Digital controller design considering hardware constraints: application in a paraplegic patient

INTRODUCTION: A methodology was developed for implementing closed-loop control algorithms and for evaluating the behavior of a system, considering certain component restrictions used in laboratory implementation. METHODS: Mathematical functions representing a model of the biological system were used for knee extension/flexion movements. A Proportional Integral Derivative (PID) controller and another one using the root locus method were designed to control a patient’s leg position by applying functional electrical stimulation (FES). The controllers were simulated in Matlab and ISIS Proteus. After the simulations were performed, the codes were embedded in a microcontroller, and tests were conducted on a paraplegic volunteer. To the best of the authors’ knowledge, this is the first time that ISIS Proteus software resources have been used prior to implementing a closed-loop system designed to control the leg position of patients. RESULTS:This method obviates the application of initial controller tests directly to patients. The response obtained in the experiment with a paraplegic patient complied with the specifications set in terms of the steady-state error, the settling time, and the percentage overshoot. The proposed procedure was successfully applied for the implementation of a controller used to control the leg position of a paraplegic person by electrical muscle stimulation. CONCLUSION:The methodology presented in this manuscript can contribute to the implementation of analog and digital controllers because hardware limitations are typically not taken into account in the design of controllers.

Relationship between peak and mean amplitudes of the stimulating output voltage for functional control of the knee by spinal cord patients and healthy volunteers

INTRODUCTION: Functional electrical stimulation (FES) may evoke movements in people with movement impairments due to neurological lesion. The mean value of electrical current or voltage during FES depends on the stimulatory profile parameters. To investigate the relationship between peak and mean amplitudes of the stimulator output voltage while causing a knee extension angle change from 90º to 40º to choose the best and safest profile to be applied in people who have suffered a spinal cord injury. METHODS: Healthy (N = 10) volunteers and those with spinal cord injuries (N = 10) participated in this study. Each FES profile (P1, P2, P3 and P4) had 1-kHz pulses (100 µs or 200 µs on and 900 µs or 800 µs off) with burst frequencies of 50 Hz (3 ms on and 17 ms off) or 70 Hz (3 ms on and 11 ms off) and peak amplitudes set between 53-125V for healthy volunteers and 68-198 V for volunteers with spinal cord injury. RESULTS: The highest mean amplitude were obtained using a FES profile with active/total pulse period of 200 us/1000 us and burst frequency of 3ms/14ms. The best results of mean amplitude were observed using a FES profile duty cycle of 10% for pulses (100 µs/1000 µs) and 15% for bursts (3 ms/20 ms). CONCLUSION: The FES profile (100 µs - 50 Hz) seems to be the most suitable for both groups, inasmuch as it presents smaller mean amplitudes and peak amplitudes similar to other FES profiles.

Influência de parâmetros da estimulação elétrica funcional na contração concêntrica do quadríceps / Influence of functional electrical stimulation parameters in quadriceps concentric contraction

INTRODUÇÃO: Sistemas de estimulacão elétrica funcional (FES) são usados na pràtica clínica para o fortalecimento muscular, assim como para a recuperacão e preservacão funcional dos músculos enfraquecidos. Porém, uma das dificuldades encontradas na sua aplicacão é a falta de padrões adequados para a realizacão de um movimento pré-estabelecido, uma vez que os parâmetros da estimulacão (frequência, intensidade de corrente e duracão do pulso) são variados heuristicamente. O presente trabalho investigou a influência dos paraêmetros da FES usada no estabelecimento da posicão angular e forca produzida na extensão de joelho. MÉTODOS: O procedimento experimental foi dividido em duas fases chamadas Fase I e Fase II. A amostra total do estudo foi composta por 41 voluntàrios saudàveis de ambos os sexos (27 na Fase I e 14 na Fase II). Durante a Fase I cada voluntàrio foi estimulado com 18 combinacões diferentes de parâmetros para a FES, com o objetivo de determinar um modelo capaz de prever o movimento realizado para cada padrão de estimulacão. RESULTADOS: As diferentes duracões de pulso aplicadas não resultaram em alteracões significativas nos movimentos produzidos. Dentre os valores de frequência investigados, 50 Hz foi escolhida para a Fase II, por ter apresentado maior diferenca estatisticamente significativa para os valores de intensidade de corrente avaliados. Durante a Fase II, a intensidade de corrente da FES foi ajustada segundo um modelo linear estabelecido durante a primeira fase e que considerou características antropométricas dos sujeitos; encontrando-se um coeficiente de correlação r = 0,798 entre o ângulo pré-estabelecido e o ângulo alcancado. CONCLUSÃO: Este trabalho apresenta um modelo para a determinação de parâmetros de FES que permitem estabelecer variações angulares da articulação do joelho associadas à eletroestimulação. Considerando a frequência e a duração de pulsos constantes, se estima, usando uma equação de primeira ordem ...

