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Electrostimulation by time-varying magnetic fields

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Abstract

Despite several investigations and publications on possible effects due to time-varying magnetic fields, the question remains as to the magnitude of the field, or its derivative with respect to time, that is capable of stimulating the human heart. It is quite surprising how little information on cardiac stimulation has entered the discussion to date. If the law of induction and the fundamental law of stimulation, both in their field forms, are combined, the result is quite different from what has been published: (1) It is the amplitude of the gradient field that is responsible for stimulation and notdB/dt. (2) The shape of the time-varying pulse has no influence on stimulation but only its mean value. (3) Owing to different rheobase and chronaxie values for cardiac tissue and peripheral nerves, the threshold for magnetostimulation of the myocardium is up to 200-fold higher than that for nerves. These results allow for the determination of safety limits that are certainly above those proposed to date. Based on these limits, technological advancement can be achieved without neglecting the patient safety requirement.

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  1. Justus-Liebig-University, Giessen, Germany

    W. Irnich

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Address for correspondence: Department of Medical Engineering, Justus-Liebig-University, Gießen, Aulweg 123,35392 Gießen, Germany. Additional reprints of this chapter may be obtained from the Reprints Department, Chapman & Hall, One Venn Plaza, New York, NY 10119.

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Irnich, W. Electrostimulation by time-varying magnetic fields. MAGMA 2, 43–49 (1994). https://doi.org/10.1007/BF01709799

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  • DOI: https://doi.org/10.1007/BF01709799

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