INSTR

UMENTATION AND LABVIEW BASED CONTINUOUS

PROCESSING FOR CHEST PHYSIOTHERAPY

Luc Marechal, Christine Barthod, G

erard Gautier, Jacques Lottin

Laboratory SYstems and Materials for MEchatronics (SYMME),University of Savoie, BP80439, Annecy-le-Vieux, France

Jean Claude Jeulin

eseau Bronchiolite de Haute Savoie (RB74), 8 avenue de champ ﬂeuri 74600, Seynod, France

Keywords:

Force Sensing Resistor Sensors, Motion Sensors, LabVIEW, Continuous Processing, Infant Chest Physiother-

apy.

Abstract:

Infant chest physiotherapy (CPT) has never been the purpose of any assessed scientiﬁc study although it is

widely used for newborn babies suffering from bronchiolitis. It is thus compulsory to quantify the limits of

the gesture to obtain the expected effect. In this paper, we present original instrumented gloves designed to

perform measurements during the CPT act on babies to characterize the gesture. Associated electronics and

software were specially developed with LabVIEW for data acquisition, continuous processing and analysis of

the characteristic parameters. The measuring system and its readout electronics were calibrated. A drive to

do measurement with babies in real situation validates the principle of the system. The analysis of the results

highlights relevant parameters for typical phases of the CPT act.

1 INTRODUCTION

As the demand for clinical or medical instrumen-

tation design increases rapidly, the techniques and

methods used to convert medical and physiological

information to electrical signals grow too. Quan-

titative responses must be relevant to allow a bet-

ter understanding of the medical or clinical analysis

through computer interfaces. In surgery or physio-

therapy for example, the characterization of the ges-

ture for a medical or a clinical act is more and more re-

quired (Davidson, 2002). The need of standard quan-

titative deﬁnition of chest physiotherapy gesture ex-

pressed by physiotherapists is at the beginning of our

study. Hardly any study concerning the character-

ization of infant chest physiotherapy technique has

been achieved. This paper presents the method and

the system for the characterization of the physiothera-

pist gesture when performing chest physiotherapy act

on newborn babies. First a chest physiotherapy tech-

nique is rapidly described in order to explain the need

of practitioners regarding the deﬁnition and character-

ization of their gesture. We present the implementa-

tion of force and displacement sensors on innovative

instrumented gloves that we designed to record the

characteristic parameters of the gesture. In a second

part, the study of the different components of a com-

puter based measuring system is detailed. In partic-

ular, the acquisition system, the readout electronics,

the acquisition program and important details of the

coding are presented. Finally, measurement results

are proposed, showing the reliable capability of the

system to give a scientiﬁc deﬁnition of the gesture.

2 MEASURING SYSTEM

2.1 Medical Context

Bronchiolitis is an acute disease of the respiratory

tract that affects young babies. In French-speaking

European countries, the two consensus conferences,

held in 1994 and 2000, concerning the management

of bronchiolitis in infants have widely recommended

the use of chest physiotherapy in order to provide care

(ANAES, 2000). These techniques aim at generat-

ing forced respirations in order to improve bronchial

pulmonary exchanges. More particularly in France,

the forced expiration maneuver used is the Increase

Marechal L., Barthod C., Gautier G., Lottin J. and Claude Jeulin J. (2008).

INSTRUMENTATION AND LABVIEW BASED CONTINUOUS PROCESSING FOR CHEST PHYSIOTHERAPY.

In Proceedings of the First International Conference on Biomedical Electronics and Devices, pages 41-46

DOI: 10.5220/0001049800410046

 SciTePress

of Expiratory Flow technique (IEF). IEF technique

is a thoracic-abdominal movement generated by the

hands of the physiotherapist on the infant’s chest. The

infant being lain on a table, the physiotherapist places

one hand on the thorax close to the neck and the other

hand on the abdomen. The ”thoracic hand” presses

uniformly with its cubital part whereas the ”abdomi-

nal hand” has a global support. The applied pressure

sequences must be synchronized with the infant free

respiratory cycle.

