Tuned vibration absorber for suppression of rest tremor in Parkinson's disease

Computational study and validation of a novel passive hand tremor attenuator

Tremors are a prevalent movement disorder due to a nervous system condition that leads to involuntary muscle movements observed in patients. This paper converts the tremorous anatomical human arm model to a single degree of freedom (SDOF) forced vibration problem. The mathematical modelling with Euler-Lagrange's equation is performed for the SDOF human arm model with two different potential vibration absorbers. A computational study is conducted on MATLAB Simulink by MathWorks Inc. (Natick, MA) to compare two absorbers, and the results are verified on the multibody dynamics simulation solution software, MSC Adams by Hexagon AB. It is concluded that the T beam-shaped vibration absorber represented a higher amplitude reduction, up to 80%, compared to the inertial mass absorber, which had an amplitude reduction of 65% over the range of frequencies. Experiments conducted with the T beam absorber prototype also support the computational findings. Future research focuses on designing an ergonomic wearable device with a proposed T-beam absorber that can passively attenuate the tremor at various frequencies.

Distribution of tremorogenic activity among the major superficial muscles of the upper limb in persons with Essential tremor

OBJECTIVE

Peripheral tremor suppression has the potential to reduce tremor, but we do not currently know where best to intervene. The purpose of this study was to characterize the distribution of tremorogenic activity among upper-limb muscles.

METHODS

Surface electromyography was recorded from the 15 major superficial muscles of the upper limb while 25 patients with Essential Tremor performed postural and kinetic tasks. We defined tremorogenic activity as power in the tremor band (4-8 Hz) and determined the distribution of this power among muscles.

RESULTS

The distribution varied considerably between patients (mean r = 0.58), but on average, the greatest power was found in the anterior deltoid and extensor carpi ulnaris muscles. Other muscles with high power included the extensor carpi radialis, pectoralis major, lateral deltoid, and brachialis muscles. This distribution was similar (mean r ≥ 0.88) for postural and kinetic tremor, various limb configurations, repetitions, and patient characteristics (sex, tremor severity, age of onset, and duration).

CONCLUSIONS

We identified a rough pattern in which muscles opposing gravity appeared to have the highest tremor-band power; we hypothesize that the distribution of tremorogenic muscle activity depends in part on the distribution of voluntary activity required by the task.

SIGNIFICANCE

Understanding which muscles exhibit the most tremorogenic activity is one of the steps in the pursuit of optimizing peripheral tremor suppression.

4D printing of soft orthoses for tremor suppression

Tremor is an involuntary and oscillatory movement disorder that makes daily activities difficult for affected patients. Hand tremor-suppression orthoses are noninvasive, wearable devices designed to mitigate tremors. Various studies have shown that these devices are effective, economical, and safe; however, they have drawbacks such as large weight, awkward shape, and rigid parts. This study investigates different types of tremor-suppression orthoses and discusses their efficiency, mechanism, benefits, and disadvantages. First, various orthoses (with passive, semi-active, and active mechanisms) are described in detail. Next, we look at how additive manufacturing (AM) has progressed recently in making sensors and actuators for application in tremor orthoses. Then, the materials used in AM are further analyzed. It is found that traditional manufacturing problems can be solved with the help of AM techniques, like making orthoses that are affordable, lighter, and more customizable. Another concept being discussed is using smart materials and AM methods, such as four-dimensional (4D) printing, to make orthoses that are more comfortable and efficient.

Graphic abstract

Distribution of tremor among the major degrees of freedom of the upper limb in subjects with Essential Tremor

OBJECTIVE

Although Essential Tremor is one of the most common movement disorders, we do not currently know which muscles are most responsible for tremor. Determining this requires multiple steps, one of which is characterizing the distribution of tremor among the degrees of freedom (DOF) of the upper limb.

METHODS

Upper-limb motion was recorded while 22 subjects with ET performed postural and kinetic tasks involving a variety of limb configurations. We calculated the mean distribution of tremor among the seven DOF from the shoulder to the wrist, as well as the effect of limb configuration, repetition, and subject characteristics (sex, tremor onset, duration, and severity) on the distribution.

RESULTS

On average, kinetic tremor was greatest in forearm pronation-supination and wrist flexion-extension, intermediate in shoulder internal-external rotation and wrist radial-ulnar deviation and then shoulder flexion-extension and elbow flexion-extension, and least in shoulder abduction-adduction. The average distribution of postural tremor was similar except for forearm pronation-supination, which played a smaller role than in kinetic tremor. Limb configuration and subject characteristics did significantly affect tremor, but practically only in forearm pronation-supination and wrist flexion-extension. There were no significant differences between repetitions, indicating that the distribution was consistent over the duration of the experiment.

