pulmonary function tests goalsgoals –don’t memorize! try to understand… what are you measuring...

Pulmonary function testsPulmonary function tests

• GoalsGoals–Don’t memorize! Try to understand…Don’t memorize! Try to understand…

• What are you measuring and why? What are you measuring and why?

• How are you measuring it?How are you measuring it?

• What do the results mean? (aka How What do the results mean? (aka How to interpret PFTs and impress your to interpret PFTs and impress your friends)friends)

Pulmonary Function Tests Pulmonary Function Tests Practical Practical goalsgoals

• Basics about measurementsBasics about measurements– What do your measurements reflectWhat do your measurements reflect

• Two broad categories of diseaseTwo broad categories of disease– Obstruction (Definition and grading of severity)Obstruction (Definition and grading of severity)

– Restriction (Definition, severity, when to Restriction (Definition, severity, when to suspect it)suspect it)

Lung Lung CancerCancer

PneumoniaPneumonia

TB and other TB and other Mycobacterial Mycobacterial

diseasediseasePulmonary Pulmonary

vascular vascular diseasedisease

AutoimmuneAutoimmune/Vasculitis/Vasculitis

EnvironmentalEnvironmental/Occupational/Occupational

Inside the mind of a Inside the mind of a pulmonologist??pulmonologist??

ObstructiveObstructiveLung DiseasesLung Diseases

RestrictiveRestrictiveLung DiseasesLung Diseases

Sleep Sleep apneaapnea

ARDSARDS

Golf, Cubs, Golf, Cubs, College College

basketballbasketball

Why measure PFTs?Why measure PFTs?

•Why do any test?Why do any test?–To look for diseaseTo look for disease

–To evaluate severity of diseaseTo evaluate severity of disease

–To determine response to To determine response to treatmenttreatment

–To prevent diseaseTo prevent disease

What measurements should you What measurements should you make?make?

• To know what to lung function to To know what to lung function to measure you need to know...measure you need to know...–What does the lung normally doWhat does the lung normally do

–How does it do itHow does it do it

–What can cause this to go wrongWhat can cause this to go wrong

What measurements:What measurements:Normal lungNormal lung

• To understand lung To understand lung function think in function think in terms of anatomyterms of anatomy– AirflowAirflow

• Gets the gas to the Gets the gas to the blood and back againblood and back again

– Gas exchangeGas exchange

• LotsLots of air of air

• ReallyReally close to the close to the capillariescapillaries

Normal anatomyNormal anatomySmall airways….Small airways….

Alveoli…gas exchange unitsAlveoli…gas exchange units

Medium airways….Medium airways….

Large airways and chest wallLarge airways and chest wall

What measurements?What measurements?• Airflow (Obstructive diseases)Airflow (Obstructive diseases)

– How fast (How fast (FForced orced eexhaled xhaled vvolume)olume)

• FEVFEV11, and FEV, and FEV11% (actually FEV% (actually FEV11/FVC) and Flow /FVC) and Flow volume loop (FVL)volume loop (FVL)

• Gas Exchange (Restrictive diseases)Gas Exchange (Restrictive diseases)– How muchHow much

– FForced orced VVital ital CCapacity, apacity, TTotal otal LLung ung CCapacity apacity (FVC, TLC)(FVC, TLC)

– Diffusion capacity (Diffusion capacity of the Diffusion capacity (Diffusion capacity of the lung for carbon monoxide)lung for carbon monoxide)

• DLDLCOCO

Vt Tidal volume Vt Tidal volume

VC Vital CapacityVC Vital Capacity

ERV/IRV Expiratory/Inspiratory ERV/IRV Expiratory/Inspiratory reserve volumereserve volumeThese are all measured easily with spirometersThese are all measured easily with spirometers

FRC Functional residual capacityFRC Functional residual capacity

RV residual volumeRV residual volume

TLC Total lung capacity TLC Total lung capacity (RV + VC)(RV + VC)

Measuring these requires more Measuring these requires more specialized equipmentspecialized equipment

VCVCFRCFRC

RVRV

TLCTLC

VVtt

NormalNormal

RVRV

ERVERV

ICIC

RVRV

VCVC

TLCTLC

RVRV

VCVC

RVRV

VCVC

RVRV

VCVC

NormalNormalObstructiveObstructive RestrictiveRestrictive

Vital capacity is reduced in both Vital capacity is reduced in both obstructive and restrictive diseasesobstructive and restrictive diseases

What are “PFT?s”?What are “PFT?s”?

