Evidence for force-feedback inhibition in chronic stroke

The presence of force-feedback inhibition was explored during reflex responses in five subjects with known incidence of stroke. Using constant velocity stretches, it was previously found that after movement onset, active reflex force progressively increases with increasing joint angle, at a rate proportional to a fractional exponent of the speed of stretch. However, after the reflex force magnitude exceeds a particular level, it begins rolling off until maintaining a steady-state value. The magnitudes of these force plateaus are correlated with the speed of stretch, such that higher movement speeds result in higher steady-state forces. Based upon these previous studies, we hypothesized that force plateau behavior could be explained by a force-feedback inhibitory pathway. To help facilitate an understanding of this stretch reflex force roll off, a simple model representing the elbow reflex pathways was developed. This model contained two separate feedback pathways, one representing the monosynaptic stretch reflex originating from muscle spindle excitation, and another representing force-feedback inhibition arising from force sensitive receptors. It was found that force-feedback inhibition altered the stretch reflex response, resulting in a force response that followed a sigmoidal shape similar to that observed experimentally. Furthermore, simulated reflex responses were highly dependent on force-feedback gain, where predicted reflex force began plateauing at decreasing levels with increases in this force-feedback gain. The parameters from the model fits indicate that the force threshold for force-sensitive receptors is relatively high, suggesting that the inhibition may arise from muscle free nerve endings rather than Golgi tendon organs. The experimental results coupled with the simulations of elbow reflex responses suggest the possibility that after stroke, the effectiveness of force-feedback inhibition may increase to a level that has functional significance. Practical implications of these findings are discussed in relation to muscle weakness commonly associated with stroke.     

A simulation study of reflex instability in spasticity: origins of clonus.

Clonus is defined as an involuntary rhythmic muscle contraction that generally occurs in people who have sustained lesions involving descending motor pathways in the neuraxis, and is usually accompanied by other signs of reflex hyperexcitability such as spasticity. This paper hypothesizes that clonus arises when two conditions occur simultaneously: 1) the reflex pathway contains long delay times (implying innervation of distal limb muscles, exacerbated when these muscles display slow twitch properties) and 2) the excitability of the motoneurons is enhanced. This paper tested this dual hypothesis by developing a computer model representing the ankle reflex pathway. This model included the ankle muscles, afferent and efferent pathways, and a monosynaptic spinal link between spindle afferents and motoneurons. Simulations show that as the motoneuron current threshold was reduced (reflecting increased excitability of spinal motoneurons), normal reflex responses became unstable and oscillations developed similar to those observed in spastic patients. In parallel, when we choose reflex delay times typical for distal leg muscles in man, system stability is poor, and oscillations occur readily with increasing motoneuron excitability. As simulated pathway delays are reduced, oscillatory behavior is also reduced, and usually damps out. Conversely, as simulated reflex delays are increased, oscillations increase in amplitude and do not decay. Finally, these two phenomena interact, so that increasing motoneuron excitability will induce reflex oscillations for intermediate loop delays. These findings support the hypothesis that unstable oscillatory behavior, such as the oscillations observed in clonus, will occur when the motoneuron excitability increases in a reflex pathway containing long delays. This change in excitability is mediated by a reduction in motoneuron firing threshold, rather than by an increase in feedback gain. Furthermore, we demonstrate that sustained oscillations occur readily through self reexcitation, which reduces the need to propose that a "central oscillator" must be involved in generating clonus.     

Gain control in reflex pathways

Summary form only given. A series of experiments was undertaken to determine the gain of the stretch reflex in decerebrate cats. Stretches are applied through a servo-controlled motor that receives length and velocity feedback which are adjusted so that it behaves like a spring of a particular stiffness. As the stiffness decreases the gain of the reflex increases until the stiffness is made much less than the intrinsic muscle stiffness. Under these conditions small brief pulses can elicit shortening of 1 mm or more and reflex forces that are larger than the force produced by the stretch itself. This suggests that the gain in the reflex is 1 or more at low frequencies. It is concluded that muscle control systems are adaptive and time-varying to accomplish the various tasks required by the organism. Although under some conditions the reflex gain is on the order of one, measurement of gain is compounded by a number of nonlinearities, and the value of these nonlinearities in various tasks remains to be determined     

