Development of magnetic defibrillator

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We developed"magnetic defibrillation"(MDF)by which ventricular fibrillation was converted to sinus rhythm in emergency. MDF can be realized if the magnetic field is strong and long enough to produce eddy currents for defibrillation. In this study key technology for MDF was developed as follows.(1)Effective stimulating coils were developed for magnetic excitation of cardiac muscle, and eddy currents produced by the coils were observed andcalculated. The coils were flat solenoids made from Be-Cu alloy, having a structure at satisfactory mechanical strength. Two coils were effectively combined to intensify stimulus fields in a target heart. The spatial distribution of the eddy current density was measured for a cylindrical volume filledwith saline solution. The result agreed well with the eddy current density calculated by the finite difference method. As a consequence, the present coil systemwas recognized for effective for MDF.(2)Magnetic nerve stimulation was experimentally and analyti … More cally studied in relation to the waveform effect in magnetic stimulation. In the experiment frog sciatic narves were stimulated by magnetic fields with damped sinusoidal oscillations. The threshold of nervous excitation depends on the cycle of the oscillation, and the one-cycle period of the stimulus is effective in exciting the nerve. In the analysis the myelinated nerve was stimulated by timevarying magnetic fields. The analysis on the waveform dependence agreed well with the experimental result.As a result, we determined effective waveforms in magnetic stimulation.(3)Magnetic heart stimulation was analytically studied on the excitation threshold for a variety of magnetic stimulus waveforms. A cell membrane of the ventricular muscle modeled by Beeler-Reuter was used. The threshold for the damped sinusoidal pulses depended on the number of cycles of the oscillation, resulting in the lowest threshold for one-quarter pulse. Applying double crowbar pulses considerably lowers the excitation threshold. Less