Margit Gföhler

Dynamic simulation of FES-cycling: influence of individual parameters

Cycling by means of functional electrical simulation (FES) is an attractive training method for spinal cord injured (SCI) subjects. FES-cycling performance is influenced by a number of parameters like seating position, physiological parameters, conditions of surface stimulation, and pedaling rate. The objective of this paper was the determination of the influence of the most important parameters on optimal muscle stimulation patterns and power output of FES-cycling on a noncircular pedal path. The rider-cycle system was modeled as a planar articulated rigid body linkage on which the muscle forces are applied via joint moments and implemented into a forward dynamic simulation of FES-cycling. For model validation, the generated drive torques that are predicted by the simulation were compared to measurements with an individual paraplegic subject. Then, a sensitivity analysis was carried out to determine the influences of the most important parameters for surface stimulation of gluteus maximus, quadriceps, hamstrings, and peroneus reflex. The results show how optimal stimulation patterns and the expected mean active power output can be estimated based on measured individual parameters and adjusted geometry and stimulation parameters for a particular SCI-subject. This can considerably improve FES-cycling performance and relieve the patients by shortening the time that is necessary for experimental adaptation of the stimulation patterns.

Feedback control of arm movements using Neuro-Muscular Electrical Stimulation (NMES) combined with a lockable, passive exoskeleton for gravity compensation.

Within the European project MUNDUS, an assistive framework was developed for the support of arm and hand functions during daily life activities in severely impaired people. This contribution aims at designing a feedback control system for Neuro-Muscular Electrical Stimulation (NMES) to enable reaching functions in people with no residual voluntary control of the arm and shoulder due to high level spinal cord injury. NMES is applied to the deltoids and the biceps muscles and integrated with a three degrees of freedom (DoFs) passive exoskeleton, which partially compensates gravitational forces and allows to lock each DOF. The user is able to choose the target hand position and to trigger actions using an eyetracker system. The target position is selected by using the eyetracker and determined by a marker-based tracking system using Microsoft Kinect. A central controller, i.e., a finite state machine, issues a sequence of basic movement commands to the real-time arm controller. The NMES control algorithm sequentially controls each joint angle while locking the other DoFs. Daily activities, such as drinking, brushing hair, pushing an alarm button, etc., can be supported by the system. The robust and easily tunable control approach was evaluated with five healthy subjects during a drinking task. Subjects were asked to remain passive and to allow NMES to induce the movements. In all of them, the controller was able to perform the task, and a mean hand positioning error of less than five centimeters was achieved. The average total time duration for moving the hand from a rest position to a drinking cup, for moving the cup to the mouth and back, and for finally returning the arm to the rest position was 71 s.

Functional and usability assessment of a robotic exoskeleton arm to support activities of daily life

An assistive device for upper limb support was developed and evaluated in terms of usability, user satisfaction and motor performance on six end-users affected by neuro-motor disorders (three spinal cord injury; one multiple sclerosis; two Friedreichs ataxia). The system consisted of a lightweight 3-degrees-of-freedom robotic exoskeleton arm for weight relief, equipped with electromagnetic brakes. Users could autonomously control the brakes using a USB-button or residual electromyogram activations. The system functionally supported all of the potential users in performing reaching and drinking tasks. For three of them, time, smoothness, straightness and repeatability were also comparable to healthy subjects. An overall high level of usability (system usability score, median value of 90/100) and user satisfaction (Tele-healthcare Satisfaction Questionnaire - Wearable Technology, median value of 104/120) were obtained for all subjects.

MODELING OF ARTIFICIALLY ACTIVATED MUSCLE AND APPLICATION TO FES CYCLING

Functional Electrical Stimulation (FES) enables paraplegics to move their paralyzed limbs; the skeletal muscles are artificially activated. The purpose of this study is to establish a mechanical muscle model for an artificially activated muscle, based on a Hill-type muscle model. In comparison to modeling a physiologically activated muscle, for the artificially activated muscle, a number of additional parameters and their influence on the force generation has to be considered. The model was implemented into a forward dynamic simulation of paraplegic cycling. The stimulation patterns were optimized for surface stimulation of gluteus maximus, quadriceps, hamstrings, and peronaeus reflex. A simulation of a startup with 50% of maximum activation in the optimized stimulation intervals analyses drive torques and mean power per cycle and the resulting riding performance of the rider-cycle system. For validation of the simulation, the results were compared to measurements of the forces applied to the crank during steady-state cycling of a paraplegic test person.

Modular Instrumented Arm Orthosis with Weight Support for Application with NMES

Activities of daily living can be facilitated for individuals with motor impairment in the upper limb, if the arm weight is compensated by an orthosis. In this work we focused on the design of a modular arm orthosis with weight compensation. Additional brakes and angle encoders at each of the three available degrees of freedom prepare the orthosis for the application in combination with Neuromuscular Electrical Stimulation if the user’s residual motor capabilities are not sufficient to perform self induced arm movements. The prototype was tested by healthy subjects and showed promising results regarding functionality, weight and range of motion.

Technical Rebuilding of Movement Function Using Functional Electrical Stimulation

To rebuild lost movement functions, neuroprostheses based on functional electrical stimulation (FES) artificially activate skeletal muscles in corresponding sequences, using both residual body functions and artificial signals for control. Besides the functional gain, FES training also brings physiological and psychological benefits for spinal cord-injured subjects. In this chapter, current stimulation technology and the main components of FES-based neuroprostheses including enhanced control systems are presented. Technology and application of FES cycling and rowing, both approaches that enable spinal cord-injured subjects to participate in mainstream activities and improve their health and fitness by exercising like able-bodied subjects, are discussed in detail, and an overview of neuroprostheses that aim at restoring movement functions for daily life as walking or grasping is given.

A Systemic Mock Circulation for In-Vitro Testing of a Pneumatically Operated Left Ventricular Assist Device

Abstract This work presents the development of a systemic mock circulation loop designed for testing of an axial flow, pneumatically operated left ventricular assist device (LVAD). A simulation of the heart proximal systemic circulation has been implemented that resembles the environment in which the LVAD will be operating, from where a hydraulic system, with several reconsiderations, has been constructed. An alternative method for measurement of the pulsatile aortic flow is suggested. A significant match between the simulated and measured system responses is demonstrated which substantially simplifies the search for parameter sets that determine the hemodynamic behavior of the system. Due to a high degree of flexibility and a wide range of hemodynamic states that can be simulated, the presented mock circulation is suitable for in-vitro experiments with the LVAD.

Closed-loop helium circulation system for actuation of a continuously operating heart catheter pump

Background Currently available, pneumatic-based medical devices are operated using closed-loop pulsatile or open continuous systems. Medical devices utilizing gases with a low atomic number in a continuous closed loop stream have not been documented to date. This work presents the construction of a portable helium circulation addressing the need for actuating a novel, pneumatically operated catheter pump. The design of its control system puts emphasis on the performance, safety and low running cost of the catheter pump. Methods and results Static and dynamic characteristics of individual elements in the circulation are analyzed to ensure a proper operation of the system. The pneumatic circulation maximizes the working range of the drive unit inside the catheter pump while reducing the total size and noise production. Separate flow and pressure controllers position the turbines working point into the stable region of the pressure creation element. A subsystem for rapid gas evacuation significantly decreases the duration of helium removal after a leak, reaching subatmospheric pressure in the intracorporeal catheter within several milliseconds. Conclusions The system presented in the study offers an easy control of helium mass flow while ensuring stable behavior of its internal components.