Monitoring the Propagation of Lung Sounds Using Electronic Stethoscope Arrays

117 Pages·2009·1.55 MB·English

Monitoring the Propagation of Lung Sounds Using Electronic
Stethoscope Arrays

Submitted by:

Kyle R. Mulligan, B. Eng

A thesis submitted to the Faculty of Graduate Studies and Research in partial fulfillment
of the requirements for the degree of

Master of Applied Science

Ottawa-Carleton Institute for Biomedical Engineering
Department of Systems and Computer Engineering

Carleton University
Ottawa Ontario, K1S 5B6
Canada
September 2009

©Copyright Kyle R. Mulligan, 2008

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The undersigned recommend to
the Faculty of Graduate Studies and Research
acceptance of the thesis

Monitoring the Propagation of Lung Sounds Using Electronic Stethoscope
Arrays

submitted by

Kyle R. Mulligan, B. Eng

in partial fulfillment of the requirements for

the degree of Master of Applied Science Biomedical Engineering

____________________________________________
Chair, Howard Schwartz, Department of Systems and Computer Engineering

_____________________________________________
Thesis Supervisor, Andy Adler

_____________________________________________
Thesis Co-Supervisor, Rafik Goubran

Carleton University
September 2009
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Abstract

This thesis presents the design and prototype testing of a novel medical instrument
designed to measure changes in to acoustic transmission properties of lung tissue. Since
tissue acoustic transmission is largely determined by the distribution of lung fluid and
lung tissue density, this instrument has potential applications for monitoring
and diagnosis of patients with such obstructive lung diseases which are associated with
accumulation of lung fluid and collapse of lung tissue. The apparatus consists of an array
of 4 electronic stethoscopes linked together via a fully adjustable harness. A White
Gaussian Noise (WGN) input sound is injected into the mouth via a modified speaker and
measured on the surface of the chest using the array of stethoscopes. Data were analysed
using the Normalized Least Mean Squares (NLMS) adaptive filtering algorithm to
develop a transfer function based on the propagation characteristics of the injected signal.
This transfer function is then analysed to determine the frequency response and the
propagation delay at each stethoscope. The system was calibrated to account for
delays in the signal acquisition equipment and verified using a chest phantom model.
System non-linearites were analysed and determined to be sufficiently small to justify the
linear model. Phantom test results show that as the volume of fluid in the lungs increases,
the sound propagation delay decreases. In-vivo results were
measured on healthy volunteers and show comparable results to the lung phantom with
no volume of water injected and that the instrument can detect sound propagation delay
variations with changes in posture. Based on these results, this instrument is able to
measure parameters of the lungs including propagation delay and frequency/impulse
responses, which show useful correspondence to known physiological changes.
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Acknowledgements

I would like to thank the following people for their support and encouragement in this
project: Dr. Andy Adler, Dr. Rafik Goubran, Michael Mulligan, Gloria Mulligan, and
Kirk Mulligan. Without these individuals, I would not have had the inspiration or the
determination to complete a successful Master’s Thesis. I would also like to acknowledge
the Natural Sciences and Engineering Research Council (NSERC) for partially funding
this project.
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Table of Contents

