biomedical engineering: systems and signal analysis

Editorial

Biomedical engineering: systems andsignal analysis

The application of electrical engineering to problems in medi-cine and biology has developed over the last ten years to thepoint today where it has a significant role to play. This evolu-tion has been reflected in the steady development within theIEE of a body of expertise which eventually resulted in theformation of a Professional Group Committee. Within theCommittee (S9), this special issue is seen as an important stepin the acceptence of medicine and biology as a legitimateapplication of engineering science.

A number of names have been coined to describe thisapplication of engineering; some of those in common use are:bioengineering, biomedical engineering, and medical andbiological engineering. Underlying these names is a vast rangeof subjects of engineering activity. In selecting topics for thespecial issue the initial approach was to cover as wide a rangeof subjects as possible. The objective was to exclude paperswhich might contain a significant element of, for example,mechanical engineering, and to concentrate purely on thosepapers which were based firmly in electrical engineering. Eventhis strategy resulted in too wide a range of topics. It wastherefore decided to limit the scope of the special issue to thearea of systems and signal analysis.

All the papers which comprise the special issue describework which involves the use of digital computers. The applica-tion of systems and signals analysis techniques to the studyof medical and biological problems has from the beginningbeen related to the development of computer technology.Many of the early modelling studies of physiological systemsused analogue computers. Almost without exception thesestudies concentrated on the fundamental dynamics of thesystems under consideration, and consequently models werefrequently implemented on analogue computers. The use ofanalogue computers also meant that such studies were almostcarried out within a research environment with little oppor-tunity for relevant practical applications. Nevertheless, even atthis early stage, electrical engineering theory was makingimportant contributions to the understanding of biologicalprocesses. (An example is the use of transmission-line theoryin the analysis of neural conduction.) In many studies equiva-lent circuits were used directly. Similarly, such equivalentcircuits are still used to model blood flow in arteries and othervessels. As computational power has increased, with concomi-tant reductions in size and cost, many applications of engin-eering theory to biological problems which were hithertoimpossible are now conceivable. This is particularly true in thearea of biochemical dynamics. In some areas of physiologicalmodelling it is entirely feasible that within a few years modelsbased on microcomputers could be used routinely in theassessment of disease states.

An important difference in engineering applications tomedicine and biology, as compared with those in other areas, isthat the work is mainly analytical. Hence, within the field ofsystems and signals analysis the problems can often be particu-larly different because the system under analysis is nonlinearand nonstationary. It is therefore conceivable that techniquesdeveloped to study biological phenomena will ultimately beapplied in more traditional areas of electrical engineering.Indeed it could be argued that this is already the case.

The papers which form the special issue represent the workof engineers and physical scientists who are specialists in thefield. There is a considerable degree of international collabora-tion, indeed all the overseas contributors have collaboratedwith UK universities. (The USA and The Netherlands areparticularly important in this regard, and the contribution ofSouth America is also reflected.) The majority of researchstudies in bioengineering are currently undertaken within theframework of a multidisciplinary group which usually containsbasic medical scientists and clinicians. It is therefore hoped thatthe readership of this issue will include many outside the fieldof electrical engineering and because of this many of the paperscontained herein contain some material that is didactic.

Several of the papers reflect the direct application of com-puter modelling to the understanding of the disease processand clinical care. The automatic regulation of blood pressurehas been pioneered within the Department of Surgery at theUniversity of Alabama. The system, which is now used routinelyin the hospital, is developed from an identification study ofthe blood pressure control system. In spite of the fact over1700 patients have now been successfully treated, the under-lying engineering analysis of the system dynamics is stillcontinuing. The work presented here reflects some of the morerecent developments particularly in relation to the dynamicsof the controller. The diagnosis and treatment of arterial diseaseis another important aspect of cardiovascular medicine. Twopapers reflect the work currently being carried out. The firstconsiders the study of Raynaud's phenomenon — a debilitatingand painful clinical condition. Earlier work on the humanthermal system established that flutuations in blood flowcould be attributed to the spontaneous activity of a numberof physiological systems, and that certain of these spontaneousfluctuations could be entrained or synchronised to externalperiodic stimuli. The paper discusses the development of aclinical testing procedure based on entrainment phenomenawhich can detect differences between Raynaud's patients andnormal subjects. A second paper considers the extraction andcharacterisation of blood velocity waveforms downstream ofan arterial stenosis. The work described combines fluid dynamicsand time series analysis. Autoregressive spectral estimation isused in the study as an alternative to Fourier analysis; themethod, which originated in geophysics, is becoming increas-ingly important in the analysis of short and quasistationarytime series. Because of the importance of the method, a com-plete paper is devoted to the subject of short time series inbiomedicine.

