E.C. Wentink

Detection of the onset of gait initiation using kinematic sensors and EMG in transfemoral amputees

In this study we determined if detection of the onset of gait initiation in transfemoral amputees can be useful for voluntary control of upper leg prostheses. From six transfemoral amputees inertial sensor data and EMG were measured at the prosthetic leg during gait initiation. First, initial movement was detected from the inertial sensor data. Subsequently it was determined whether EMG could predict initial movement before detection based on the inertial sensors with comparable consistency as the inertial sensors. From the inertial sensors the initial movement can be determined. If the prosthetic leg leads, the upper leg accelerometer data was able to detect initial movement best. If the intact leg leads the upper leg gyroscope data performed best. Inertial sensors at the upper leg in general showed detections at the same time or earlier than those at the lower leg. EMG can predict initial movement up to a 138 ms in advance, when the prosthetic leg leads. One subject showed consistent EMG onset up to 248 ms before initial movement in the intact leg leading condition. A new method to detect initial movement from inertial sensors was presented and can be useful for additional prosthetic control. EMG measured at the prosthetic leg can be used for prediction of gait initiation when the prosthetic leg is leading, but for the intact leg leading condition this will not be of additional value.

Comparison of muscle activity patterns of transfemoral amputees and control subjects during walking

BackgroundOnly few studies have looked at electromyography (EMG) during prosthetic gait. Differences in EMG between normal and prosthetic gait for stance and swing phase were never separately analyzed. These differences can give valuable information if and how muscle activity changes in prosthetic gait.MethodsIn this study EMG activity during gait of the upper leg muscles of six transfemoral amputees, measured inside their own socket, was compared to that of five controls. On and off timings for stance and swing phase were determined together with the level of co-activity and inter-subject variability.Results and conclusionsGait phase changes in amputees mainly consisted of an increased double support phase preceding the prosthetic stance phase. For the subsequent (pre) swing phase the main differences were found in muscle activity patterns of the prosthetic limb, more muscles were active during this phase and/or with prolonged duration. The overall inter-subject variability was larger in amputees compared to controls.

Power spectral density analysis of physiological, rest and action tremor in Parkinson’s disease patients treated with deep brain stimulation

BackgroundObservation of the signals recorded from the extremities of Parkinson’s disease patients showing rest and/or action tremor reveal a distinct high power resonance peak in the frequency band corresponding to tremor. The aim of the study was to investigate, using quantitative measures, how clinically effective and less effective deep brain stimulation protocols redistribute movement power over the frequency bands associated with movement, pathological and physiological tremor, and whether normal physiological tremor may reappear during those periods that tremor is absent.MethodsThe power spectral density patterns of rest and action tremor were studied in 7 Parkinson’s disease patients treated with (bilateral) deep brain stimulation of the subthalamic nucleus. Two tests were carried out: 1) the patient was sitting at rest; 2) the patient performed a hand or foot tapping movement. Each test was repeated four times for each extremity with different stimulation settings applied during each repetition. Tremor intermittency was taken into account by classifying each 3-second window of the recorded angular velocity signals as a tremor or non-tremor window.ResultsThe distribution of power over the low frequency band (<3.5 Hz – voluntary movement), tremor band (3.5-7.5 Hz) and high frequency band (>7.5 Hz – normal physiological tremor) revealed that rest and action tremor show a similar power-frequency shift related to tremor absence and presence: when tremor is present most power is contained in the tremor frequency band; when tremor is absent lower frequencies dominate. Even under resting conditions a relatively large low frequency component became prominent, which seemed to compensate for tremor. Tremor absence did not result in the reappearance of normal physiological tremor.ConclusionParkinson’s disease patients continuously balance between tremor and tremor suppression or compensation expressed by power shifts between the low frequency band and the tremor frequency band during rest and voluntary motor actions. This balance shows that the pathological tremor is either on or off, with the latter state not resembling that of a healthy subject. Deep brain stimulation can reverse the balance thereby either switching tremor on or off.

Intention detection of gait initiation using EMG and kinematic data

Gait initiation in transfemoral amputees (TFA) is different from non-amputees. This is mainly caused by the lack of stability and push-off from the prosthetic leg. Adding control and artificial push-off to the prosthesis may therefore be beneficial to TFA. In this study the feasibility of real-time intention detection of gait initiation was determined by mimicking the TFA situation in non-amputees. EMG and inertial sensor data was measured in 10 non-amputees. Only data available in TFA was used to determine if gait initiation can be predicted in time to control a transfemoral prosthesis to generate push-off and stability. Toe-off and heel-strike of the leading limb are important parameters to be detected, to control a prosthesis and to time push-off. The results show that toe-off and heel-strike of the leading limb can be detected using EMG and kinematic data in non-amputees 130-260 ms in advance. This leaves enough time to control a prosthesis. Based on these results we hypothesize that similar results can be found in TFA, allowing for adequate control of a prosthesis during gait initiation.

