Tremor Component Research Articles

Admittance-Based Voluntary-Driven Motion With Speed-Controlled Tremor Rejection

In the elderly, there have been reports of above 10% of the population being diagnosed with pathological tremor. Some patients find the conventional medical solutions, which primarily include medications and surgery, insufficient to treat their conditions. Technologies to mechanically suppress tremor have been proposed as a potential alternative. Robotic solutions for suppressing human tremor typically revolve around identifying and isolating the tremor motion component. This study proposes instead to only estimate the intentional movement and reject any disturbance that interferes with such an intended movement. By designing the control feedback such that motions other than the voluntary are rejected, the tremor component is attenuated. The controller components include an outer-loop admittance feedback loop and an internal velocity feedback loop. Additionally, a state feedback is utilized to improve the velocity tracking. To test the proposed approach, a benchtop tremor simulation device (TSD) was developed. The TSD consists of two motors, which, respectively, simulate the motion of a human joint and the suppressing action of a mechanical suppression system. A parametric stability analysis of the proposed tremor-suppression strategy is presented. A motion profile recorded from a person with tremor is used as human input in the TSD to experimentally validate the proposed tremor rejection strategy. Spectral analysis results show a 99.8% tremor reduction; the power reduction related to the voluntary movement is instead negligible (0.18%). Tracking of a velocity profile results in a small root-mean-square (rms) error (0.58 rad/s). The paper concludes by comparing the proposed approach to others presented in the literature.

Estimation of pathological tremor from recorded signals based on adaptive sliding fast Fourier transform

Pathological tremor is an approximately rhythmic movement and considerably affects patients’ daily living activities. Biomechanical loading and functional electrical stimulation are proposed as potential alternatives for canceling the pathological tremor. However, the performance of suppression methods is associated with the separation of tremor from the recorded signals. In this literature, an algorithm incorporating a fast Fourier transform augmented with a sliding convolution window, an interpolation procedure, and a damping module of the frequency is presented to isolate tremulous components from the measured signals and estimate the instantaneous tremor frequency. Meanwhile, a mechanism platform is designed to provide the simulation tremor signals with different degrees of voluntary movements. The performance of the proposed algorithm and existing procedures is compared with simulated signals and experimental signals collected from patients. The results demonstrate that the proposed solution could detect the unknown dominant frequency and distinguish the tremor components with higher accuracy. Therefore, this algorithm is useful for actively compensating tremor by functional electrical stimulation without affecting the voluntary movement.

LO028: Prospective validation of an iOS app to evaluate tremor in patients with alcohol withdrawal syndrome

Introduction: Ideal management of alcohol withdrawal syndrome (AWS) incorporates a symptom driven approach, whereby patients are regularly assessed using a standardized scoring system (Clinical Institute Withdrawal Assessment for Alcohol-Revised; CIWA-Ar) and treated according to severity. Among the domains assessed by the CIWA-Ar, tremor is the most objective indicator of withdrawal severity, however, the ability of clinicians to reliably quantify tremor is highly dependent on experience. The objective of this study was to prospectively validate an objective, reliable tool to standardize and quantify the severity of alcohol withdrawal tremor using the built-in accelerometer of an iOS application. Methods: A prospective observational study of patients ≥18 years presenting to an academic emergency department in alcohol withdrawal was conducted from Oct 2014 to Aug 2015. Assessments were videotaped by a research assistant and subsequently reviewed by 3 clinical experts, blinded to the primary clinical assessment. Tremor severity was scored using the 8-point CIWA scale (0=no tremor, 7=severe tremor). Accelerometer derived results were compared to expert assessments of each video. Inter-rater agreement was estimated using Cohen’s kappa (k) statistic. Results: 76 patients with 78 tremor recordings were included. Accelerometer derived tremor scores matched exactly with expert assessor scores in 36 (46.2%) cases, within 1 point for 73 (93.6%) cases and differed by ≥ 2 points in 5 (6.4%) cases. The overall kappa for agreement within 1 point for tremor severity was ‘very good’ 0.92 (95% CI: 0.86, 0.99). Conclusion: iOS accelerometer based assessment of the tremor component of the CIWA-Ar score is reliable and has potential to more accurately assess the severity of patients in alcohol withdrawal. We anticipate this resource will be easily disseminated and will impact and improve the care of patients with alcohol withdrawal.

Voluntary-Driven Elbow Orthosis with Speed-Controlled Tremor Suppression.

