The passage of electric currents through tissues : (with particular reference to the percutaneous stimulation of human nerve and muscle)

Abstract

The physiologist enjoys a great advantage over the clinical neurologist in the electrical stimulation of muscle, in that he is generally able to kill or anaesthetise his experimental animal and to excise or expose the tissues to be stimulated. The electrical impedance of the preparation is predominantly resistive, and the question of the comfort and safety of the animal scarcely arises. The stimulation of human muscle, on the other hand, normally has to be carried out on ac cious subject, whose comfort and safety must be considered, by means of electric currents applied through electrodes placed in contact with the skin, which exhibits very complex electrical properties. Conflict arises between the requirements of technical accuracy and ease of interpretation of results on the one hand, and comfort and convenience on the other. This thesis represents an attempt to assemble as much as possible of the information required for intelligent solution of the problems encountered in the percutaneous stimulation of muscle. Part I of the thesis reviews published information on nerve, muscle and denervated muscle, the electrical impedance of tissues, and diagnostic and therapeutic stimulation of muscle. Part II describes the author's personal research into the electrical impedance of the body, the interplay between body impedance, stimulator impedance and the electrical excitability characteristics of nerve and muscle, and the influence of these various factors on stimulator performance. In view of the variety of topics involved, the material has been arranged in separate more or less self-contained sections, including discussion of the implications of the results in each section. Technical details of the main electronic devices used are given in the Appendix, (Part III, together with details of the various mathematical analyses and calculations. Part of the work on which this thesis is based was carried out during the tenure of a temporary lectureship in Biophysics donated by the late Sir David Russell, to whom the author is deeply indebted. The author is also greatly indebted to Professor A. E. Ritchie for creating the circumstances which made this work possible, for permitting the author access to unpublished material, and for his patient encouragement and support of this protracted project; to Dr J. Crossland for assistance in the translation of German texts, and to Mr E. Carstairs for advice and assistance in devising the photographic techniques used in recording and reproducing the experimental results.