Clinical Physiological Investigations to Evaluate the Effects of Repetitive Peripheral Magnetic Stimulation (RPMS) – Experimental Set-Ups

Abstract

RPMS is an innovative approach for the treatment of central paresis, e.g., after a stroke, by inducing muscle contractions. For nerve fiber depolarization, a high time and spatially varying magnetic field impulse is applied. This impulse is repeated with a frequency of 20Hz. To evaluate the different effects of RPMS, 5000 stimuli with a break of 2 seconds after every 30 impulses are applied. The concept is based on the activation of a reorganization process in the CNS due to the induced proprioceptive inflow to the CNS. The presented poster shows an overview of the technical approaches and experimental set-ups in order to evaluate the RPMS-dependent effects: 1) Impulse Response: In order to compare the basic effect of magnetic stimulation with the well known electric stimulation, the contraction over time induced by a single stimulation impulse is presented. 2) Index of Spasticity: During a voluntary extension of the index finger, the EMG of the paretic finger extensors and spastic finger flexors as well as the displacement (accelerometer) are registered. This shows a clear decrease of the flexor activity (spasticity) and an increase of the displacement even though the extensor activity is decreased. 3) Video and EMG: To investigate the effect of RPMS concerning goal directed movements a coordinated registration of video data (20 pictures per s) and EMG (6250 samples per s) has been developed and used 4) Cognition: The aim of this experimental set-up is to investigate the improvement in body scheme by RPMS. The position sense under static conditions and target movement by non-visual control are registered. The difference between the angle of the elbow joint and the position of a reference point represents the accuracy of the subject's position sense. 5) Muscle tone: A torque motor is used to elicit a passive movement of the relaxed forearm. To differentiate between viscoelasticity and tonic activity slow movements of 2.5 deg. per s. are applied while the EMG of the biceps and the triceps is recorded together with the torque in the elbow joint. The understanding of these effects is the basis for the development of a non-linear adaptive closed loop control (see separate poster), which is used to induce coordinated movements. These movements elicit a near physiological proprioceptive inflow in order to facilitate the reorganization in the CNS.