programmability feature of our stimulator.     

The Internal Human Conditioning System: a multipurpose programmable biomedical system

A proposed general-purpose implantable biomedical system is described. This Internal Human Conditioning System (IHCS) is capable of measuring biomedical data of various kinds on a number of independent input channels. The number and specifications of these channels are software selectable by means of a low-power microprocessor. The system is also equipped with different programmable stimulation devices. These stimulators can deliver a programmable waveform in order to stimulate a specific muscle or to carry out an impedance measurement.

The on-board eight bit microprocessor is used for communication with the outside world, by means of a serial link. The processor used is the 68HC11 from Motorola. By extensive use of the processorapos;s ‘sleep’ mode and by switching off all unnecessary electronics, the amount of power consumed is drastically reduced. At present, a two-channel input chip and a programmable stimulator chip have been developed so that a complete system can be produced. For the sake of illustration, some realized and possible future applications are discussed.     

A review of the design and clinical evaluation of the ShefStim array-based functional electrical stimulation system

Functional electrical stimulation has been shown to be a safe and effective means of correcting foot drop of central neurological origin. Current surface-based devices typically consist of a single channel stimulator, a sensor for determining gait phase and a cuff, within which is housed the anode and cathode. The cuff-mounted electrode design reduces the likelihood of large errors in electrode placement, but the user is still fully responsible for selecting the correct stimulation level each time the system is donned. Researchers have investigated different approaches to automating aspects of setup and/or use, including recent promising work based on iterative learning techniques. This paper reports on the design and clinical evaluation of an electrode array-based FES system for the correction of drop foot, ShefStim. The paper reviews the design process from proof of concept lab-based study, through modelling of the array geometry and interface layer to array search algorithm development. Finally, the paper summarises two clinical studies involving patients with drop foot. The results suggest that the ShefStim system with automated setup produces results which are comparable with clinician setup of conventional systems. Further, the final study demonstrated that patients can use the system without clinical supervision. When used unsupervised, setup time was 14 min (9 min for automated search plus 5 min for donning the equipment), although this figure could be reduced significantly with relatively minor changes to the design.     

Bipedal gait model for precise gait recognition and optimal triggering in foot drop stimulator: a proof of concept

Electrical stimulators are often prescribed to correct foot drop walking. However, commercial foot drop stimulators trigger inappropriately under certain non-gait scenarios. Past researches addressed this limitation by defining stimulation control based on automaton of a gait cycle executed by foot drop of affected limb/foot only. Since gait is a collaborative activity of both feet, this research highlights the role of normal foot for robust gait detection and stimulation triggering. A novel bipedal gait model is proposed where gait cycle is realized as an automaton based on concurrent gait sub-phases (states) from each foot. The input for state transition is fused information from feet-worn pressure and inertial sensors. Thereafter, a bipedal gait model-based stimulation control algorithm is developed. As a feasibility study, bipedal gait model and stimulation control are evaluated in real-time simulation manner on normal and simulated foot drop gait measurements from 16 able-bodied participants with three speed variations, under inappropriate triggering scenarios and with foot drop rehabilitation exercises. Also, the stimulation control employed in commercial foot drop stimulators and single foot gait-based foot drop stimulators are compared alongside. Gait detection accuracy (98.9%) and precise triggering under all investigations prove bipedal gait model reliability. This infers that gait detection leveraging bipedal periodicity is a promising strategy to rectify prevalent stimulation triggering deficiencies in commercial foot drop stimulators.

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Graphical abstract Bipedal information-based gait recognition and stimulation triggering

     

Methods for gait event detection and analysis in ambulatory systems

After stroke, hemiparesis is a common problem resulting in very individual needs for walking assistance. Often patients suffer from foot drop, i.e. inability to lift the foot from the ground during the swing phase of walking. Functional electrical stimulation is commonly used to correct foot drop. For all supporting stimulation devices, it is vital to adequately detect the gait events, which is traditionally obtained by a foot switch placed under the heel. To investigate present methods of gait analysis and detection for use in ambulatory rehabilitation systems, we carried out a meta-analysis on research studies. We found various sensors and sensor combinations capable of analyzing gait in ambulatory settings, ranging form simple force based binary switches to complex setups involving multiple inertial sensors and advanced algorithms. However additional effort is needed to minimize donning/doffing efforts, to overcome cosmetical aspects, and to implement those systems into closed loop ambulatory devices.     

The development of corticospinal projections to tail and hindlimb motoneurons studied in infant macaques using magnetic brain stimulation

Summary The EMG responses evoked in tail, leg and foot muscles by magnetic stimulation (MS) of the brain were investigated in two male macaque monkeys under ketamine sedation. The animals were studied longitudinally over a period of 7 months (from 2.75 to 9.75 months old). MS was generally ineffective in eliciting responses when the animals were 2.75–4.5 months old, even at maximum stimulator output (1.5 Tesla). After this time the threshold for evoking EMG responses decreased considerably, and there was an increase in the probability of occurrence of the responses. These age-related changes plateaued at about 7.5 months, after which they remained fairly constant at adult levels. In both animals the maturation of these responses in tail and hindlimb muscles occurred later than in forelimb muscles.