Medical Bionics - Theses
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ItemThe utility of an instrumented pull test to evaluate postural instability in Parkinson’s disease( 2019)Postural instability is one of the cardinal symptoms of Parkinson’s disease (PD). Postural instability can present on diagnosis, and commonly becomes more prominent with disease progression, resulting in subsequent falls and diminished quality of life. The treatment of postural instability is challenging, as it is often refractory to management with levodopa and deep brain stimulation of conventional targets such as the subthalamic nucleus. To assess postural instability, the most commonly used measure in the clinical setting is the pull test according to item 30 of the Unified Parkinson’s disease rating scale (UPDRS), where an examiner performs a brisk backward tug at the patient’s shoulder level and grades the corrective response. While easy to administer, outcomes can vary due to variability in test administration and interpretation. A comprehensive literature review revealed laboratory based assessments provided a more objective method to measure postural responses compared to clinical assessments in people with PD. These techniques were conventionally employed in people with PD in later disease stages who already demonstrate postural instability. Laboratory based assessments presented a method to identify abnormalities before postural instability is clinically evident and effects of therapies. The recent development of instrumentation of clinical balance tests offered an alternative technique to precisely quantify postural responses. Here, we developed an instrumented version of the pull test and investigate its utility to quantify postural instability in people with PD ranging from mild to moderate disease severity. In Study 1, the sensitivity of the instrumented pull test was investigated in healthy young participants. Postural responses were modified by presenting a startling auditory stimulus concurrent with the backwards pull. Such stimuli evoke StartReact effects and are known to speed reaction times. The instrumented pull test could detect small 10 ms decreases in postural reaction time evoked by the startling stimulus. The ability to detect such changes in healthy individuals highlights the utility of instrumented techniques and justifies further investigation in people where changes to balance is of interest. Subsequently, the instrumented pull test was used to characterise postural responses in eighteen people with mild PD (Hoehn and Yahr less than 2) in Study 2. Subclinical abnormalities in trunk and step responses were detected in participants with mild PD compared to healthy controls. Furthermore, levodopa did not restore postural responses in participants with PD to that of healthy controls (Study 3). These findings demonstrate changes to postural stability can occur in mild disease. Abnormalities of postural responses which remain refractory to levodopa also suggest non-dopaminergic pathways may be implicated in the pathophysiology of postural instability in mild PD. Pedunculopontine deep brain stimulation (PPN DBS) is a therapy developed specifically to alleviate axial symptoms of gait and postural abnormalities unresponsive to conventional therapies such as levodopa. In Study 4, the instrumented pull test was used to quantify postural responses in five people with PD and moderate to severe postural instability receiving PPN DBS. Off and on stimulation, the instrumented pull test was able to detect postural responses with greater resolution compared to clinical assessments (axial items 27 to 30 of the motor subsection of the Unified Parkinson’s disease rating scale (UPDRS) and the Mini-BESTest. However, the use of the instrumented pull test, and interpretation of findings was limited by the small sample size and highly variable postural responses in participants with moderate to severe postural instability. On stimulation, improvement in overall balance scores was demonstrated across all participants with the Mini-BESTest but not axial items of the UPDRS. This thesis demonstrated the utility of the instrumented pull test as a potential assessment tool to evaluate postural instability in PD. Identification of postural abnormalities provides valuable insights in the assessment and management of postural instability in people with PD. Clinicians should consider that subclinical postural abnormalities can be present in people with mild PD, even when patients are on levodopa. Findings from this thesis strongly support the need for further studies to explore variables of postural responses that may be useful to detect people with PD at risk of falls and for clinicians to deliver targeted interventions earlier in disease course.