Ortho-Monitorizer: A Portable Device to Monitor the Use of Upper

Limb Orthoses - A Concept Proof

Raquel Gonc¸alves

, Carla Quint

1,2

, Ricardo Vig

ario

1,2

and Cl

audia Quaresma

1,2

Departamento de F

ısica, Faculdade de Ci

encias e Tecnologia, Universidade Nova de Lisboa,

2829-516 Caparica, Portugal

LIBPhys - UNL, Faculdade de Ci

encias e Tecnologia, Universidade Nova de Lisboa, 2829-516 Caparica, Portugal

Keywords:

Rehabilitation, Orthoses, Monitorization, Temperature, Pressure, Compliance, Upper-limb, Wearable.

Abstract:

This article presents the development of a wearable and portable system, the Ortho-Monitorizer, which allows

an objective, continuous and simultaneous monitoration of the temperature and pressure exerted on the skin on

the 3 main pressure points derived from the use of a hand and wrist orthosis. It also allows the monitorization

of the patient’s compliance to the orthosis, providing its time of use. This way, adjustments to the orthosis can

be optimized, reducing the discomfort felt by the patient, increasing compliance, reducing the risk of pressure

sores’ formation derived from inadequate levels of pressure applied, and consequently, increasing the effec-

tiveness of orthosis’ use. Therefore, an Arduino Uno, powered by a powerbank, is used as microcontroller.

Three force sensors and three temperature sensors are controlled by the microcontroller to detect the pressure

and temperature. A Bluetooth Low Energy module is used to send data from the Arduino to an android appli-

cation under development, which will allow healthcare professionals to consult all the information and clinical

history relating to each patient, as well as allowing the patient to develop a greater awareness and sense of

responsibility regarding their performance in relation to the guidelines provided by the health professional.

1 INTRODUCTION

Wrist and hand orthoses have been used in hand injury

recoveries, pain relieve and prevention of muscular

disorders of chronic diseases, such as Carpal Tunnel

Syndrome and stroke (Tan et al., 2020).

Orthoses are support technologies that play an im-

portant role and are recurrently used. These devices

are generally produced using low-temperature ther-

moplastics to be possible adapt them to each patient’s

hand and they seek to act in limiting or promoting

movement, positioning anatomical structures, pro-

tecting body segments and reducing pain (Tan et al.,

2020).

The use of orthoses in patients is usually encour-

aged to be as frequently as possible, normally for a

long period of time depending on the injury. For ten-

don injuries is approximately 4 to 6 weeks whereas

for post-stroke patients is perhaps years, for exam-

ple (Tan et al., 2020).

However, currently, the study of its effectiveness

is still insufﬁcient (Pritchard et al., 2019), and it can

even be said that studies in the ﬁeld of rehabilitation

need greater solidity, scope and a broad international

consensus (Costa, 2019).

One of the main reasons of low patient’s compli-

ance is the discomfort experienced by patients, which

leads to decreased effectiveness of hand and wrist

orthoses and often to the formation of pressure ul-

cers due to prolonged exposure to inadequate pressure

(Tan et al., 2020).

Thus, objective monitoring of patient adherence to

orthosis, identiﬁcation of pressure points and changes

in tissue temperature are important areas of study and

development in order to solve many of the challenges

encountered in clinical practice, such as identifying

and minimizing the excessive pressure exerted by the

orthosis, as well as, identifying a potential tissue in-

ﬂammation by a local temperature increasing. This

monitoring will also allow efﬁcient orthosis’ adjust-

ments, reducing the possible discomfort felt by the

patient.

Regarding the objective monitoring of patient’s

compliance to orthosis, there are already some de-

vices on the market that allow this monitoring, but

none is designed for hand orthoses (Benish et al.,

2012; Davies et al., 2020). Additionally, there are al-

ready some studies that try to develop pressure and/or

Gonçalves, R., Quintão, C., Vigário, R. and Quaresma, C.

Ortho-Monitorizer: A Portable Device to Monitor the Use of Upper Limb Orthoses - A Concept Proof.

DOI: 10.5220/0011012000003123

In Proceedings of the 15th International Joint Conference on Biomedical Engineering Systems and Technologies (BIOSTEC 2022) - Volume 1: BIODEVICES, pages 94-101

ISBN: 978-989-758-552-4; ISSN: 2184-4305

temperature monitoring devices, however there are

none on the market yet (Lou et al., 2005). Neverthe-

less, there are studies directed to hand orthoses but

only concerning pressure (Tan et al., 2020). As re-

gards the simultaneous study of the three parameters,

there are again some studies but none of them allows

the monitoring of all three simultaneously on upper-

limb orthoses (Lou et al., 2002; Chalmers et al., 2015;

Mao et al., 2018).