Spectral analysis also forms the basis of a paper on the elec-tromyogram (EMG). The EMG can be used to monitor theperformance of skeletal muscle because the electrical activityin the muscle and its ability to produce a force are inter-related. Although the study of muscular contraction is a topicof considerable physiological importance, from an engineeringviewpoint it can form the basis for the design of powered arti-ficial limbs, and may be applicable to robotic research. Electri-cal activity in another physiological system, the cardiovascularsystem, is examined in terms of the frequency content ofelectrocardiographic waveforms and an analysis of the cardiacconducting system. In the first of these papers the use of phase

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information as a means of delineating deterministic and randomprocesses is rigorously examined. The generality of the phenom-ena indicates that the methods described could be significantin the wider context of signal analysis. The second paper de-scribes software and hardware methods developed to examinethe small electrical signals which occur in the specialisedcardiac conduction system and which co-ordinate and controlthe muscular activity of the heart.

Another important application of spectral analysis, epidemi-ology, is discussed in relation to a study of a multifocal measlesepidemic. Today the relevance of the subject to world healthis clearly recognised. The use of signal analysis methods allowsthe possibility of detailed spaciotemporal estimates of aparticular disease. In the work presented the weekly caseoccurrence data collected from 232 towns in the state of RioGrande do Sul is analysed to examine measles epidemics inthis area of Brazil. Sudden infant death syndrome (SIDS) isnot as common a childhood malady as measles but is neverthe-less extremely distressing for the parents. The cause of 'cot

deaths', as SIDS is colloquially known, is still unknown,although current opinion is that the condition arises frommalfunction of the cardiorespiratory control mechanisms. Anumber of studies of SIDS which involve the analysis oflarge quantities of respiratory and heart rate data are beingcarried out in the UK. The material presented here describes asystem which improves the rate of analysis of the respiratoryand electrocardiographic data which is central to such studies.The final paper considers the application of systems analysisto renal dialysis. The use of renal dialysis is widespread in theclinical context although the system dynamics are not clearlyunderstood. Identification of the system dynamics is thereforelikely to be of some importance in the design of treatment.

As previously stated, the aim in designing the specialissue has been to provide the reader with an ensemble ofpapers which cover one aspect of the application of electricalengineering to medicine and biology. It is hoped that youfind the papers interesting.

R.I. KITNEY

Richard Kitney was born in Glasgow,Scotland, in 1945. He received an M.Sc.degree in systems engineering from theUniversity of Surrey in 1969. Dr. Kitney'sdoctoral research was undertaken in theEngineering in Medicine Laboratory,Imperial College, from 1969-1972; theproject examined the dynamics of thehuman thermal control system. In 1972he joined the staff of the BiophysicsDepartment, Chelsea College, London

University, leaving in 1979 to return to Imperial College, wherehe is currently Head of the Engineering in Medicine Sectionin the Department of Electrical Engineering. His researchinterests involve the application of systems and signals analysistechniques to the study of biological control systems. Themajority of this work has concentrated on the dynamicbehaviour of the human cardiovascular system. One aspectof the research, the dynamics of heart rate variability on abeat by beat basis, led to the publication of a book by theOxford University Press, in collaboration with O. Rompelman.Dr. Kitney is also a Visiting Professor at the Georgia Instituteof Technology, where he is currently engaged in collaborativeresearch on blood flow disturbances created by vascularstenoses.

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