Non-linear dynamical feature of center of pressure extracted by approximate entropy in people with various stages of Parkinson’s Disease

Abstract Introduction : Postural instability, one of the most important features of Parkinson’s Disease (PD), is associated with increased falls and loss of independence in these population. It is postulated the abilities of individuals to adjust to environmental perturbation for postural control is different in various stages of PD. The aim of current study is to investigate the non-linear dynamical feature of COP in various stages of PD and in different environmental challenges. Method : 38 persons with PD (mild PD =19, moderate PD =6 and sever PD =13) and 33 healthy aged, gender, weight and height matched subjects were asked to stand on force plate in four test conditions included: 1) Rigid Surface with Opened Eyes, 2) Rigid Surface with Closed Eyes, 3) Foam Surface with Opened Eyes, and 4) Foam Surface with Closed Eyes. COP velocity and Approximate Entropy (ApEn) in both Anteroposterior (AP)/Mediolateral (ML) directions were calculated. A Mixed ANOVA 4*2*2 (Group*Vision*Surface) test was applied for statistical analysis . Results : Both COP velocity and COP ML ApEn were significantly higher in participants with PD in comparison to healthy individuals. Moreover, COP ML ApEn increased by eye closure in all studied groups but the amount of this increase was lesser in PD groups. For COP velocity, vision, surface and group interaction was significant in all directions (P ≤ 0.016). For COP ApEn, vision, surface and group interaction (P = 0.002) were statistically meaningful in only ML direction. Conclusion : Balance system irregularity is more in people with PD compared to healthy matched individuals. In addition, their adaptive capacity of the postural control system in response to environmental perturbation is reduced. PD induced complexity of the postural control system is associated with the loss of adaptive behavior that is organized over the confluence of constraints of the individual, environment and task.