Thomas C. Bulea

Development of hybrid orthosis for standing, walking, and stair climbing after spinal cord injury

This study explores the feasibility of a hybrid system of exoskeletal bracing and multichannel functional electrical stimulation (FES) to facilitate standing, walking, and stair climbing after spinal cord injury (SCI). The orthotic components consist of electromechanical joints that lock and unlock automatically to provide upright stability and free movement powered by FES. Preliminary results from a prototype device on nondisabled and SCI volunteers are presented. A novel variable coupling hip-reciprocating mechanism either acts as a standard reciprocating gait orthosis or allows each hip to independently lock or rotate freely. Rotary actuators at each hip are configured in a closed hydraulic circuit and regulated by a finite state postural controller based on real-time sensor information. The knee mechanism locks during stance to prevent collapse and unlocks during swing, while the ankle is constrained to move in the sagittal plane under FES-only control. The trunk is fixed in a rigid corset, and new ankle and trunk mechanisms are under development. Because the exoskeletal control mechanisms were built from off-the-shelf components, weight and cosmesis specifications for clinical use have not been met, although the power requirements are low enough to provide more than 4 hours of continuous operation with standard camcorder batteries.

A Variable Impedance Knee Mechanism for Controlled Stance Flexion During Pathological Gait

A variable impedance knee mechanism (VIKM) has been developed as an orthotic intervention for individuals with weakened or paralyzed knee extensors. The purpose of the VIKM is to substitute for the function of eccentric quadriceps contraction to allow controlled levels of knee flexion during stance phase of gait and stair descent. The design concept, mechanism optimization, fabrication, bench testing, and initial results from walking tests with an able-bodied subject are reported. The VIKM utilizes a linear magnetorheological (MR) fluid damper with a four-bar linkage transmission to provide controllable resistance to knee motion. The design of the linkage enables the VIKM to provide large torques to resist motion at any knee angle. The prototype VIKM and full leg orthosis weigh 3.50 kg. The VIKM can provide a maximum of 64.5xa0N·m of torque in 35 ms. The average passive resistance is less than 4 N·m at an angular velocity of 210°/s. The ability of the VIKM to lock against knee flexion and allow knee motion under high loading is also demonstrated. Future work will focus on the development of a closed loop control system to automatically adjust the resistance level of the VIKM during walking and on clinical evaluation of the VIKM in pathological gait.

Sensor-Based Hip Control with Hybrid Neuroprosthesis for Walking in Paraplegia

The objectives of this study were to test whether a hybrid neuroprosthesis (HNP) with an exoskeletal variable-constraint hip mechanism (VCHM) combined with a functional neuromuscular stimulation (FNS) controller can maintain upright posture with less upper-limb support and improve gait speed as compared with walking with either an isocentric reciprocating gait orthosis (IRGO) or FNS only. The results show that walking with the HNP significantly reduced forward lean in FNS-only walking and the maximum upper-limb forces by 42% and 19% as compared with the IRGO and FNS-only gait, respectively. Walking speed increased significantly with VCHM as compared with 1:1 reciprocal coupling and by 15% when using the sensor-based FNS controller as compared with HNP with fixed baseline stimulation without the controller active.

Restoration of stance phase knee flexion during walking after spinal cord injury using a variable impedance orthosis

A hybrid neuroprosthesis (HNP) combines lower extremity bracing with functional neuromuscular stimulation (FNS) to restore walking function and enhance the efficiency of ambulation. This report details the development of a novel HNP containing a variable impedance knee mechanism (VIKM) capable of supporting the knee against collapse while allowing controlled stance phase knee flexion. The design of a closed loop, finite state controller for coordination of VIKM activity with FNS-driven gait is presented. The controller is verified in testing during able bodied gait. The improved functionality provided by this system has the potential to delay the onset of fatigue and to expand FNS driven gait to allow walking over uneven terrains and down stairs.

