P. A. Lynn

Miniature skin-mounted preamplifier for measurement of surface electromyographic potentials.

MEASUaEMENT of the surface electromyogram (e.m.g.) in normal subjects, or patients with motor disorders, demands ideally a recording system with the following properties : amplification and recording of the signals should be achieved without contamination by electrical interference or noise; the electrodes should be firmly a t tached to the skin and be imperceptible to the subject. In many recording situations the electrodes are connected to amplifying and recording equipment by wires which may be up to several metres in length. The small amplitude and high source impedance of the signals make such a system inherently vulnerable to pick up of mains hum and other electrical interference. Furthermore, microphonic artefacts can be generated in the wires during movements made by the subject. An alternative approach, which has been described by BASMAJIAN and HUDSON (1974), with reference to e.m.g, recordings using needle electrodes, is to amplify the e.m.g, signals at the electrode site before transmitting them along wires at relatively high-amplitude and low impedance levels. By this means the effect of electrical interference is substantially reduced, and microphonics are virtually eliminated. When surface e.m.g.s are to be measured it is convenient to combine the electrode pair and a differential ampiifier within a single module. A multichannel e.m.g, measurement system of this type has been designed for use in limband trunkmovement studies on normal subjects and stroke patients (Fig. 1). Each electrode-amplifier module is connected to the battery pack by four flexible wires~two for power supply, one for earth and one for signal output. The characteristics of the module are such that its operation and the transmisssion of the amplified e.m.g, signals are essentially independent of the type or length or wires used. One of the preamplifier modules is shown in Fig. 2. It measures 4 0 • 2 1 5 and comprises a miniature

Assessment of recovery of arm control in hemiplegic stroke patients. 2. Comparison of arm function tests and pursuit tracking in relation to clinical recovery

In a preliminary study, return of arm function in hemiplegic patients has been assessed for periods up to 64 weeks after stroke using two methods of testing. The first method concerns the performance of simple motor tasks involving the arm and hand. The second method is a pursuit tracking task using elbow movements. Patients were divided into two groups depending on whether they scored above 80% (Group I) or below 80% (Group II) on the first method at 16 weeks after stroke. When the two arm assessment methods were compared with clinical assessments for all the patients, general agreement was shown. Among Group I patients there was also significant agreement between the assessments; among Group II patients the agreement was poor. The two arm assessment methods, however, showed mutual agreement. In conclusion, both arm assessments provide a general prediction of the recovery of movement control of patients following stroke.

Some applications of human-operator research to the assessment of disability in stroke.

The present assessment of partially-paralysed victims of stroke is complicated by a lack of objective measurement. A tracking task of the type widely used to measure the performance of skilled operators in a manual control taks is used here to encourage controlled movement in the semiparalysed arm. Quantitative measures derived from such tests provide sensitive indication of trends in performance during rehabilitation, which cannot be detected by routine clinical examination.SommaireÀ présent, le domaine de l’évaluation des victimes partiellement paralysées par les attaques, est compliqué, faute de mesurage objectif. Ici, on se sert d’une ‘tâche de piste’, du type beaucoup utilisé pour mesurer la performance d’opérateurs spécialisés, qui font une tâche de contrôle manuelle pour encourager le mouvement contrôlé dans le bras demi-paralysé. Des mesures quantitatives obtenus par de telles épreuves, donnent une indication sensible des tendances de performance pendant la rééducation, qu’on ne peut pas détecter a l’examen clinique courant.

Transversal resonator digital filters: Fast and flexible online processors for biological signals

In a transversal resonator digital filter (t.r.d.f.) all multipliers are small integers. A wide range of filter characteristics may readily be programmed on currently available 16-bit mini- and microcomputers using elementary machine-code instructions. Online sampling rates up to a few kilohertz are possible. After discussion of the theoretical background, this paper includes a Fortran IV program to aid the design of low-pass, high-pass, and bandpass filters with raised-cosine rolloff characteristics and pure linear phase responses. The practical applications of the t.r.d.f. method are illustrated by designing a set of bandpass filters for e.e.g. analysis and matched filters for the detection of e.c.g. waveforms in noise.