Man-machine communications through brain-wave processing

The possibility of monitoring voluntarily produced changes in the electroencephalogram (EEG) of a subject and translating these changes into a set of commands to be issued to an external device was investigated. Subjects performed five distinct tasks under both eyes-open and eyes-closed conditions. A feature set consisting of the asymmetry ratios and the power values for each lead at four frequency bands-delta (0-3 Hz) theta (4-7 Hz), alpha (8-13 Hz), and beta (14-20 Hz)-was used to characterize the EEG. The feature sets created from an estimate of the spectral density of the EEG for each task were used to test classification accuracy among the various tasks using a Bayes quadratic classifier. The results show that it is possible to distinguish, to a high degree of accuracy, among the various mental tasks studied, using only the EEG.     

Impact of TMS on the primary motor cortex and associated spinal systems.

Repetitive transcranial magnetic stimulation (rTMS) is able to modulate corticospinal and intracortical motor cortex excitability, depending on the stimulation parameters. In the present study, we explored the effects of highand low-frequency rTMS on spinal reflex monosynaptic responses (H waves or H reflexes) in humans recorded from the flexor carpi radialis (FCR) muscle. After 1-Hz rTMS, H-wave minimal and optimal thresholds were decreased by 14-22% of their pre-rTMS values. The maximal H-wave and H/M amplitude ratio were both significantly increased by 52-54%, whereas direct muscle responses (M waves) remained unchanged. The area under the H-wave recruitment curve was also significantly increased by 86 /spl plusmn/ 21% of its pre-rTMS baseline values. Conversely, after 20-Hz rTMS, H-wave minimal and optimal thresholds were both increased by 15-26%. The maximal H wave and H/M amplitude ratio were significantly decreased by -37 /spl plusmn/ 11%, whereas M responses remained unchanged. The area under the H-response recruitment curve was also significantly decreased by -45/spl plusmn/5%. Neither 20-Hz nor 1-Hz sham rTMS induced noticeable changes in M or H responses. We conclude that 1-Hz rTMS applied to primary motor areas increases the monosynaptic spinal cord H reflex, whereas 20-Hz rTMS induces the opposite effect, presumably by modulating inhibitory descending conicospinal projections onto spinal motoneurons. These results offer an opportunity to influence the level of spinal excitability and modify descending corticospinal influences in a controlled manner using noninvasive approaches that could prove useful in the study of the pathophysiology and eventual treatment of spasticity.     

Interpretation of Muscle Spindle Afferent Nerve Response to Passive Muscle Stretch Recorded With Thin-Film Longitudinal Intrafascicular Electrodes

In this study, we explored the feasibility of estimating muscle length in passive conditions by interpreting nerve responses from muscle spindle afferents recorded with thin-film longitudinal intrafascicular electrodes. Afferent muscle spindle response to passive stretch was recorded in ten acute rabbit experiments. A newly proposed first-order model of muscle spindle response to passive sinusoidal muscle stretch manages to capture the relationship between afferent neural firing rate and muscle length. We demonstrate that the model can be used to track random motion trajectories with bandwidth from 0.1 to 1 Hz over a range of 4 mm with a muscle length estimation error of 0.3 mm (1.4$^circ$ of joint angle). When estimation is performed using four-channel ENG there is a 50% reduction in estimate variation, compared to using single-channel recordings.      

