Dissertation/Thesis Abstract

Control Methods for Improving Mobility for Persons with Lower Limb Paralysis
by Ekelem, Andrew, Ph.D., Vanderbilt University, 2018, 116; 13877286
Abstract (Summary)

Paralysis or paresis induced by upper motor neuron damage often leaves the lower limbs dysfunctional for basic activities such as walking and climbing stairs. Nearly five and one half million people in the United States, or approximately one in fifty, have some degree of paralysis [4]. The sustained duration and high level of impairment attributed to paralysis motivates research and development for technologies that alleviate the associated deficiencies.

The Indego exoskeleton (Parker-Hannifin, OH) and Chimera muscle stimulator are mechatronic devices developed for the reanimation of paretic limbs. Indego employs electric motors to actuate an orthosis for the restoration of controlled legged mobility, while the Chimera interfaces with the nervous system through transcutaneous electrical stimulation to administer functional electrical stimulation (FES). Described herein are rehabilitative intervention methods that: 1) enable paraplegics to ascend and descend stairs with a lower limb exoskeleton; 2) enhance exoskeleton assisted walking with supplemental FES to overcome moderate to severe spasticity; and 3) suppress clonus using FES during seated mobility. Chapter 2 describes the hardware developed for and/or employed in this research.

Chapter 3 describes the development and assessment of a controller for the Indego that enables paraplegics to ascend and descend stairs. The stair controller expands on a previous implementation of predefined trajectory tracking with an emulated passive state that enables gravity to extend the leg until it meets the next stair tread, then a trajectory is calculated in real-time to perform the intended task of stair ascent independent of step height. The ascent and descent controllers were evaluated by three paraplegic users who traversed numerous size stairs safely within two hours of tuning and training. The resulting controller enabled stair climbing with light exertion despite complete paraplegia.

Subjects with moderate to severe spasticity are typically ineligible for exoskeleton assisted gait due to pathological muscle activation that opposes exoskeleton mediated motion. A novel supplemental stimulation controller was implemented with the Indego exoskeleton and integrated Chimera stimulator in an effort to expand the inclusion criteria of exoskeletons to individuals with severe spasticity whereby FES enhances the synergy between muscles and motors. Chapter 4 explores the effects of spasticity and FES on robot mediated gait for paraplegics and describes the hybrid system’s controller that enabled two paraplegic individuals with moderate to severe spasticity to achieve substantially improved gait kinematics.

Mobility impairment of paraplegia can also entail clonus, a self-exciting reflex that can manifest as involuntary shaking of the ankle, a common pathology experienced during wheelchair propulsion. Chapter 5 expands the frontiers of clonus research with the first reported evaluation methods wheelchair clonus 2 and the efficacy of a novel FES intervention to treat pathological clonus during wheelchair propulsion over rough terrain. The clonus intervention was shown to robustly suppress clonus. The treatment may provide a noninvasive and economical alternative to invasive and commonplace pharmacological interventions.

The remainder of the introduction serves to provide background information pertaining to the nervous system, neurological impairment and the state of the technologies used to restore deficiencies that arise from comorbidities of paralysis.

Indexing (document details)
Advisor: Goldfarb, Michael
Commitee: Barth, Eric, Bastas, Gevasimos, Emfiger, William, Galloway, Kevin, Goldfarb, Michael, Zelik, Karl
School: Vanderbilt University
Department: Mechanical Engineering
School Location: United States -- Tennessee
Source: DAI-B 80/08(E), Dissertation Abstracts International
Subjects: Biomedical engineering, Mechanical engineering, Robotics
Keywords: Exoskeleton, Functional electrical stimulation, Rehabilitation robotics, Spinal cord injury
Publication Number: 13877286
ISBN: 9781392060599
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