Parkinson’s Disease Tremor Suppression

A Double Approach Study - Part 1

Wellington C. Pinheiro, Bruno E. Bittencourt, Lucas B. Luiz, Lucas A. Marcello, Vinicius F. Antonio,

Paulo Henrique A. de Lira, Ricardo G. Stolf and Maria Claudia F. Castro

Department of Electrical Engineering, University Center of FEI, S

ao Bernardo do Campo, Brazil

Keywords:

Parkinson’s Disease, Tremor Suppression, Orthosis, Functional Electric Stimulation.

Abstract:

Parkinson’s Disease (PD) is a neurodegenerative disorder that affects mostly elderly people. Approximately

2% of world population, over 60 years old, lives with PD. This pathology is recognized not only by motor

symptoms such as tremor, postural gait and rigidity, but also, nonmotor symptoms as depression and sleep

abnormalities may be developed as well. In Brazil, according to the Ministry of Health, 200,000 people face

the challenge to develop day-by-day activities due to PD. More than just a disease causing motor disturbances,

PD brings to patients uncertainties about their ability to take care of themselves independently. In this con-

text, assistive technologies assume an important position in order to bring back life quality and self-trust to

PD patients. This work aims to study techniques, develop hardware and software for a better approach in

tremor suppression in order to bring back life quality to PD patients. This study approaches the problem of

ﬂexion/extension carpi radialis tremor suppression using two different strategies. The ﬁrst is a mechanical sup-

pression based on a servomotor opposing to tremor movement. The second strategy is a functional electrical

stimulator. Both systems are triggered by electromyogram (EMG).

1 INTRODUCTION

Parkinson’s disease is the second most common neu-

rodegenerative disorder in the world, loosing only to

Alzheimer’s. According to Dexter and Jenner (2013)

2% of the world population, over 60 years old, lives

with PD. In Brazil, numbers from Ministry of Health

estimates that 200,000 Brazilians are living with PD,

among those 75% have tremors as a main symptom

(Helmich et al., 2012). As a matter of fact, the

increasing life expectancy rates, also increases PD

prevalence. Projections from United Nations (UN) in-

dicate that in six decades the elderly population will

be 3 times bigger than now, achieving 2 billion peo-

ple world wide. The Brazilian Institute of Geography

and Statistics (IBGE) estimates that in 2050 Brazilian

aged population will be around 54.8 million people.

Economic related aspects of Parkinson’s disease are

also relevant. According to Findley (2007), just in the

United States, PD moves the economy in 23 billion

dollars yearly, considering direct and indirect costs.

A PD patient costs on average US$ 10,000 every year

in the United States (Dexter and Jenner, 2013).

In this context, assistive technology has a crucial

role, not only because market growing projections,

but also to help an increasing portion of world popu-

lation to live without all impairments imposed by PD.

This work focus on action tremor and presents two

methods of tremor suppression based on a mechanical

orthosis controlled by a servomotor and a functional

electrical stimulation (FES) system, both of them trig-

gered by eletromyography (EMG). It is organized as

follow: Section 1 presents an introductory view and

clinical aspects of PD. Section 2 presents alternatives

for PD symptoms control. Section 3 presents materi-

als and methods. Section 4 introduces hardware de-

velopment. Section 5 shows signal processing strate-

gies applied to EMG signal of PD. Finally, section

6 presents results of hardware and software develop-

ment and tests.

1.1 Clinical Aspects

The central nervous system (CNS) consists of neu-

rons interconnected as a network through synapses

Corresponding author: Maria Claudia F. Castro, PhD

(mclaudia@fei.edu.br). University Center of FEI, Depar-

tament of Electrical Engineering. Avenida Humberto de

Alencar Castelo Branco, 3972, S

ao Bernardo do Campo -

SP, Zip: 09850-901

Pinheiro W., Bittencourt B., Luiz L., Marcello L., Antonio V., de Lira P., Stolf R. and Castro M.

Parkinsonâ

Zs Disease Tremor Suppression - A Double Approach Study - Part 1.

DOI: 10.5220/0006152501490155

In Proceedings of the 10th International Joint Conference on Biomedical Engineering Systems and Technologies (BIOSTEC 2017), pages 149-155

ISBN: 978-989-758-216-5

149

which includes dendrites and axons. Communication

neuron to neuron takes place using neurotransmitters.