Acquisition and analysis of electromyographic data associated with dynamic movements of the arm

A standardised movement task has been developed for an investigation of normal patterns of electromyographic (e.m.g.) activity. The subject is required to turn a cranked wheel with his arm which is supported horizontally in front of him. The movement is standardised by positioning the subject using anatomical landmarks and is defined by a single parameter, the angle of the wheel. The present report describes the acquisition and processing of e.m.g. signals from a group of arm and trunk muscles and shows that characteristic patterns of e.m.g. activity in relation to the position of the wheel can be defined. Further processing by computer may be used to obtain simple parameters for the comparison of patterns. Two normal subjects were tested in a number of sessions to demonstrate the repeatability of the processing techniques and results from a group of 20 normal subjects used to define average patterns. Preliminary results from stroke patients show significant departures from these normal patterns.

Identification of the stretch reflex using pseudorandom excitation: Electromyographic response to displacement of the human forearm

System identification techniques are applied to the human stretch reflex by crosscorrelating a random displacement of the forearm with a surface electromyographic signal obtained from biceps muscle. Since the random forcing function is too fast to be tracked by the subject, the resulting responses reflect components of the limb control system which are automatic. Clear responses are obtained for small displacement amplitudes, typically 0·5 mm at the wrist, with a test duration of about 1 minute. The results, which are highly reproducible, are compared with simulations based upon a linear model of the stretch reflex.

New approaches to modelling the disabled human operator.

Tracking tasks are increasingly used to quantify eye/limb co-ordination and control, especially in patients with neurological disorders. However, the usual measures of a patient’s performance take no account of the movement strategy employed. Two new approaches to the characterisation of tracking by disabled patients are therefore developed: one based on probabilistic modelling techniques, the other on the theory of fuzzy sets. Although applied here to hemiplegic stroke patients, the work is of potential interest for a wide range of human movement studies.

Frequency-modulation conversion for conventional tape recorders.

THE low-frequency content of many biological signals precludes direct recording on a conventional tape recorder. Although this can be overcome by use of an f.m. recorder of instrumentation quality, such a machine is always expensive and often has a performance and flexibility far in excess of requirements. This note describes an inexpensive f.m. conversion unit for recording up to three low-frequency (0-8 Hz) signals on one track of a conventional stereo tape recorder, leaving the second track free for (say) a voice log. The design could be quite easily modified to accommodate larger signal bandwidths. offset of the demodulators, and may also be recorded on short sections of tape to allow any slow temperature drift in the system to be recognised during playback.

Examination of stretch reflexes in biceps and triceps muscles of the human arm using pseudo-random stimulation

The reflex electromyographic responses to stretch of biceps and triceps muscles in the human arm have been examined using small-amplitude random displacements of the forearm, which produce flexion and extension at the elbow joint. The method of input-output cross-correlation allows the reflex system to be characterised in terms of its impulse response. Only those components of the output signals (biceps or triceps electromyogram) which are systematically related to the random muscle stretch contribute to the response, so that by using a task of sufficient duration a small response can be recovered from a substantial level of background noise. The approach offers several advantages: the use of small displacements for which the response appears linear, separation of automatic reflex components from voluntary components, and a potentially simple method for examining reflex responses in neurological patients.

Inexpensive multichannel analogue/digital conversion without timing skew.

THERE is a widespread requrement in medical laboratories to convert a number of relatively low-frequency bio; logical signals into digital form for subsequent off-line processing by digital computer. In such a situation it is common practice to use a single analogue/digital convertor (a.d.c.) and to accommodate the various channels by time-division multiplexing. However, the timing skew introduced by this method may well be unacceptable unless a fast, and therefore expensive, a.d.c, is purchased; and, in this case, storage buffers must be provided if samples from the various channels are to be presented sequentially to a relatively slow recording device such as a paper-tape punch. An alternative approach, which has been used to digitise up to three low-frequency signals obtained in human-movement studies, is described here. The input signals are sampled simultaneously, before transmitting the held values sequentially to a single a.d.c. This arrangement permits the use of a low-speed a.d.c., and eliminates timing skew in the digitised data.