Robotic technology is gradually becoming commonplace in the medical sector and in the service of patients. Medical conditions that have benefited from significant technological development include stroke, for which rehabilitation with robotic devices is administered, and surgery assisted by robots. Robotic devices have also been proposed for assistance of movement disorders. Pathological tremor, among the most common movement disorders, is one such example. In practice, the dissemination and availability of tremor suppression robotic systems has been limited. Devices in the marketplace tend to either be non-ambulatory or to target specific functions, such as eating and drinking. We have developed a one degree-of-freedom (DOF) elbow orthosis that could be worn by an individual with tremor. A speed-controlled, voluntary-driven suppression approach is implemented with the orthosis. Typically tremor suppression methods estimate the tremor component of the signal and produce a canceling counterpart signal. The suggested approach instead estimates the voluntary component of the motion. A controller then actuates the orthosis based on the voluntary signal, while simultaneously rejecting the tremorous motion. In this work, we tested the suppressive orthosis using a one DOF robotic system that simulates the human arm. The suggested suppression approach does not require a model of the human arm. Moreover, the human input along with the orthosis forearm gravitational forces, of non-linear nature, are considered as part of the disturbance to the suppression system. Therefore, the suppression system can be modeled linearly. Nevertheless, the orthosis forearm gravitational forces can be compensated by the suppression system. The electromechanical design of the orthosis is presented, and data from an essential tremor patient is used as the human input. Velocity tracking results demonstrate an RMS error of 0.31 rad/s, and a power spectral density shows a reduction of the tremor signal by 99.8%, while the intentional component power was reduced by <1%.

Correlates Between Force and Postural Tremor in Older Individuals with Essential Tremor.

Essential tremor (ET) is commonly associated with kinetic tremor. However, other forms of tremor, such as force and postural tremor, may occur in ET with less severity. This study objectively assessed force and postural tremor characteristics in ET with the purpose of identifying the relationships between these tremors. Ten individuals with ET (age 71 ± 5years) and ten healthy controls (age 70 ± 5years) participated in the study. Force tremor was quantified as fluctuations in index finger abduction force during isometric contractions at 10% maximum voluntary contraction (MVC) and 60% MVC. Postural tremor was quantified as index finger acceleration when the subjects held their entire arm unsupported, and when their arm was supported so that only the index finger could move. Time- and frequency-domain parameters were extracted from tremor data, and then correlations within, and between, tremor subtypes were examined. ET force tremor was dependent on contraction intensity whereas postural tremor was unaffected by the level of limb support. Significant correlations existed between frequency components of postural tremor and force tremor amplitude. Force tremor amplitude normalised to the level of contraction intensity correlated to the proportion of power for postural tremor. These correlations were observed for both contraction intensities and both levels of postural support. The proportion of power represents the output of central oscillators in ET patients and therefore correlated well to force tremor. Given that significant relationships existed between spectral features of postural tremor and the overall force tremor amplitude, it is clear that these tremor modalities are not completely independent in older adults with ET.

Tremor in Charcot-Marie-Tooth disease: No evidence of cerebellar dysfunction

ObjectivesTremor in Charcot-Marie-Tooth disease (CMT) can be disabling. Cerebellar abnormalities are thought to underpin neuropathic tremor. Here, we aim to clarify the potential role of the cerebellum in CMT tremor. MethodsWe assessed prevalence of tremor by questionnaire in 84 patients with CMT. Of those, 23 patients with CMT with and without arm tremor and healthy controls underwent a clinical assessment, classical eyeblink conditioning, electro-oculography, visuomotor adaptation test, tremor recording with surface EMG and accelerometry, and retrospective correlation with nerve conduction studies to investigate the possible mechanisms of tremor generation. ResultsThe prevalence study revealed tremor in 21% of patients and in 42% of those it caused impairment of function. Tremor recordings revealed a mild-to-moderate amplitude tremor with a weight load-invariant 7.7Hz frequency component. Performance on classical eyeblink conditioning, visuomotor adaptation and electro-oculography were no different between tremulous and non-tremulous patients and healthy controls. ConclusionsThese results argue against a prominent role for an abnormal cerebellum in tremor generation in the patients studied with CMT. Rather, our results suggest an enhancement of the central neurogenic component of physiological tremor as a possible mechanism for tremor in the patients studied. SignificanceThis study is the first to propose differing pathogenic mechanisms for subtypes of neuropathic tremor.

Dominant component in muscle fatigue induced hand tremor during laparoscopic surgical manipulation.

