Preface - 2001.11.20
Preface
Bioelectric phenomena have been a part of medicine throughout
its history. The first written document on bioelectric events is an ancient
Egyptian hieroglyph of 4000 B.C. describing the electric sheatfish.
Bioelectromagnetism is, of course, based strongly on the general theory of
electromagnetism. In fact, until the middle of the nineteenth century the
history of electromagnetism was also the history of bioelectromagnetism. From
the viewpoint of modern science, bioelectric phenomena have had scientific value
for the past 200 years. Many of the fundamental contributions to the theory of
bioelectromagnetism were made in the nineteenth century. Only in the past 100
years has bioelectromagnetism had real diagnostic or therapeutic value. As we
know, this is actually the case for most of medicine as well. During the past few decades,
the advances in the theory and technology of modern electronics have led to
improvements in medical diagnostic and therapeutic methods and, as a result,
bioelectric and biomagnetic phenomena have become increasingly important. Today
it is impossible to imagine a hospital without electrocardiography and
electroencephalography. The development of microelectronics has made such
equipment portable and has increased their diagnostic power. Implantable cardiac
pacemakers have allowed millions of people to return to normal life. The
development of superconducting technology has made it possible to detect the
weak biomagnetic fields induced by bioelectric currents. The latest advances in
the measurement of electric currents flowing through a single ion channel of the
cell membrane with the patch clamp have opened up completely new applications
for bioelectromagnetism. With the patch clamp, bioelectromagnetism can also be
applied to molecular biology, for instance, in developing new pharmaceuticals.
These examples illustrate that bioelectromagnetism is a vital part of our
everyday life. This
book first provides a short introduction to the anatomy and physiology of
excitable tissues, and then introduces the theory and associated equations of
bioelectric and biomagnetic phenomena; this theory underlies all practical
methods. The book then describes current measurement methods and research
results and provides an account of their historical development. The chapters dealing with the
anatomy and physiology of various organs are necessarily elementary as
comprehensive texts are available in these disciplines. Nevertheless, we wanted
to include introductory descriptions of the anatomy and physiology of neural and
cardiac tissues in particular so that the readers would have a review of the
structures and functions upon which electrophysiological models are based. We
have also introduced readers to the relevant vocabulary and to important general
references. The theory
of bioelectromagnetism deals mainly with electrophysiological models of
bioelectric generators, excitability of tissues, and the behavior of bioelectric
and biomagnetic fields in and around the volume conductors formed by the body.
Because of the nature of the bioelectric sources and the volume conductors, the
theory and the analytic methods of bioelectromagnetism are very different from
those of general electromagnetism. The theoretical methods are presented as a
logical structure. As part of this theory the lead field theoretical approach
has been emphasized. Besides the obvious benefits of this approach, it is also
true that lead field theory has not been discussed widely in other didactic
publications. The lead field theory ties together the sensitivity distribution
of the measurement of bioelectric sources, the distribution of stimulation
energy, and the sensitivity distribution of impedance measurements, in both
electric and magnetic applications. Moreover, lead field theory clearly explains
the similarities and differences between the electric and the corresponding
magnetic methods, which are tightly related by Maxwell's equations. Thus, all
the subfields of bioelectromagnetism are closely related. We have aimed to present
bioelectromagnetism as a theoretical discipline and, in later chapters to
provide much practical material so that the book can also serve as a reference.
These chapters also provide an opportunity to introduce some relevant history.
In particular, we wanted to present the theory and applications of
bioelectricity in parallel with those of biomagnetism to show that in principle
they form an inseparable pair. This gave us an opportunity to introduce some
relevant history so that readers may recognize how modern research is grounded
in older theory and how the fundamentals of many contemporary methods were
actually developed years ago. Our scope in the later chapters is necessarily
limited, and thus readers will find only an overview of the topics
(applications). Despite their brevity, these applications should help clarify
and strengthen the reader's understanding of basic principles. While better
measurement methods than those existing today will undoubtedly be developed in
the future, they will necessarily be based on the same theory and mathematical
equations given in this book; hence, we believe that its underlying "truth" will
remain relevant. This
book is intended for readers with a background in physics, mathematics, and/or
engineering (at roughly the second- or third-year university level). Readers
will find that some chapters require a solid background in physics and
mathematics in order to be fully understood but that most can be understood with
only an elementary grounding in these subjects. The initiative for writing this
book came from Dr. Jaakko Malmivuo. It is for the most part based on lectures he
has given at the Ragnar Granit Institute (formerly Institute of Biomedical
Engineering) of Tampere University of Technology and at Helsinki University of
Technology in Finland. He has also lectured on bioelectromagnetism as a visiting
professor at the Technical University of Berlin, at Dalhousie University in
Halifax, and at Sophia University in Tokyo, and has conducted various
international tutorial courses. All the illustrations were drawn by Dr. Malmivuo
with a microcomputer using the graphics program CorelDRAW!. The calculations of
the curves and the fields were made with MathCad and the data were accurately
transferred to the illustrations. The manuscript was read and
carefully critiqued by Dr. Milan Horá ek at Dalhousie University and Dr. David
Geselowitz of Pennsylvania State University. Their valuable comments are
acknowledged with gratitude. Sir Alan Hodgkin and Sir Andrew Huxley read Chapter
4. We are grateful for their detailed comments and the support they gave our
illustration of the Hodgkin-Huxley membrane model. We are grateful also to the
staff of Oxford University Press, especially Jeffrey House, Dolores Oetting,
Edith Barry, Roaalind Corman, and Alasdair Ritchie. Dr. Ritchie carefully read
several chapters and made detailed suggestions for improvement. We also thank
the anonymous reviewer provided by Oxford University Press for many valuable
comments. Ms. Tarja Erälaukko and Ms. Soile Lönnqvist at Ragnar Granit Institute
provided editorial assistance in the preparation of the manuscript and the
illustrations. We also appreciate the work of the many students and colleagues
who critiqued earlier versions of the manuscript. The encouragement and support
of our wives, Kirsti and Vivian, are also gratefully acknowledged. Financial support from the
Academy of Finland and Ministry of Education in Finland is greatly appreciated.
We hope that this book
will raise our readers' interest in bioelectromagnetism and provide the
background that will allow them to delve into research and practical
applications in the field. We also hope that the book will facilitate the
development of medical diagnosis and therapy.
Tampere, Finland
J.M.
Durham, North Carolina
R.P.
September 1993
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