Research On Human Pathological Tremor Suppression Based On Functional Electrical Stimulation

Pathological tremor, as a motor disorder caused by neurological diseases, is a rhythmic and involuntary movement and significantly impacts patients’ daily living activities and social communications. The mechanism of tremor is still uncertain and can’t be determined by the doctors. However, it is proved that tremulous patients still have intact neural pathway and normal ability of muscle contractions. Functional electrical stimulation(FES) as a novel rehabilitation technique has the characteristics of high integration and esthetic appearance, and it is widely used in the area of cerebral apoplexy, musculoskeletal disorder or geriatric rehabilitation etc. FES provides electric pulses with low frequency instead of the missing normal neural commands to stimulate the impair or dysfunction limb with purpose of inducing muscle contraction. Finally, the motor function of limbs is recovered. Therefore, the research on the pathological tremor suppression based on FES is beneficial to modulate the stimulation intensity with the feedback of tremor signals. The antagonistic muscles will be activated to resist tremor without affecting the patients’ intentional movement.The physiological characteristics of human body are analyzed together with the output properties of the electric stimulation system. Furthermore, the mechanism of limb movement induced by the antagonistic muscle contraction through stimulating the muscles round the joint is explored. Based on the analysis on the biomechanics characteristics of the upper limb, the upper limb is approximat ely considered as a second-order system with muscle torque as the input and the limb motion as output. Therefore, the couple system between the FES and human body is developed. The influence of the electric stimulation on the impedance coefficients of coup led system is analyzed. Meanwhile, the response of system to the external stimulation is also discussed. The results verify that FES can be employed to adjust the intensity of muscle contraction and the stiffness of elbow joint and lay the theoretical basi s for suppressing tremulous motion with high frequency and retaining voluntary motion.The tremulous signals measured from patients usually include the tremulous and voluntary components and are employed to modulate the suppression torque. Therefore, the extraction of tremulous signals from the measured signals is important to resist the tremor without impacting the intended motions. Based on the analysis on the tremor characteristic and data, the tremor signal of a certian individual is a roughly harmonic signal with stable frequency range and significantly variable amplitude. Therefore, an adaptive sliding band limited multiple Fourier linear combiner(ASBMFLC) algorithm is proposed with the combining frequency range sliding in the common frequency band wi th the dominant frequency of signals. Meanwhile, it could be employed to estimate the tremulous signals measured from different patinets without the pre-analysis on the measured signals. Besides, the sliding fast Fourier transformation algorithm(SFFT) is also developed by inlucding the module of siliding FFT, the interpolation method and frequency damping module to estimate the dominant frequency and providing effective characteristic parameters of tremor signals for control system of FES.Based on the modified Hill-type muscle model, the musculoskeletal model of the elbow joint is developed. With the analysis on the sensitivity of model parameters, the calibrated model approximating the individuals is obtained with the optimization alogrithm. The desired electrical stimulation intensity is drived by the pulse width modulation technology imposed on EMG signals. Meanwhile, the electric pulses are employed to activate the tuned model instead of the neural commands and the movements with out phase of tremor are got. Furthermore, the mechanism of center nervous system, the position feedback of muscle spindle and the force feedback of Golgi tendon is analyzed to established the neuromusculoskeletal model of the elbow joint. The suppression efficiency is evaluated by activating the model with the electrical stimulation optimized by control algorithm. The qualitative relationship between the model parameters of Matsuoka oscillator and the amplitude and frequency of oscillating output s is anlayzed. Meanwhile, the nonlinear threshold function of oscillator is linearized and the explicit relations is obtained under the free state and forced state. A novel control method is proposed with central pattern generation as forward controller, and with the amplitude modulated by fuzzy controller and the intermittent estimation of tremulous frequency as the feedback. This approach can adjust the aparameters of central oscillation controller with respect to the amplitude nad freuqency of outputs based on the temor suppression. Finally, the stimulation intentisity imposed on human body is modulated.Based on the programmable electrical stimulator independently designed by the laboratory, the experimental platform for suppressing tremor of the elbow joint is developed. The characteristic parameters of pulses are determined by analyzing the response of healthy participants to stimulation pulses with different amplitudes and frequencies. Moreover, the rationality of the patch position is verified through comparing the influence of the electrode patch positions and loads on the response of the body. Comparing the different performance of healthy subjects in daily activities under the natural condition and the electrical stimulation, the influence of tremor on human movements and the intention of healthy participants to tremor suppression are analyzed. In addition, the pulse characteristic parameters are modulated based on the simulated tremor signals and the musculoskeletal model. Meanwhile, the effectiveness of the control approach is verified by comparing the response of upper limb to the modulated electrical pulse with simulated tremor signals. Besides, two electrical stimulators are employed to trigger and suppress the tremor of healthy subjects in the experiments, respectively, with the purpose of decreasing the effect of intentions on the tremor suppression. It further proves that the control method of tremor suppression can effectively inhibit the rest tremor and the action tremor.