Vibrotactile stimulation of the upper leg: Effects of location, stimulation method and habituation

In this study vibrotactile stimulation of the upper leg and its usability for feedback was tested. Three experiments were performed on ten healthy subjects using pager motors. The first experiment was to test the perception of the vibration at different frequencies and at different locations of the upper leg. The second experiment tested the ability of subjects to estimate location and number of stimuli in an array. In addition it was evaluated whether simultaneous or sequential stimulation is better interpretable. Thirdly the habituation of the vibration was determined. The experiments showed that vibrotactile stimulation is well perceived and can be useful in providing feedback on the upper leg. Further experiments are needed to determine the effectiveness of vibrotactile stimulation for feedback in trans-femoral prostheses.

Variable stiffness actuated prosthetic knee to restore knee buckling during stance: A modeling study

Most modern intelligent knee prosthesis use dampers to modulate dynamic behavior and prevent excessive knee flexion, but they dissipate energy and do not assist in knee extension. Energy efficient variable stiffness control (VSA) can reduce the energy consumption yet effectively modulate the dynamic behavior and use stored energy during flexion to assist in subsequent extension. A principle design of energy efficient VSA in a prosthetic knee is proposed and analyzed for the specific case of rejection of a disturbed stance phase. The concept is based on the principle that the output stiffness of a spring can be changed without changing the energy stored in the elastic elements of the spring. The usability of this concept to control a prosthetic knee is evaluated using a model. Part of the stance phase of the human leg was modeled by a double pendulum. Specifically the rejection of a common disturbance of transfemoral prosthetic gait, an unlocked knee at heel strike, was evaluated. The ranges of spring stiffnesses were determined such that the angular characteristics of a normal stance phase were preserved, but disturbances could also be rejected. The simulations predicted that energy efficient VSA can be useful for the control of prosthetic knees.

Feasibility of error-based electrotactile and auditive feedback in prosthetic walking.

Background and aim: Several studies have shown that feedback in upper-leg prostheses is possible, but slow or difficult to interpret. In this study, electrotactile and auditive error-based feedback, only giving feedback when an undesired event occurs, were tested for its use in upper-leg prosthesis when provided during a perturbation. Technique: A total of nine healthy subjects walked on a prosthetic simulator which was disturbed at the end of the swing phase. They received either no feedback, electrotactile feedback, or auditive feedback at the time of the perturbation. Discussion: The reaction time of the subjects only improved by 40 ms when using auditory feedback, compared to the no-feedback condition. No changes in reaction time were found in the electrotactile feedback condition. Considering perturbation detection was not taken into account in this study, this improvement is not enough for practical applications in upper-leg prosthesis. Clinical relevance Many transfemoral amputees are insecure about their prosthesis, are afraid of falling, or actually fall. Providing feedback specifically during a perturbation may prevent them from falling, or at least give them a chance to react.

Quantitative assessment of rest and action tremor and the effect of cueing in Parkinson’s disease patients treated with deep brain stimulation

Introduction: In Parkinson’s disease rest and action tremor may occur. High frequency deep brain stimulation in basal ganglia nuclei has proved to be effective in the suppression of tremor. In addition, rhythmic auditory cues have shown to result in improved performance of repetitive movements, possibly by suppressing action tremor. The aim of this study was to investigate if electrical stimulation has similar effects on rest and action tremor, and whether in case of action tremor, the effect of electrical stimulation is similar to or enhanced by auditory cueing. Methods: Three exercises were carried out by 7 Parkinson’s disease patients treated with deep brain stimulation of the subthalamic nucleus: 1) sitting at rest; 2) performing a hand tapping movement as fast as possible; 3) performing hand movements on the rhythm of an auditory cueing signal. Inertial sensors registered the movement of the hands during the tests. The exercises were repeated for four different stimulation settings. Results: Electrical stimulation may either enhance or suppress rest and/or action tremor. Power spectral density analysis shows that tremor suppression is accompanied by an increase in relative power in the low frequency band for both rest and action tremor. Most patients could (temporarily) phase lock their hand movements to the cueing signal of 1.6 Hz. Cueing signals at higher frequencies (3.2 and 4.8 Hz) could result in (n:m) phase locking of tremor as well as movement. Conclusion: Electrical stimulation results in a re-scaling of tremor, while auditory cueing may enhance suppression.

Effectiveness of deep brain stimulation in subthalamic nucleus in Parkinson’s disease — a somatotopic organisation

Deep Brain Stimulation (DBS) in subthalamic nucleus (STN) has substantially improved the suppression of symptoms in Parkinsons disease (PD). However, a quantitative understanding of the high-frequency stimulation opn the neuronal elements surrounding the electrode and the resulting effects for the different symptoms for upper and lower extremities is missing. The aim of the study is to investigate if there is a somatotopic organisation of the STN.