2.2 Assesment of Needs

These last years, due to management with the IEF

technique, results have shown an improvement of the

clinical evolution of babies’ health preventing many

of them from reaching the critical state of the hospi-

talisation (Postiaux et al., 2006). Consequently, the

CPT act is more and more used and the efﬁciency of

this physiotherapy technique is now currently admit-

ted in France. Although the IEF technique requires

a good know-how, the physiotherapist has an empiric

approach and relies his practicing on his own percep-

tion. He adapts and controls the magnitude and the

frequency of the gesture versus the sound of the in-

fant respiratory system and his own sense of touch.

A qualitative protocol for the IEF technique has been

deﬁned (Fausser et al., 2002) but no quantitative def-

inition has been made. The demand is then twofold:

on one hand, to prove the efﬁciency of the gesture for

validating the technique; on the other hand, to char-

acterize the gesture to enhance learning and create di-

dactical situations.

2.3 Implementation of Force and

Displacement Sensors

As it was decided to quantitatively deﬁne the basic

gesture of the IEF technique, technical discussions

between instrumentalists and expert physiotherapists,

about the practical knowledge for doing the efﬁcient

gesture, allowed to choose its physical parameters to

record. So, speciﬁc instrumented gloves were de-

signed to measure during the CPT act (Mar

echal et al.,

2007): the space displacement of the physiotherapist

hands, and the distribution of the force applied by the

hands on the infant’s chest. A third relevant parameter

consisting of the sound of the infant respiratory sys-

tem has to be taken into account too. Thus, the mea-

surement system should neither modify the physio-

therapist’s gesture nor being cumbersome or disturb-

ing for the infant.

Since the force measurement system must be thin,

ﬂexible and painless for the baby, and because the

force applied by the practitioner is as well quasi-static

as dynamic, Force Sensing Resistor sensors (FSR)

from Interlink Electronics were chosen. FSR are

polymer thick ﬁlm (PTF) devices which exhibit a de-

crease in resistance with an increase in the force ap-

plied to the active surface (Interlink, 2004). After an

exhaustive comparative study of different sensors, we

have chosen the most appropriate one as far as their

size and cost are the lowest, for equivalent technical

properties. Such sensors have already been used for

biomedical devices (Morris et al., 2006).

The FSR sensors are glued on a cotton glove by

an adhesive band (supplied by 3M). What is innova-

tive with such gloves is the location of the sensors.

Investigation of the contact between the physiother-

apist hands and the infant body has been led so that

we can characterize it. The contact shapes have been

determined after several tests according to the refer-

ent physiotherapist, so that the most interesting pres-

sures applied during the IEF act can be seen and mea-

sured. Regarding hygiene and medical environment, a

thin medical latex glove is worn over the instrumented

glove so that the sensors are not directly in contact

with the skin of the toddler.

Besides, the measurement of the position of the

hands of the physiotherapist is performed thanks to

a six-degree of freedom electromagnetic tracking de-

vice, the Flock of Birds (FoB, from Ascension Tech-

nology). It is composed of one transmitter and two re-

ceivers. Each receiver is placed on a cotton glove on

the upper side of the back of each hand. Manufacturer

claims that the system accuracy is 1.8 mm and 0.5

◦

RMS for position and orientation respectively within

a working range of ± 1.2 m in any direction. No con-

ductive material must be present near the system be-

cause interferences produce signiﬁcant error measure-

ment (LaScalza et al., 2003). This system is suited

to our application because the transmitter is placed 30

cm far from the head of the baby and the displacement

of the hands doesn’t exceed 5 cm in each direction.

2.4 Signal Conditionning

Preliminary trials were made with the referent physio-

therapist in order to determine the range for our appli-

cation. Then, we designed the FSR signal condition-

ing according to the manufacturer’s advices among

suggested electrical interfaces.

