DEVELOPMENT OF STRATHCLYDE UNIVERSITY DATA

LOGGING SYSTEM (SUDALS) FOR USE WITH FLEXIBLE

ELECTROGONIOMETERS

Vivek Padmanaabhan Indra Mohan, G. Valsan and P. J. Rowe

Health Qwest, Bioengineering Unit, University of Strathclyde, Wolfson Centre, Glasgow, G4 0NW, U.K.

Keywords: Flexible electrogoniometer, Activities of daily living (ADL), User-friendly system, Remote control,

Wireless data transmission.

Abstract: We have developed a 6 channel battery operated remote control microprocessor based system that collects

data from flexible electrogoniometers and force sensing resistors attached to the lower extremities of the

body. During functional activities, the user-friendly system stores the data from these transducers and

transfers the same to a PC at the end of the recording period via a bluetooth connection. Software on the PC

then displays the angular displacement and allows visual inspection of the entire sequence of recordings or

particular events of interest. This system was tested on 10 normal subjects and the pattern pertaining to the

flexion/extension of knee during range of activities of daily living (ADL) such as walking, ascending and

descending stairs, in and out of a chair and deep squatting were recorded and found to be reproducible and

similar to those reported in the literature.

1 INTRODUCTION

Normal lower limb activity and goal directed

movements are essential for the well-being of an

individual. However, such movements and efficient

functioning of the lower limb can be seriously

affected for a variety of reasons and one such

common cause is Osteoarthritis. This degenerative

joint disorder is often disabling and is characterized

by pain and physical limitation. (Rowe et al, 2005).

As a result, functions of lower limb are affected,

causing individuals to have problems with ADL

such as; walking, climbing stairs, getting in and out

of chair, getting in and out of bath etc. At this point

of time, rehabilitation and health care professionals

play a very crucial role by improving the functional

ability of their clients. Periodic assessment of the

individuals is necessary to aid the health professions

in assessing efficiency of their interventions.

Currently, two types of assessment techniques are

available for this purpose: questionnaire based

assessment and assessment based on clinical gait

analysis.

The former technique makes use of knee scoring

questionnaires such as the Western Ontario and

McMaster Universities Osteoarthritis Index

(WOMAC) and Knee Society Clinical Rating

System. (Rowe et al, 2005). Even though, these

questionnaires are popular, easy to administer and

characterize the overall performance of an

individual, research reveals that they are highly

subjective and do little to reveal any objective

information regarding the actual restoration of the

knee function required by an individual to perform

ADL.

On the other hand, clinical gait analysis is an

expensive and time consuming process. (Rowe et al,

2005). Alternatively, researchers have started using

electrogoniometry to record the dynamic knee joint

movement during a range of functional activities due

to its simpler, cheaper and reproducible nature.

(Rowe et al, 2005, Rowe et al, 2001) Mostly, such

body mounted transducers are used in combination

with information storage devices known as “Data

Loggers”. (Rowe et al, 2005).The role of these

devices is not merely to store the data collected from

these transducers but also to convert the signals

obtained from the transducers to an understandable

form. Many such devices have been developed in the

past and are also being currently used along with a

wide range of transducers such as flexible

electrogoniometers, accelerometers and strain

198

Padmanaabhan Indra Mohan V., Valsan G. and J. Rowe P. (2009).

DEVELOPMENT OF STRATHCLYDE UNIVERSITY DATA LOGGING SYSTEM (SUDALS) FOR USE WITH FLEXIBLE ELECTROGONIOMETERS .

In Proceedings of the International Conference on Biomedical Electronics and Devices, pages 198-203

DOI: 10.5220/0001533301980203

 SciTePress

gauges for mobility assessment, recording of plantar

pressure etc. (Zhu et al, 1991). Wireless

communication is finding its way into various

medical technological applications (Zhang.Z &

Liu.P, 2004), but most data loggers remain

hardwired. It was the premise of this work that the

data logger currently used with flexible

electrogoniometers needs further improvement in

functionality so that, the process of collecting a large

stream of data and extracting the relevant sections

could be carried out more efficiently. Further, such a

system should be able to be used by any allied health

professional in a multi centered clinical trial

evaluating post-operative rehabilitation. The lack of

such a system merits the development of a user

friendly system, whereby pushing a button would

start, stop, collect multiple data sets and transmit the

same without any physical contact between the

subject and the operator.

