Prototype and Graphical Interface for Selective Exhaled Air

Acquisition

Fábio Dias

, José Alves

, Fábio Januário

2,3

, José Luís Ferreira

1,3

and Valentina Vassilenko

1,3

Centre of Physics and Technological Research (CeFITec), Faculty of Sciences and Technology, NOVA University of

Lisbon, Campus FCT UNL, 2829-516 Caparica, Portugal

Electrical Engineering Department, Faculty of Sciences and Technology, NOVA University of Lisbon, Campus FCT UNL,

2829-516 Caparica, Portugal

NMT, S.A, Edifício Madan Parque, Rua dos Inventores, 2825-182 Caparica, Portugal

Keywords: Exhaled Air, Selective Air Acquisition, Capnography, Ion Mobility Spectrometry.

Abstract: The recent advances in technology and detection methods, as well as its economic viability have pointed the

analysis of exhaled breath as a promising tool for medical diagnosis or therapy monitoring. Since the

concentration of the most Volatile Organic Compounds (VOCs) present in the exhaled breath is very low

(ppb

– ppt

range) it is important to have a selective sampling system for alveolar air. In this work we

present the design and instrumentation of a prototype that allows real time monitoring of the breathing cycle

and automatically decide the correct moment for acquisition and channel the acquired sample to the Ion

Mobility Spectrometer with Multi-Capillary Column pre-separation (MCC-IMS). The prototype is

composed by a flow meter, signal packaging circuits and a flow commuting circuit (three-way valve). Two

graphical interfaces were also developed to help controlling the whole process of acquisition making it easy,

quick and reliable.

1 INTRODUCTION

Nowadays the development of a fast, effective, non-

invasive, low-cost and painless diagnosis method is

under special interest of medical and scientific

community (Mashir and Dweik, 2009). From this

point of view breath analysis is extremely attractive,

sometimes even appointed as an alternative method

of biochemical blood analysis (Baumbach, 2009).

It is well known in the medical community that

the Volatile Organic Compounds (VOCs) present in

the exhaled air can provide important information

about the health status (Kim et al., 2012). More than

200 different compounds have been detected in the

exhaled breath and some of them are identified as

biomarkers of common diseases such as diabetes,

liver or kidney failure, pulmonary cancer (Spanel et

al., 1999) or allograft rejection (Miekisch et al.,

2004).

The VOCs present in the exhaled breath are in

very low concentrations, typically from parts-per-

billion (ppb) or microgram/litre (μg/l) to parts-per-

trillion (ppt) or nanogram/litre (ng/l). Thus the

spectrometric methods used for the detection of the

different metabolic processes products must have a

high sensitivity (low ppb range) and provide a direct

analysis in real time or in a few minutes (Baumbach

2006). All these requirements can be realised by Ion

Mobility Spectrometry (IMS). This technique is

based on the drift of ions given their mobility in the

gas phase, at ambient pressure, under the influence

of an electric field (Baumbach, 2006). Compared

with other methods of breath analysis, the IMS

offers a tenfold higher detection rate of VOCs.

By coupling the ion mobility spectrometer with a

multi-capillary column as a pre-separation unit, IMS

offers the advantage of an immediate twofold

separation of VOCs with visualisation in a three-

dimensional chromatogram (Jünger et al., 2010).

From other side, direct breath analysis by

analytical methods implies to use an effective

sample collection system in order to provide the

VOCs of endogenous origin only. These compounds

are present in the alveolar air which is in chemical

equilibrium with the alveolar capillary blood vessels.

Therefore it is necessary to develop selective

acquisition systems that are able to identify and

collect only the alveolar air.

216

Dias F., Alves J., Januário F., Luís Ferreira J. and Vassilenko V..

Prototype and Graphical Interface for Selective Exhaled Air Acquisition.

DOI: 10.5220/0004329402160219

In Proceedings of the International Conference on Biomedical Electronics and Devices (BIODEVICES-2013), pages 216-219

ISBN: 978-989-8565-34-1

 2013 SCITEPRESS (Science and Technology Publications, Lda.)

2 CAPNOGRAPHY

One of the most used techniques to do that selection

is capnography. This technique provides information

about the CO

levels, pulmonary perfusion,

ventilation and respiratory patterns.

Capnography consists in the graphic display of

the instantaneous concentration of CO

in function

of Time or in function of Volume during a breathing

cycle.

The time capnogram is the most used and can be

divided into two segments, inspiration (Phase 0) and

expiration (comprises Phases I, II and III) (Bhavani-

Shankar et al., 1995).

There are different terminologies to designate the

different phases of a capnogram and we decided to

adopt the one suggested by Bhavani-Shankar,

Kumar, Moseley and Ahyee-Hallsworth (1995).

Figure 1: Phases of a time capnogram.

During the first portion of expiration (Phase I)

the PCO

is zero. This phase corresponds to the

anatomic dead space and the equipment dead space.

As expiration continues, a sigmoid curve

corresponding to the abrupt rise on CO

concentration appears, (Phase II) at this stage there’s

already a mix of alveolar air and dead space air.

In the last segment of the expiration we find a

plateau in the PCO

(Phase III) which represents the

alveolar region, this is the portion of the exhaled

breath we are looking to acquire as it’s entirely

composed of alveolar air.

