Experimental results are presented which tend to validate a previously developed theory of sound production in the human lung over a particular Reynolds number range. In addition, a new, presently nonunderstood, phenomenon was observed at higher Reynolds number. These results, which show how sound generation in the lung depends upon the physiologically important variables of volume flow rate and bronchial diameter, have potentially important application in noninvasive lung examination and the diagnosis of lung disease

Hardin, J. C.

Patterson, J. L.

Seiner, J. M.

English

NASA Technical Reports Server

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i -------------- NASA Technical Memorandum 81897
NASA-TM-81897 19810004208
GENESIS OF BREATH SOUNDS--
PRELIMINARY VERIFICATION OF THEORY
JOHN L. PATTERSON J JR' J JAY C. HARDIN J AND
JOHN M. SEINER
OCTOBER 1980
NI\SI\·
National Aeronautics and
Space Administration
Langley Research Center
Hampton, Virginia 23665
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NOV J. a
https://ntrs.nasa.gov/search.jsp?R=19810004208 2020-03-21T14:44:32+00:00Z

GENESISOF BREATHSOUNDS--
PRELIMINARYVERIFICATIONOF THEORY
JohnL. Patterson,Jr.
Departmentof Medicine
' MedicalCollegeof Virginia
•Richmond,Va. 23219 USA
and
Jay C. Hardinand JohnM. Seiner
NASALangleyResearchCenter
Hampton,Va. 23365 USA
ABSTRACT
Experimentalresultsare presentedwhichtendto validatea previously
developedtheoryof soundproductionin the humanlungovera particular
Reynoldsnumberrange. Inaddition,a new,presentlynonunderstood,phenomenon
was observedat higherReynoldsnumber. Theseresults,whichshowhow sound
generationin the lungdependsuponthephysiologicallyimportantvariablesof
volumeflowrateand bronchialdiameter,havepotentiallyimportantapplication
in noninvasivelungexaminationand thediagnosisof lungdisease.
INTRODUCTION
In a recentpaperI,Hardinand Pattersondevelopeda theoryof sound
generationin the humanlungbasedupontheobservationby Schroterand Sudlow2
thatlow Reynoldsnumberflow in a repeatedlybranchingsystemsuchas the
bronchialtreeproducesvorticesin eachbranch. Two and fourvorticesare
generatedin eachof the bronchialtubesin thecorrectReynoldsnumberrange
by inspiratoryandexpiratoryflowsrespectively.Hardinand Pattersonanalyzed
a mathematicalmodelof thisphenomenonwhichconsistedof rectilinearvortex
filamentsin a rigidcylinderand foundthatthe vortexcoresexecuteorbits
,MI-1'21'7
2whosesize is dependentuponthe position of formation of the vortices. This
oscillation, which has been observedduring flow visualization by the present
authors,is responsiblefor the productionof soundwhichcan be calculated
fromtheCoriolisaccelerationof thevorticesutilizingthevortexsoundtheory
L
of Powell3•
When thisanalysisis coupledwitha modelof the humanbronchialtree,
suchas thatof Weibel_, relationsbetweenthe frequencyof soundgeneratedin
eachorderof bronchiand the physiologicallyimportantvariablesof volume
flowand bronchialdiameterare obtained.This resultis of immensepotential
significanceas itmay allowthedevelopmentof a noninvasivetechniquefor
lungdiagnosis.The amplitudesand frequenciesof the soundgeneratedat
moderateflowratesare highenoughto be readilydiscernedand appearto change
dramaticallywith smallperturbationsof the internallunggeometry_, ThUs,
aftera periodof humantestingto.determinethesoundsignatureof various
lungdiseasesand the naturalvariabilityfrompersonto person,theearly
diagnosisof potentiallungproblemsshouldbe possible.
The purposeof thispaperis to presentpreliminaryexperimentalevidence
whichtendsto verifythetheoryof Hardinand PattersonI overa particular
R_ynoldsnumber•rangeas wellas tosuggestthe presenceof another,as yet
notunderstood,phenomenonat higherReynoldsnumberwhichmay alsobe useful
in thediagnosisof lungdisease.