CONCLUSIONS

This paper presents a thorough characterization of tremor distribution from the shoulder to the wrist.

SIGNIFICANCE

Understanding which DOF exhibit the most tremor may lead to more targeted peripheral tremor suppression.

A Soft Exoskeleton for Tremor Suppression Equipped with Flexible Semiactive Actuator

Pathological tremor is a kind of movement disorder that affects a wide range of patients with Parkinson's disease and essential tremor. Different from available clinical treatments for tremor, including drug and surgery therapy, a novel soft exoskeleton for tremor suppression (SETS) based on assistive technologies is proposed in this study. The SETS system is equipped with a controllable flexible semiactive actuator based on magnetorheological fluid. To overcome the drawbacks of traditional fluidic semiactive actuators, we devise a soft semiactive actuator that is a combination of cylinder-piston damper and elastic fluidic damper. The overall system is characterized with low mass, compact structure, comfortable wearability as well as real-time adjustability for tremor attenuation with varying intensity. The SETS can assist in suppressing tremor of wrist joint in three degrees of freedom. The prototype weighs about 255 g and can yield a maximum damping force of about 11 N. Simulation studies and experimental tests were carried out to evaluate the performance of the system. The results show that the SETS could reduce wrist tremor regarding magnitude of acceleration and angular velocity by 61.39% and 56.22%, respectively, which validate the manifest mechanical efficiency of this functional system.

Hand tremor suppression device for patients suffering from Parkinson's disease

In this study, a wearable device is developed as a mechanical treatment to suppress hand tremors in people with Parkinson's disease (PwPD). The biodynamic modelling of the human hand was done by considering the hand as a primary mass-spring-damper system. Dual passive vibration absorbers have been designed to match the frequencies of tremors. The performance assessment of the device was performed using the temporal response of hand tremors. The results showed that the device reduced the amplitude of the angular movement of the wrist by 57.25%. The device fabricated in the form of a bracelet was easy to wear by PwPD when needed.

EFFECT OF GYROSCOPE PARAMETERS ON GYROSCOPIC TREMOR SUPPRESSION IN A SINGLE DEGREE OF FREEDOM

Although tremor is one of the most common movement disorders, there are few effective tremor-suppressing options available to patients. Gyrostabilization is a potential option, but we do not currently know how to optimize gyrostabilization for tremor suppression. To address this gap, we present a systematic investigation of how gyrostabilizer parameters affect tremor suppression in a single degree of freedom (DOF). A simple model with a single DOF at the wrist and a gyroscope mounted on the back of the hand was used to focus on the most basic effects. We simulated the frequency response of the system (hand + gyroscope) to a tremorogenic input torque at the wrist. Varying system parameters one at a time, we determined the effect of individual parameters on the system’s frequency response. To minimize the bandwidth without adding significant inertia, the inertia and spin speed of the flywheel should be as high as design constraints allow, whereas the distance from the wrist joint axis to the gyroscope and the precession stiffness and damping should be kept as low as possible. The results demonstrate the potential of gyroscopic tremor suppression and can serve as foundation for further investigations of gyroscopic tremor suppression in the upper limb.

Controlling a motorized orthosis to follow elbow volitional movement: tests with individuals with pathological tremor

BACKGROUND

There is a need for alternative treatment options for tremor patients who do not respond well to medications or surgery, either due to side effects or poor efficacy, or that are excluded from surgery. The study aims to evaluate feasibility of a voluntary-driven, speed-controlled tremor rejection approach with individuals with pathological tremor. The suppression approach was investigated using a robotic orthosis for suppression of elbow tremor. Importantly, the study emphasizes the performance in relation to the voluntary motion.

METHODS

Nine participants with either Essential Tremor (ET) or Parkinson's disease (PD) were recruited and tested off medication. The participants performed computerized pursuit tracking tasks following a sinusoid and a random target, both with and without the suppressive orthosis. The impact of the Tremor Suppression Orthosis (TSO) at the tremor and voluntary frequencies was determined by the relative power change calculated from the Power Spectral Density (PSD). Voluntary motion was, in addition, assessed by position and velocity tracking errors.