Therefore, the need for this project arises, whose

objective is to develop a device and an objective and

simultaneous analysis methodology of all these pa-

rameters, through the coupling of pressure and tem-

perature sensors to the orthoses. This way, it will

not only be possible to monitor patient’s compliance,

identify risk situations through changes in pressure

and temperature, but it will also allow the interven-

tion of health professional to adapt the orthoses to the

needs of each patient.

2 ORTHO-MONITORIZER

The Ortho-Monitorizer was developed in collabora-

tion with the Department of Physical Medicine and

Rehabilitation of Hospital Curry Cabral – Centro

Hospitalar de Lisboa Central.

Its main objective is to allow a quantitative, con-

tinuous and simultaneous monitoring of patient’s

compliance to the orthosis (wearing time), as well as

the pressure and temperature values associated with

the use of the orthosis.

For the development of the system, several prereq-

uisites were taken into account, namely:

• Light and compact device, to make it a wearable

and comfortable device;

• Portable device with wireless and real-time data

transmission, to allow a satisfactory degree of

freedom to the patient while guaranteeing con-

stant monitoring;

• Device with low consumption, to allow greater

autonomy;

• Small sensors, so that when inserted in the ortho-

sis, they do not cause discomfort or possible in-

juries to the patient;

• Device designed by modules, that is, the sensors

could be decoupled from the rest of the circuit, to

facilitate the removal of the device;

• Application with functionalities adapted to each

type of user, namely, patients, therapists and ad-

ministrator;

• User-friendly interfaces, to be accessible to any

user.

Considering all the previous characteristics, the

block diagram presented on ﬁgure 1, was designed.

It can be observed that the system is divided into

two major parts: the device itself and its android ap-

plication.

Ar duino Uno

Power bank

4.0 AT-09

BLE TI

CC2541

B57164K0472J000

Portable Device

Mobile Phone

FSR400

Andr oi d

Application

System

Bluetooth

FSR400 FSR400

B57164K0472J000 B57164K0472J000

Figure 1: Block diagram of the proposed system.

2.1 Portable Device

Figure 2 shows the implemented circuit. The entire

circuit is placed inside a box modelled in 3D that have

the ideal dimensions and the necessary holes so that is

possible to power the microcontroller using a power-

bank, as well as the ﬁtting of the sensors. The device

measures 90 mm x 72 mm x 43 mm and weighs, ap-

proximately, 112.5 g. However, an industrial imple-

mentation and the use of a smaller microcontroller,

such as, Arduino IOT, would enable a reduction in its

size to an estimate of 49 mm x 22 mm x 30 mm.

Figure 2: Circuit implementation.

2.1.1 Pressure Sensor

The occurrence of discomfort and pressure sores were

conventionally considered in bony prominences, how-

ever there are other regions that are also sensitive to

the high levels of applied pressure.

A study (Tan et al., 2020) sought to analyse the

main critical points of discomfort or those that pre-

Ortho-Monitorizer: A Portable Device to Monitor the Use of Upper Limb Orthoses - A Concept Proof

sented high pressure magnitudes when using a hand

without thumb stabilization orthosis, and concluded

that there are 3 critical points, represented in the Fig-

ure 3, namely:

• At the most prominent point of the abductor digiti

minimi;

• At the distal end of ulna;

• At the distal end of radius and near the anatomic

snuffbox.

Figure 3: Three main critical points: (7) the most promi-

nent point of the abductor digiti minimi; (8) the distal end of

ulna; (13) distal end of radius and near the anatomic snuff-

box. Adapted from (Tan et al., 2020).

According to this study, the sensors should cover

the range of values between 0.02 MPa to 0.078 MPa.

After searching the market for a sensor with di-

mensions and cost suitable for the intended purpose,

it was concluded that the FSR-400 sensor would be a

good candidate.

The FSR-400’s active area is a circle and its area

is 20.26 mm

As it was mentioned the intensity of minimum

pressure P

min

applied on the skin should be 0.02 MPa,

i.e. 0.02 N/mm

. Thus, the minimum force F

min

that

FSR400 should measure is 0.4 N.

Likewise, the intensity of maximum pressure P

max

and maximum force F

max

that will be applied on

FSR400 are 0.078 N/mm

and 1.58 N, respectively.