Abstract .............................................................................................................................. iii
Acknowledgements ............................................................................................................ iv
Table of Contents ................................................................................................................ v
List of Tables ..................................................................................................................... ix
List of Figures ..................................................................................................................... x
List of Abbreviations ....................................................................................................... xiv
Chapter 1 – Introduction ..................................................................................................... 1
1.1 Overview .............................................................................................................. 1
1.2 Problem Statement ............................................................................................... 3
1.3 Thesis Objectives ................................................................................................. 4
1.4 Thesis Contributions ............................................................................................ 6
1.5 Thesis Organization.............................................................................................. 8
Chapter 2 – Background Review ...................................................................................... 10
2.1 Overview of Human Lung Anatomy ...................................................................... 10
2.1.1 Obstructive Lung Diseases .............................................................................. 12
2.2 Lung Sounds ........................................................................................................... 16
2.2.1 Acoustical Properties of the Lungs and Thorax ............................................... 17
2.3 The Stethoscope ...................................................................................................... 18
2.4 Electronic Stethoscope Arrays ................................................................................ 21
2.5 Adaptive Filters ....................................................................................................... 22
2.6 Lung Models ........................................................................................................... 25
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2.7 Breathing Manoeuvres ............................................................................................ 28
2.7.1 Pursed Lip Breathing Technique ..................................................................... 28
2.7.2 Diaphragmatic Breathing ................................................................................. 28
2.8 Current Lung Monitoring Technologies ................................................................. 29
2.8.1 Positron Emission Tomography (PET) ............................................................ 29
2.8.2 Magnetic Resonance Imaging (MRI) ............................................................... 30
2.8.3 Electrical Impedance Tomography (EIT) ........................................................ 30
2.8.4 Acoustic Imaging of the Human Chest ............................................................ 30
Chapter 3 – Measurement Apparatus Setup...................................................................... 33
3.1 Data Acquisition ..................................................................................................... 34
3.2 Data Processing ....................................................................................................... 40
3.2.1 Instrument Calibration ..................................................................................... 40
3.2.2 Algorithm Implementation............................................................................... 46
3.3 Chapter Summary ................................................................................................... 48
Chapter 4 – Simulation Results......................................................................................... 48
4.1 Input Signal Selection ............................................................................................. 48
4.2 Adaptive Filter Parameter Selection ....................................................................... 49
4.3 Verification with Adaptive Filter Simulator and FFT ............................................ 50
4.4 Chapter Summary ................................................................................................... 57
Chapter 5 – In Vitro Chest Phantom Experiments............................................................ 58
5.1 Open Air Column Phantom .................................................................................... 58
5.1.1 Description ....................................................................................................... 58
5.1.2 Results .............................................................................................................. 59
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5.1.3 Model Limitations ............................................................................................ 60
5.2 Plastic Bucket Phantom .......................................................................................... 61
5.2.1 Description ....................................................................................................... 61
5.2.2 Results .............................................................................................................. 63
5.2.3 Model Limitations ............................................................................................ 63
5.3 Chest Phantom ........................................................................................................ 63
5.3.1 Description ....................................................................................................... 63
5.3.2 Results .............................................................................................................. 66
5.3.3 Model Limitations ............................................................................................ 68
5.4 Chapter Summary ................................................................................................... 69
Chapter 6 – In Vivo Experiments ..................................................................................... 70
6.1 Experimental Protocol ............................................................................................ 70
6.2 In Vivo Results – Patient Sitting ............................................................................. 71
6.3 In Vivo Results – Patient Lying on Back................................................................ 72
6.4 In Vivo Results – Lying on Right Side ................................................................... 73
6.5 In Vivo Results – Lying on Left Side .................................................................... 76
6.6 In Vivo Results – Flat on Stomach ......................................................................... 78
6.7 In Vivo Results – All Stethoscopes ........................................................................ 79
6.8 Chapter Summary ................................................................................................... 87
Chapter 7 – Non-Linearities within the System ................................................................ 84
7.1 – Non-Linear Systems............................................................................................. 84
7.2 – Non-Linearities within the System Apparatus ..................................................... 84
7.3 – Chapter Summary ................................................................................................ 92
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Chapter 8 – Conclusions and Future Work ....................................................................... 93
References ......................................................................................................................... 95
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List of Tables

Table 1 - Acoustical Impedance for Various Organs within the Thorax (Lundqvist, 2008) ... 17
Table 2 - Features of the Electronic Stethoscope (DS32A Digital Electronic Stethoscope) ... 21
Table 3 - Materials used to Construct the Stethoscope Array Harness.................................... 36
Table 4 - Components used to construct the sound emitting and recording apparatus ............ 39
Table 5 - Experimental Results that Compare Sound Propagation Delay Calculations
between Three Algorithms ....................................................................................................... 60
Table 6 - Materials used to build the Plastic Bucket Model .................................................... 61
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List of Figures

Figure 1 - The Human Respiratory System (Reproduced from Illustration of Human
Respiratory System, 2008) ................................................................................................ 12
Figure 2 - X-Rays demonstrating a patient with healthy lungs (A) and a patient diagnosed
with pneumonia (B). An accumulation of mucus (shown in white) in the patient’s right
lung can be observed. ........................................................................................................ 15
Figure 3 - Anterior and Posterior View of the Human Thorax with Auscultation Points (1-
7) (Reproduced from Lung Sound Auscultation Trainer, 2008). ...................................... 16
Figure 4 - Mechanical Stethoscope Frequency Response (Reproduced from Webster,
1998) ................................................................................................................................. 20
Figure 7 - Example Lung Model (Reproduced from (McKee, 2004)) ............................. 26
Figure 8 - Example Lung Model (Reproduced from (McKee, 2004)) ............................. 27
Figure 9 - Sketch of Measurement Apparatus and Setup on a Patient.............................. 34
Figure 10 - Fully Adjustable Stethoscope Array Harness Attached to a Human Participant
........................................................................................................................................... 37
Figure 12 - Actual Off the Shelf Components of the Medical Instrument ....................... 39
Figure 13 - Medical Instrument Block Diagram of Off the Shelf Components with
Internal Components ......................................................................................................... 41
Figure 14 - Face Panel of Firepod Preamplifier. Boxes Show Channels 1 and 2 of the
Preamplifier....................................................................................................................... 42
Figure 15 - Detecting the Delay of the Pre-Amplifier ...................................................... 42
Figure 16 - NLMS Coefficients upon Convergence of the Filter ..................................... 43
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