Stance controlled knee flexion improves stimulation driven walking after spinal cord injury

BackgroundFunctional neuromuscular stimulation (FNS) restores walking function after paralysis from spinal cord injury via electrical activation of muscles in a coordinated fashion. Combining FNS with a controllable orthosis to create a hybrid neuroprosthesis (HNP) has the potential to extend walking distance and time by mechanically locking the knee joint during stance to allow knee extensor muscle to rest with stimulation turned off. Recent efforts have focused on creating advanced HNPs which couple joint motion (e.g., hip and knee or knee and ankle) to improve joint coordination during swing phase while maintaining a stiff-leg during stance phase.MethodsThe goal of this study was to investigate the effects of incorporating stance controlled knee flexion during loading response and pre-swing phases on restored gait. Knee control in the HNP was achieved by a specially designed variable impedance knee mechanism (VIKM). One subject with a T7 level spinal cord injury was enrolled and served as his own control in examining two techniques to restore level over-ground walking: FNS-only (which retained a stiff knee during stance) and VIKM-HNP (which allowed controlled knee motion during stance). The stimulation pattern driving the walking motion remained the same for both techniques; the only difference was that knee extensor stimulation was constant during stance with FNS-only and modulated together with the VIKM to control knee motion during stance with VIKM-HNP.ResultsStance phase knee angle was more natural during VIKM-HNP gait while knee hyperextension persisted during stiff-legged FNS-only walking. During loading response phase, vertical ground reaction force was less impulsive and instantaneous gait speed was increased with VIKM-HNP, suggesting that knee flexion assisted in weight transfer to the leading limb. Enhanced knee flexion during pre-swing phase also aided flexion during swing, especially when response to stimulation was compromised.ConclusionsThese results show the potential advantages of incorporating stance controlled knee flexion into a hybrid neuroprosthesis for walking. The addition of such control to FNS driven walking could also enable non-level walking tasks such as uneven terrain, slope navigation and stair descent where controlled knee flexion during weight bearing is critical.

Sensor-Based Stance Control With Orthosis and Functional Neuromuscular Stimulation for Walking After Spinal Cord Injury

ABSTRACT An isocentric reciprocal gait orthosis (IRGO) was combined with a multichannel functional neuromuscular stimulation (FNS) in a prototype hybrid neuroprosthesis (HNP) to take advantage of each subsystem in providing stability and power for forward progression for walking in paraplegia, respectively. In this HNP, a hydraulic stance control knee mechanism (SCKM) was combined with a sensor-based FNS controller to provide knee stability during stance and foot-ground clearance during swing while minimizing knee extensor stimulation. The feasibility of reducing both the upper limb loading applied to a walking aid and muscle stimulation duty cycle was examined in an individual with paraplegia using this HNP. The SCKM supported the user during stance while the FNS controller deactivated stimulation to the knee extensor muscles once the knee was constrained in extension by the SCKM. The HNP reduced the average vertical upper limb forces on the walking aid by 36% and 17% as compared with walking with FNS only and IRGO, respectively. The HNP was also capable of reducing the stimulation duty cycle of the knee extensor muscles by 68% of the preprogrammed baseline levels used in FNS-only walking. Furthermore, the additional mass and internal friction of the SCKM was shown to have minimal effect on knee angle trajectory during swing. These results show that the HNP can significantly reduce the user’s upper limb loading and the amount of muscle stimulation, potentially enabling individuals with paraplegia to walk longer distances and with less effort than with either bracing or FNS alone.

Feasibility of a Hydraulic Power Assist System for Use in Hybrid Neuroprostheses.

Feasibility of using pressurized hydraulic fluid as a source of on-demand assistive power for hybrid neuroprosthesis combining exoskeleton with functional neuromuscular stimulation was explored. Hydraulic systems were selected as an alternative to electric motors for their high torque/mass ratio and ability to be located proximally on the exoskeleton and distribute power distally to assist in moving the joints. The power assist system (PAS) was designed and constructed using off-the-shelf components to test the feasibility of using high pressure fluid from an accumulator to provide assistive torque to an exoskeletal hip joint. The PAS was able to provide 21u2009Nm of assistive torque at an input pressure of 3171u2009kPa with a response time of 93u2009ms resulting in 32° of hip flexion in an able-bodied test. The torque output was independent of initial position of the joint and was linearly related to pressure. Thus, accumulator pressure can be specified to provide assistive torque as needed in exoskeletal devices for walking or stair climbing beyond those possible either volitionally or with electrical stimulation alone.

Design and Experimental Evaluation of a Vertical Lift Walker for Sit-to-Stand Transition Assistance

A walker capable of providing vertical lift support can improve independence and increase mobility of individuals living with spinal cord injury (SCI). Using a novel lifting mechanism, a walker has been designed to provide sit-to-stand assistance to individuals with partially paralyzed lower extremity muscles. The design was verified through experiments with one individual with SCI. The results show the walker is capable of reducing the force demands on the upper and lower extremity muscles during sit-to-stand transition compared to standard walkers. The walker does not require electrical power and no grip force or harness is necessary during sit-to-stand operation, enabling its use by individuals with limited hand function. The design concept can be extended to aid other populations with lower extremity weakness.