Background

Assessing postural stability in Parkinson’s disease (PD) often relies on measuring the stepping response to an imposed postural perturbation. The standard clinical technique relies on a brisk backwards pull at the shoulders by the examiner and judgement by a trained rater. In research settings, various quantitative measures and perturbation directions have been tested, but it is unclear which metrics and perturbation direction differ most between people with PD and controls.

Objectives

(1) Use standardized forward vs. backward perturbations of a support surface to evaluate reactive stepping performance between PD and control participants. (2) Evaluate the utility of using principal components analysis to capture the dynamics of the reactive response and differences between groups.

Methods

Sixty-two individuals participated (40 mild-to-moderate PD, off medication). Standardized rapid translations of the support surface were applied, requiring at least one step, backward or forward, to restore balance. The number of steps taken and the projection of the first principal component (PC1) of the center of pressure (COP) time series were entered in linear repeated-measures mixed effect models.

Results

Forward falls required significantly fewer steps to recover than backward falls. PC1 captured more than half of the variance in the COP trajectory. Analysis of the PC1 projection revealed a significant interaction effect of group (PD vs. controls) by direction, such that there was a group difference in forward stepping, but not backward.

Significance

Forward reactive stepping in PD differed from controls more than backward-stepping. PC1 projections of the COP trajectory capture the dynamics of the postural response and differ between PD and controls.

中文翻译：

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轻中度帕金森病前向和后向姿势扰动的比较

背景

评估帕金森病 (PD) 的姿势稳定性通常依赖于测量对施加的姿势扰动的步进反应。标准的临床技术依赖于检查者在肩膀上的轻快向后拉，并由训练有素的评估者判断。在研究环境中，已经测试了各种定量测量和扰动方向，但尚不清楚 PD 患者和对照组之间哪些指标和扰动方向差异最大。

目标

(1) 使用支撑表面的标准化前向和后向扰动来评估 PD 和控制参与者之间的反应性步进性能。(2) 评估使用主成分分析捕捉反应动态和组间差异的效用。

方法

62 人参与（40 名轻度至中度 PD，停药）。应用了支撑表面的标准化快速平移，需要至少一步，向后或向前，以恢复平衡。将采取的步数和压力中心 (COP) 时间序列的第一主成分 (PC1) 的投影输入到线性重复测量混合效应模型中。

结果

向前跌倒所需的恢复步骤比向后跌倒要少得多。PC1 捕获了 COP 轨迹中一半以上的方差。对 PC1 投影的分析揭示了组（PD 与对照组）在方向上的显着交互作用，因此在向前迈出时存在组差异，但不向后。

意义

PD 中的前向反应性步进与控制的不同之处多于后向步进。COP 轨迹的 PC1 投影捕获了姿势响应的动态，并且在 PD 和控件之间存在差异。