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Editorial: Biomedical engineering and electrophysiology

The human body conveniently provides much electrical data about the way it functions, and it can use electrical stimulation to replace or supplement fimetions no longer working correctly or adequately. Electrophysiology is the term used to encompass all electrical aspects of physiology, and its study covers the instrumentation and techniques to pick up the electrical signal from the body, process the data, provide diagnostic information, tailor stimulation techniques for specific functions, and monitor that these functions are being provided. Medical engineers have developed, and continue to research, many of the techniques used in the field of electrophysiology.

This extra issue of Medical and Biological Engineering and Computing is possible only because of the large number of research papers submitted in this area. The reputation of the Journal is still stretching to the limit our ability to publish papers quickly. Therefore, to enable more papers to be published this year and to speed up publication times, this extra issue is being produced. From the papers submitted, those with an electrophysiology theme have been drawn together. All papers published in this issue were submitted in the normal way and have been subjected to the full standard peer review process.

The themes covered include electromyography, evoked response measurement, electrode techniques, electrical stimulation of muscle and nerve, electrical impedance m~tsurements, and signal analysis in electrophysiology. No specific grouping of electrocardiography measurements has been made, as this area was covered in the extra issue published last year as Electrocardiography, myocardial contraction and blood flow (MURRAY, 1994). There are, however, some examples of signal analysis in electrocardiography included in the signal analysis subsection.

Electromyography continues to be important as it can be used to diagnose many muscular disorders. In this issue, papers cover the themes of non-invasive muscle characterisation during sustained muscle contraction, conduction velocity estimation under difficult conditions, and the assessment of respiratory activity in neonates from an analysis of the diaphragmatic electromyograrn. Evoked potentials from a variety of stimulation sources can also provide valuable clinical information, and as they require signal averaging over many stimulations, any improvement or simplification of the techniques would be valuable. Research here covers a new method of recovering evoked potentials, and the detection of changes in evoked potentials due to cerebral artery occlusion or ischaemia. No matter where the electrical signals are to be picked up from the body, improvements in electrodes would be welcome. All too often the electrode contact is considered unimportant, and yet it is often the source of much noise. One paper in this issue considers improvements in electrode technology.

Medical engineering is heavily involved in all aspects of functional nerve stimulation or in the wider areas of clinical stimulation. Although progress has been made in these areas, much further work is needed. Several papers are included on electrical stimulation. A better knowledge of the current distribution under the electrode could result in improved stimulation techniques. Multiple electrodes may have value, and one paper covers the uses of a dual-anode electrode stimulator and another a multi-electrode array for more selective stimulation. The effects of prolonged stimulation are also researched to note the effect of frequency and amplitude on possible neural damage. Human mobility can be aided by stimulation, and the optimisation of initial stimulation parameters and parameter adaptation is investigated for paraplegic gait, and the mechanical properties of human joints assessed using stimulation techniques.

Changes in electrical impedance, such as with respiration, have proved useful for monitoring. Papers included in this issue use electrical impedance measurement techniques to assess the pulsatile component of cerebral circulation, and the effects of disease on skin admittance.

Signal analysis is an area of major bioengineering research, and although most papers in this issue include aspects of signal analysis, a separate subsection has been allocated for specific signal analysis techniques related to electrophysiology. Papers cover improving coding for signal compression using a Markov process: mapping action potential wavefronts through cardiac or smooth muscle; wavelet transform analysis in the terminal part of the signal averaged electrocardiogram; minimising the problem of electro-oculogram artefact on the electroencephalogram; an adaptive technique for fitting time-dependent autoregressive moving-average models to non-stationary signals with applications demonstrated in electroencephalography and in laser Doppler analysis; and classification of electro- myogram da~ using neural network models.

Electropbysiology techniques are vital for clinical diagnosis and therapy. Biomedical engineers have an important role to play in this area. This special issue has concentrated on some of the current research. Obviously, there is much other research being conducted, but this issue should give an interesting snapshot of current progress, and hopefully stimulate further bioengineering progress.

Reference

MURRAY, A. (Ed.) (1994): ' E l ~ i o g r a p h y , myocardial contraction and blood flow,' Med Biol. Eng. Comp., 32, (4), pp. S1-S184

ALAN MURRAY DEPUTY EDrrOR and Editor of this Special issue

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