[Dissertation] Quantification of Abnormal Coupling Between the Paretic Upper Arm and Hand of Individuals with Chronic Hemiparetic Stroke Using Neurophysiological and Biomechanical Measurements

Abstract (summary)

Following a stroke, two stereotypical movement patterns–the flexion and extension synergies–often emerge in the paretic arm. In these patterns, movements of the shoulder, elbow, and hand are coupled together, and the capacity to control the joints independently is substantially reduced, particularly in individuals with moderate-to-severe impairment. Such multi-joint coupling may reflect an underlying neural coupling between the joints due to an increased influence of bulbospinal pathways. The hand is often the most impaired portion of the arm and presents the biggest barrier to functional use of the arm during activities of daily living.

Although abnormal multi-joint coupling can be observed clinically after stroke, the majority of quantitative experimental work has examined the paretic hand in isolation from proximal joints, making it difficult to generalize results to hand behavior during functional arm movements. Additionally, new rehabilitation technologies for the paretic hand are continually introduced. However, their pace of development exceeds the current depth of understanding of paretic hand behavior during functional arm movements.

In a series of experiments, we attempted to bridge these gaps in scientific understanding by examining the effect of shoulder and elbow activation on voluntary and synergy-driven paretic hand behavior. To do so in a comprehensive way, simultaneous joint torques and surface electromyography (EMG) were measured from the entire arm. Additionally, time and frequency domain analysis of motor unit discharge was conducted on data decomposed from high-density surface EMG grids.

The overall finding of this dissertation is that activation of shoulder and elbow muscles in a variety of circumstances results in substantial synergy-driven production of wrist and finger flexion torques and flexor EMG. Furthermore, coupling at the hand increases with the descending motor drive required to complete a task. In addition, post-stroke individuals have little-to-no ability to lessen synergy-driven flexion by attempting to open the hand, demonstrating the degree to which they are constrained to the flexion and extension synergy patterns. Results are consistent with the hypothesis that the emergence of these patterns may be due to the increased influence of bulbospinal pathways. They also have implications for developing improved physical therapy interventions and rehabilitation technologies.

via Open Access Dissertation – ProQuest.