函数／任意波形发生器SCPI解释器设计与实现

SCPI是程控仪器标准命令集,被广泛应用于测试测量仪器的操作控制。SCPI解释器是使得仪器能够“理解”控制器发送命令的关键工具。本文针对函数／任意波形发生器的SCPI命令子集,分别使用已排序数组链表和二分查找算法存储、查询命令节点,使用数组存储命令参数的语法信息,并使用词法分析和语法分析相结合的方法分析命令的参数部分,最后在Windows平台上实现了对应的SCPI解释器。与传统的使用树存储结构,按孩子指针查询命令节点的方法所设计的SCPI解释器相比,提出的SCPI解释器具有更高的解释效率。     

Decentralized adaptive command following and disturbance rejection for subsystems with local full‐state feedback

We present a decentralized model reference adaptive control method, where each local controller uses full‐state feedback from the local subsystem. The controller is strictly decentralized, meaning that no information (including reference‐model trajectories) is shared between local controllers. This decentralized controller achieves stabilization, command following, and disturbance rejection provided that the reference‐model commands and the disturbances are sinusoidal with known spectrum. The controller is effective for multi‐input subsystems with arbitrarily large subsystem interconnections. Copyright © 2014 John Wiley & Sons, Ltd.     

通用型紧急指令传输接口优化设计

针对用电平型信号作为紧急命令传输可靠性低的问题,分别从硬件和软件两方面进行了优化设计。在硬件方面,通过对相关参数的理论计算,采用光继电器发送指令,经过电缆用光电耦合器接收指令的电路组合;在软件逻辑方面,将紧急指令以连续脉冲形式发送,经过冗余设计后,对收到接收端FPGA的指令进行滑窗判别,保证指令在接收后判别的可靠性。经测试,优化后的指令传输接口设计简单、功耗低、应用广泛,能实现紧急指令在80 m电缆下长期可靠地传输。     

Rotor resistance identification and stability control method in bearingless induction motor drives

Generally, vector controllers in induction motors tend to suffer from the influence of rotor resistance variation caused by temperature and load torque conditions. Several rotor resistance identification methods have been proposed in the literature. In this paper, a novel rotor resistance identification technique is proposed based on variables in the magnetic suspension control loops. When static force, such as a shaft weight, is applied, force commands are automatically generated in the opposite direction to satisfy the force equilibrium. However, the amplitude and direction of the force command vary in accordance with the rotor resistance variation. Thus, the rotor resistance can be identified from the suspension force command. In addition, influence of temperature drift in gap sensors is investigated. The effectiveness is confirmed experimentally. © 2008 Wiley Periodicals, Inc. Electr Eng Jpn, 164(1): 86–97, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20423     

Cardiovascular variability

The cardiovascular system is composed of a variety of specialized subsystems that interact with each other under the influence of internal and external inputs, including central commands, reflex mechanisms, and humoral factors. The concomitant action of all these subsystems produces continuous adjustments in the cardiovascular variables (e.g., heart rate, heart contractility, blood pressure, vascular tone, etc.) referred to as cardiovascular variability. A large body of evidence indicates that this variability includes linear and nonlinear components and conveys important biological information that might help in the understanding of the underlying physiology and facilitate diagnosis and prognosis of cardiovascular dysfunctions.     

The effects of long-term FES-assisted walking on intrinsic and reflex dynamic stiffness in spastic spinal-cord-injured subjects

The effects of long-term functional electrical stimulation (FES)-assisted walking on ankle dynamic stiffness were examined in spinal cord-injured (SCI) subjects with incomplete motor function loss. A parallel-cascade system identification method was used to identify intrinsic and reflex contributions to dynamic ankle stiffness at different ankle positions while subjects remained relaxed. Intrinsic stiffness dynamics were well modeled by a linear second-order model relating intrinsic torque to joint position. Reflex stiffness dynamics were accurately described by a linear third-order model relating halfwave rectified velocity to reflex torque. We examined four SCI subjects before and after long-term FES-assisted walking (>16 mo). Another SCI subject, who used FES for only five months was examined 12 mo latter to serve as a non-FES, SCI control. Reflex stiffness decreased in FES subjects by an average of 53% following FES-assisted walking, intrinsic stiffness also dropped by 45%. In contrast, both reflex and intrinsic stiffness increased in the non-FES, SCI control. These findings suggest that FES-assisted walking may have therapeutic effects, helping to reduce abnormal joint stiffness.     