We have developed a portable, battery operated,

remote control microprocessor based system that

allows recording, deleting and transmitting the data

obtained from two flexible electrogoniometers and

four force sensing resistors. The data is stored in

static random access memory (SRAM) and can

subsequently be transferred via Bluetooth to a PC

which processes and analyzes the data.

2 METHOD

2.1 Overall System

The flexible electrogoniometer consists of a strain

gauged shim (a thin flexible strip) which runs the

length of the device. Damage to the device and

injury to the test subjects is prevented by enclosing

the shim in a spring. To facilitate the attachment of

device to the subjects, two light weight plastic plates

are fastened to the ends of the shim. The resulting

transducer does not have a specific centre of rotation

and is flexible in both medio-lateral and anterior-

posterior directions. Each electrogoniometer was

attached using double sided medical grade tape

laterally to the shank and thigh of individuals via

two flexible plastic strips – adjusted to the length of

their shank and thigh. In addition to this, light

weight force sensing resistors (FSR) or footswitches

were attached to the first metatarsal area of the toe

and to the heel for marking the events by indicating

the contact between the foot and the floor. Since the

transducer was mounted in the sagittal plane of the

knee, the output of the device represented the

flexion-extension angle of the knee. Both the

electrogoniometers and footswitches were interfaced

to SUDALS via thin flexible cables.

2.2 Hardware Design

The entire prototype was built on an evaluation

board – Eval ADUC7026 which consists of a 12 bit

successive approximation type Analog to Digital

converter (ADC), with an on chip 32 bit

microcontroller. The microcontroller provides both

high performance and low power consumption. The

microcontroller has several on chip facilities

including programmable watchdog timer and 12

channel multiplexer. Hence, an additional

multiplexer or a sample or hold circuit was not used

in our system. The ADC chip analogue input range

is 0 to 2.5V DC, whereas, the output of the flexible

electrogoniometer is a differential voltage. As a

result, the voltage signals from these transducers

were conditioned using high precision

Instrumentation amplifier (INA101) with suitable

gain resistors so as to make these signals compatible

with the input range of ADC. Due to the low

temperature drift feature of this amplifier, the system

will not be significantly affected by ambient

temperature. Six 1.2V alkaline AA batteries are used

for powering the evaluation board, which is

regulated via an on chip voltage regulator to 3.3V.

This is used to drive the digital side of the board and

the same voltage is being filtered by the on chip

features to drive the analog side of the board. In

addition to this, the output from the batteries is

stepped down to +/- 5V via DC-DC converter to

power the amplifiers, the transducers and other

signal conditioning components on board. The data

from two flexible electrogoniometers and from the

four force sensing resistors are sampled at 50 HZ

and the digital values are stored in a 32KB x 16

static RAM – an external memory chip interfaced

via the footprint provided on the evaluation board.

To the same memory, the data from the FSR

channels are compressed to on/off data and saved as

a single byte.

The data from the external memory is transferred

to a personal computer via a bluetooth transmitter

(HDWBTRS232 – wireless RS232 Transceiver)

interfaced to the Eval ADUC7026 via the universal

asynchronous transmitter (UART) terminal provided

on board and a transmitter line driver ADM202. The

transmitter works on a voltage range of 5V-9V DC,

which is being provided using the same AA batteries

on board. Due to high power draining application

(wireless transmission), batteries chosen for the

operation of this system has a high power rating of

DEVELOPMENT OF STRATHCLYDE UNIVERSITY DATA LOGGING SYSTEM (SUDALS) FOR USE WITH

FLEXIBLE ELECTROGONIOMETERS

199

2400 mah. A Baud rate of 19200 was used to

transmit the collected data to a personal computer

(PC) in less than a minute. At the PC end a software

code written in MATLAB is used to receive the

transmitted data and store the data in the format of

excel files which are analyzed further depending

upon the user requirement. We simultaneously

measured the knee flexion / extension angles during

activities of daily living such as; walking, ascending

and descending the stairs, sitting in and out of a

chair and deep squatting and established that the

portable system could faithfully reproduce the

signal. The obtained data is analyzed for maximum

and minimum knee flexion / extension during these

activities and the results are compared against the

normal knee range of motion during these activities

published in the literature. The overall block

diagram of the system is as shown in Figure 1.