Neurotransmitters are brain chemical signaling, with

inhibitory and excitatory function, which is released

at synaptic gap. In this context, substantia nigra pars

compacta (SNpc) has as its role dopamine production,

a inhibitory neurotransmitter. SNpc is connected with

other neuronal structures such as striatum (caudate

and putamen), globus pallidus internal and external

and subthalamic nucleus, together called basal gan-

glia as shown in ﬁgure 1 (Jankovic and Tolosa, 2006).

Figure 1: Sagittal and Coronal view. Adapted from Purves

et al. (2011).

For PD these structures are quite important be-

cause when a ”movement command” is started at

motor cortex, the electrical impulses are transmitted

through the striatum, which works like a ﬁlter. In the

case of an voluntary movement, the striatum increases

thalamic and cortical neuronal activity making the

movement more likely to happen. However, if it is an

involuntary movement, SNpc neurons are activated,

that in turn use dopamine as inhibitory neurotrans-

mitter, diminishing thalamic and cortical activity sup-

pressing undesired movements. Parkinson’s disease,

among many other problems, affects dopamine pro-

duction causing its diminishment, consequently mak-

ing striatum hyperactivated and difﬁculting move-

ment control (Jankovic and Tolosa, 2006).

Some motor symptoms are classically used to di-

agnose PD such as bradykinesia, tremor, rigidity, pos-

tural problems, difﬁcult to speak or swallow. How-

ever, there are also some important nonmotor symp-

toms, even though it is hard to associate them with

PD at the ﬁrst sight, symptoms such as sleep depri-

vation, depression and cognitive impairment may be

observed as well (Helmich et al., 2012).

1.2 Classiﬁcation and Deﬁnitions of

Tremor

Tremor can be deﬁned as an oscillatory rhythmic

activity, even though many pathologies may cause

tremor as a symptom, it is important to emphasize that

voluntary movements is accompanied with tremors,

and the boundary between normal and pathological

tremor is hard to deﬁne (Jankovic and Tolosa, 2006).

According to Jankovic and Tolosa (2006) tremors

can be largely classiﬁed into three categories as rest-

ing tremor, action tremor and postural tremor. Rest-

ing tremor is deﬁned as the oscillatory manifestation

when a limb is not voluntarily activated and com-

pletely supported against gravity action. The postu-

ral variant is deﬁned when tremor happen on an indi-

vidual maintaining a position opposed to gravity ac-

tion. Action tremor is the one which occur concomi-

tantly to muscular contraction for voluntary move-

ment. This work focus on action tremor because it is

more disabling than rest and postural tremors (Rahimi

et al., 2009).

Another important factor is tremor frequency, also

in agreement with Jankovic and Tolosa (2006) it is

classiﬁed as low, medium and high frequency tremor.

Low frequency are tremors with oscillation frequency

lower than 4Hz, medium frequency 4 to 10Hz, and

high frequency bigger than 10Hz.

2 ALTERNATIVES FOR PD

TREMOR SUPPRESSION

Regular treatment for PD has not change too much

over the last decades. It is based on dopaminergic

drugs intake, due to inefﬁciency in some cases, or

even side effect, new technologies have been devel-

oped to reduce Parkinson’s disease effects on daily

life. Some initiatives are extremely invasive, such as

Deep Brain Stimulation (DBS), and presents inher-

ent risks of a surgical procedures and promising re-

sults. Others are non-invasive technologies some for

tremor suppression on the limbs such as FES and or-

thoses, or for tremor handling devices such as Lyft-

ware and Gyroglove, trying to avoid tremor related

inconveniences. It is important to emphasize that un-

til present moment all approaches, pharmaceuticals or

not, treat just PD symptoms and do not avoid disease

progression, and consequently worsen of associated

symptoms.

2.1 Deep Brain Stimulation (DBS)

Deep Brain Stimulation (DBS) is one of the most so-

phisticated neuromodulation techniques in the world

today. It is analogous to a pacemaker as presented in

ﬁgure 2, but differently from a pacemaker it applies

electrical impulses to deep structures into the brain,

with the objective of change or modulate electrical

activity in important structures for motor disorders

BIODEVICES 2017 - 10th International Conference on Biomedical Electronics and Devices

150

Figure 2: Deep Brain Stimulation Device - Illustrative ﬁg-

ure adapted from Medtronic Catalog.

(Oluigbo et al., 2012). It is an alternative for drug

resistant patients.

Although DBS has been considered a highly ef-

ﬁcient method (70-90% successful rate), a large list

of cons must be considered. First of all surgery

for DBS implantation are highly invasive, and also

two surgical procedures are needed for implantation.

