G.M. Lyons

A review of gas sensors employed in electronic nose applications

This paper reviews the range of sensors used in electronic nose (e‐nose) systems to date. It outlines the operating principles and fabrication methods of each sensor type as well as the applications in which the different sensors have been utilised. It also outlines the advantages and disadvantages of each sensor for application in a cost‐effective low‐power handheld e‐nose system.

A Review of Approaches to Mobility Telemonitoring of the Elderly in Their Living Environment

Rapid technological advances have prompted the development of a wide range of telemonitoring systems to enable the prevention, early diagnosis and management, of chronic conditions. Remote monitoring can reduce the amount of recurring admissions to hospital, facilitate more efficient clinical visits with objective results, and may reduce the length of a hospital stay for individuals who are living at home. Telemonitoring can also be applied on a long-term basis to elderly persons to detect gradual deterioration in their health status, which may imply a reduction in their ability to live independently. Mobility is a good indicator of health status and thus by monitoring mobility, clinicians may assess the health status of elderly persons. This article reviews the architecture of health smart home, wearable, and combination systems for the remote monitoring of the mobility of elderly persons as a mechanism of assessing the health status of elderly persons while in their own living environment.

The use of accelerometry to detect heel contact events for use as a sensor in FES assisted walking

Current sensors for the control of functional electrical stimulation (FES) assisted walking in hemiplegic individuals are not wholly satisfactory, as they are either not implantable or ineffectual in the detection of heel contact events. This study describes the use of an accelerometer placed on the trunk to detect heel contact events of both legs based on the examination of the anterior-posterior horizontal acceleration signal. Four subjects wore an accelerometer over their lumbar spine. Footswitches placed on the sole of one foot recorded the heel contact and heel off times for that foot. The acceleration signal was reduced to a series of pulses by studying the negative-positive changes in acceleration. It was found that there was approximately a 150 ms delay between heel contact and the negative-positive change in acceleration. This delay was consistent across different walking speeds, but was different between subjects and when hemiplegic gait was simulated. Therefore, accelerometers placed on the trunk are valid sensors for the detection of heel contact events during FES assisted walking.

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.

Application of higher order statistics techniques to EMG signals to characterize the motor unit action potential

The electromyographic (EMG) signal provides information about the performance of muscles and nerves. At any instant, the shape of the muscle signal, motor unit action potential (MUAP), is constant unless there is movement of the position of the electrode or biochemical changes in the muscle due to changes in contraction level. The rate of neuron pulses, whose exact times of occurrence are random in nature, is related to the time duration and force of a muscle contraction. The EMG signal can be modeled as the output signal of a filtered impulse process where the neuron firing pulses are assumed to be the input of a system whose transfer function is the motor unit action potential. Representing the neuron pulses as a point process with random times of occurrence, the higher order statistics based system reconstruction algorithm can be applied to the EMG signal to characterize the motor unit action potential. In this paper, we report results from applying a cepstrum of bispectrum based system reconstruction algorithm to real wired-EMG (wEMG) and surface-EMG (sEMG) signals to estimate the appearance of MUAPs in the Rectus Femoris and Vastus Lateralis muscles while the muscles are at rest and in six other contraction positions. It is observed that the appearance of MUAPs estimated from any EMG (wEMG or sEMG) signal clearly shows evidence of motor unit recruitment and crosstalk, if any, due to activity in neighboring muscles. It is also found that the shape of MUAPs remains the same on loading.

Long-term telemonitoring of mobility trends of elderly people using SMS messaging

A telemonitoring system, based on short message service (SMS), has been developed to remotely monitor the long-term mobility levels of elderly people in their natural environment. Mobility is measured by an accelerometer-based portable unit, worn by each monitored subject. Mobility level summaries are transmitted hourly, as an SMS message, directly from the portable unit to a remote server for long-term analysis. Each subjects mobility levels are monitored using custom-designed mobility alert software, and the appropriate medical personnel are alerted by SMS if the subjects mobility levels decrease

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.

Validity of the prosthetic activity monitor to assess the duration and spatio-temporal characteristics of prosthetic walking

The prosthetic activity monitor (PAM) is an instrument to assess over the long-term the duration and spatio-temporal characteristics of walking of amputees, during normal daily life. In this study, the validity of PAM-derived measurements was investigated. Twelve transtibial amputees performed an activity protocol, consisting of stationary and walking activities, and activities associated with nonlocomotor movements. The protocol also included potential sources of error and activities assumed to be prone to misdetection. Measurements consisted of the PAM and video recordings. Agreement between video analysis and PAM output was the main outcome measure. The PAM generally correctly classified stationary activities (100% inactive, 0% active, 0% locomotion), nonlocomotor activities (45% inactive, 55% active, 0% locomotion) and walking activities (0% inactive, 1.8% active, 98.2% locomotion). When walking, the number of strides taken was slightly underestimated (-1.0%). The underestimation of distance travelled (-6.2%) and walking speed (-5.8%) was greater. The agreement with video output decreased when the PAM was misaligned, when persons walked at a speed below the defined minimum speed, and when persons walked with crutches. The PAM provides valid data on activity classes and number of strides. Although the majority of the distance data was satisfactory, in some cases considerable differences were found between the PAM and the video data. The impact of alignment, walking speed, and use of assistive devices on the PAMs operation should be considered.

The development of a potential optimized stimulation intensity envelope for drop foot applications

An optimized stimulation intensity envelope for use in hemiplegic drop foot applications has been developed. The traditional trapezoidal stimulation intensity approach has been examined and found to be inconsistent with the muscle activity patterns observed in healthy gait and therefore unsuitable. Experimental functional electrical stimulation (FES)-elicited tibialis anterior (TA) electromyography (EMG) data was taken over the ankle range of interest (occurring during active dorsiflexion and loading response) while also taking into account the type of TA muscle contraction occurring (concentric, eccentric, and isometric) and the speed of hemiplegic ankle joint rotation. Using the processed data, a model of normalized EMG versus pulsewidth was developed. Implementation of this model showed the unsuitability of the trapezoidal approach in the reproducing of a natural EMG profile. An optimized stimulation intensity profile is proposed which is expected to accurately reproduce the natural TA EMG profile during gait.

A computer game-based EMG biofeedback system for muscle rehabilitation

The development and clinical evaluation of a computer game-based EMG biofeedback system is described, whose purpose is to enable or disable the playing of a computer game by a user, based on the intensity of muscle activity recorded from the muscle of interest. The game can be used in the development of increased muscle function or in the suppression of muscle spasticity. Biofeedback is provided as the system allows the subject to control game play using muscle contraction/relaxation. A built-in calibration mechanism caters for varying muscle sizes and strengths. Clinical evaluation of the biofeedback system, for muscular rehabilitation, has been carried out on 8 adult subjects with cerebral palsy over a four-week period.