3 FLOWMETRY AND

REFERENCE RESPIRATORY

RHYTHMS

Fluxogram is the graphical monitoring of respiratory

air variation with time. A time capnogram

overlapped with a fluxogram (Bhavani-Shankar and

Philip, 2000) can provide a clear identification for

the area of end-tidal breath (see figure 2). By this

only a flow meter can be used for selective

assessment to the last segment of the expiration

which represents the alveolar region with high CO

concentration.

Figure 2: Comparison between respiratory flow rate and

time capnogram. (Adapted from Bhavani-Shankar and

Philip, 2000).

As a first step it was necessary to create

reference rhythms which the user shall follow during

the flow measurements. Taking into consideration a

probability to need use our breath acquisition system

in different situations, we choose to use three kinds

of rhythms: Slow, Normal and Fast.

For each of these reference rhythms were

determined the average frequency and the mean time

for each breathing cycle. Mean values were

calculated from the statistical analysis of

measurements of respiratory flow of healthy persons

of both gender, male and female. Each volunteer

have performed the test for approximately 60

seconds at three different paces. The respiratory

flow was monitored by SS11LA flow transducer

connected to the MP35 acquisition unit from Biopac

Systems, INC. The BSL PRO 3.7 graphical software

was used for further calculations of the average

values for each breathing cycle and determination

the reference value for the phase of inspiration and

expiration.

The reference values for the breathing cycle

were established as follows: for the normal rhythm

the total cycle´s time is 3,66 seconds, where 1,63

seconds are for inspiration; the slow rhythm has 7,01

seconds cycle, from which 3,25 seconds are for

inspiration; finally the fast rhythm takes 2,23

seconds to fulfill a cycle, being 1,22 seconds of the

inspiratory phase.

4 PROTOTYPE FOR SELECTIVE

SAMPLING OF ALVEOLAR

AIR

The prototype for selective acquisition of exhaled

PrototypeandGraphicalInterfaceforSelectiveExhaledAirAcquisition

217

Figure 3: Block diagram from the prototype for exhaled air acquisition.

breath was developed in two different cells,

hardware and software.

The hardware is responsible for the data

acquisition, analog to digital conversion and data

transmission to the computer, a flow commuting

system was also developed (see figure 3).

The software is a graphical interface that helps

the user pace his breathing cycle and by using some

algorithms identifies and triggers the correct sample

to be acquired.

4.1 Selective Acquisition System

The developed physical part of the prototype is

divided in four blocks: (1) SS11LA flow transducer;

(2) the signal packaging circuit; (3) acquisition and

communication circuit; (4) flow commuting circuit.

The user breathes through the flow transducer

which has a differential output proportional to the

measured flow.

The signal packaging circuit is divided in three

parts, a differential amplifier which detects the

differential output, single waves it and gives it a

4000 gain, one low-pass filter which cuts the

existing noise and a non-inverting adder that places

the whole signal in the digital window of the

microcontroller.

The acquisition and communication circuit uses a

microcontroller that through its AD converter

digitalizes the electrical signal from the packaging

circuit and sends this data to a computer with the

help of a Wireless Bluetooth module.

The flow commuting circuit is composed of a

relay, a three-way valve and a coupling circuit

connecting it to the microcontroller.

4.2 Graphical Interfaces

We have developed two graphical interfaces, one in

LabVIEW

and the other in Java™, both with the

ability to instruct the user to follow a desired

breathing rhythm.

The LabVIEW

graphical interface (see figure 4)

was developed to determine if this way of collecting

exhaled air samples was valid and accurate. This aim

was confirmed in interaction with the selective

acquisition system.

Figure 4: LabVIEW

graphical interface.

Therefore, we developed another user interface

using Java™ (see figure 5) aiming to do the same

process, but using a programming language that did

not need purchase of commercial software.

Figure 5: Java™ graphical interface.

In both interfaces, the user is asked to breathe

according a slide representation of a previously

chosen reference signal (breathing rhythm).

In a first step, the developed algorithm checks if

the signals are synchronous at least for the three

complete respiratory cycles. When this condition is

reached the initial and final instant of the alveolar

region of the breathing cycle are identified. At this

time a command is sent to the microcontroller,

which in turn operates the relay valve, allowing the

valve to remain open only between these instants.

This process ensures that only alveolar air is

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sampled into the system for its further analysis by

Ion Mobility Spectrometry or some other suitable

analytical technique.

5 CONCLUSIONS

The proposed method for monitoring and selective

sampling of exhaled air through the respiratory flow

represents a reliable alternative method to the

capnography.

The developed prototype is cheaper than any fast

capnograph and it can be used for a long period of

time. It can also be easily assembled to the MCC

IMS apparatus for further sensitive analysis of the

VOCs from alveolar air.

The successfully developed graphical interfaces

make a process of breath samples collection more

user friendly for the operator, as well as for the

patients.

However some parts of the implemented

algorithm have to be optimized for better

performance in real healthcare environments.

However some parts of the implemented

algorithm have to be optimized for better

performance, especially for the patients with some

diseases or respiratory problems.

So the future work will concern to the extensive

statistical tests of the developed prototype with large

groups of population, regarding the specificity of its

age and gender. This is important in order to

improve the accuracy of the reference rhythms of

breathing. Within this topic it shall be acquired

respiratory rhythms from children and people with

limited medical conditions, as well as create models

and special menu for this kind of patients.

It can also be added an instructional movie or

help menu to allow to the patient follow the

respiratory reference rhythm in a better way.

ACKNOWLEDGEMENTS

We are grateful to all volunteers that offer their time

to perform the tests for the acquisition of their

respiratory cycles.

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