Rouhani Hossein, Same Michael, Masani Kei, Li Ya Qi, Popovic Milos R
Department of Mechanical Engineering, University of AlbertaEdmonton, AB, Canada.
Rehabilitation Engineering Laboratory, Lyndhurst Centre, Toronto Rehabilitation Institute, University Health NetworkToronto, ON, Canada.
Front Neurosci. 2017 Jun 20;11:347. doi: 10.3389/fnins.2017.00347. eCollection 2017.
Closed-loop controlled functional electrical stimulation (FES) applied to the lower limb muscles can be used as a neuroprosthesis for standing balance in neurologically impaired individuals. The objective of this study was to propose a methodology for designing a proportional-integral-derivative (PID) controller for FES applied to the ankle muscles toward maintaining standing balance for several minutes and in the presence of perturbations. First, a model of the physiological control strategy for standing balance was developed. Second, the parameters of a PID controller that mimicked the physiological balance control strategy were determined to stabilize the human body when modeled as an inverted pendulum. Third, this PID controller was implemented using a custom-made Inverted Pendulum Standing Apparatus that eliminated the effect of visual and vestibular sensory information on voluntary balance control. Using this setup, the individual-specific FES controllers were tested in able-bodied individuals and compared with disrupted voluntary control conditions in four experimental paradigms: (i) quiet-standing; (ii) sudden change of targeted pendulum angle (step response); (iii) balance perturbations that simulate arm movements; and (iv) sudden change of targeted angle of a pendulum with individual-specific body-weight (step response). In paradigms (i) to (iii), a standard 39.5-kg pendulum was used, and 12 subjects were involved. In paradigm (iv) 9 subjects were involved. Across the different experimental paradigms and subjects, the FES-controlled and disrupted voluntarily-controlled pendulum angle showed root mean square errors of <1.2 and 2.3 deg, respectively. The root mean square error (all paradigms), rise time, settle time, and overshoot [paradigms (ii) and (iv)] in FES-controlled balance were significantly smaller or tended to be smaller than those observed with voluntarily-controlled balance, implying improved steady-state and transient responses of FES-controlled balance. At the same time, the FES-controlled balance required similar torque levels (no significant difference) as voluntarily-controlled balance. The implemented PID parameters were to some extent consistent among subjects for standard weight conditions and did not require prolonged individual-specific tuning. The proposed methodology can be used to design FES controllers for closed-loop controlled neuroprostheses for standing balance. Further investigation of the clinical implementation of this approach for neurologically impaired individuals is needed.
应用于下肢肌肉的闭环控制功能性电刺激（FES）可作为一种神经假体，用于帮助神经功能受损个体维持站立平衡。本研究的目的是提出一种方法，用于设计一种比例积分微分（PID）控制器，该控制器应用于脚踝肌肉的FES，以在存在干扰的情况下维持数分钟的站立平衡。首先，建立了站立平衡生理控制策略的模型。其次，确定了模仿生理平衡控制策略的PID控制器的参数，以便在将人体建模为倒立摆时使人体稳定。第三，使用定制的倒立摆站立装置实现该PID控制器，该装置消除了视觉和前庭感觉信息对自主平衡控制的影响。利用这个设置，在健全个体中测试了个体特异性FES控制器，并在四个实验范式中与干扰自主控制条件进行了比较：（i）安静站立；（ii）目标摆角突然变化（阶跃响应）；（iii）模拟手臂运动的平衡干扰；（iv）具有个体特异性体重的摆的目标角度突然变化（阶跃响应）。在范式（i）至（iii）中，使用标准的39.5千克摆，涉及12名受试者。在范式（iv）中，涉及9名受试者。在不同的实验范式和受试者中，FES控制和干扰自主控制的摆角的均方根误差分别<1.2度和2.3度。FES控制平衡中的均方根误差（所有范式）、上升时间、调节时间和超调量[范式（ii）和（iv）]明显小于或趋于小于自主控制平衡时观察到的值，这意味着FES控制平衡的稳态和瞬态响应得到了改善。同时，FES控制平衡所需的扭矩水平与自主控制平衡相似（无显著差异）。对于标准体重条件，所实现的PID参数在受试者之间在一定程度上是一致的，并且不需要长时间的个体特异性调整。所提出的方法可用于设计用于站立平衡的闭环控制神经假体的FES控制器。需要进一步研究这种方法在神经功能受损个体中的临床应用。