For a force-to-voltage conversion, the FSR device

is the input of a current-to-voltage converter. In the

shown conﬁguration (Figure 1), the output voltage is

inversely proportional to the FSR resistance. An out-

put swing of 0 V to 10 V is desired to enhance the

sensitivity of the measurement system. Vref is set to -

BIODEVICES 2008 - International Conference on Biomedical Electronics and Devices

5 V. It is to be noticed that a variation of the reference

voltage would lead to a variation of the output volt-

age. The supply voltage should be constant. Hence,

a precision voltage reference, the AD584, was cho-

sen for that purpose. The current through the FSR

should be limited to less than 1 mA/cm

of applied

force, to prevent from damaging the sensor. Rg value

of 15 kΩ was chosen to limit the current and maxi-

mize the output voltage range. Moreover, the risk of

electronic noise is avoided with these sensors because

the value of resistance in the feedback loop is high

enough. This circuit is simple, easy to implement, re-

liable and costless.

Figure 1: FSR associated electronics.

3 DATA ACQUISITION AND

PROGRAMMING

FSR sensors voltage responses are acquired using

a NI-9205 DAQ card and NI cDAQ-9172 compact

chassis for USB interface communication. It fea-

tures a 32 single-ended analog inputs with a sampling

rate up to 250 ksamples per second. Figure 2 is a

block diagram of the system. The program is written

in Graphical programming using National Instrument

LabVIEW version 7.1 since dataﬂow language is well

adapted for application with parallel tasks. Sampling

rate was chosen at 200 Hz for each sensor. This has

been deﬁned after tests and recordings of the CPT act:

observation of the gesture pointed out important vari-

ations lasting about 100 ms. In order to have enough

samples to acquire and plot the signals, we chose

a resolution of 5 ms which is well adapted to have

enough accuracy.

Figure 2: Acquisition block diagram.

3.1 Continous Processing (Figure 3)

In the aim to display the measurements when the

gesture is being performed, we decided to process

the signals on-the-ﬂy during their acquisition. The

length of the trial, up to several minutes, and the num-

ber of signals (ﬁfteen) increase rapidly the amount

of the collected data. Regarding these parameters,

the recording of the data must be done throughout

the measurement. The DAQ board performing the

acquisition stocks the samples in its circular mem-

ory. The Ni DAQmx driver ensures the continuous

transfer of the digitized data to the computer memory.

The reading of the samples is done block by block

with the LabVIEW program by the Analog Input (AI)

Read routine returning data from the buffer. This high

level priority routine is expensive in terms of perfor-

mance. As a matter of fact, for slow frequency rate

acquisition when AI Read is called, data might not be

all present in the buffer. So, AI Read will wait for

data to be available. This waiting time from a pri-

ority task involves heavy performance cost. To rem-

edy this, Ch

alons recommends an optimisation of the

computer resources when a continuous processing is

desired (Ch

alons, 2001). In order to acquire and pro-

cess a continuous amount of data, we used a new pro-

gramming technique in our code which stands for a

call of the AI Read routine only when needed. To do

so, a variable is used to indicate the number of analog

input data remaining in the buffer. The new version

of the DAQ driver NI-DAQmx 8.3 makes easier the

programming by using a simple Read property node

that returns the state of the buffer. This frees enough

resources to activate other asynchronous tasks that are

less time critical such as display and ﬁle storage, and

allows continuous display.

This solution is low cost to perform ”real time”

acquisition and display, in comparison to Real Time

hardware modules. The program runs on a conven-

tional Laptop PC, Pentium M CPU at 1.6 GHz with

512 MB RAM under Windows 2000. Any reasonably

current PC should be compatible with our measure-

ment system. The program has been tested and shown

to operate reliably.