Since, the range of force sensor FSR400 is 0.1 N -

20 N, it is suitable for this purpose. The FSR’s fea-

tures are provided in Table 1.

To implement the FSRs, a current-to-voltage con-

verter circuit was used. The implementation circuit of

one single FSR is shown in Figure 4.

In this circuit the sensor is the input of the current-

to-voltage converter and its supply voltage is -5 V.

The op-amp LM324N must be able to swing be-

low ground, from 0 V to 5 V, therefore dual sided sup-

plies are necessary.

The criteria for choosing R

was to maximize

sensor’s accuracy according to the deﬁned range of

Figure 4: The circuit diagram of a current to voltage con-

verter that was used for a single FSR Sensor.

values (0.4 N – 1.58 N). Thus, R

= 2150 Ω.

The relation between output voltage V

Out

and the

value read by Arduino’s ADC (V

) is given by:

Out

5 × V

1023

(1)

By replacing the V

Out

value in the constructed cal-

ibration curve, the pressure value is obtained.

This calibration curve was previously constructed

by collecting the voltage values from the Arduino,

when placing progressively various weights on the ac-

tive area of the sensor.

Table 1: Pressure Sensor Parameters.

Manufacturer Interlink Electronics

Model FSR-400

Force Sensitivity

Range

0.1 - 20 N

Diameter 7.62 mm

Active Area 5.08 mm

Nominal Thickness 0.3 mm

Temp Operating

Range

-30 ºC to +70 ºC

(Recommended)

Number of Actuations

(Life time)

10 Million tested, Without

failure

2.1.2 Temperature Sensor

The normal human skin temperature on the trunk is

36-37 °C, however, since blood circulation is faster

near the heart than in other parts of the body, the

trunk’s skin temperature is always higher than the skin

temperature of the limbs, being lower, namely on pro-

truding and markedly curved parts, such as the ﬁn-

gers (Bierman, 1936).

The temperature of the surface of the skin varies

with the temperature of the body and with conditions

in the skin and in the structures lying beneath. It also

shows large ﬂuctuations when the body is exposed

to changes in environmental temperatures (Childs,

2018). In Figure 5, there are the skin surface tem-

peratures at nine body sites in hot (A: 33 °C) ther-

BIODEVICES 2022 - 15th International Conference on Biomedical Electronics and Devices

moneutral (B: 28–30 °C), and cool (C: 20 °C) ambient

conditions (Childs, 2018).

From the table provided by Figure 5, although

they correspond to values from a sample that may

not represent the general population, it shows that the

temperature of the ﬁngers can vary from 21.0 ºC in

cold environments to 35.9 ºC in hot environments,

similarly, the arm can vary from 27.6 ºC and 35.9 ºC,

in cold and hot environments, respectively.

Thus, it is possible to realize that the choice of

temperature sensors that will measure the temperature

of the skin of the upper limb should cover, at least, the

range of values from 21 °C to 36°C.

Figure 5: Distribution of temperatures within the human

body into core and shell during exposure to cold, ther-

moneutral and warm environments (Childs, 2018).

The most common temperature sensors are ICs,

RTDs, thermocouples and thermistors.

These represent contact sensors that measure the

average temperature between the sensor and the skin

surface.

Considering the characteristics presented in Ta-

ble 2, it appears that all types of sensors have value

ranges that include the values needed to be measured.

However, a good precision is important, since

there is a need to detect small temperature variations

Table 2: Comparing temperature sensing technologies.

Adapted from (Texas Instruments, 2019).

IC Sensors Thermistors RTDs Thermocouples

Range -55 ºC to 200 ºC -100 ºC to 500 ºC -240 ºC to 600 ºC -260 ºC to 2,300 ºC

Accuracy Good/Best

Calibration-

dependent

Best Better

Size Smallest Small Moderate Large

Complexity Easy Moderate Complex Complex

Linearity Best Low Best Better

Price

Low to

moderate

Low to

moderate

Expensive Expensive

at the points where we will measure the temperature.

For this reason, due to its accuracy, price and size,

both ICs and thermistors would be good options.

For this reason, B57164K0472J000 thermistors

were implemented since they were available in the

laboratory, the size was adequate, they had a range of

values that allows measuring the desired values, they

were low cost, easy to implement and already had a

calibration curve that facilitated the conversion of the

obtained values to temperature values. The thermis-

tors’ features are presented in Table 3.

