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Doctor of Philosophy with a Major in Bioengineering

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https://hdl.handle.net/1853/72221
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    Mechanical performance characterization of manual wheelchairs using robotic wheelchair operator with intermittent torque-based propulsion
    (Georgia Institute of Technology, 2020-12-06) Misch, Jacob P.
    The current manual wheelchair design process lacks consistent and objective connection to performance-based metrics. The goal of this research was to empirically assess over-ground manual wheelchair performances and identify important design trade-offs through the use of a robotic apparatus with a novel cyclic propulsion control method. This research had four specific aims: 1) to design, implement, and validate torque-based propulsion to emulate the intermittent human propulsion cycle with an existing robotic wheelchair tester, 2) to investigate the influence of incremental mass additions to the wheelchair frame on over-ground propulsion characteristics, 3) to demonstrably improve the performance of a representative high-strength lightweight wheelchair by leveraging existing component-level test results, and 4) to characterize the mechanical performances of representative folding and rigid ultra-lightweight wheelchair frames. The outcomes of this research include an objective, repeatable, and validated test method to assess over-ground performances of manual wheelchairs in realistic contexts of use, as well as insight on the mechanics of the system that were previously under-studied or confounded by variabilities within human subject testing. Controlled propulsion tests are used to identify differences between wheelchair configurations. The outcome variable of propulsion cost represents the energetic requirements of propelling each chair a given distance and has direct relevance to manufacturers, clinicians, and wheelchair users alike. Ultimately, these outcomes will inform clinicians and manufacturers about how configuration choices influence propulsive efforts, which can be used in turn to improve their classification techniques and existing design processes. This knowledge will additionally empower wheelchair users to make informed choices during the wheelchair selection process based on objective mechanical performance metrics.
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    Biomechanical responses to seated full body tilt and their relationship to clinical application
    (Georgia Institute of Technology, 2009-08-19) Sonenblum, Sharon Eve
    The overall goal of this research is to improve the use of seated tilt to increase function, health and quality of life for people using power wheelchairs. Specifically, the objective of this dissertation is to evaluate the biomechanical responses to seated full body tilt and their relationships to the actual use of tilt-in-space wheelchairs. In the first phase of this study, researchers remotely monitored how 45 fulltime power wheelchair users used their tilt-in-space systems. Participants spent an average of 12.1 hours in their wheelchair each day. They spent more than 2 hours seated at positions greater than 15° and performed tilts of 5° or greater every 27 minutes, but rarely performed tilts past 30°. Two distinct types of tilt behavior were identified: uni-modal (staying at a single position more than 80% of the time) and multi-modal (staying at a single position less than 80% of the time). Participants in the multi-modal group tilted significantly more frequently (4 times per hour) than the uni-modal group, and did not have a single typical position. Participants without sensation were more likely to exhibit uni-modal behavior. In the second phase of this study, researchers used interface pressure measurements and laser Doppler flowmetry to study changes in localized loading and superficial blood flow at the ischial tuberosities across different amounts of tilt. Eleven participants with spinal cord injuries were studied in a laboratory setting. Results showed that biomechanical responses to tilt were highly variable. Pressure reduction at the ischial tuberosity was not present at 15°, but did occur with tilts to 30° and greater, and could be explained by the tilt position and upright pressure. Unlike pressure, blood flow increased with all tilts from an upright position, but did not increase when tilting from 15° to 30°. Only 4 of 11 participants had a considerable increase (≥10%) in blood flow at 30° tilt, whereas 9 participants did during maximum tilt (i.e., 45°-60°). Based on the results of this study, tilting for pressure reliefs as far as the seating system permits is recommended to maximize the potential for significant blood flow increases and pressure relief.