PROGRAM | Biomedical Engineering

By: Margo Donlin Chair: Jill Higginson

ABSTRACT

Stroke often causes significant impairments to mobility and function, frequently characterized by decreased walking speed and propulsion. Standardized rehabilitation programs do not address individual impairments and are not robust to the heterogeneity of the post-stroke population, resulting in rehabilitation protocols that work for some people and not for others. However, fully individualizing rehabilitation protocols for each person would not be time- or cost-effective, motivating the need to develop novel customizable rehabilitation protocols. The overall purpose of this dissertation was to develop and evaluate novel adaptive rehabilitation methods to improve propulsion after stroke. This was accomplished through experimental analyses of healthy and post-stroke gait as well as design and implementation of a novel rehabilitation device.

In Aim 1, we evaluated the stride-to-stride variability of young adults while walking on a novel adaptive treadmill that changes speed in real-time based on measured gait parameters. We recruited and tested a sample of 22 young healthy individuals and compared variability between the adaptive and fixed-speed treadmills. This study found that stride-to-stride variability of spatiotemporal and propulsive measures differs between adaptive and fixed-speed treadmills. Variability on the adaptive treadmill was similar to previously established overground variability, indicating that adaptive treadmill walking may be more like overground walking. Additionally, increases in propulsion at one stride were more likely to persist for subsequent strides on the adaptive treadmill, suggesting that the adaptive treadmill may be beneficial for increasing propulsion during post-stroke rehabilitation. While the adaptive treadmill is a useful tool for physical therapy and rehabilitation, some stroke survivors may have more limited function and need additional assistance.

In Aim 2, we developed and evaluated a novel adaptive functional electrical stimulation system that was used in conjunction with the adaptive treadmill. This adaptive functional electrical stimulation system updated stimulation amplitudes at every stride based on measured gait parameters to form a fully adaptive rehabilitation environment when combined with the adaptive treadmill. In a validation study with individuals post-stroke, stimulation amplitudes were adjusted with over 99% accuracy and stimulation was delivered with over 90% temporal accuracy, thus reducing the frequency of erroneous stimulation deliveries. We found that the adaptive functional electrical stimulation system performed well across variable post-stroke gait patterns and delivered stimulation with a high degree of accuracy.

Finally, in Aim 3, we compared the performance of the novel adaptive functional electrical stimulation system to the existing functional electrical stimulation system. We recruited and tested 24 individuals with chronic post-stroke hemiparesis who completed six trials across two treadmill conditions and three stimulation conditions. Walking speed was statistically significantly faster on the adaptive treadmill compared to the fixed-speed treadmill. However, there were no significant differences in walking speed, propulsion, or dorsiflexion angle between the stimulation conditions. Some individuals benefitted greatly from the stimulation while other individuals did not see the same benefits, further reflecting high variability and heterogeneity as a hallmark of stroke survivors.

Overall, this dissertation represents an important step in the process of developing post-stroke rehabilitation protocols that work for all participants. Future work should further analyze individual subject behavior to determine which individuals will respond to which rehabilitation protocol and continue working toward effective rehabilitation methods for all stroke survivors.

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