3.2 Monitoring and Visualization

Before each trial, a user friendly interface enables the

user to supply information about the management of

the patient. Sex, age, size, weight and pathology are

also asked. A text box is dedicated to comments and

evolution of the clinical state. All information are

saved in a result ﬁle detailed further. While gesture is

performed by the physiotherapist, waveform plot dis-

INSTRUMENTATION AND LABVIEW BASED CONTINUOUS PROCESSING FOR CHEST PHYSIOTHERAPY

Figure 3: Structure of the LabVIEW acquisition program: (1) acquisition conﬁguration; (2) deﬁnition of buffer size; While

loop: (3) reading buffer state; (4) reading of samples by AI read routine if the buffer is fulﬁlled; (5) graphical display update

and (6) ﬁle storage when AI read routine is not solicited.

plays signals issued from each sensor in ”real time”.

The monitoring screen is presented Figure 4.

Figure 4: Monitoring screen.

Simultaneously to force measurements, the trajec-

tories of the hands are recorded with the FoB sensors

located on the gloves. The whole system is presented

Figure 5.

3.3 File Output

For each trial the program saves the data in a *.txt ﬁle.

Spreadsheet ﬁle format compliant for common soft-

ware such as Microsoft Excel or OpenOfﬁce Calc was

not chosen because they have a limitation of 65536

rows. The ﬁle contains the values of the output data

of the ﬁfteen sensors versus the time, for each mea-

surement. It also contains the acquisition parameters:

measurement rate, trial start and end times. The aver-

age size of the result ﬁles is of 10 MB which is accept-

able in comparison with actual disk space capabilities.

Figure 5: Whole measuring system.

4 FIRST RESULTS

4.1 Calibration System Validation

Calibration of FSR devices before use is of inevitable

occurrence. Calibration curves supplied by the man-

ufacturer are carried out with the sensor placed be-

tween two rigid materials. However, it is worthwhile

noting that the response of this kind of sensor depends

on the nature and shape of the contact. Consequently,

FSR sensors should be calibrated in the same situa-

tion as the use. Former studies focused on measur-

ing forces developed by the human hand when grip-

ping objects (Nikonovas et al., 2004). In this work,

Nikonovas used FSR sensors between human hand

tissues and stiff surface, nevertheless calibration was

not made in the conditions of their use. Besides, Cas-

tro (Castro and CliquetJr, 1997) placed small rigid

BIODEVICES 2008 - International Conference on Biomedical Electronics and Devices

plates over and under the active area of the sensor

to improve its behaviour during use, but for calibra-

tion the force was applied thanks to a small sphere.

Regarding our application, the contact is between hu-

man hand tissues and human body tissues. Pertaining

to the work of Castro, in order to enhance FSR re-

sponse, we thought to insert plates on both sides of

the sensors, but we can’t mount them on rigid sub-

strates since they could injure the infant during the

CPT act. For use and calibration, we also tried to in-

sert the sensors between different ﬂexible substrates

such as thin layers of polymer materials or silicones

but it had no relevant effect on sensor response.

A speciﬁc workbench is implemented to calibrate

the sensors in order to be in a situation closest as pos-

sible as between hand covered by cotton material and

body (Figure 6). A plate of metal covered with a poly-

mer layer realises the distribution of the applied force.

We made comparative calibration to highlight the im-

pact of the substrate. Dead loads in range of 0.1 kg to

1 kg were applied to the active surface of each sensor.

With the same applied force but with different im-

plementations, the sensor’s response is strongly dif-

ferent. Figure 7 shows the calibration curves for the

same sensor; alone (a) and implemented on the glove

(b). In the end, keeping in mind that the stiffness of

the hands of two physiotherapists may be very dif-

ferent, we decided to calibrate the sensor with identi-

cal impementation for all measurements. So, we use

the static calibration curve obtained with the bench

described before, the FSR being implemented on the

cotton glove and covered with a medical glove.

However, the calibration gives the part-to-part re-

peatability but is not able to provide the absolute force

magnitude during the measurement on newborn ba-

bies.

Figure 6: Calibration System.

4.2 Measurement Results

The measurement with the whole system was per-

formed in a physiotherapist consulting room from

Figure 7: FSR calibration curves: (a) alone; (b) imple-

mented on the glove.

