Book Review: Gail. D. Baura: SYSTEM THEORY AND PRACTICAL APPLICATIONS OF BIOMEDICAL SIGNALS. IEEE Press Series in Biomedical Engineering. Wiley-IEEE Press, 2002, 440 pp., glossary, index.

The notions of signals and systems are immanent to each electrical engineering curriculum. Furthermore, a definite line of thought may be drawn from (electrical) circuit theory towards system(s) theory. It is, therefore, not surprising that system theory plays a central role in biomedical engineering methodology also. The idea of this book is to combine, and even to confront, basic theoretical notions of system theory with practical operation and performance of concrete realised medical instruments and systems in various clinical settings, in order to attain a kind of "down to earth" feeling of how those instruments function in praxis. This very ambitious goal has been attempted by Gail D. Baura, herself being trained in electrical and biomedical engineering.

The book has 18 chapters organised into four parts. In Part 1, filtering techniques for real-time applications are discussed, including frequency-selective filters, the pseudorandom binary sequence, adaptive filters, time-frequency representations, and time-scale representations. In Part 2, modelling techniques for real-time applications are discussed, such as autoregressive moving average with exogenous input model, the artificial neural network model, and the fuzzy model. In Part 3, linear and nonlinear compartmental models are discussed. These models are applied to physiologic data. In Part 4, algorithmic implementations and the need for more system theory in the medical instrumentation industry are highlighted. Chapters are organised into pairs, with the first chapter describing a system theory technology, and the second chapter describing an industrial application of this technology. Textbooks that may serve as references for each technology are recommended at the end of each theory chapter. Each application chapter also contains a history of the corresponding medical instrument, summary of appropriate physiological knowledge, discussion of the problem of interest and its previous empirical solutions, as well as a review of a solution that utilizes the theory in the previous chapter. As a result, the following practical (and diverse) bioengineering problems have been covered in the book: low flow rate occlusion detection using resistance monitoring, improved pulse oximetry, improved impedance cardiography, external defibrillation waveform optimisation, improved screening for cervical cancer, continuous noninvasive blood pressure monitoring, pharmacologic stress testing using close-loop drug delivery, compartmental modelling in development of antiobesity drugs, and need for more system theory in low-cost medical applications.

Among the references one may find a myriad of classical texts in the broad field covered, by such well-known names as: Oppenheim, Schafer, and Papoulis, for digital signal processing, Ljung, Soderstrom, and Stoica, for system identification, Zadeh and Kosko for fuzzy logic, and so on. This suggests the almost encyclopedic scope of this book, although written by a single author, which is to be congratulated for its ambitiousness. Dr. Gail Laura s bio, indeed, suggests an impressive bredth of coverage of the field.

Some particular observations follow. A quite unorthodox definition is to be found on the page 395: "system theory is the transdisciplinary study of the synthesis and design od systems, and the analysis of their performance"? I would put things the other way around; first is the mathematical theory, then comes the engineering design, and finally the analysis of performance of real systems in clinical settings. Nevertheless, Dr Baura's engineering and patents experience (as oposed to the experience of the writer of this review) should justify her the opportunity to express this new viewpopint; one should let the reader judge its appropriateness. While there are professionals trained in areas covered by particular chapters of this book, it is not easy to find a competent reader for the book as a whole. An interesting remark, then, is to be found on pp. 381, about a 30 year delay for digital signal processing (excluding frequency-selective filters) implementation in low-cost industrial monitors. The remark is true, however, it reflects a general inertia present in the spread of high technology implementations in consumer industries. The field of biomedical engineering as a whole has, traditionally, suffered the phenomenon that military and space research areas have been at the forefront of high technology development and applications, while biomedical engineering applications came as spin-offs decades later. A similar process is happening to the implementation of system theory, according to Dr. Baura.

This is an unorthodox book. From one side, classical system theory texts are usually mathematically biased while on the other, medical instrumentation books are mostly electronics instrumentation texts (circuit construction, amplifiers, filters, hardware and software aspects, digital signal processing implementation, embedded systems). The approach chosen by Dr. Baura is original and is to be congratulated for its ambitiousness. I would recommend the book to existing biomedical engineering experts working in environments where solving practical problems is the issue (such as in large hospitals, in development teams of biomedical instrument firms, etc). In addition, it could be very useful as a class text in a medical instrumentation series in a graduate biomedical engineering curriculum.

Prof. dr. Vladimir Medved