Figure 1: System block diagram.

2.3 System Functionality

The system is aimed to perform 5 functions

corresponding to data collection. These include;

recording a test, scrapping a failed test, transmitting

the collected data from the electrogoniometers and

footswitches and resetting the entire system. In

addition to this, the system also facilitates zeroing of

the electrogoniometers prior to each recording

depending upon the user requirements. This is

accomplished by making use of an Operational

amplifier 3240 at the hardware end.

Initially, when the system is connected to the

sensors and switched on, the system is ready to zero

the sensors and to record the data corresponding to

the knee flexion/extension. Once, a singe recording

is completed, then the system facilitates the user to

make use of other functions such as; scrapping the

recorded data ‘if needed’, else transmit the collected

data via wireless and reset the entire system for next

set of data collection. Each of these above

mentioned functions can be accomplished by

providing interrupt service routines (ISR) to the

microcontroller to start or stop that specific function

via an Infra red remote transmitter and receiver

interfaced with the microcontroller, when the LED

corresponding to that function illuminates. Since, all

these functions operate within a loop arrangement;

the user can perform single recording or multiple

recording, store it in the external memory and then

transmit it to the PC via wireless. The functional

flow chart of this system is as shown in Figure 2.

2.4 System Evaluation

The system was evaluated by carrying out a pilot

study, during which the data pertaining to the

flexion/extension of the knee of the 10 young

normal healthy subjects who volunteered for this

study was collected via the flexible

electrogoniometer interfaced with this portable unit.

All the 10 subjects were asked to perform the

following 6 activities – Walking, In and Out of a

Chair, Stair ascent, Stair descend and deep squat

corresponding to daily living.

Start and stop commands were given at the

beginning and completion of each task and the

subjects were asked to repeat these tasks three times

for reproducibility and repeatability purposes.

Further, the event marking was taken into account

by the FSR’s attached to the toes and heels of each

subject.

After data collection a 4

order low pass

Butterworth filter at a cut-off frequency of 6 Hz was

used to eliminate the noise present in the data. The

data collected during these activities were averaged

for each subject individually and were analyzed for

maximum and minimum knee flexion. The

excursion of the knee during these activities for each

individual was obtained by calculating the difference

between the maximum angle and minimum angle.

This procedure was carried out for both the left and

right knees and was then averaged to provide the

group mean. The excursion of the knees from

SUDALS is as shown in Table 1. Table 2 shows the

maximum knee flexion angle reached during each of

these ADL. The results were compared against the

values published in the literature as shown in Table

The mean normalized gait cycle obtained by

SUDALS during the experimentation is shown in

figure3.

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200

Figure 2: System functional flowchart.

Table 1: Knee ROM during ADL from SUDALS.

ADL SUDALS - excursion

Left Knee Right Knee

Gait 66.0° 66.4°

Stair up 71.3° 71.8°

Stair

Down

69.7° 61.5°

Chair in 101.7° 100.9°

Chair

Out

102.4° 107.1°

Squat 116.4° 111.7°

Table 2: Knee Flexion angles during ADL from SUDALS.

Table 3: Knee flexion angles from literature.

2.5 Discussion

The system described here was able to record, store

and transmit the data corresponding to the ADL.

Our results indicate that, the average maximum

knee flexion angle for all the 10 subjects during the

above mentioned ADL lies within the results

published in the literature as shown in Table3.

Transmit

Start

Switch

ste

Record

/Zero?

Zeroing

Recording

Enable trigger via

Remote Control to

Start performing

desired function.

Enable trigger to stop

erformin

the functio

Is 1 recording

com

lete?

Scrap/

transmit/reset?

Scrap?

Transmit?

Reset?

Reset

Data

Transmit

Data

Scrap

Data

Has all

recordings

tted?

Switch

off the

System.

Retransmit

Data

Reset

Y N

DEVELOPMENT OF STRATHCLYDE UNIVERSITY DATA LOGGING SYSTEM (SUDALS) FOR USE WITH

FLEXIBLE ELECTROGONIOMETERS

201

Figure 3: Normalized average Gait Cycle.