January to March 2007. The study was managed tak-

ing into account a population of 25 infants aged from

5 to 7 months suffering from bronchiolitis. This ran-

dom trial was performed by the same expert physio-

therapist, J.C. Jeulin.

Figure 8(a) shows the sensors responses acquired

on the thoracic hand glove during two compressions

on the chest of a 5-month-old infant, for a sequence

of the gesture called ”fast IEF”. The FSR responses

evolve synchronously. They are repeatable since the

rising time of the applied pressure and the magnitude

of the forces remain constant for each sensor in each

compression. The displacement of the thoracic hand

in the direction perpendicular to the table plane dur-

ing one compression of a ”fast IEF” is reported on

Figure 8(b). These ﬁrst results are consistent with

the gesture qualitatively described as the referent one

by the expert.

5 CONCLUSIONS

The measuring system, designed and created to record

hands applied pressures and displacement during the

act, has been validated. The choice of the sensors

and their implementation respect the medical environ-

ment. Speciﬁc calibration according to the use has

been achieved. Low cost portable hardware is used

to acquire sensors signals. Custom optimized soft-

ware has been developed with LabVIEW to process

and display the data as in real time. The ﬁrst results

obtained are reproducible and consistent with the ex-

pert sensations. Our ongoing work in the framework

INSTRUMENTATION AND LABVIEW BASED CONTINUOUS PROCESSING FOR CHEST PHYSIOTHERAPY

Figure 8: (a) Pressure (two FSR) and (b) displacement

(FoB) responses of sensors on the thoracic glove.

of CPT enables quantitative investigations of the ges-

ture.

ACKNOWLEDGEMENTS

Authors thank Laboratory Amp

ere (Lyon, France),

for lending us one Flock of Birds device, and the As-

sembl

ee des Pays de Savoie for funding this project.

REFERENCES

ANAES (2000). Consensus conference of management of

bronchiolitis in infant. Arch.Ped2001.

Castro, M. and CliquetJr, A. (1997). A low-cost instru-

mented glove for monitoring forces during object ma-

nipulation. IEEE Trans. Rehab. Eng., 5(2):140–147.

alons, J. (2001). Acquisition and processing, daq-sc-01-

jmc-a40119. SAPHIR. www.saphir.fr.

Davidson, K. (2002). Airway clearance strategies for the

pediatric patient. Respir Care, 47(7):823–830.

Fausser, C., Breheret, V., and Lopes, D. (2002). Aug-

mentation du ﬂux expiratoire (afe) et tol

erance. KS,

(428):21.

Interlink (2004). Force sensing resistor integration guide.

Interlink Electronics.

LaScalza, S., Arico, J., and Hughes, R. (2003). Effect of

metal and sampling rate on accuracy of ﬂock of birds

electromagnetic tracking system. Journal of Biome-

chanics, 36(1):141–144.

Mar

echal, L., Lottin, J., Barthod, C., Gautier, G., Goujon,

L., and Jeulin, J. (2007). Instrumented gloves for ges-

ture characterization during chest physiotherapy act

on babies. In 8th International workshop on Research

and Education in Mechatronics, Tallin, pages 171–

176.

Morris, S., LaStayo, P., Dibble, L., Musselman, J., and

Raghavendra, S. K. D. (2006). Development of a

quantitative in-shoe measurement system for assess-

ing balance: sixteen-sensor insoles. In 28th IEEE

EMBS annual International Conference, New York,

pages 6041–6044.

Nikonovas, A., Harrison, A., Hoult, S., and Sammut, D.

(2004). The application of force-sensing resistor sen-

sors for measuring forces developed by the human

hand. Proc Inst Mech Eng, 218(2):121–126.

Postiaux, G., Dubois, R., Marchand, E., Denay, M., Jacquy,

J., and Mangiaracina, M. (2006). Chest physiother-

apy in infant bronchiolitis: a new approach - ncpt

including elpr-expiration lente prolong

ee and tp-toux

provoqu

ee. Kinesither. Rev., (55):35–41.

BIODEVICES 2008 - International Conference on Biomedical Electronics and Devices