An Approach to Interpreting Spirometry - AAFP

The forced expiratory volume in one second (FEV1) is the volume of air exhaled in the first second of the FVC maneuver. The FEV1/FVC ratio ... Advertisement search close Chronicobstructivepulmonarydisease(COPD)isthemostcommonrespiratorydiseaseandthefourthleadingcauseofdeathintheUnitedStates.1Despitepreventiveefforts,thenumberofnewpatientswithCOPDhasdoubledinthepastdecade,andthistrendislikelytocontinue.2,3Evidenceindicatesthatapatient'shistoryandphysicalexaminationareinadequatefordiagnosingmildandmoderateobstructiveventilatoryimpairments.4Althoughacompletepulmonaryfunctiontestprovidesthemostaccurateobjectiveassessmentoflungimpairment,spirometryisthepreferredtestforthediagnosisofCOPDbecauseitcanobtainadequateinformationinacost-effectivemanner. Agreatdealofinformationcanbeobtainedfromaspirometrytest;however,theresultsmustbecorrelatedcarefullywithclinicalandroentgenographicdataforoptimalclinicalapplication.Thisarticlereviewstheindicationsforuseofspirometry,providesastepwiseapproachtoitsinterpretation,andindicateswhenadditionaltestsarewarranted. Background TheNationalHealthSurveyof1988to1994foundhighratesofundiagnosedanduntreatedCOPDincurrentandformersmokers.5Population-basedstudieshaveidentifiedvitalcapacity(VC)asapowerfulprognosticindicatorinpatientswithCOPD.TheFraminghamstudyidentifiedalowforcedvitalcapacity(FVC)asariskfactorforprematuredeath.6TheThirdNationalHealthandNutritionalExaminationSurveyandthemulticenterLungHealthStudyshowedpotentialbenefitsforpatientswithearlyidentification,intervention,andtreatmentofCOPD.7,8TheLungHealthStudywasthefirststudytoshowthatearlyidentificationandinterventioninsmokerscouldaffectthenaturalhistoryofCOPD.7Thesesurveysalsoshowedthatsimplespirometrycoulddetectmildairflowobstruction,eveninasymptomaticpatients. IncreasedpublicawarenessofCOPDledtotheformationoftheNationalLungHealthEducationProgram(NLHEP)aspartofanationalstrategytocombatchroniclungdisease.9TheWorldHealthOrganizationandtheU.S.NationalHeart,Lung,andBloodInstituterecentlypublishedtheGlobalInitiativeforChronicObstructiveLungDiseasetoincreaseawarenessoftheglobalburdenofCOPDandtoprovidecomprehensivetreatmentguidelinesaimedatdecreasingCOPD-relatedmorbidityandmortality.10 SpirometricvaluesFVC—Forcedvitalcapacity;thetotalvolumeofairthatcanbeexhaledduringamaximalforcedexpirationeffort.FEV1—Forcedexpiratoryvolumeinonesecond;thevolumeofairexhaledinthefirstsecondunderforceafteramaximalinhalation.FEV1/FVCratio—ThepercentageoftheFVCexpiredinonesecond.FEV6—Forcedexpiratoryvolumeinsixseconds.FEF25–75%—ForcedexpiratoryflowoverthemiddleonehalfoftheFVC;theaverageflowfromthepointatwhich25percentoftheFVChasbeenexhaledtothepointatwhich75percentoftheFVChasbeenexhaled.MVV—Maximalvoluntaryventilation.LungvolumesERV—Expiratoryreservevolume;themaximalvolumeofairexhaledfromend-expiration.IRV—Inspiratoryreservevolume;themaximalvolumeofairinhaledfromend-inspiration.RV—Residualvolume;thevolumeofairremaininginthelungsafteramaximalexhalation.VT—Tidalvolume;thevolumeofairinhaledorexhaledduringeachrespiratorycycle.LungcapacitiesFRC—Functionalresidualcapacity;thevolumeofairinthelungsatrestingend-expiration.IC—Inspiratorycapacity;themaximalvolumeofairthatcanbeinhaledfromtherestingexpiratorylevel.TLC—Totallungcapacity;thevolumeofairinthelungsatmaximalinflation.VC—Vitalcapacity;thelargestvolumemeasuredoncompleteexhalationafterfullinspiration. SpirometryMeasurementsandTerminology