Accuracy of laparoscopic surgery gets affected by the hand tremor of the surgeons. Though cognitive load is inevitable in such activity which promotes tremor, muscle fatigue induced tremor is significant among the most important sources of tremor. Characteristic of fatigue induced hand tremor and its dominant directional properties are reported in this work. For a fixed laparoscopic tool grip with temporally synchronized predefined task protocols, characteristics of fatigue induced tremors have been studied. Dominant component of tremor was found to be in the sagittal plane in case of both static and dynamic tasks. In order to relate it with the muscle fatigue level, spectral properties of surface electromyography (SEMG) were also investigated simultaneously. A study of transient effect on tool positioning was also included, which conjointly advocates the other experimental results on fatigue induced hand tremor as well.

Smartphone-based evaluation of parkinsonian hand tremor: quantitative measurements vs clinical assessment scores.

With an ever-growing number of technologically advanced methods for the diagnosis and quantification of movement disorders, comes the need to assess their accuracy and see how they match up with widely used standard clinical assessment tools. This work compares quantitative measurements of hand tremor in twenty-three Parkinson's disease patients, with their clinical scores in the hand tremor components of the Unified Parkinson's Disease Rating Scale (UPDRS), which is considered the "gold standard" in the clinical assessment of the disease. Our measurements were obtained using a smartphone-based platform, which processes the phone's accelerometer and gyroscope signals to detect and measure hand tremor. The signal metrics used were mainly based on the magnitude of the acceleration and the rotation rate vectors of the device. Our results suggest relatively strong correlation (r>0.7 and p<;0.01) between the patients' UPDRS hand tremor scores and the signal metrics applied to the measured signals.

Infrasonic component of volcano-seismic eruption tremor

Air-ground and ground-air elastic wave coupling are key processes in the rapidly developing field of seismoacoustics and are particularly relevant for volcanoes. During a sustained explosive volcanic eruption, it is typical to record a sustained broadband signal on seismometers, termed eruption tremor. Eruption tremor is usually attributed to a subsurface seismic source process, such as the upward migration of magma and gases through the shallow conduit and vent. However, it is now known that sustained explosive volcanic eruptions also generate powerful tremor signals in the atmosphere, termed infrasonic tremor. We investigate infrasonic tremor coupling down into the ground and its contribution to the observed seismic tremor. Our methodology builds on that proposed by Ichihara et al. (2012) and involves cross-correlation, coherence, and cross-phase spectra between waveforms from nearly collocated seismic and infrasonic sensors; we apply it to datasets from Mount St. Helens, Tungurahua, and Redoubt Volcanoes.

Targeting the Red Nucleus for Cerebellar Tremor

Deep brain stimulation of the thalamus (and especially the ventral intermediate nucleus) does not significantly improve a drug-resistant, disabling cerebellar tremor. The dentato-rubro-olivary tract (Guillain-Mollaret triangle, including the red nucleus) is a subcortical loop that is critically involved in tremor genesis. We report the case of a 48-year-old female patient presenting with generalized cerebellar tremor caused by alcohol-related cerebellar degeneration. Resistance to pharmacological treatment and the severity of the symptoms prompted us to investigate the effects of bilateral deep brain stimulation of the red nucleus. Intra-operative microrecordings of the red nucleus revealed intense, irregular, tonic background activity but no rhythmic components that were synchronous with upper limb tremor. The postural component of the cerebellar tremor disappeared during insertion of the macro-electrodes and for a few minutes after stimulation, with no changes in the intentional (kinetic) component. Stimulation per se did not reduce postural or intentional tremor and was associated with dysautonomic symptoms (the voltage threshold for which was inversed related to the stimulation frequency). Our observations suggest that the red nucleus is (1) an important centre for the genesis of cerebellar tremor and thus (2) a possible target for drug-refractory tremor. Future research must determine how neuromodulation of the red nucleus can best be implemented in patients with cerebellar degeneration.

