Power amplifier circuits for functional electrical stimulation systems

Abstract Introduction: Functional electrical stimulation (FES) is a technique that has been successfully employed in rehabilitation treatment to mitigate problems after spinal cord injury (SCI). One of the most relevant modules in a typical FES system is the power or output amplifier stage, which is responsible for the application of voltage or current pulses of proper intensity to the biological tissue, applied noninvasively via electrodes, placed on the skin surface or inside the muscular tissue, closer to the nervous fibers. The goals of this paper are to describe and discuss about the main power output designs usually employed in transcutaneous functional electrical stimulators as well as safety precautions taken to protect patients. Methods A systematic review investigated the circuits of papers published in IEEE Xplore and ScienceDirect databases from 2000 to 2016. The query terms were "((FES or Functional electric stimulator) and (circuit or design))" with 274 papers retrieved from IEEE Xplore and 29 from ScienceDirect. After the application of exclusion criteria the amount of papers decreased to 9 and 2 from IEEE Xplore and ScienceDirect, respectively. One paper was inserted in the results as a technological contribution to the field. Therefore, 12 papers presented power stage circuits suitable to stimulate great muscles. Discussion The retrieved results presented relevant circuits with different electronic strategies and circuit components. Some of them considered patient safety strategies or aimed to preserve muscle homeostasis such as biphasic current application, which prevents charge accumulation in stimulated tissues as well as circuits that dealt with electrical impedance variation to keep the electrode-tissue interface within an electrochemical safe regime. The investigation revealed a predominance of design strategies using operational amplifiers in power circuits, current outputs, and safety methods to reduce risks of electrical hazards and discomfort to the individual submitted to FES application.

Estimulação elétrica neuromuscular e estimulaçäo eletrotáctil na restauraçäo artificial da preensäo e da propriocepçäo em tetraplégicos / Neuromuscular electrical stimulation and electron-tactile stimulation in rehabilitation of artificial prehension and proprioception in tetraplegic patients

Este trabalho discute o uso da estimulação elétrica na reabilitação sensoriomotora de membros superiores paralisados. A restauração da função motora de preensão foi obtida pela aplicação da estimulação elétrica neuromuscular, em seqüência de ativação adequadas a realização de atividades do cotidiano como comer, beber, escrever e digitar. Uma luva instrumentalizada com sensores de força possibilitou quantificar o padrão de movimento exercido artificialmente. Esse sistema foi utilizado como alçã de realimentação para a restauração de uma propriocepção através da aplicação da estimulação eletrotáctil, possibilitando a evocação de sensações tácteis codificadas, relacionadas ao movimento artificial. A integração sensoriomotora se deu pela aplicação simultânea dos sistemas desenvolvidos, possibilitando desde a restauração de padrões funcionais de preensão, até o reconhecimento do padrão de movimento exercido através das sensações evocadas artificialmente.