Spirometrymeasurestherateatwhichthelungchangesvolumeduringforcedbreathingmaneuvers.Spirometrybeginswithafullinhalation,followedbyaforcedexpirationthatrapidlyemptiesthelungs.Expirationiscontinuedforaslongaspossibleoruntilaplateauinexhaledvolumeisreached.Theseeffortsarerecordedandgraphed.(AglossaryoftermsusedinthisarticlecanbefoundinTable1.) Lungfunctionisphysiologicallydividedintofourvolumes:expiratoryreservevolume,inspiratoryreservevolume,residualvolume,andtidalvolume.Together,thefourlungvolumesequalthetotallungcapacity(TLC).Lungvolumesandtheircombinationsmeasurevariouslungcapacitiessuchasfunctionalresidualcapacity(FRC),inspiratorycapacity,andVC.Figure111showsthedifferentvolumesandcapacitiesofthelung. ThemostimportantspirometricmaneuveristheFVC.TomeasureFVC,thepatientinhalesmaximally,thenexhalesasrapidlyandascompletelyaspossible.Normallungsgenerallycanemptymorethan80percentoftheirvolumeinsixsecondsorless.Theforcedexpiratoryvolumeinonesecond(FEV1)isthevolumeofairexhaledinthefirstsecondoftheFVCmaneuver.TheFEV1/FVCratioisexpressedasapercentage(e.g.,FEV1of0.5LdividedbyFVCof2.0LgivesanFEV1/FVCratioof25percent).Theabsoluteratioisthevalueusedininterpretation,notthepercentpredicted. PulmonaryfunctiontestNormalvalue(95percentconfidenceinterval)FEV180%to120%FVC80%to120%AbsoluteFEV1/FVCratioWithin5%ofthepredictedratioTLC80%to120%FRC75%to120%RV75%to120%DLCO>60%to<120% SomeportableofficespirometersreplacetheFVCwiththeFEV6forgreaterpatientandtechnicianease.Theparameterisbasedonasix-secondmaneuver,whichincorporatesastandardtimeframetodecreasepatientvariabilityandtheriskofcomplications.Oneofthepitfallsofusingthistypeofspirometeristhatitmustbecalibratedfortemperatureandwatervapor.ItshouldbeusedwithcautioninpatientswithadvancedCOPDbecauseofitsinabilitytodetectverylowvolumesorflows.However,theFEV1/FEV6ratioprovidesaccuratesurrogatemeasurefortheFEV1/FVCratio.12ThereportedFEV1andFEV6valuesshouldberoundedtothenearest0.1LandthepercentpredictedandtheFEV1/FEV6ratiotothenearestinteger.13 DifferentspirographicandflowvolumecurvesareshowninFigure2.11ItisimportanttounderstandthattheamountexhaledduringthefirstsecondisaconstantfractionoftheFVC,regardlessoflungsize.ThesignificanceoftheFEV1/FVCratioistwofold.ItquicklyidentifiespatientswithairwayobstructioninwhomtheFVCisreduced,anditidentifiesthecauseofalowFEV1.NormalspirometricparametersareshowninTable2.14 IndicationsforOfficeSpirometry