Thalamic physiology of intentional essential tremor is more like cerebellar tremor than postural essential tremor

The neuronal physiological correlates of clinical heterogeneity in human essential tremor are unknown. We now test the hypothesis that thalamic neuronal and EMG activities during intention essential tremor are similar to those of the intention tremor which is characteristic of cerebellar lesions. Thalamic neuronal firing was studied in a cerebellar relay nucleus (ventral intermediate, Vim) and in a pallidal relay nucleus (ventral oral posterior, Vop) during stereotactic surgery for the treatment of tremor. Nine patients with essential tremor were divided clinically into two categories: one with a substantial component of tremor with intention (termed intention ET) and the other without (postural ET). These types of essential tremor were compared with patients having intention tremor plus other clinical signs of cerebellar disease (cerebellar tremor). Neurons in patients with either intention ET or cerebellar tremor had lower firing rates and lower spike×EMG coherence than those in patients with postural ET. Patients with intention ET had a lower spike×EMG phase lead than those with postural ET. Overall, thalamic activity measures of intention ET were different from postural ET but not apparently different from those of cerebellar tremor. One patient with the intention ET (number 4) had a good response to a left thalamotomy and then suffered a right cerebellar hemispheric infarct five years later. After the stroke the intention ET recurred, which is consistent with our hypothesis that intention ET is similar to that of the intention tremor which is characteristic of cerebellar lesions.

Fluctuation strength on real sound: Motorbike exhaust and marimba tremolo

Psychoacoustics research has been contributed on evaluating the timbre of acoustic signals. The fluctuation strength (FS) has been respected as the important index which describes the sensory fluctuation of the acoustic signal based on its amplitude, frequency and the combination of them as well. Although FS has been calculated by tremor components on acoustic signals, here points out not only the inappropriateness of the calculation when simply based on literatures but also a method which focuses on the shape of the waveform in order to extract parameters from it, so that the FS is newly calculated by our original method with estimation results of the subjective scores of sensory fluctuation. Signals dealt with are motorbike exhaust sounds and tremolo played by marimba. The developed method is then applied to the design of an electric vehicle approaching sound for pedestrians in order to let pedestrians notice the approaching car without rising up the sensory loudness, on which designed sounds have a fluctuation with irregular pulses proven to give us the sensory fluctuation so that it is expected to be noticeable for pedestrians. This paper discusses the possibility to apply the prestigious psychoacoustic indexes to industrial and artistic sounds.

On-Off Tremor Suppression Orthosis with Electromagnetic Brake

Pathological tremor is a common neurological movement disorder characterized by involuntary rhythmic oscillation of body parts. Available treatments are often insufficiently effective or are accompanied by severe side effects. This work proposes a lightweight, portable elbow tremor suppression orthosis using an electromagnetic brake (EB) with on-off actuation scheme. The device reduces tremor amplitude and could potentially be donned under clothes. At this stage of the project, the focus is on action tremor (postural) such as essential tremor. The elbow joint is commonly affected by tremor; it can be modelled as a single Degree Of Freedom (DOF) joint and was selected to test our hypothesis and prototype. The orthosis is actuated by an (EB). The algorithm alternates between full suppression and no suppression, and relies on the high frequency nature of tremor relative to the frequency of Activities of Daily Living (ADL). A MEMS gyro signal is processed to assess the tremor component. The system successfully reduces tremor amplitude with over 88% of tremor signal power reduction.

The resonant component of human physiological hand tremor is altered by slow voluntary movements

Limb resonance imparts a characteristic spectrum to hand tremor. Movement will alter the resonance. We have examined the consequences of this change. Rectified forearm extensor muscle EMG and physiological hand tremor were recorded. In postural conditions the EMG spectrum is relatively flat whereas the acceleration spectrum is sharply peaked. Consequently, the gain between EMG and acceleration is maximal at the frequency where the tremor is largest (∼8 Hz). The shape of the gain curve implies mechanical resonance. Substantial alterations in posture do not significantly change the characteristics of the tremor or the shape or size of the gain curve. By contrast, slow or moderately paced voluntary wrist flexion–extension movements dramatically increase the hand tremor size and lower its peak frequency. These changes in size and frequency of the tremor cannot be attributed to changes in the EMG. Instead they reflect a very large change in the size and shape of the gain curve relating EMG to acceleration. The gain becomes larger and the peak moves to a lower frequency (∼6 Hz). We suggest that a movement-related (thixotropic) alteration in resonant properties of the wrist provides a simple explanation for these changes. The mechanism is illustrated by a model. Our new findings confirm that resonance plays a major role in wrist tremor. We also demonstrate that muscles operate very differently under postural and dynamic conditions. The different coupling between EMG and movement in posture and when moving must pose a considerable challenge for neural predictive control of skeletal muscles.