EXPERIMENTALAPPARATUSAND DATAANALYSIS '
The basicbuildingblockof thebronchialtreeis a Y-tubewherethe flow
fromtwo branchesis mergedintoone or the flowfromone branchis splitinto
two,dependentuponwhetherexpiratoryor inspiratoryflow is considered.The
3vorticesobservedby SchroterandSudlow2 are producedby thenecessityof
changingthedirectionof flowthroughan angleat the branch. Sincethisis
the simplestconfigurationforwhichthe theoryis valid,it was decidedthat
the preliminaryacoustictestingshouldbe carriedout on a singleY-tube.
" A fullsizesketchof themodelis shownin figureI. It ismade of glassand
is nominallysymmetric.The diametersand branchingangleof thetubewere
chosento approximatelyrepresenthe 4th and 5thordersof bronchiin the
humanlung_. Forthe purposeof discussion,the standarddescriptionof the
largerbranchas the "parent"and thesmallerbranchesas "daughter"will be
employed.The lengthsof the branchesare considerablylongerthanthosein
the lung,whichare typically3 diameters,for easeof manufactureand testing.
The theoryindicatesthatthetubelengthsare not criticalto the soundgenera-
tionprocess.
For testing,the tubewas placedin a large(approximately2.5 x 3.4 x
4.0meters)anechoicchamberwitha lowfrequencycut-offof 150Hz. Figure2
is a photographof themodelin positionfor testing.The anechoicchamber
was primarilyusedto reducethe influenceof externalambientacousticdis-
turbanceswhichwouldotherwisemask the desiredacousticphenomena.Tests
weremadeonly in the expiratorymode due to theadditionalcomplicationof two
matchedsoundsourcespresentfor the inspiratorycase. As can be seenin
figure2, a 2.54cmmicrophone(frequencyresponseflatover lO-15,000Hz)with
itscap removedwas placedat 90° to theaxisof the parenttubeas closeas
O
possible(=lcm) to thetubewithoutflowimpingingon themicrophoneitself.
° Flowwas suppliedto themodelby a systemwhichis shownschematically•
in figure3. The standardshopair supply(pressure6 x lO5 Newton/m2) was
passedthrougha seriesof two controlvalvesin orderto reduceit to the
4smallpressuresand flowratesrequiredfor thistesting.The flowthenwent
intoa flowmeterto measurethevolumeflowwhichthengavethe testvelocity
throughknowledgeof thetubearea. Finally,theflowexitedintoan acoustic
mufflerto removenoisegeneratedin theflowreductionsequence.The muffler
actuallywas a commercialwaterfilterhousingin whicha dualchamberfilled
withfiberglassproducedverylowbackgroundnoiselevelsat all flowratesof
interestin the tests,as will be seenin subsequentspectra.
The flowthenpassedthrougha very longsupplytube (:7m) intothe
anechoicchamberandwas splitby a commercialY-tubeintothe two flows
requiredby the test. The commercialY-tubehadall threebranchesof the
samediameter,0.954cm, and thusthe flowwas decelerateduponpassingthrough
thisjunction.Eachflowthenproceededthrougha contractionsectionto
reduceit to thediameter,0.34cm, of thedaughterbranchesof themodeland
thenthroughTygontubesof approximately0.5m in lengthbeforeenteringthe
model. Noisespectrawhichwere obtainedat eachjunctureof thisflow system
were broadbandwithno unusualfeatures.
Testsrunoverthe Reynoldsnumber(Re = UoDo/_whereUo and DO are the
velocityand diameterof the parenttube,respectively,and _ is the kinematic
viscosityof air)range50-4500whereSchroterand Sudlow2 observedthe vortices
were completed.Belowthe Reynoldsnumberof 965,nothingcouldbe.observed
over thebackgroundnoiseof thesystem. Of course,thisrangecorrespondsto
very lowpressuresand flowratesin the system. As the flowratewas further
increased,intensetonesbeganappearingin the spectrum.Thesetonesformeda
J
harmonicserieswith theamplitudeof thefundamentalat least20 dB abovethe
backgroundleveland 15 dB abovethe levelof any harmonic,of whichtherewere
5as manyas ninereadilyobserved.A typicalspectrumin thisregionis shownin
figure4. Thisbehaviorwas observedup to Reynoldsnumberof 1488wherethe
, tonescompletelydisappearedintothe backgroundlevel. Overthisrange,the
fundamentalfrequencyvariedfrom200 to 360Hertz.
