MODELING OF FATIGUE AND RECOVERY IN FES: CAN MUSCLE FORCE BE PREDICTED?
Joseph Mizrahi and Oron Levin (Department of Bio-medical Engineering, Technion IIT, Haifa, Israel)
Muscle fatigue is a limiting factor in Functional Electrical Stimulation (FES). In complete paralysis on-line monitoring of muscle fatigue during activation is of great interest, since sensory feedback from the muscles to indicate fatigue and prevent failure is missing. During interrupted stimulation, fatigue and recovery occur in sequence and the history-dependency of the muscle's response to FES becomes significant. This study presents a model by which the quadriceps muscle force in interrupted FES can be predicted.
The measured peak-to-peak amplitude of the EMG M-wave serves to evaluate the neural excitation of the muscle, which is further used to predict the activation of the contractile mechanism. The temporal metabolic shift obtained by 31p MR spectroscopy includes: inorganic phosphorus (Pi, H2PO4-); Creatine phosphate (PCr); and intracellular pH. These are used to define a fatigue function of the contractile element.
Feeding forward of the kinetics of either Pi or H2PO4- and of the temporal myoelectric data into high order model of the musculoskeletal system, result in an accurate prediction of the knee torque during primary fatigue (p < 0.001). The kinetics of the Pi also provides a reliable prediction of the torque during post recovery fatigue following rest durations of 30 sec to 1 min. It fails however, to predict recovery of the mechanical output of the muscle for rest duration longer than 3 min.
We suggest that full recovery of the muscle may not be attributed solely to the recovery of the above-mentioned metabolites and myoelectric measurements but also, to full recuperation of the ATP level and/or to the extracellular acid regulation within the muscle.
APPLICATION AND LIMITATION OF UPPER EXTREMITY FES
Yasunobu Handa (Tohoku University, Sendai, Japan)
Abstract: THIS paper describes clinical application and limitation of FES for the paralyzed upper extremities in the stroke and spinal cord injury (SCI) patients.
A percutaneous stimulation system with 30 output channels which we developed were used for the control of joint movements of the upper extremities.
Any joints of the paralyzed upper extremities including the shoulder in the stroke and SCI patients could basically be controlled for some of the activities of daily living (ADL) by the percutaneous FES system as far as severe denervation did not exist in the muscles to be controlled.
In C6 and C7 quadriplegic patient, control of prehension and release movement of the hand was practically available for ADL Simultaneous control of the wrist and hand was needed for the control of C5 patients. All of the joints of the upper extremity was required in C4 patients. In our C4 patients, however, shoulder girdle muscles were more or less denervated and, therefore, shoulder control was achieved by using an balanced forearm orthosis.
FES control of the paretic or paralyzed upper extremities in the hemiplegic patients also provided them with an assistant role in the upper extremity function for ADL.
However, multipurpose flexible control as healthy people cannot be achieved by the present computer system. In addition, most of the hemiplegic patients can use their uninvolved upper extremities. Therefore, determination of the purpose or goal of upper extremity FES is important for practical usage.