However, the knee flexion angles obtained

during squatting seem to be a little lower than the

values published in the literature. One of the

possible reasons for this could be the way in which

the subjects performed this activity. Though, the

subjects were shown what they were suppose to

perform during the process of recording, certain

subjects were unable to completely squat as it was a

difficult task and required a lot of effort. Due to this,

certain subjects performed half squat instead of a

complete squat. As a result, the knee flexion angle

recorded during this activity would be different from

those reported by Wyss.U et al - 2003, where the

subjects have performed a complete squat.

Moreover, most of the authors, other than

Huddleston.J et al - 2006, haven’t used flexible

electrogoniometer for measuring the knee flexion

angles. At the same time, though these authors have

reported the maximum knee flexion angles during

ADL, none of them have reported the knee

excursion of the subjects during these activities. On

the other hand, most of the studies by Rowe.P.J et al

– 2005, have reported the obtained knee excursion

during various ADL, but most of his studies are

concerned with the follow-up of TKA and elderly

population. Hence, the results from this study of

young healthy subjects were unable to be compared

with those published by Rowe et al. Most of the day

to day activities can be accomplished in less than a

minute.

Evidently, during our experimentation, we

noticed that the time taken to complete a single trial

of all the above mentioned six ADL by all the

subjects was less than a minute. Henceforth, despite

the usage of a 512 KB SRAM as prescribed by the

manufacturers of the evaluation board, we were able

to record, store and transmit the biomechanical

motions corresponding to six ADL with a little

difficulty. This ability to record, store and then

rapidly transmit the data facilitates data collection in

a free living environment and enables the user to

check whether the data recorded is reliable or not. In

this case, the user can re-record the activity

immediately unlike the commercially available

Biometrics data acquisition systems with flash

memory, where the user has to wait until the entire

data collection process is completed to check for

reliability and reproducibility of the data.

Currently, most of the portable data acquisition

systems that are used with flexible

electrogoniometer do not facilitate remote control

operation. Consequently, every time the users have

to physically change the settings of the data logger

such as starting, stopping or resetting; once it’s

being worn by the subjects. However, we were able

to control the entire process of data collection by

staying at a convenient distance of less than a foot

from the subjects. This would not only avoid any

physical contact with the subjects, but at the same

time, it would also minimize the degree of

inconvenience to the subjects. None of our subjects

reported any discomfort with SUDALS during the

process of data collection. Due to high power

draining application (wireless transmission of data),

we have used 6 x 1.2 V AA high wattage batteries of

2400 mah in our system. Further, unlike the

commercially available systems, SUDAL also has a

provision similar to the car battery charger for

recharging the batteries without removing them from

the system. Charging these batteries for 2 hours

enables us to use the system for more than 8 hours.

Though our system doesn’t facilitate real time

waveform display, simultaneous data collection and

transmission almost replicates those systems with

real time waveform display. Thus, the users would

be able to analyze the transmitted data stored in the

form of excel files. Figure 4 shows the usage of

SUDALS in an experimental set up.

3 CONCLUSIONS

In summary, the system worked without any

technical difficulties and was able to accurately

measure the knee flexion/extension during activities

of daily living in healthy subjects. The results of the

present study in conjunction with the literature

review support the use of SUDALS together with

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202

flexible electrogoniometers as a complimentary

instrument along with other functional assessment

questionnaires in providing objective data to the

clinicians. This would in turn help the rehabilitation

professionals to improve their intervention. In the

future, we plan to validate SUDALS against vicon

system (Gold standard) and use the system to

evaluate the functional outcomes of patients

following Total Knee Arthroplasty. The system can

be further developed to interface with mobile

devices and provide real time display of data

collected. Thus, a flexible, compact, powerful and

portable multi-channel data collecting system of

flexible electrogoniometry has been designed and

developed.

Figure 4: SUDALS mounted on a subject during

experimentation.

ACKNOWLEDGEMENTS

I would like to thank the University of Strathclyde

for funding my PhD with the Overseas research

student award (ORSA) and I would also like to

thank Mr. John Mcclean (Technician –

Bioengineering Unit, University of Strathclyde),

who has dedicated his time in assisting us with all

technical issues that were present during the

development of the system.

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FLEXIBLE ELECTROGONIOMETERS

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