Whentheflowratewas stillfurtherincreased,nothinginterestingwas
observeduntilthe Reynoldsnumberof 1787was reachedwherea new setof tones
appeared.Thesetonesweremuch higherin frequencyand againformeda
harmonicserieswiththe fundamentalamplitude30 dB abovethe backgroundlevel
and lO dB abovethehighestharmonicamplitude.As many as fourharmonicswere
seenin the rangeof analysis.A typicalspectrumin thisregionis shownin
figure5. This behaviorwas observedup to the Reynoldsnumberof 2360where
thetonesagaindisappearedintothe broadbandflownoise. OverthisReynolds
numberrange,thefrequencyof the fundamentalvariedfrom1210to 1775Hertz.
Furtherincreasesin flowrateshowedno furtherinterestingbehavior,onlya
generalrisein thebroadbandflownoise. Thesephenomenawerequiterepeat-
able,appearingat the samevelocitiesregardlessof whetherthe flowrate
was beingraisedor loweredand turnedon and off quitesharplywithonly
smallchangesin velocity.
Thisexperimentwas designedto testthe theorydevelopedby Hardinand
PattersonI forsoundproductionin thehumanlung. This theorypredicted
that,on expiration,eachbronchuswithflowin the Reynoldsnumberrange
° 50-4500wouldgeneratesoundwith fundamentalfrequency,fo' givenby
Uo DI_.I)2" fo=o.212 (I)
whereUo and Do are the previouslydefinedvelocityand diameterof the parent
6bronchusrespectivelyand D1 is the diameterof the daughterbronchi (.assuming
symmetry). The theory also predictsthat the first harmonicof this frequency
will be generatedas well. Note that the theory shows the frequencyto be
directlyproportionalto the velocity,i.e. as the velocitygoes to zero, the
frequencygoes to zero.
In figure 6, this theory is comparedwith the data obtainedin this experi-
ment. The figure is a plot of the frequenciesat which the tones appearedas
a functionof the Reynoldsnumberof the flow inthe parent tube. The tone
frequencieswere obtaineddirectlyfrom the acousticspectrasuch as figures
4 and 5, and the Reynoldsnumberswere calculatedfrom the known velocityand
diameterof the parent tube using the value of 0.154 cm2/secfor the kinematic
viscosityof air. Note the appearanceof severalharmonicsas discussedearlier.
For the purposeof this comparison,Eq. (1) has been rewrittenin terms of
the Reynoldsnumberas
fo= 0.212 D-_ Re (2)
This linearrelationis the solid linemarked "Theory"on figure6. As can be
seen, this theory agreesquite well with the fundamentalfrequencyof the
phenomenonobservedin the lower Reynoldsnumber range,965 _ Re _ 1488. The
tone frequenciesexhibita linear dependenceupon Reynoldsnumberwhose slope
is almost preciselythat predictedby the theory,althoughthe theorydoes
slightlyoverpredictthe frequenciesthemselves. This slight overprediction
is probablydue to the upper bound estimateof the circulationof the vortices
employedin referenceI.
The phenomenonobserved in the higherReynoldsnumber range, 1787_ Re
2360, however,appearsto be somethingdifferent. Althoughthe frequenciesare
still a linear functionof the Reynoldsnumber,the slope is much greaterthan
7thatfoundin the lowerReynoldsnumberrange. Further,if the phenomenonwere
extrapolatedbackto lowerReynoldsnumbers,it is clearfromthe figurethat
• the frequencywouldgo to zeroat a finiteReynoldsnumberratherthanzeroas
the otherphenomenondid. Thus,it seemsclearthatthe flowphysicswhich
J
producethesetwophenomenaare different.The beautyof the secondphenomenon,
in termsof lungdiagnosis,is thatits higherfrequenciesare moreeasily
discernedabovethe backgroundlevelsin typicalexaminationenvironments.
Furthertestingshouldallowit to be understoodandpredictedjustas is the
firstphenomenon.
DISCUSSIONOF RESULTS
In theirinitialvisualizationstudiesof flowin Y-tubes,Schroterand
Sudlow2 claimedto haveobservedfourvorticesin expiratoryflowover the
entireReynoldsnumberrange50< Re< 4500. Thisis supportedby theworkof
Hardin,Yu, Pattersonand Tribles who foundthe pressure/flowrelationin a
largerfourordermodelof the bronchialtreenot to varyoverthisrange. The
presentstudy,however,suggeststhatat leasttwo differentphenomenaoccurin
thissameReynoldsnumberrange.