RESULTS

The suppressive orthosis resulted in a 94.4% mean power reduction of the tremor (p < 0.001) - a substantial improvement over reports in the literature. As for the impact to the voluntary motion, paired difference tests revealed no statistical effect of the TSO on the relative power change (p = 0.346) and velocity tracking error (p = 0.283). A marginal effect was observed for the position tracking error (p = 0.05). The interaction torque with the robotic orthosis was small (0.62 Nm) when compared to the maximum voluntary torque that can be exerted by adult individuals at the elbow joint.

CONCLUSIONS

Two key contributions of this work are first, a recently proposed approach is evaluated with individuals with tremor demonstrating high levels of tremor suppression; second, the impact of the approach to the voluntary motion is analyzed comprehensively, showing limited inhibition. This study also seeks to address a gap in studies with individuals with tremor where the impact of engineering solutions on voluntary motion is unreported. This study demonstrates feasibility of the wearable technology as an effective treatment that removes tremor with limited impediment to intentional motion. The goal for such wearable technology is to help individuals with pathological tremor regain independence in activities affected by the tremor condition. Further investigations are needed to validate the technology.

Toward quantitative characterization of essential tremor for future tremor suppression

Tremor is the most common movement deficit and manifests in a variety of disorders, including Essential Tremor, Parkinson's Disease, Dystonia, and Cerebellar Ataxia. Although medication and surgical interventions have significantly reduced patient suffering, they are only partially effective and can carry undesired side effects, leaving many patients without satisfactory treatment options. Wearable tremor-suppressing devices could provide an alternative to medication and surgery. Multiple research groups have developed orthotic prototypes to low-pass filter tremor, but these devices have not yet been optimized for in-vivo use. Optimizing non-invasive tremor suppression requires an understanding of where the tremor originates mechanically (which muscles) and how it propagates to the hand (where it matters most). Here we present on the beginnings of our multi-pronged work to determine the origin, propagation, and distribution of Essential Tremor, and we provide preliminary results.

Design of a noninvasive and smart hand tremor attenuation system with active control: a simulation study

This paper presents the design and simulation of a handheld device for people with hand tremor, such as Parkinson's and essential tremor patients. This device can be used as a pen for smartphones or as a spoon. The designed system includes two links, which are connected to two servomotors, which are mounted in orthogonal directions. To attenuate the effect of hand tremor on the tip of device, PID and computed torque methods are used to actively control the system. These controllers are used to control the rotation of the motors for moving the links in opposite directions of the hand tremor. Performance of the device with mentioned controllers is studied for different applications and finally, the results of both controllers are discussed and compared. Based on the presented results in this study, the designed device is able to suppress the hand tremor up to 75% during eating and 65% during following a spiral pattern. Graphical abstract Design of a noninvasive and smart hand tremor attenuation system: a simulation study.

Tremor Reduction at the Palm of a Parkinson's Patient Using Dynamic Vibration Absorber

Parkinson’s patients suffer from severe tremor due to an abnormality in their central oscillator. Medications used to decrease involuntary antagonistic muscles contraction can threaten their life. However, mechanical vibration absorbers can be used as an alternative treatment. The objective of this study is to provide a dynamic modeling of the human hand that describes the biodynamic response of Parkinson’s patients and to design an effective tuned vibration absorber able to suppress their pathological tremor. The hand is modeled as a three degrees-of-freedom (DOF) system describing the flexion motion at the proximal joints on the horizontal plane. Resting tremor is modeled as dual harmonic excitation due to shoulder and elbow muscle activation operating at resonance frequencies. The performance of the single dynamic vibration absorber (DVA) is studied when attached to the forearm and compared with the dual DVA tuned at both excitation frequencies. Equations of motion are derived and solved using the complex transfer function of the non-Lagrangian system. The absorber’s systems are designed as a stainless steel alloy cantilevered beam with an attached copper mass. The dual DVA was the most efficient absorber which reduces 98.3%–99.5%, 97.0%–97.3% and 97.4%–97.5% of the Parkinson’s tremor amplitude at the shoulder, elbow and wrist joint.

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%.

Essential tremor suppression by a novel self-balancing device

BACKGROUND

There are many associated devices using impedance method. However, they cannot completely suppress tremor. Other methods using active vibration control have been a challenging problem for industrial and academic researchers. Potential applications of the latter for tremor patients are still not realized.

OBJECTIVES

This article presents a novel method for suppressing human lower arm tremor in essential tremor by using a self-balancing technique.

STUDY DESIGN

In this article, a rotating unbalanced mass actuator was used to imitate an arm tremor with the same frequency range obtained from clinical sources. A novel counter-balance device was designed to attach the fictitious arm. The tremor reduction is expecting quantitatively.