Spirometryisdesignedtoidentifyandquantifyfunctionalabnormalitiesoftherespiratorysystem.TheNLHEPrecommendsthatprimarycarephysiciansperformspirometryinpatients45yearsofageorolderwhoarecurrentorformersmokers;inpatientswhohaveaprolongedorprogressivecoughorsputumproduction;orinpatientswhohaveahistoryofexposuretolungirritants.9Otherindicationsforspirometryaretodeterminethestrengthandfunctionofthechest,followdiseaseprogression,15,16assessresponsetotreatment,17,18andobtainbaselinemeasurementsbeforeprescribingdrugsthatarepotentiallytoxictothelungs,suchasamiodarone(Cordarone)andbleomycin(Blenoxane).19Spirometryalsoishelpfulinpreoperativeriskassessmentformanysurgeries20–23andoftenisusedinworkers'compensationanddisabilityclaimstoassessoccupationalexposuretoinhalationhazards.24Tables3and4listindicationsandcontraindicationsforspirometry. DetectingpulmonarydiseaseHistoryofpulmonarysymptomsChestpainororthopneaCoughorphlegmproductionDyspneaorwheezingPhysicalfindingsChestwallabnormalitiesCyanosisDecreasedbreathsoundsFingerclubbingAbnormallaboratoryfindingsBloodgasesChestradiographAssessingseverityorprogressionofdiseasePulmonarydiseasesChronicobstructivepulmonarydiseaseCysticfibrosisInterstitiallungdiseasesSarcoidosisCardiacdiseasesCongestiveheartfailureCongenitalheartdiseasePulmonaryhypertensionNeuromusculardiseasesAmyotrophiclateralsclerosisGuillain-BarrésyndromeMultiplesclerosisMyastheniagravisRiskstratificationofpatientsforsurgeryThoracicsurgeriesLobectomyPneumonectomyCardiacsurgeriesCoronarybypassCorrectionofcongenitalabnormalitiesValvularsurgeryOrgantransplantationGeneralsurgicalproceduresCholecystectomyGastricbypassEvaluatingdisabilityorimpairmentSocialSecurityorothercompensationprogramsLegalorinsuranceevaluations InterpretingSpirometryResults Spirometryrequiresconsiderablepatienteffortandcooperation.Therefore,resultsmustbeassessedforvaliditybeforetheycanbeinterpreted.17,25Inadequatepatienteffortcanleadtomisdiagnosisandinappropriatetreatment.AnalgorithmforinterpretingspirometryresultsisgiveninFigure3. Acutedisordersaffectingtestperformance(e.g.,vomiting,nausea,vertigo)Hemoptysisofunknownorigin(FVCmaneuvermayaggravateunderlyingcondition.)PneumothoraxRecentabdominalorthoracicsurgeryRecenteyesurgery(increasesinintraocularpressureduringspirometry)RecentmyocardialinfarctionorunstableanginaThoracicaneurysms(riskofrupturebecauseofincreasedthoracicpressure) Theclinicalcontextofthetestisimportantbecauseparametersinpatientswithmilddiseasecanoverlapwithvaluesinhealthypersons.26Normalspirometryvaluesmayvary,andinterpretationofresultsreliesontheparametersused.Thenormalrangesforspirometryvaluesvarydependingonthepatient'sheight,weight,age,sex,andracialorethnicbackground.27,28Predictedvaluesforlungvolumesmaybeinaccurateinverytallpatientsorpatientswithmissinglowerextremities.FEV1andFVCaregreaterinwhitescomparedwithblacksandAsians.FVCandVCvaluesvarywiththepositionofthepatient.Thesevariablescanbe7to8percentgreaterinpatientswhoaresittingduringthetestcomparedwithpatientswhoaresupine.FVCisabout2percentgreaterinpatientswhoarestandingcomparedwithpatientswhoaresupine. Todeterminethevalidityofspirometricresults,atleastthreeacceptablespirogramsmustbeobtained.Ineachtest,patientsshouldexhaleforatleastsixsecondsandstopwhenthereisnovolumechangeforonesecond.ThetestsessionisfinishedwhenthedifferencebetweenthetwolargestFVCmeasurementsandbetweenthetwolargestFEV1measurementsiswithin0.2L.Ifbothcriteriaarenotmetafterthreemaneuvers,thetestshouldnotbeinterpreted.Repeattestingshouldcontinueuntilthecriteriaaremetoruntileighttestshavebeenperformed.26 