INTRODUCTION: Functional electrical stimulation (FES) is used in clinical practice for muscle strengthening, as well as for functional recovery and preservation of weakened muscles. However, one of the problems in clinical application is the lack of adequate standards for determining the attainment of a predetermined movement, since the stimulation parameters are often adjusted heuristically. The present study investigated the influence of some parameters (frequency, current intensity and pulse duration) of the FES used to establish the joint angle and force produced in knee extension. METHODS: The experimental procedure was divided in two phases (Phase I and Phase II). The total sample included 41 healthy volunteers of both sexes (27 and 14 in Phase I and Phase II). During Phase I 18 profiles of FES were applied in the quadriceps muscle of subjects, changing the above-mentioned FES parameters. RESULTS: It was observed that the pulse duration of the electrical stimulation pulse did not exhibit significant relevance in the evoked movements. Among the discrete values of frequency investigated, the stimulation at 50 Hz was selected because it showed higher statistical significant difference considering the values of current intensity measured. During the Phase II, devoted to place the knee joint angle in a pre-determined value, the current intensity of the FES was adjusted according to the linear model established during the Phase I, which considered anthropometric characteristics of the subjects. In this Phase we found a correlation coefficient r = 0,798 between the pre-determined angle and the reached one. CONCLUSION: This paper presents a model for the determination of FES parameters for establishing angular variations of the knee associated with electrical stimulation. Considering frequency and pulse duration constants we estimate, using a first order equation and correlation coefficient of 0.72, the current intensity dependent of desired angle variation.

Functional Electrical Stimulation for Motor Function Rehabilitation (review) / 中国康复理论与实践

@# Functional electrical stimulation (FES) has already used in many aspects of rehabilitation medicine, including the rehabilitation of motor function especially after stroke or spinal cord injury. This paper reviewed the parameters for and the effects on motor function rehabilitation.

Implantable Functional Electrical Stimulation with Inductive Power and Data Transmission System / 영남의대학술지

Functional electrical stimulation (FES) has developed over the last 35 years to become a scientifically, technologically and clinically recognized field of interest in clinical medicine. FES has been applied to locomotion, grasping, ventilation, incontinence, and decubitus healing. However, all of these achievements illustrate the initial applications of FES; its true potential has not yet been realized. Recently, FES systems, which are miniaturized stimulation devices, have been utilized in the clinical setting. However, because the stimulating electrodes of the current FES devices are percutaneous electrodes, which are susceptible to wire breakage, and skin infection an implantable FES stimulating electrode has been introduced in the U.S. and Japan. In the present study, an external power supply method using radio frequency (RF) coupling and data transmission was developed for the control of the implantable FES device. In addition, we review the current understanding of FES devices and their application in clinical medicine.