METHODS

A Proportional-Integral-Derivative controller and an algorithm programmed in LabVIEW are proposed to control a rotating unbalanced mass actuator, anti-shaker, in order to counter the tremor. The self-balancing system for the new approach was obtained when both amplitudes and frequencies of anti-shaker and tremor are the same.

RESULTS

The results show that this method can reduce vibration of tremor in the order of 0.001 rad/s(2).

CONCLUSION

This method can suppress the vibration and can also auto-tune to counter the tremor in a range of 4-12 Hz bandwidth.

CLINICAL RELEVANCE

The therapy of arm tremor was associated with using counter-devices to palliate the vibration magnitude. Conventional methods such as physical surgery and drugs cannot completely eliminate tremor. The novel counter-device is an alternative technique with promising application for clinical uses for tremor patients without involving harmful surgery.

Robust controller for tremor suppression at musculoskeletal level in human wrist

Tremor is a rhythmical and involuntary oscillatory movement of a body part and it is one of the most common movement disorders. Orthotic devices have been under investigation as a noninvasive tremor suppression alternative to medication or surgery. The challenge in musculoskeletal tremor suppression is estimating and attenuating the tremor motion without impeding the patient's intentional motion. In this research a robust tremor suppression algorithm was derived for patients with pathological tremor in the upper limbs. First the motion in the tremor frequency range is estimated using a high-pass filter. Then, by applying the backstepping method the appropriate amount of torque is calculated to drive the output of the estimator toward zero. This is equivalent to an estimation of the tremor torque. It is shown that the arm/orthotic device control system is stable and the algorithm is robust despite inherent uncertainties in the open-loop human arm joint model. A human arm joint simulator, capable of emulating tremorous motion of a human arm joint was used to evaluate the proposed suppression algorithm experimentally for two types of tremor, Parkinson and essential. Experimental results show 30-42 dB (97.5-99.2%) suppression of tremor with minimal effect on the intentional motion.

Hybrid learning control for improving suppression of hand tremor

Patients with hand tremors may find routine activities such as writing and holding objects affected. In response to this problem, an active control technique has been examined in order to lessen the severity of tremors. In this article, an online method of a hybrid proportional-integral control with active force control strategy for tremor attenuation is presented. An intelligent mechanism using iterative learning control is incorporated into the active force control loop to approximate the estimation mass parameter. Experiments were conducted on a dummy hand model placed horizontally in a tremor test rig. When activated by a shaker in the vertical direction, this resembles a postural tremor condition. In the proportional-integral plus active force control, a linear voice coil actuator is used as the main active tremor suppressive element. A sensitivity analysis is presented to investigate the robustness of the proposed controller in a real-time control environment. The findings of this study demonstrate that the intelligent active force control and iterative learning controller show excellent performance in reducing tremor error compared to classic pure proportional, proportional-integral and hybrid proportional-integral plus active force control controllers.

A telemedicine instrument for remote evaluation of tremor: design and initial applications in fatigue and patients with Parkinson's disease

INTRODUCTION

A novel system that combines a compact mobile instrument and Internet communications is presented in this paper for remote evaluation of tremors. The system presents a high potential application in Parkinson's disease and connects to the Internet through a TCP/IP protocol. Tremor transduction is carried out by accelerometers, and the data processing, presentation and storage were obtained by a virtual instrument. The system supplies the peak frequency (fp), the amplitude (Afp) and power in this frequency (Pfp), the total power (Ptot), and the power in low (1-4 Hz) and high (4-7 Hz) frequencies (Plf and Phf, respectively).

METHODS

The ability of the proposed system to detect abnormal tremors was initially demonstrated by a fatigue study in normal subjects. In close agreement with physiological fundamentals, the presence of fatigue increased fp, Afp, Pfp and Pt (p < 0.05), while the removal of fatigue reduced all the mentioned parameters (p < 0.05). The system was also evaluated in a preliminary in vivo test in parkinsonian patients. Afp, Pfp, Ptot, Plf and Phf were the most accurate parameters in the detection of the adverse effects of this disease (Se = 100%, Sp = 100%), followed by fp (Se = 100%, Sp = 80%). Tests for Internet transmission that realistically simulated clinical conditions revealed adequate acquisition and analysis of tremor signals and also revealed that the user could adequately receive medical recommendations.

CONCLUSIONS

The proposed system can be used in a wide spectrum of telemedicine scenarios, enabling the home evaluation of tremor occurrence under specific medical treatments and contributing to reduce the costs of the assistance offered to these patients.