A threshold-based fall-detection algorithm using a bi-axial gyroscope sensor.

A threshold-based algorithm, to distinguish between Activities of Daily Living (ADL) and falls is described. A gyroscope based fall-detection sensor array is used. Using simulated-falls performed by young volunteers under supervised conditions onto crash mats and ADL performed by elderly subjects, the ability to discriminate between falls and ADL was achieved using a bi-axial gyroscope sensor mounted on the trunk, measuring pitch and roll angular velocities, and a threshold-based algorithm. Data analysis was performed using Matlab to determine the angular accelerations, angular velocities and changes in trunk angle recorded, during eight different fall and ADL types. Three thresholds were identified so that a fall could be distinguished from an ADL: if the resultant angular velocity is greater than 3.1 rads/s (Fall Threshold 1), the resultant angular acceleration is greater than 0.05 rads/s(2) (Fall Threshold 2), and the resultant change in trunk-angle is greater than 0.59 rad (Fall Threshold 3), a fall is detected. Results show that falls can be distinguished from ADL with 100% accuracy, for a total data set of 480 movements.

Evaluation of a threshold-based tri-axial accelerometer fall detection algorithm.

Using simulated falls performed under supervised conditions and activities of daily living (ADL) performed by elderly subjects, the ability to discriminate between falls and ADL was investigated using tri-axial accelerometer sensors, mounted on the trunk and thigh. Data analysis was performed using MATLAB to determine the peak accelerations recorded during eight different types of falls. These included; forward falls, backward falls and lateral falls left and right, performed with legs straight and flexed. Falls detection algorithms were devised using thresholding techniques. Falls could be distinguished from ADL for a total data set from 480 movements. This was accomplished using a single threshold determined by the fall-event data-set, applied to the resultant-magnitude acceleration signal from a tri-axial accelerometer located at the trunk.

Effect of walking speed changes on tibialis anterior EMG during healthy gait for FES envelope design in drop foot correction.

Functional electrical stimulation may be used to correct hemiplegic drop foot. An optimised stimulation envelope to reproduce the EMG pattern observed in the tibialis anterior (TA) during healthy gait has been proposed by O'Keeffe et al. [O'Keeffe, D.T., Donnelly, A.E., Lyons, G.M., 2003. The development of a potential optimised stimulation intensity envelope for drop foot applications. IEEE Transactions on Neural Systems and Rehabilitation Engineering]. However this envelope did not attempt to account for changes in TA activity with walking speed. The objective of this paper was to provide data to enable the specification of an algorithm to control the adaptation of an envelope with walking speed. Ten young healthy subjects walked on a treadmill at 11 different walking speeds while TA EMG was recorded. The results showed that TA EMG recorded around initial contact and at toe off changed with walking speed. At the slowest velocities, equivalent to hemiplegic walking, the toe-off burst (TOB) of EMG activity had larger peak amplitude than that of the heel-strike burst (HSB). The peak amplitude ratio of TOB:HSB was 1:0.69 at the slowest speed compared to, 1:1.18 and 1:1.5 for the self-selected and fastest speed, respectively. These results suggest that an FES envelope, which produces larger EMG amplitude for the TOB than the HSB, would be more appropriate at walking speeds typical of hemiplegic patients.

Comparison of the performance of the activPAL Professional physical activity logger to a discrete accelerometer-based activity monitor.

The aim of this study was to assess the accuracy of the 'activPAL Professional' physical activity logger by comparing its output to that of a proven discrete accelerometer-based activity monitor during extended measurements on healthy subjects while performing activities of daily living (ADL). Ten healthy adults, with unrestricted mobility, wore both the activPAL and the discrete dual accelerometer (Analog Devices ADXL202)-based activity monitor that recorded in synchronization with each other. The accelerometer derived data were then compared to that generated by the activPAL and a complete statistical and error analysis was performed using a Matlab program. This program determined trunk and thigh inclination angles to distinguish between sitting/lying, standing and stepping for the discrete accelerometer device and amount of time spent on each activity. Analysis was performed on a second-by-second basis and then categorized at 15s intervals in direct comparison with the activPAL generated data. Of the total time monitored (approximately 60 h) the detection accuracies for static and dynamic activities were approximately 98%. In a population of healthy adults, the data obtained from the activPAL Professional physical activity logger for both static and dynamic activities showed a close match to a proven discrete accelerometer data with an offset of approximately 2% between the two systems.