The Optimal Electrical Stimulation Frequency to Improve the Muscle Endurance in Spinal Cord Injured Rabbit

OBJECTIVE: Clinical application of Functional Electrical Stimulation (FES) was limited due to the muscle fatigue phenomenon. This study was undertaken to find an electrical stimulation frequency, which optimally improves muscle endurance in spinal cord injured rabbit. METHOD: Fifteen rabbits were experimentally spinal cord injured at the T10 or T11 spinal cord level. Three kinds of stimulation frequency (10, 20, 40 Hz) and sham control stimulation were applied to the tibialis anterior muscle of each four group for 1 hour per day, for 2 weeks. Muscle fatigue index and peak torque were measured during electrical stimulation, and proportion of the type I musclefiber was measured at ATPase (pH 9.4) staining. RESULTS: Complete paraplegia was obtained in all 12 rabbits. Muscle fatigue index and peak torque were not changed after 2 weeks of electrical stimulation in all four groups. The proportion of the type I muscle fiber was reduced in all four groups after 2 weeks. However, 40 Hz stimulation group showed less decline in proportion of type I muscle fiber than control or 10 Hz group. CONCLUSION: High frequency electrical stimulation applied at an early stage of spinal cord injury is more effective in preserving muscle endurance than low frequency stimulation.

Ideal Carrier Waveform for Functional Electrical Stimulation in Upper Extremity

OBJECTIVE: This study was purposed to find the ideal carrier waveform in burst wave in Functional Electrical Stimulation (FES) for upper limbs after selection of proper site of electrode. METHOD: The 10 healthy men's non-dominant hands were studied. In 5 muscles (adductor pollicis, flexor digitorum sublimis, flexor pollicis longus, extensor digitorum communis and extensor pollicis brevis), the site where electric stimulus induced the best of purposed response was selected. A burst wave contains three carrier waveforms : sine, triphasic & rectangular. The amount of mean current was measured during key grip and open motion. Discomfort of subject was scored by three degree and compared among three waveforms. RESULTS: The amount of mean current in key grip and open motion is lowest at triphasic wave (31.3 mA, 50.5 mA) and highest at rectangular wave (79.4 mA, 82.1 mA). For the discomfort, rectangular waveform provoke the greatest discomfort in key grip and open motion. There is no statistical difference between sine and triphasic waveform. CONCLUSION: In FES of upper limbs, triangular wave can be an useful carrier waveform which require less amount of current for performing the same motion and less discomfort than rectangular or sine waveform.

The Effect of Functional Electrical Stimulation on Hemiplegic Shoulder Subluxation

OBJECTIVE: The purpose of this study is to evaluate the effect of functional electrical stimulation (FES) on hemiplegic shoulder subluxation in post-acute stroke patients. METHOD: Forty-four patients who had shoulder subluxation as a consequence of their first stroke were included and randomly assigned to either a control group (22 subjects) or a study group (22 subjects). Patients in both groups received physiotherapy and used an arm sling. The study group received, FES therapy to shoulder muscles (supraspinatus and posterior deltoid) for 30 minutes, five days a week for 6 weeks. The effect of FES therapy was evaluated by assessment of the severity of subluxation using radiologic measurements before and after treatment. RESULTS: 1) The severity of subluxation was significantly increased after 6 weeks (p0.05). 2) In the group of patients with early treatment (onset duration, less than 6 months), the control group showed a significant increase in subluxation (p<0.05), but the study group showed significantly reduced (p<0.05) shoulder subluxation after treatment period. 3) In the group of patients with mild shoulder subluxation before treatment (less than 1 finger breadth), the control group showed a significant increase in subluxation (p<0.05), but the study group showed significantly reduced (p<0.05) shoulder subluxation after treatment period. CONCLUSION: The FES therapy is effective in preventing and reducing the severity of hemiplegic shoulder subluxation in post-acute stroke patients, especially if duration since stroke onset was less than six months and the severity of subluxation before treatment was mild.

Fundamental Study for Rolling-Over Motion of the Body by Functional Electrical Stimulation (FES) / 영남의대학술지

A method to roll-over the paralyzed body by means of Functional Electrical Stimulation (FES) is considered. It is demonstrated that individual joint motions necessary for the rolling-over are realized by electrical stimulation. EMG measurements are also performed to analyze the cooperative activities of the muscles during rolling-over motion in a case where an upper extremity was used. These results of two experiments using normal subjects verifies the fundamental feasibility of body control by FES.