Table 3: Temperature Sensor Parameters.

Manufacturer EPCOS/TDK

Product Category NTC Thermistors

Operating

Temperature

-55 ºC to +125 ºC

Diameter 5.5 mm

Length 2 mm

Width 5 mm

A voltage divider converter circuit followed by a

1.5x ampliﬁcation circuit was used to implement the

temperature sensors. The implementation circuit of

one single B57164K0472J000 thermistor is shown in

Figure 6.

The ampliﬁcation circuit was used to achieve the

desired accuracy (0.2 °C).

The relation between output voltage V

Out

and the

value read by Arduino’s ADC (V

) is given by:

Out

5 × V

1023 × 1.5

(2)

Then, it is possible to obtain the value of thermis-

tor resistance R using the voltage divider expression:

R = R2 ×

Out

− 1

(3)

The calibration curve was constructed from the

resistance values for each temperature, given by the

manufacturer, followed by the adjustment of a expo-

nential curve in order to obtain its equation.

By replacing the R in the previously constructed

calibration curve the temperature value is obtained.

Ortho-Monitorizer: A Portable Device to Monitor the Use of Upper Limb Orthoses - A Concept Proof

Figure 6: The circuit diagram of the voltage divider for a

single B57164K0472J000 thermistor.

2.1.3 Power Supply

Several circuits were implemented in order to opti-

mize the accuracy of the sensors. Even single supply

circuits were tested to try to reduce the power supply

complexity. However, through the use of a dual sup-

ply better results were found. Once Arduino is only

capable of providing positive voltage, a voltage regu-

lator and conversor were used to produce the required

negative voltage value. The power supply circuit used

is presented on ﬁgure 7.

Figure 7: Power supply circuitry.

2.1.4 Wireless Communication

Wireless communication techniques are required to

transfer the data acquired by the sensors to the an-

droid application.

There are several wireless technologies, and the

characteristics of the main wireless communication

technologies used in wearable devices are presented

in Table 4.

Ideally, a low-cost, low energy-consuming and

with a high level of security was sought, since the

objective will be the transmission of patient clinical

data, .

It is also intended a wide range of communication,

which allows a satisfactory degree of freedom to the

patient while ensuring constant monitoring. Consid-

ering the above characteristics, there is a preferential

selection for ZigBee, 2.4G Wireless and Bluetooth.

It was decided to use a Bluetooth module, since it

is the communication where there was a greater de-

gree of familiarity. However, due to its consumption,

a Bluetooth Low Energy (BLE) module was chosen

because it has signiﬁcantly lower consumption.

The module used was the 4.0 AT-09 BLE TI

CC2541 and its features are presented in Table 5.

Table 5: BLE Module Parameters.

Input Voltage 3.3 V/ 5 V

Power consumption

8.5 mA (Transfer)

90 µA ∼ µA (Sleep mode)

Coverage up to 60 m

2.2 Android Application

Ortho-Monitorizer also has an application that is un-

der development.

The main goal of this application is to allow

healthcare professionals to consult easily all the in-

Table 4: Main wireless communication technologies’ characteristics. Adapted from (Yu et al., 2016).

BIODEVICES 2022 - 15th International Conference on Biomedical Electronics and Devices

formation and clinical history relating to each patient,

as well as allowing the patient to develop a greater

awareness and sense of responsibility regarding their

performance in relation to the guidelines provided by

the health professional.

The interfaces of this application are simple and

intuitive to facilitate its use by any user.

The application has 3 types of users, namely, pa-

tients, therapists and administrators, and each of these

types have access to different functionalities adapted

to their needs.

When starting the application, the user will need

to register, being able to register either as a patient

or as a therapist. However, if the user registers as a

therapist, he will need to be authenticated by the ad-

ministrator to get access to therapist functionalities.

Regarding the features of each type of user:

• Pacient: Able to change his personal information,

have access to instructions for use and cleaning of

orthosis and also receive alerts derived from inad-

equate pressure and temperature values.

• Therapist: Able to change his personal informa-

tion and has access to all patients data including

the info about the injury, the orthosis applied and

clinical history.

• Administrator: Has all the functionalities of the

therapist, but is still able to manage the func-

tionalities of all health professionals registered in

the application. It means that he can provide or

remove access to functionalities of therapists or

even administrator.

The application is linked to a database, so that the

storage of user’s data and clinical data, as well as their

consultation, are possible.

In addition, the application receives pressure and

temperature data from the portable device, via Blue-

tooth, and is primarily responsible for its processing

and for displaying some graphics.