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.

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.

An electrode configuration technique using an electrode matrix arrangement for FES-based upper arm rehabilitation systems.

An upper limb electrical stimulation technique has been developed which features a novel self-configuration approach, to obtain an ideal wrist response from the patient. The system uses an analogue de-multiplexer in conjunction with an electrode matrix so that different electrode sites can be tested using only one channel of stimulation. A twin axis goniometer is attached to the patient's wrist and flex sensors are attached to the patient's fingers so that the control algorithm can assess the wrist response. A data acquisition unit logs the data for further analysis. A clinical investigation on healthy subjects was conducted to test the proposed system. The results show a high variation in hand response across different subjects. In addition, for all subjects tested an ideal response was found which shows some justification for the use of the proposed technique.

A review of technological approaches to venous ulceration.

Leg ulceration is a chronic condition affecting about 1-2% of the adult population. The main causes of leg ulceration are venous hypertension, arterial insufficiency, diabetes, or a combination of these aetiologies (causes) or malignancy. Venous ulcers account for approximately 80% of all leg ulcers and are a result of venous hypertension. The current mainstay of treatment of venous ulcers is the application of graduated compression bandaging to the limb. In spite of the application of the best evidence-based therapy, healing rates for venous leg ulcers remain disappointing, at 50-70% after 12 weeks of treatment, depending on initial size and chronicity of the ulcer. Thus, a large number of ulcers are unhealed by this time, and many patients suffer from long-term leg ulceration, some remaining for years, and those that heal often recur. There is an obvious need to develop new treatments that would improve healing rates. This review provides a complete overview of the anatomy of venous circulation and the physiology pertaining to it, the pathophysiology of venous disease, the pathogenesis of ulceration, and a review of treatments currently employed in healing venous leg ulcers and their supporting evidence. The aim of this article is to encourage a fresh look at this chronic problem and stimulate ideas on how healing rates can be improved.

Rectus femoris surface myoelectric signal cross-talk during static contractions.

The clinical application of EMG requires that the recorded signal is representative of the muscle of interest and is not contaminated with signals from adjacent muscles. Some authors report that surface EMG is not suitable for obtaining information on a single muscle but rather reflects muscle group function [J. Perry, C.S. Easterday, D.J. Antonelli, Surface versus intramuscular electrodes for electromyography of superficial and deep muscles. Physical Therapy 61 (1981) 7-15]. Other authors report however, that surface EMG is adequate to determine individual muscle function, once guidelines pertaining to data acquisition are followed [D.A. Winter, A.J. Fuglevand, S.E. Archer. Cross-talk in surface electromyography: theoretical and practical estimates. Journal of Electromyography and Kinesiology 4 (1994) 15-26]. The aim of this study was to determine whether surface EMG was suitable for monitoring rectus femoris (RF) activity during static contractions. Five healthy subjects, having given written informed consent, participated in this trial. Surface and fine wire EMG from the rectus femoris and the vastus lateralis (VL) muscles were recorded simultaneously during a protocol of static contractions consisting of knee extensions and hip flexions. Ratios were used to quantify the relationship between the surface EMG amplitude value and the fine wire EMG amplitude value for the same contraction. The results showed that hip flexion contractions elicited RF activation only and that knee extension contractions elicited fine wire activity in VL only. When the relationship between RF surface and RF fine wire electrodes was compared for hip flexion and knee extension contractions, it was observed that for all subjects, there was a tendency for increased RF surface activity in the absence of RF fine wire activity during knee extensions. It was concluded that the activity recorded by the RF surface electrode arrangement during knee extension consisted of EMG from the vastii, i.e., cross-talk and that vastus intermedius was the most likely origin of the erroneous signal. Therefore it is concluded that for accurate EMG information from RF, fine wire electrodes are necessary during a range of static contractions.

A description of an accelerometer-based mobility monitoring technique.