Its surgery risks, may include infection, hemorrhage

or even implant rejection. These risks may be in-

creased with patient’s age and previous health con-

ditions. Secondly, DBS surgery is not yet an world

wide affordable treatment.

2.2 Lyftware and Gyroglove

Fortunately not all tremor handling technologies are

invasive or risky. Utensils for daily routine improve-

ment are also being developed. Technologies such as

Liftware 3(b) or Gyroglove 3(a) may be one step in di-

rection to PD patient life quality. According to Mertz

(2016), the idea behind lyftware was not only create

a technology which compensate tremors while people

are eating, but also that patients had the experience of

using fork and spoon as any other person. All sen-

sors and processing are placed at the spoon handle,

and the implemented algorithm compensates tremor

through mechanical actuators continuosly.

Another initiative is Gyroglove. The project con-

sists of a glove equipped with gyroscope, and through

the angular momentum conservation principle oppose

to tremor. It is achieved varying gyroscope spin ve-

locity. After tests in July 2015 in an essential tremor

patient with positive results, Gyroglove’s team be-

lieve clinical trials will begin at the end of 2016.

(a) GyroGlove (b) Liftware

Figure 3: Assistive new technologies for tremor handling

(Mertz, 2016).

2.3 Functional Electrical Stimulation -

FES

Functional electrical stimulation has been deﬁned by

Sujith (2008) as the electrical stimulation of mus-

cles deprived of nervous control in order to improve

impaired motor function. According to Lynch and

Popovic (2008) contractions generated using FES can

be coordinated to actuate joints by stimulating mus-

cles that exert torque about the joint. In this tech-

nology, electrical stimuli is delivered to the patient

through surface or implanted electrodes. Other stud-

ies such as Maneski et al. (2011) and Zhang and Ang

(2007) have used FES as a tremor suppression alter-

native.

2.4 Orthoses

Orthoses are devices used to imobilize, mobilize, ad-

just, alleviate or stabilize limbs affected by motor

disorders or accidents with motor impairment. As

any other medical treatment, they must be prescribed

by an specialized physician (Ottobock, 2016). As

biomedical engineering advances, orthoses perform

an important role in rehabilitation, being applied for

a large number of health problems. According to Ro-

con et al. (2005), upper limbs rehabilitation is based

on affected joint stabilization. Orthoses can be con-

sidered rehab robots used to apply forces or mechan-

ical charges to determined limb. Studies developed

by Hogan (1984), and clinical observations made in

the following years have shown that tremor answers

in different ways to biomechanical charges, acting

as a parallel impedance to the affected limb. This

impedance change has direct effect on tremor. This

property of biomechanical systems brings the possi-

bility to satisfactory handle upper limb tremors us-

ing an orthoses approach (Hogan, 1984; Rocon et al.,

2005). Some works such as those from Taheri et al.

(2014), Seki et al. (2011), Rahimi et al. (2009) and

Rocon et al. (2005) were developed for tremor han-

dling with application of orthoses.

3 MATERIALS AND METHODS

This work was divided into three parts consisting of

candidates selection, electromyography (EMG) sig-

nal acquisition for prototyping purposes and clinical

tests. All procedures described in this section were

submitted and approved by Plataforma Brasil ethical

committee. Medical aspects such as patient selection

were performed by neurologists from Federal Univer-

sity of S

ao Paulo (UNIFESP).

Parkinsonâ

Zs Disease Tremor Suppression - A Double Approach Study - Part 1

151

As part of the ﬁrst stage of this work three PD

patients, with tremor as main symptom, were se-

lected in accordance with Hughes et al. (1992) and

United Kingdom Parkinson’s Disease Society Brain

Bank criteria, and one healthy volunteer was selected

for control purposes. Initially, all four volunteers

were clariﬁed about this work risks, tests and pos-

sible achievements. After their agreement and sig-

nature of control documentation a questionnaire was

applied to each one individually, in order to assess

any other medical conditions that might be relevant

to this work. After that, all patients were familiarized

with the procedure for EMG acquisition and aspects

related to both systems in development, FES and me-

chanical orthosis based suppression.

At the second section, which occurred later at

the same day, four surface electrodes were positioned

in agreement with protocols established by ”Surface

EMG for Non-Invasive Assessment of Muscles” (SE-

NIAM), two on wrist ﬂexor muscle, and two on wrist

extensor muscle, to record EMG activity in PD pa-

tients and the control volunteer. The protocol fol-

lowed the sequence of movements previewed in ﬁg-

ure 4.