One possibleexplanationfor thesedifferingresultsis thata critical
variableis not beingcontrolledin the experiments.It is the presentauthors'
suspicionthatthisvariableis the geometryof thejunction.Schroterand
, Sudlow2, who used"perspex"tubes,madean initialstudyof thiseffect.
Theyutilizedtwotubeshavingthe ratioof the radiusof curvatureof the outer
J
wall of thejunctionto the radiusof the parenttubeequalto one and four
respectivelyandfoundthata largeregionof reversedflowoccurredin the first
modelwhilethe flowin the secondremainedattached.However,theeffectof
the carinaor flowdividerwherethe twodaughtertubesmeetwas not considered.
8In the present study, where glass tubes were employed, the experimenters
had very little control over the geometry of the junction, having to take
whatever the glass shop produced. This often resulted in quite wavy walls in
the region of the junction. Thus, some tubes were tested in which no tonal
phenomenawere observed. Others were tested in which the tone phenomenawere
not as distinct as those reported here. Such assymmetries would also explain
the appearance of many harmonics in the data, while the theory predicted only
one.
In attempting to study a laminar flow phenomenon, particularly in the
region above Re = 2000 where Poiseuille flow in the tube would tend to go
turbulent 6, it is not surprising that inflow and geometric conditions should
be critical to the experiment. Thus, the present authors have planned a further
series of tests which will employ machined tubes and rubber lined tubes to
control the geometry and to yield more precise inflow conditions. These con-
siderations are not important in the actual human lung as physiological surfaces
tend to be smooth such that the inflow is laminar.
Another phenomenonwhich was observed in earlier tests with larger tubes
was the presence of organ pipe tones. These are readily recognized as they
tend to form an almost harmonic series with fundamental frequency given approxi-
mately .,,7_>
f = _ (3)0 4L
where c is the speed of sound and L is the lengthof the tube. Thus, the fre-
quencyof this series of tones does not change as the flow in the tube is ,
changed.
Finally, it is of interest to comment on the fact that at least two
different phenomenawere observed. This behavior is reminiscent of that
9producedby flowovera cylinder8. At low Reynoldsnumber,thewake consists
of a veryorderlyvortexstreet. As the flowspeedis raised,thewake degen-
eratesintoa veryconfusedmotionin whichno ordercan be observed.Then,
Q
witha stillfurtherincreasein speed,the orderlyvortexstreetreturnsonce
more until,at a veryhighReynoldsnumber,it disappearsand returnsno more.
Whatmay be happeningin theY-tubeis thatthe flowis initiallyin the
stablefourvortexconfigurationobservedby Schroterand Sudlow2. Then,as
the flowis increased,thisconfigurationbecomesunstableand confused.A
furtherincreasemay thenfindthe flowin a new stableconfiguration,suchas
eightvortices,whichthendegeneratesintoturbulence.Suchstatetransitions
arequitecommonlyobservedin laminarflows9, althoughprecisepredictionof
suchbehaviorhas notyet beenachieved.Moreextensivevisualizationand
measurementprogramsare plannedto betterunderstandthisbehavior.
CONCLUSION
Thispaperhaspresentedexperimentalresultswhichtendto validatea
previouslydevelopedtheoryof soundgenerationin the humanlungovera
particularReynoldsnumberrange. In addition,the presenceof a second
phenomenonis reported.Thesephenomenahaveimportantapplicationin the
diagnosisand preventionof lungdiseaseas theyallowthe determinationof
bronchialdiametersfromspectraof soundproducedby the lung. Furtherexperi-
mentsare neededto increasetheunderstandingof thissecondphenomenonand to
betterdefinethecriticalparametersof the lungsoundgenerationprocess.
I0
REFERENCES
I. Hardin,J. C. and Patterson,J. L., Jr.: MonitoringtheStateof the Human
Airwaysby Analysisof RespiratorySound. ActaAstronautica,vol.6, 1979,
pp. 1137-1151.
2. Schroter,R. C. andSudlow,M. F.: FlowPatternsin Modelsof the Human
BronchialAirways. Resp.Physiol.,vo1.7, 1969,pp. 341-355.
3. Powell,A.: Theoryof VortexSound. J. Acoust.Soc.Am., vol.36, 1964,
pp. 177-195.
4. Weibel,E. R.: Morphometryof theHumanLung. AcademicPressInc.,New
York,N.Y.,1963.