Accurate monitoring of the mobility status of older adults, over the long-term, is important in rehabilitation medicine, as regular physical activity is central to maintaining both physical and mental health, as well as evaluating quality of life. This technical note describes an accelerometer-based mobility monitoring technique, which can distinguish between static and dynamic activities and can detect the basic postures of sitting, standing and lying. The technique allows thresholds for these postures to be set and two different posture threshold methods are described: mid-point and "best estimate". Preliminary results from using these methods are presented. This preliminary evaluation of the technique was carried out over the long-term (>29 h) in an uncontrolled environment and the method used to carry out the evaluation is described in detail. The two different posture thresholding methods were tested on long-term mobility data from one older adult subject. The subject did not have to follow a specific activity protocol during the recording period (4 days) and was shadowed by an observer in order to evaluate the accuracy of this technique. The monitoring hardware consisted of two accelerometer devices, one on the trunk and the other on the thigh and a pocket-sized ambulatory data-logger. Applying 'best estimate' thresholding, as opposed to mid-point thresholding, improved sitting detection accuracy by 18%, to 93% and lying detection accuracy by 5%, to 84%. Thus, based on these preliminary data, an accurate mobility monitoring system for older adults is described and it was observed that the actual posture threshold limits applied have a high impact on the mobility monitoring system's accuracy and are particularly important for accurately detecting postures when used over the long-term, in an uncontrolled environment.

Stimulus artifact removal using a software-based two-stage peak detection algorithm.

The analysis of stimulus evoked neuromuscular potentials or m-waves is a useful technique for improved feedback control in functional electrical stimulation systems. Usually, however, these signals are contaminated by stimulus artifact. A novel software technique, which uses a two-stage peak detection algorithm, has been developed to remove the unwanted artifact from the recorded signal. The advantage of the technique is that it can be used on all stimulation artifact-contaminated electroneurophysiologic data provided that the artifact and the biopotential are non-overlapping. The technique does not require any estimation of the stimulus artifact shape or duration. With the developed technique, it is not necessary to record a pure artifact signal for template estimation, a process that can increase the complexity of experimentation. The technique also does not require the recording of any external hardware synchronisation pulses. The method avoids the use of analogue or digital filtering techniques, which endeavour to remove certain high frequency components of the artifact signal, but invariably have difficulty, resulting in the removal of frequencies in the same spectrum as the m-wave. With the new technique the signal is sampled at a high frequency to ensure optimum fidelity. Instrumentation saturation effects due to the artifact can be avoided with careful electrode placement. The technique was fully tested with a wide variety of electrical stimulation parameters (frequency and pulse width) applied to the common peroneal nerve to elicit contraction in the tibialis anterior. The program was also developed to allow batch processing of multiple files, using closed loop feedback correction. The two-stage peak detection artifact removal algorithm is demonstrated as an efficient post-processing technique for acquiring artifact free m-waves.

Decelerative changes in heart rate are associated with performance on tasks that assess intelligence.

Changes in heart rate, chin electromyographic (EMG) activity, and respiration rate were monitored during the performance of three tasks that are commonly employed to assess intelligence in human adults. Stimuli from the digit span subtest (Expt. 1) of the Wechsler scales of intelligence, the picture completion subtest (Expt. 2), and the picture arrangement subtest (Expt. 3) were employed. A 10-s warning preceding the onset of each stimulus was also used in each of the experiments. During all three tasks there was an initial increase in heart rate during the first 3-4 s of the warning signal, followed by a decrease in heart rate during the last 5-6 s of the warning signal. Mean heart rate during the 5 s immediately preceding the presentation of stimuli to which subjects gave correct responses was significantly lower than mean heart rate during the 5 s immediately preceding the presentation of stimuli to which subjects gave incorrect responses. In addition, mean heart rate during the 5 s immediately preceding the presentation of stimuli to which subjects gave correct responses decreased significantly below the pre-warning baseline level, whereas mean heart rate during the 5 s preceding the presentation of stimuli to which subjects gave incorrect responses did not decrease below the baseline level. The differential heart rate results for correct and incorrect responses were consistent across the three tasks. No significant changes in chin EMG and respiration rate were noted during any of the tasks. Relationships among heart rate, attention to environmental information, and the role of attention in measures of intelligence are discussed.

Data logging technology in ambulatory medical instrumentation.

