The Influence of Dopaminergic Medication on Gait and Balance Automaticity and Nonlinear Regularity in Parkinson’s Disease

Dual-tasking studies have shown that gait and balance automaticity in Parkinson’s disease (PD) is significantly diminished. It is also well accepted that dopaminergic medication improves single-task gait and some aspects of balance. Yet, how dopaminergic medication influences gait and balance automaticity in PD is not well understood. Additionally, gait and balance automaticity studies in PD have almost exclusively employed linear measures to describe outcomes. Unlike linear measures, nonlinear analyses like Approximate Entropy and Recurrence Quantification Analysis account for the regularity of the entire signal and can help determine the automaticity of the intended movement pattern. Therefore, this study aimed to determine how dopaminergic medication influenced the automaticity of gait and balance via linear and nonlinear analyses of joint angle and center of pressure (COP) path signals while single and dual-tasking in PD. Sixteen subjects with PD completed single- and dual-task walking and standing (eyes open and eyes closed) for 3 minutes off and on medication. Gait velocity, cadence, and stride length were measured, as well as kinematic variables (mean, maximum, and SD angles of bilateral hip, knee, and shoulder joint) were calculated to describe gait performance. For balance, 95% confidence ellipse area, anterior-posterior sway velocity, medial-lateral sway velocity, and integrated time to boundary were calculated. For the nonlinear analyses, approximate entropy and percent determinism were calculated for bilateral hip, knee, and shoulder joints, as well as the COP path. Data were statistically analyzed with a series of repeated measures ANOVAs and linear mixed effects models controlling for gait velocity for the linear and nonlinear analyses of joint angle data. For gait, the analysis indicated that dopaminergic medication significantly improved gait velocity (p = 0.007) and several kinematic variables. Dualtasking significantly interfered with cadence (p = 0.042), stride length (p < 0.001), and some kinematic measures, despite medication state. Dopaminergic medication mostly impacted the less PD-affected hip and knee joints, while dual-tasking primarily affected the less-PD affected hip joints. For balance, dopaminergic medication significantly increased ellipse area (p = 0.002) and decreased the performance on the secondary task (p = 0.004), while dual-tasking significantly increased sway velocity in both directions (anterior-posterior = p < 0.001, medial-lateral = p < 0.004) and integrated time to boundary (p < 0.001). There were also several medication*task interactions among the balance variables. Overall, both dopaminergic medication and dual tasking seemed to hinder balance performance, when analyzed using traditional interpretations. However, because medication only increased sway area, we propose that PD medication improved balance maneuverability without a decrease in stability. For the nonlinear analyses, there were significant medication effects on the Approximate Entropy of the more-PD affected knee while dual tasking (p = 0.014) and the less-PD affected knee while dual-tasking (p = 0.004), both of which indicated that off medication dual-tasking was more regular than on-medication dual tasking. The analysis also revealed that balance task complexity, specifically eyes open vs. eyes closed, was reflected in the analysis of the COP path, with more complex tasks eliciting significantly less regular/deterministic results. Overall, the significant gait differences in dual tasking between off- and on medication states indicated motor improvements from taking dopaminergic medication improved dualtasking. However, the lack of significant interactions and secondary task effects did not support a medication-induced improvement in gait automaticity. Lastly, the nonlinear characteristics of gait and balance in PD seemed to be differently affected by medication and task complexity. The medication-induced decreases in regularity, coupled with accepted improvements in gait performance with medication, may indicate that PD patients are too regular in their joint movements off medication.