EMG-Based Characterization of Pathological Tremor Using the Iterated Hilbert Transform

The identification and characterization of pathological tremor are necessary for the development of techniques for tremor suppression, for example, based on functional electrical stimulation. For this purpose, the amplitude and phase characteristics of the tremor signal should be estimated by effective detection techniques, either from the kinematics or from muscle recordings. This paper presents an approach for the estimation of the characteristics of pathological tremor from the surface electromyogram (EMG) signal based on the iterated Hilbert transform (IHT). It is shown that the IHT allows an asymptotically exact modeling of the tremor and the voluntary activity components in the surface EMG, and an effective demodulation of the pathological tremor parameters. The method was tested on signals generated by a recent model for tremor generation as well as experimentally recorded from patients affected by pathological tremor. The results showed the ability of the proposed approach to demodulate effectively the tremor amplitude (average correlation with imposed amplitude: R(2)=0.52), the frequency (root mean square error in frequency estimation: 2.6 Hz), and phase, as well as the degree of voluntary activity (correlation with simulated inertial load: R(2)=0.62). The application of the method to the experimental data indicated that the estimated tremor component closely resembles inertial measurements of limb movement (peak cross correlation across four patients: 0.62±0.15). Compared to the performance of empirical mode decomposition, the proposed method proved to be more accurate for tremor characterization without a priori knowledge of the tremor characteristics. This method can be used as a part of a control system in strategies for suppression of tremor.

10 Hz periodic component influences lower frequency component of the physiological tremor at low force levels

A positive correlation has been reported between the amplitudes of the 10 Hz and lower frequency components of the physiological tremor (PT) at low force levels, though the generation mechanisms based on motor unit (MU) firing properties are different. This study aimed to investigate the causal relation between these fluctuations. A computer simulation was performed to alter the fluctuation intensity, which enabled manipulation of MU firing properties. Two types of MU contributions to synchronization activity were considered to influence the intensity of the 10 Hz PT: (1) number of MUs involved in synchronization and (2) synchrony between MUs. The impact of oscillatory excitatory input from the central nervous system on the generation of the 10 Hz PT was also evaluated. The results showed that the lower frequency fluctuation (LF fluctuation) was influenced by the number of MUs contributing to the 10 Hz PT amplitude. The synchrony between MUs and the oscillatory excitatory input had no influence on the LF fluctuation. In conclusion, MU synchronization in a certain frequency range increased the fluctuations not only at the synchronizing frequency but also at lower frequencies, and the number of MUs involved in synchronization was a plausible factor to explain the correlation between the 10 Hz and LF fluctuations.

Estimation of physiological tremor from accelerometers for real-time applications.

Accurate filtering of physiological tremor is extremely important in robotics assisted surgical instruments and procedures. This paper focuses on developing single stage robust algorithms for accurate tremor filtering with accelerometers for real-time applications. Existing methods rely on estimating the tremor under the assumption that it has a single dominant frequency. Our time-frequency analysis on physiological tremor data revealed that tremor contains multiple dominant frequencies over the entire duration rather than a single dominant frequency. In this paper, the existing methods for tremor filtering are reviewed and two improved algorithms are presented. A comparative study is conducted on all the estimation methods with tremor data from microsurgeons and novice subjects under different conditions. Our results showed that the new improved algorithms performed better than the existing algorithms for tremor estimation. A procedure to separate the intended motion/drift from the tremor component is formulated.

Gender differences in hand stability of normal young people assessed at low force levels

To examine gender differences in hand stability, finger position and force holding tasks at low force levels were conducted with 30 male and 30 female young adults. Total fluctuation was defined as the standard deviation of measured data and fluctuation and the 10-Hz component of the physiological tremor were compared between maleand female subjects. In all tasks, the total fluctuation and the 10-Hz tremor were significantly larger in male subjects than females. On average, the fluctuation was 1.3 times larger and the 10-Hz tremor was 1.6 times larger. The results of this study suggest that women have superior hand stability compared with men at low force levels. Finger length, maximal voluntary contraction and surface electromyography were also measured and factors related to gender differences in hand stability are discussed. Statement of Relevance: Hand stability is crucial for precise manual operations. This study demonstrated gender differences in hand steadiness at low force levels. Though hand dexterity cannot be explained only by hand stability, the results of thisstudy are useful not only for occupational aptitude tests but also for neuropsychological tests.

P150 The central component of physiologic tremor is not a positive predictive factor for the incidence of a pathologic tremor

P150 The central component of physiologic tremor is not a positive predictive factor for the incidence of a pathologic tremor

On the Need for Rectification of Surface EMG

to the editor: The electromyogram (EMG) as an indirect measure of motor unit activity has proved invaluable in motor control studies. Increasingly, the application of frequency domain techniques to EMG signals has provided important insight into the structure and function of the human motor system.