Figure425showsnormalflow-volumeandtime-volumecurves.Noticethatthelinesoftheflow-volumecurvearefreeofglitchesandirregularities.Thevolume-timecurveextendslongerthansixseconds,andtherearenosignsofearlyterminationorcutoff. Ifthetestisvalid,thesecondstepistodeterminewhetheranobstructiveorrestrictiveventilatorypatternispresent.WhentheFVCandFEV1aredecreased,thedistinctionbetweenanobstructiveandrestrictiveventilatorypatterndependsontheabsoluteFEV1/FVCratio.IftheabsoluteFEV1/FVCratioisnormalorincreased,arestrictiveventilatoryimpairmentmaybepresent.However,tomakeadefinitivediagnosisofrestrictivelungdisease,thepatientshouldbereferredtoapulmonarylaboratoryforstaticlungvolumes.IftheTLCislessthan80percent,thepatternisrestrictive,anddiseasessuchaspleuraleffusion,pneumonia,pulmonaryfibrosis,andcongestiveheartfailureshouldbeconsidered. AreducedFEV1andabsoluteFEV1/FVCratioindicatesanobstructiveventilatorypattern,andbronchodilatorchallengetestingisrecommendedtodetectpatientswithreversibleairwayobstruction(e.g.,asthma).Abronchodilatorisgiven,andspirometryisrepeatedafterseveralminutes.ThetestispositiveiftheFEV1increasesbyatleast12percentandtheFVCincreasesbyatleast200mL.Thepatientshouldnotuseanybronchodilatorforatleast48hoursbeforethetest.Anegativebronchodilatorresponsedoesnotcompletelyexcludethediagnosisofasthma. Themid-expiratoryflowrate(FEF25–75%)istheaverageforcedexpiratoryflowrateoverthemiddle50percentoftheFVC.Itcanhelpinthediagnosisofanobstructiveventilatorypattern.BecauseitisdependentonFVC,theFEF25–75%ishighlyvariable.Inthecorrectclinicalsituation,areductioninFEF25–75%oflessthan60percentofthatpredictedandanFEV1/FVCratiointhelowtonormalrangemayconfirmairwayobstruction.29 Themaximalvoluntaryventilation(MVV)maneuverisanothertestthatcanbeusedtoconfirmobstructiveandrestrictiveconditions.Thepatientisinstructedtobreatheashardandfastaspossiblefor12seconds.Theresultisextrapolatedto60secondsandreportedinlitersperminute.MVVgenerallyisapproximatelyequaltotheFEV1×40.AlowMVVcanoccurinobstructivediseasebutismorecommoninrestrictiveconditions.IftheMVVislowbutFEV1andFVCarenormal,poorpatienteffort,aneuromusculardisorder,ormajorairwaylesionmustbeconsidered. Oncetheventilatorypatternisidentified,theseverityofthediseasemustbedetermined.TheAmericanThoracicSocietyhasdevelopedascaletoratetheseverityofdiseasebasedonpredictedFEV1andTLC.29 Thefinalstepininterpretingspirometryistodetermineifadditionaltestingisneededtofurtherdefinetheabnormalitydetectedbyspirometry.Measurementofstaticlungvolumes,includingFRC,isrequiredtomakeadefinitivediagnosisofrestrictivelungdisease. FinalComment Basicspirometrycanbeperformedinthefamilyphysician'sofficewithrelativeeaseandinexpensiveequipment.Inmostcases,officespirometryprovidesanadequateassessmentofpulmonaryfunction.Inaddition,spirometrymaybeusedtoaddressmajorissuesinclinicalmanagementandhealthscreening. ContinueReading Advertisement MoreinAFP MoreinPubmed ArticleSections Copyright©2004bytheAmericanAcademyofFamilyPhysicians. 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