(a) Isometric (b) Grabbing a

cup

Figure 4: Applied protocol for signal acquisition.

First of all, PD patients were oriented to keep both

arms extended in front of the body in isometric posi-

tion as shown in ﬁgure 4(a) then the ﬁrst EMG data set

was recorded. The second EMG acquisition was per-

formed based on ﬁgure 4(b) where PD patients were

challenged to develop a small movement of grab a

cup and move it to the mouth. The third and last

set of EMG data was recorded with the patient do-

ing repeatedly the pinch movement as represented in

ﬁgure 4(c). The equipment used for all acquisition

during this stage was DELSYS Trigno EMG system.

4 HARDWARE DEVELOPMENT

Following the acquisition stage, the hardware and

software development stage had started. The goal

here was to develop an EMG acquisition and stimu-

lation hardware and a software responsible for tremor

detection and suppression.

The hardware was developed inspired by ar-

duino’s shields. In order to achieve a modular project,

each one of projects represented by 5(a) and 5(b)

were built by modules. The ﬁrst module is a prepro-

cessing board which integrates a differential ampliﬁer

(INA121P) for EMG signal acquisition, a low pass ﬁl-

ter with cut-off frequency of 500Hz in order to atten-

uate signals other than EMG, and a notch ﬁlter tuned

in 60Hz to attenuate power-line noise. Both imple-

mented with UAF42 IC. As a second step EMG signal

is digitalized by the microprocessor A/D converter,

buffered and processed to assess tremor frequency.

The microprocessor chosen was STM32F407. The H-

bridge circuit is used in both alternatives FES and me-

chanical. In the FES system it is responsible for ap-

ply a biphasic current-controlled impulse to patient’s

wrist extensor or ﬂexor muscle. For the orthosis sys-

tem, H-bridge is responsible for change direction of

motor torque. The boost circuit is used only for FES

system, because its need for a higher voltage to apply

stimuli to the arm.

(a) Functional Electrial Stimulator

(b) Orthosis

Figure 5: Block Diagram of both approaches studied.

An orthosis was also developed using 3D printing

technology as shown in ﬁgure 6.

Figure 6: Mechanical prototype for wrist ﬂexor/extensor

tremor suppression.

5 SIGNAL PROCESSING

STRATEGY

EMG raw signal from volunteers was ﬁrst treated at

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152

at a preprocessing board. EMG signal was passed

through a low pass ﬁlter with cut-off frequency of

500Hz, at this step the goal was attenuate frequen-

cies higher than those that characteristically compose

EMG signals. After that EMG signal was treated with

a notch ﬁlter in order to attenuate 60Hz component

from power line. Convert analog EMG into digital

was next step as shown in ﬁgure 7 ﬂowchart. The dig-

italized EMG signal was then stored into a buffer in

order to be ofﬂine processed. The choice of an ofﬂine

processing was to avoid stimulus related artifacts and

muscle response artifacts mentioned by Widjaja et al.

(2009).

As the ﬂowchart indicates, signal was normalized

and passed through a Fast Fourier Transform (FFT)

in order to assess tremor frequency. According to

Jankovic and Tolosa (2006), Ruonala et al. (2013),

and Helmich et al. (2012) tremor frequency may vary

from patient to patient, but the most common range is

4-10Hz. FFT results were analyzed in the interval 4-

10Hz to ﬁnd the maximum value that FFT assumed,

and for consequence tremor frequency.

Figure 7: EMG signal processing ﬂow chart.

Using the EMG signal in time domain, the max-

imum point was identiﬁed, and using tremor period

calculated through FFT previous steps, impulses were

synthesized based on maximum position and tremor

period. After that the goal was to synchronize either

FES or orthoses actuator with tremor manifestation.

It was achieved using an interruption port and timers

from STM32F407 discovery microprocessor board.

For FES system, circuits were designed to apply

electrical stimulus to wrist ﬂexor muscle, a count-

down timer was implemented and stimulus was ap-

plied to wrist extensor muscle 90ms later. To orthosis

system, circuits implemented change rotation direc-

tion of an electrical motor to oppose wrist movement

cause by ﬂexor contraction and 90ms later due to ex-

tensor contraction.