基于暂态阻尼增强的改进VSG控制策略

针对虚拟同步发电机(virtual synchronous generator, VSG)并网运行时在有功指令和电网频率扰动下存在输出有功暂态振荡问题,提出了一种基于暂态阻尼增强的改进VSG控制策略。首先,基于状态反馈理论,分析了所提控制方法的物理意义,即该策略是通过在常规VSG有功控制环中加入角频率和电磁功率的高频分量来增强系统暂态阻尼。然后,基于所提的控制方法,建立了系统的有功控制环闭环小信号模型,并通过对系统特征根的根轨迹进行分析揭示了所提控制方法对VSG有功功率振荡抑制的影响。并给出了各状态反馈参数的设计准则,指导了反馈系数的设计。所提控制策略能有效抑制有功指令突变和电网频率突变时VSG输出有功功率振荡,并且不会影响系统的稳态特性。最后,通过仿真和实验对比分析,表明所提控制方法具有更好的有功功率振荡抑制效果,并且能消除稳态偏差,且适用于不同电网强度。     

A current-free and parameter-free control algorithm

A method of synthesizing a control system comprising a most inner positive voltage feedback loop and an inner negative voltage feedback loop and an outer negative voltage feedback loop is presented. The control system error is forced to zero in steady state and minimized in transient in response to either input command change or external disturbance. No current through the plant under the control is sensed and no parameters of the plant are required to be known implying minimization of measurement noise and adaptive/self-tuning operation, respectively. The method is used to synthesize load-independent and input-voltage-independent switch-mode power converters as well as electric motor drive systems, incorporating any kind of electric motor, of maximized disturbance rejection ratio and minimized dynamics     

Development of a quantitative reflex hammer for measurement of tendon stretch reflex

Quantification of tendon stretch reflex requires precise measurement of the tapping force of a reflex hammer. A quantitative reflex (QR) hammer consisting of two cut rubber pieces from a generic rubber reflex hammer and a uniaxial force transducer was constructed. Finite element stress analyses were conducted to estimate the natural frequency characteristics of the hammer and to find the stress distributions during the impact. Pendulum impact testing was conducted at four different heights to assess the calibration linearity and repeatability of the measurement The QR hammer had a fundamental natural frequency of 515 Hz and showed minimal displacement and stress at the tip from the finite element simulation of the impact. The QR hammer also provided reliable and repeatable measurements as demonstrated with high coefficients of determination, exceeding 0.994 and small coefficients of variations, less than 4%. The calibration linearity was 0.64% compared with the reference force platform measurement. The QR hammer demonstrated sufficient accuracy and reliability for precise clinical assessment of tendon stretch reflexes.     

基于OpenSSL的配电网终端遥控加密测试软件实现方式

随着配电网系统的发展,配电网主站与终端通过公共网络传输数据,包括遥控命令。为防止由公共网络引入对配电网的攻击,保障遥控命令的安全,新的配电网终端在执行遥控命令时需要对其进行完整性检验,并对发送遥控命令的配电网主站进行身份验证。介绍了运用散列运算和非对称加密技术实现完整性检验和对配电网主站的身份验证,描述了基于OpenSSL加密开发包实现配电网终端遥控加密测试软件的过程。该测试软件能模仿配电网主站生成复合遥控命令,对配电网终端的安全防护能力进行测试。     

Nerve cuff recordings of muscle afferent activity from tibial and peroneal nerves in rabbit during passive ankle motion.