This paper reviews the advancements made in ambulatory data logging used in the study of human subjects since the inception of the analogue tape based data logger in the 1960s. Research into the area of ambulatory monitoring has been rejuvenated due to the development of novel storage technologies during the 1990s. Data logging systems that were previously impractical due to lack of processing power, practical size and cost are now available to the practitioner. An overview of the requirements of present day ambulatory data logging is presented and analogue tape, solid-state memory and disk drive storage recording systems that have been described in the literature are investigated in detail. It is proposed that digital based technology offers the best solution to the problems encountered during human based data logging. The appearance of novel digital storage media will continue the trend of increased recording durations, signal resolution and number of parameters thus allowing the momentum gained throughout the last several decades to continue.

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 255 micros, 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 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 degrees owing to this increased pulse-width.

Finite state control of functional electrical stimulation for the rehabilitation of gait.

Finite state control is an established technique for the implementation of intention detection and activity co-ordination levels of hierarchical control in neural prostheses, and has been used for these purposes over the last thirty years. The first finite state controllers (FSC) in the functional electrical stimulation of gait were manually crafted systems, based on observations of the events occurring during the gait cycle. Subsequent systems used machine learning to automatically learn finite state control behaviour directly from human experts. Recently, fuzzy control has been utilised as an extension of finite state control, resulting in improved state detection over standard finite state control systems in some instances. Clinical experience over the last thirty years has been positive, and has shown finite state control to be an effective and intuitive method for the control of functional electrical stimulation (FES) in neural prostheses. However, while finite state controlled neural prostheses are of interest in the research community, they are not widely used outside of this setting. This is largely due to the cumbersome nature of many neural prostheses which utilise externally mounted gait sensors and FES electrodes. FES-based control of movement has been subject to the constraints of artificial sensor and FES actuator technologies. However, continued advances in natural sensors and implanted multi-channel stimulators are broadening the boundaries of artificial control of movement, driving an evolutionary process towards increasingly human-like control of FES-based gait rehabilitation systems.

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.

An investigation of the effect of electrode size and electrode location on comfort during stimulation of the gastrocnemius muscle.

The use of surface neuromuscular electrical stimulation (SNMES) in medicine is well established. However, discomfort has been identified as limiting the use of SNMES in these applications. This pilot study investigated the influence of various electrode sizes and their positioning on perceived pain and discomfort during neuromuscular electrical stimulation (NMES) of the gastrocnemius muscle using surface electrodes. This study formed part of a research project to develop a therapeutic device for calf muscle blood flow assist applications. Twelve healthy subjects (n=12) participated in this pilot study. Each participant attended the trial centre for testing which consisted of SNMES to four different electrode stimulation sites using two electrode sizes (round with areas 19.63 and 38.48 cm2). Comfort was assessed by asking the subjects to indicate the stimulation amplitude corresponding to the onset of discomfort (pain threshold) and the amplitude at which the discomfort became unbearable (pain tolerance). Of the four stimulation sites tested, two were deemed unsuccessful as it was very difficult to obtain a muscle contraction using these sites, while the remaining two sites elicited good muscle contraction. The most comfortable stimulation was achieved by placing the cathode electrode high on the calf, below the proximal end of the muscle heads and the anode electrode towards the end of the muscle belly and when the 19.63 cm2 electrodes were used at these sites (p=<0.001).

Does size matter? The impact of calf muscle volume on venous return in patients with venous leg ulcers.

OBJECTIVES: The calf muscle pump is recognized as an integral component of effective venous return from the lower limbs. The aim of this study was to determine if there is a correlation between calf muscle volume and venous blood flow among patients with venous leg ulcers. METHODS: Nine patients with venous leg ulceration were recruited for this study. These patients underwent haemodynamic testing using duplex ultrasound to measure peak venous velocities in response to voluntary maximum plantar flexion, with and without compression bandaging. Each patient then had magnetic resonance imaging (MRI) of the lower limbs. Calf muscle volume was calculated from the MRI images using a specially designed Matlab computer program to identify and count muscle pixels. Analyses applied Pearson's correlation coefficient to determine correlation between calf muscle volume and mean peak venous velocities in response to voluntary contraction. RESULTS: No correlation was seen between calf muscle volume and haemodynamic venous return in response to voluntary contraction, with or without compression bandaging. CONCLUSION: The volume of calf muscle available for promoting venous return alone may not be an accurate indicator of muscle functioning capability.