5. Hardin,J.C.;Yu,J. C.; Patterson,J. L., Jr.;andTrible,W.: The
Pressure/FlowRelationin BronchialAirwayson Expiration.Biofluid
Mechanics2, Ed. by D. Schneck,PlenumPress,New York,1980.
6. Prandtl,L. and Tietgens,O. G.: AppliedHydro-and Aeromechanics,Chap.
II, DoverPublications,NewYork,1934.
7. Rayleigh,C. W. S.: Theoryof Sound. Vol.II,Chap.12,DoverPublications,
New York,1945.
8. Roshko,A.: Experimentson theFlowPasta CircularCylinderat Very High
ReynoldsNumbers.J. FluidMech.,vol.lO,pt. 3, May 1961,pp. 345-356.
o
9. Monin,A. S. and Yaglom,A. M.: StatisticalFluidMechanics.Vol.l, Chap.2,
M.I.T.Press,1971.
\I.D. =4ram
70.4 i
Figure 1: Full Scale Sketch of Experimental Model
I
•Figure 2: Model in Anechoic Chamber
SHOP COARSE FINE
AIR __ REDUCING_ REDUCING_ FLOW
SUPPLY VALVE VALVE METER -- MUFFLER m
i:
MODEL o COMMERCIAL :i;
Y-TUBE
Figure 3: Schematicof Flow Supply
50-I
i
40 L
I
1
30
10'~984 5 "6 T
FREQUENCY, kHz
321
-10
-20
-30
. 0
! 20
i VELOCITY Re NO.
PSD, -' I (emf sec)10~dB 535 1427
0
Figure 4: Typical Spectrum in Lower Region
'.
30-
20
VELOCITY ReNO.
PSD, i (cm/secl
dB i0 698. 1861
0
_201
1
_30Ll , I , I , I , i l , _ , 3 ,0: 2 4: 6. 8 10
FREQUENCY.kHz
Figure5: Typical Spectrumin Upper Region
400
00
3 0 0
0
a
0 0 0
0 0 0
f, 0 0kHz 2 0
0 0 00
00 0 ooP
00 0 0
1 00 0 /:THEORY00
00 0g-3--U OJ
0 200 300 400 500 600 700 800 . -I100 900 Uo (em· see )I I I I I I I I I I
260 520 780 1040 1300 1560 1820 2080 2340
Re
Figure 6: Comparison of Tone Frequencies with Theory
..
1. Report No.
NASA H1-81897
2. Government Accession No. 3. Recipient's Catalog No.
4. Title and Subtitle
Genesis of Breath Sounds--Preliminary Verification of Theor,Y
5. Report Date
October 1980
6. Performing Organization Code
2640
7. Author(s) 8. Performing Organization Report No.
John L. Patterson, Jr.*, Jay C. Hardin, and John M. Seiner
I--------------------------~ 10. Work Unit No.
9. Performing Organization Name and Address
NASA Langley Research Center
Hampton, VA 23665
141-20-20-10
11. Contract or Grant No.
Technical Memorandum
14. Sponsoring Agency CodeNational Aeronautics and Space Administration
Washington, DC 20546
12. Sponsoring Agency Name and Address
1- --1 13. Type of Report and Period Covered
15. Supplementary Notes
Presented at the 5th International Lung Sounds Conference in London, EnglandSeptember 15-16, 1980.
*Medica1 College of Virginia, Richmond, VA 23219
16. Abstract
Experimental results are presented which tend to validate a previously developed
theory of sound production in the human lung over a particular Reynolds number range.
In addition, a new, presently nonunderstood, phenomenon was observed at higher
Reynolds number. These results, which show how sound generation in the lung depends
upon the physiologically important variables of volume flow rate and bronchial
diameter, have potentially important application in noninvasive lung examination and
the diagnosis of lung disease.
17. Key Words (Suggested by Author(s))
Lung Sounds
Pulmonary Acousti'cs
Respiratory Acousti'cs
18. Distribution Statement
Unclassified - Unlimited
Star Category 51
19. Security Classif. (of this report)
Unclassified
20. Security Classif. (of this page)
Unclassified
\
21. No. of Pages
16
22. Price'
A02
• For sale by the National Technical Information Service, Springfield, Virginia 22161
III
-I
1
41,
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Genesis of breath sounds-Preliminary verification of theory

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