Activity from muscle afferents regarding ankle kinesthesia was recorded using cuff electrodes in a rabbit preparation in which tactile input from the foot was eliminated. The purpose was to determine if such activity can provide information useful in controlling functional electrical stimulation (FES) systems that restore mobility in spinal injured man. The rabbit's ankle was passively flexed and extended while the activity of the tibial and peroneal nerves was recorded. Responses to trapezoidal stimulus profiles were investigated for excursions from 10 degrees to 60 degrees using velocities from 5 degrees/s to 30 degrees/s and different initial ankle positions. The recorded signals mainly reflect activity from primary and secondary muscle afferents. Dorsiflexion stretched the ankle extensors and produced velocity dependent activity in the tibial nerve, and this diminished to a tonic level during the stimulus plateau. The peroneal nerve was silent during dorsiflexion, but was activated by stretch of the peroneal muscles during ankle extension. The responses of the two nerves behaved in a reciprocal manner, but exhibited considerable hysteresis, since motion that relaxed the stretch to the driving muscle produced an immediate cessation of the prior stretch induced activity. A noted difference between the tibial and peroneal nerve responses is that the range of joint position change that activated the flexor afferents was greater then for the extensor afferents. Ankle rotation at higher velocities increased the dynamic stretch evoked responses during the stimulus ramp but showed no effect on the tonic activity during the stimulus plateau. Prestretching the muscles by altering the initial position increased the response to the ramp movement, however, for the peroneal nerve, when the prestretch brought the flexor muscles near to their maximal lengths, the response to additional stretch provided by the ramp movement was diminished. The results indicate that the whole nerve recorded muscle afferent activity may be useful for control of FES assisted standing, because it can indicate the direction of rotation of the passively moved ankle joint, along with coarse information regarding the rate of movement and static joint position.     

Performance improvement of induction motor speed sensor‐less vector control system using an adaptive observer with an estimated flux feedback in low‐speed range

Because of various errors caused by the dead time of an inverter, temperature variation of resistances, and so on, speed estimation error is inevitable in speed sensor‐less vector control of an induction motor. In particular, the speed control loop becomes unstable at near‐zero frequencies. In order to solve these problems, this paper proposes a novel design of an adaptive observer for speed estimation. By adding a feedback loop of the error between the estimated flux and the flux command, the sensitivity of speed estimation and primary resistance identification is improved. The proposed system is analyzed and appropriate feedback gains are derived. Experimental results showed good performance in the low‐speed range. © 2009 Wiley Periodicals, Inc. Electr Eng Jpn, 169(3): 33–46, 2009; Published online in Wiley InterScience ( www.interscience. wiley.com ). DOI 10.1002/eej.20909     

含位置给定轨迹优化的位置伺服复合控制系统研究

位置动态响应速度快和响应无超调是目前高性能位置伺服系统的两个重要指标。单纯的比例或比例微分位置调节器无法同时满足这两个要求,所以提出了一种新型定位复合控制策略。首先为保证运动过程柔滑无冲击而设定速度余弦函数曲线给定,从而根据平滑变化的速度给定对位置给定信号进行轨迹优化,避免了加速度突变带来的冲击。系统控制结构上提出在前馈控制的基础上引入位置伪微分负反馈控制环节,该环节增加了系统阻尼,减少位置超调量,同时结合前馈控制保证了位置快速跟踪性能。由于采用了伪微分结构代替位置微分运算,避免了微分带来的量化噪声干扰,进一步提升了系统跟踪性能。最后给出了结构参数的取值范围。仿真和试验结果验证了该控制策略的可行性和有效性。     

A study of shoulder motions as a control source for adolescents with C4 level SCI.

This study quantitatively examined and compared the shoulder motions of C4 level spinal cord injury (SCI), C5 level SCI, and able-bodied persons as a command source. The study was motivated by both the success of shoulder control in functional electrical stimulation (FES) systems designed for C5 level SCI people and the lack of quantitative information on the shoulder motion of persons with C4 level SCI. A dual-axis transducer was used to monitor the elevation/depression and protraction/retraction angles of each subject's shoulder while they performed three experimental sections which examined: the range of active shoulder motion; the ability to move incrementally to discrete positions with the aid of visual feedback; and the ability to hold discrete shoulder positions for an extended period without visual feedback. Results indicated that each group had the largest average shoulder displacements (abled = 23 degrees +/- 4 degrees, C5's = 14 degrees +/- 3 degrees, and C4's = 9 degrees +/- 3 degrees) while attempting to elevate and that on average the C4 group had the smallest range of active shoulder motion. No statistically significant differences between the groups were found in either the accuracy or stability of reaching discrete positions with the aid of visual feedback or in the accuracy of holding discrete shoulder positions for an extended period without visual feedback. The results suggest that within their limited range of motion the individuals with C4 level SCI retained shoulder control sufficient for use as an neuroprosthetic command interface.