6 RESULTS

During the signal analysis developed to better under-

stand PD dynamics, EMG signals from wrist exten-

sor and ﬂexor muscles were acquired with DELSYS

Trigno EMG system. Considering ﬁrst a time domain

approach, as presented in ﬁgure 8, exists a delay in

activation between ﬂexor and extensor muscles which

for our three volunteers is approximately 90ms.

Figure 8: Delay between extensor and ﬂexor electrical ac-

tivity in the right arm (RA).

For the development of an orthosis or a FES sys-

tem was important to ﬁgure out tremor oscillation fre-

quency which was assessed through a FFT. Figure 9

represents FFT analysis of an volunteer with PD and

a control volunteer. Although signal on the time do-

main (bottom) analysis is unclear, on the frequency

domain is possible to verify the existence of a 4.55

Hz which was called oscillation frequency. The fre-

quency found is also supported by other studies pre-

sented before.

EMG signal was then squared in order to study

energy features and to establish tremor zones as pre-

sented in ﬁgure 10. One important aspect consid-

ered was how consistent signal was in time, keep-

ing through relatively long periods of 20 to 30 sec-

onds tremor pattern. To test graphically this consis-

tence, impulses were synthesized and placed based

on the period of oscillation, in this case calculated by

osc

. The result can be seen in ﬁgure 11.

In this analysis was possible to identify that syn-

thesized impulses placed every T

osc

interval were con-

sistently into tremor zone, which is an indicator of

Parkinsonâ

Zs Disease Tremor Suppression - A Double Approach Study - Part 1

153

Figure 9: Fast Fourier Transform Analysis wrist extensor

right arm (RA).

Figure 10: Tremor zones deﬁnition based on EMG energy.

Figure 11: EMG signal power and predictability analysis.

Figure 12: Simulated tremor EMG acquired with developed

hardware.

consistence and predictability. Based on this result the

synchronization strategy chosen was a peak detection

of EMG signal. This peak detection start all timers

in order to apply stimulus on FES case, or apply op-

posed torque for orthosis case. Figure 12 represents

a simulated tremor EMG acquired with hardware de-

veloped by our team and it presents all requisites for

the following stages of this work.

The project is now entering in ﬁnal stage with clin-

ical tests in partnership with neurology department of

Federal University of S

ao Paulo. In this stage the goal

is to test the prototype in real PD patients with med-

ical supervision. Fine adjust are expected to be nec-

essary due to each volunteer characteristics and sensi-

bility to electrical stimulus. Variables such as stimu-

lus frequency and applied torque to wrist joint can be

easily adapted to each patient through software cod-

ing.

It is also important to emphasize some differences

among this work and approaches studied before. Dif-

ferently from Zhang and Ang (2007) on FES, this

work is focused on wrist ﬂexion/extension tremor in-

stead of elbow joint related tremors, and uses an of-

ﬂine processing in order to avoid EMG stimulation ar-

tifacts. Filters for artifact suppression as proposed by

Zhang and Ang (2007) are planned for a next stage.

Some works such as Maneski et al. (2011) consider

essential tremor (ET) and PD as targeted diseases.

However, this work focus only in PD in order to keep

the boundary conditions well established, once ac-

cording to Thenganatt and Louis (2012) tremors am-

plitude may be 2.7 times higher in PD. Diferently

from all cited works, our team is also developing an

electrical stimulator and that will bring more ﬂexibil-

ity to develop stimuation protocols.

Considering the mechanical approach for tremor

suppression some differences are also important. Ro-

con et al. (2005) in his study did not use EMG as

signal for controlling orthosis. Later Maneski et al.

(2011) discussed that only motion sensors may not be

enough to assess frequency and phase of a tremor dur-

ing tremor suppression stage. Therefore, our work in

the ﬁrst stage uses EMG as a control signal, and for

modeling purposes.

In conclusion, completely customized hardware

and software were developed to bring ﬂexibility to PD

tremor suppression protocols. A processing algorithm

was implemented to control FES and mechanical or-

thosis. The clinical tests will begin soon, then ﬁne

adjustments may be needed for each patient and all

hypothesis related to PD dynamics can be validated.

Future work comprehends insertion of an ac-

celerometer for both approaches (orthosis and FES)

to close the control loop and possibly achieve better

results through tremor energy analysis.

ACKNOWLEDGEMENTS

Authors would like to thank University Center of FEI

for funding and project support, and Federal Univer-

sity of S

ao Paulo by its support to clinical portions of

this work.

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154

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