Applied Bioelectricity: From Electrical Stimulation to Electropathology

I first reviewed an earlier version of this book in 1992 for another journal, and strongly recommended it. One of the few criticisms I had was that the then title `Electrical Stimulation and Electropathology' did not really convey an impression of its contents. In particular, `electropathology', defined as an undesirable reaction or biological damage caused by the application of electricity to the body, was not a well-known term. The original title has now been relegated to a subtitle in this renamed and updated edition, although the new name still only hints at the wide scope, detailed content and general interest of this valuable book. The subject of the book is the reaction of biological systems, and in particular the human body, to electricity (and also to magnetic fields by virtue of their ability to induce currents). The book assumes a basic, as opposed to specialist, knowledge of both physics and physiology. Hence its contents should be amenable to a wide readership who have an interest in the effects of electricity on the human body, and especially to medical physicists. The author is well known for his own research work in the field of electrical stimulation, particularly in the areas of nerve fibre modelling and the perception of transient currents. He has enlisted the help of additional contributors to write specialist chapters on the electrical properties of the heart, skeletal muscle effects and high voltage and current injuries. The book opens with a chapter that introduces the main effects of electricity on the body, including sensory perception, muscular stimulation, thermal effects, stimulation with induced currents and electroporation. Interesting statistics on USA electrical fatalities (now sadly over ten years out of date) show a twofold decrease over the period 1975-87. This is followed by a clear and straightforward introduction to the concepts of conductivity, permittivity and the electrical properties of skin, which provides an admirable grounding in these key areas for the non-specialist. Body impedance data is discussed in some detail because of its obvious relevance to electric shock. A brief, and slightly bizarre, new section looks at the electrical impedance of domestic animals in the context of hazards to them from earth leakage currents; experimental data on their sensory responses is presented later. The author uses his own expertise to good effect in two chapters covering the electrical properties of excitable membranes and how they, and propagating action potentials, can be modelled. The responses of the models to a wide variety of stimuli, including monophasic, biphasic and repetitive pulses are described in detail and compared later with experimental data. The central part of the book provides a wealth of experimental data on the sensory and motor effects of a wide range of electrical stimuli, as diverse as the startle response to static discharges and ventricular fibrillation. Specialist background is provided by invited chapters on the electrical properties of the heart and on the response of skeletal muscle to electrical stimulation. Contained within the latter is an analysis of the hazards associated with electric shock and a detailed consideration of the `let-go' phenomenon. A short section on functional neuromuscular stimulation (or FES as it is perhaps more commonly known) provides an overview of some of the technical problems involved, including electrode design, selective recruitment of muscle fibres and damage to tissue at the electrode-tissue interface. Coverage of the effects on man of radiated low-frequency electric and magnetic fields has been expanded considerably from the previous version of this book. This reflects the continuing debate concerning the effects of power frequency (50/60 Hz) fields on man, the increasingly widespread use of MRI as an imaging modality with its attendant switched gradient magnetic fields, and the continuing growth in the use of local magnetic stimulation both as a diagnostic and as a therapeutic modality. The emphasis of the coverage is, quite properly, primarily on the physics involved; the temptation to speculate on possible deleterious effects based on unknown mechanisms is largely resisted. The induction of current flow in the body when exposed to low-frequency fields is described, along with the mechanisms by which such fields can be directly perceived, such as hair vibration and magnetophosphenes. In common with the general thrust of the book, much useful experimental data from the literature is presented, enabling the reader to get a quantitative feel for the subject. The section on local magnetic stimulation includes simplified examples of the circuit topography and of waveforms used in commercial devices along with some idealized head models to indicate the distribution of induced fields. Somewhat surprisingly the author proposes a novel stimulation configuration, based on two coils of unequal size driven by stimulators with different frequencies, as a significant advance in producing localized stimuli. The work has apparently been published only in abstract form and the conclusions, based upon a theoretical model of membrane non-linearities, has yet to be confirmed experimentally. If you have ever wondered why lightning (or other forms of high intensity electric shock) is bad for you, the penultimate chapter gives graphic information on the damage that can ensue. The path of the current through the body, and its thermal and neurological consequences, are discussed, and the lack of quantitative human data can perhaps be excused on this occasion! The book concludes with a review of the international safety standards that limit human exposure to electromagnetic fields and presents the rationale behind them. The author here addresses the vexed issue of the possible effects of chronic exposure to very low-level fields and presents the thermal noise argument as setting a possible lower level below which effects are unlikely to occur. Mechanisms of interaction are grouped into established (membrane depolarization, heating, etc.) and proposed (ion resonance, radical pair mechanisms, etc.), an approach that is useful in trying to make sense of the literature. I would have valued an attempt to further divide the `proposed' category into likely and unlikely, based on the author's wide experience of electromagnetic interactions with the body, but perhaps too much controversy would ensue. In summary, this is a splendid book. It is well written, clearly illustrated, covers a wide subject area in considerable detail and brings together a wealth of data from an often disparate literature. If you have a question about the effects of electricity on the body, this is a good place to look for the answer.