These charts will facilitate the analysis of each pa-

tient’s clinical history by the responsible therapist, be-

cause it will allow the therapist to easily see in which

days there were inadequate values of applied pressure

and temperature, as well as verifying patient’s com-

pliance.

2.3 Measured Results

In order to show the results and the performance of

the portable device, data was collected for a period of

30 minutes in a volunteer.

Figure 8 shows the experimental setup used for

data acquisition.

Figure 8: Experimental setup and implementation of the

whole prototype. Pressure and temperature values were ob-

tained at the end of ulna (1), at the distal end of radius and

near the anatomic snuffbox (2) and at the most prominent

point of the abductor digiti minimi (3).

Although the graphical appearance is not yet what

it will look like in the end, the pressure and temper-

ature graphs were obtained, which are shown in Fig-

ure 9 and 10, respectively.

Figure 9: Pressure values obtained during 30 minutes at the

distal end of ulna (1), at the distal end of radius and near the

anatomic snuffbox (2) and at the most prominent point of

the abductor digiti minimi (3).

Figure 10: Temperature values obtained during 30 minutes

at the distal end of ulna (1), at the distal end of radius and

near the anatomic snuffbox (2) and at the most prominent

point of the abductor digiti minimi (3).

Ortho-Monitorizer: A Portable Device to Monitor the Use of Upper Limb Orthoses - A Concept Proof

From the results expressed in both graphs it is pos-

sible to see that both the pressure and temperature val-

ues are within the expected values according to the

study carried out by X. Tan (Tan et al., 2020).

Observing the graphs, it can also be seen that at

the pressure graphic, time series 1 showed the greatest

variations in pressure values, which can be explained

because it corresponds to a place where there is more

movement. This is observable at a quantitative level,

since by looking at the standard deviations (SD) of

each time series (from 1 to 3) (0.026 ± 0.003 MPa),

(0.029 ± 0.002 MPa) and (0.019 ± 0.001 MPa), we

conclude that the ﬁrst one shows the biggest SD.

Regarding temperature, it can be observed that

time series 1 and 2 have relatively close temperature

values, whereas the values of time series 3 are sig-

niﬁcantly lower than the previous ones. The quali-

tative results are supported by the mean and SD of

temperature values, (25.9 ± 0.2 °C), (26.5 ± 0.3 °C),

(23.8 ± 0.3 °C), from 1 to 3 time series, respectively.

This can be justiﬁed by the fact that the sensor on

the abductor digiti minimum is near to the end of the

upper limb, and consequently more exposed to envi-

ronmental temperature, while the others, in addition

to being further away from the upper-limb end, were

also relatively covered by the patient’s sweatshirt.

A slight temperature decrease over time can be

also detected in time series 3 since when the hand

was still, it started to cool off, tending its tempera-

ture to the value of the environmental temperature (≈

23 ºC).

Through a continuous analysis of the pressure and

the temperature it will be possible to detect inade-

quate values of pressure and variation of temperature

values which may indicate inﬂammation on the tis-

sues. The combination of the analysis of both types

of sensors will allow a more accurate assessment of

patient’s compliance.

These results prove that the equipment is func-

tional, demonstrating that the prototype is viable to

be tested in real situations.

3 CONCLUSIONS AND FUTURE

WORK

This article presents a portable system capable of ob-

jectively, continuously and simultaneously doing the

monitorization of pressure and temperature values.

Through the processing of these data, it will also al-

low monitoring the patient’s compliance, that is, its

time of use. The portable device can be adapted to

monitor these parameters in other types of orthotics.

Regarding the application, it is in the development

stage, and at this moment its graphic appearance and

user interface are being improved.

After concluding the development of the applica-

tion, the next step will be to apply the device in real

situations.

By using this approach, the device will allow a

greater and better monitoring of the treatment, as well

as reducing discomfort and the formation of pressure

sore, since it will not only allow improving adjust-

ments in the preparation of the orthosis, but also the

detection of risky situations.

In addition, it will also make possible to store and

manage the patient’s clinical history, in order to fa-

cilitate and assist health professionals, as well as al-

lowing the patient to develop a greater awareness and

sense of responsibility regarding their performance in

relation to the guidelines provided by the health pro-

fessional.

ACKNOWLEDGEMENTS

The authors would like to thank all the healthcare pro-

fessionals of Hospital Curry Cabral - Centro Hospita-

lar Lisboa Central.

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