• SpirometrySpirometry is just the measure of is just the measure of dynamic lung mechanicsdynamic lung mechanics– FEVFEV11 and FVC, and the FEV and FVC, and the FEV11/FVC ratio/FVC ratio

• Lung volume measurementsLung volume measurements– Usually measured as part of “Usually measured as part of “Full PFTsFull PFTs” or ” or

“Complete PFTs”“Complete PFTs”– Involves more sophisticated (Involves more sophisticated (aka expensiveaka expensive) )

equipment and technician timeequipment and technician time

• Diffusion capacity or Diffusion capacity or DLCODLCO

SpirometrySpirometry

Spirometry requires that you perform a Spirometry requires that you perform a forced expiratory forced expiratory maneuver (FEM)maneuver (FEM)

How are the measurements made?How are the measurements made?SpirometrySpirometry

Most “PFTs” mean simple spirometry, which is all most patients Most “PFTs” mean simple spirometry, which is all most patients need to accomplish the goals of obtaining “PFT’s” in the first placeneed to accomplish the goals of obtaining “PFT’s” in the first place

How are measurements made?How are measurements made?Measuring lung volumesMeasuring lung volumes

Some patients also require “Full PFT’s” or lung volume Some patients also require “Full PFT’s” or lung volume measurements in addition to spirometrymeasurements in addition to spirometryThese are usually the patients in whom restrictive lung disease is These are usually the patients in whom restrictive lung disease is suspectedsuspected

Gas dilution method of measuring FRCGas dilution method of measuring FRC May underestimate TLC if the patient has emphysemaMay underestimate TLC if the patient has emphysema

CC11=N/V=N/Vboxbox

CC22=N/(V=N/(Vboxbox++FRC)FRC)

Body plethysmographBody plethysmograph

PPlunglungxx V Vlunglung=P’=P’lunglungxx V’ V’lunglung

V’V’lunglung = = VVlunglung +∆V+∆V

P’P’lunglung =P =Plunglung+∆P+∆P

PPboxbox x x V Vboxbox== P’P’boxbox xx V’ V’boxbox V’V’boxbox =V =Vboxbox+∆V+∆V

P’P’boxbox =P =Pboxbox+∆P+∆P

PPlunglung

PPboxbox x V x Vboxbox

VVlunglung

Plethysmography- measures total thoracic gas volume, but is Plethysmography- measures total thoracic gas volume, but is more cumbersome. Uses Boyle’s law to calculate RV.more cumbersome. Uses Boyle’s law to calculate RV.

Why measure residual volume?Why measure residual volume?Look at two people with identical vital capacityLook at two people with identical vital capacity

VCFRC

RVRV

TLC

VtVt

VC

FRCRVRV

TLC

SummarySummary

• What we measureWhat we measure– Airflow, and gas exchangeAirflow, and gas exchange

• Why we measure itWhy we measure it– Diagnose, follow treatment, prognosticateDiagnose, follow treatment, prognosticate

• How we measureHow we measure

• What do you do with the results?What do you do with the results?

What do the results mean?What do the results mean?(aka How to interpret PFTs and impress your friends)(aka How to interpret PFTs and impress your friends)

• Remember the question you want to Remember the question you want to answer in the first placeanswer in the first place– To look for diseaseTo look for disease

– To evaluate severity of diseaseTo evaluate severity of disease

– To determine response to treatmentTo determine response to treatment

– To prevent diseaseTo prevent disease

• For most of these you need a For most of these you need a “normal” value for comparison“normal” value for comparison

What are normal values?What are normal values?• You don’t have to worry about memorizing You don’t have to worry about memorizing

normal values! (woohoo)normal values! (woohoo)– All modern PFT labs have a set of nomograms which they use All modern PFT labs have a set of nomograms which they use

to predict normal valuesto predict normal values

• What you What you shouldshould know know– Normals are derived just like any normal lab valueNormals are derived just like any normal lab value

– There are limitations to these estimatesThere are limitations to these estimates

• Predicted values are only as good as the Predicted values are only as good as the population in which they were measuredpopulation in which they were measured

• The patient should be from the population from The patient should be from the population from which the normals are calculatedwhich the normals are calculated

yy eess nn oo

yy eess nn oo

yy eess nn oo

What do the results mean: Algorhithim for PFT'sWhat do the results mean: Algorhithim for PFT'sIs the FEM adequate? Is the FEM adequate?

Is the FEV1/FVC lower Is the FEV1/FVC lower than predicted?than predicted?

Interpretation may be Interpretation may be limited by falsely low limited by falsely low FVCFVC

This is the definition of This is the definition of obstructionobstructionMildMild FEV1 >70%FEV1 >70%ModerateModerate FEV1 60-70%FEV1 60-70%Mod severeMod severe FEV1 50-60%FEV1 50-60%SevereSevere FEV1 <50%FEV1 <50%Very severeVery severe FEV1 <40%FEV1 <40%

Is FVC reduced?Is FVC reduced?

Restriction Restriction maymay be present; be present; Need TLC to definitively Need TLC to definitively diagnose restrictiondiagnose restriction

Lung volumes:Lung volumes:Severity determined bySeverity determined bythe reduction in TLCthe reduction in TLCMildMild 65-80%65-80%ModerateModerate 50-65%50-65%SevereSevere <50%<50%

Spirometry:Spirometry:Severity is determinedSeverity is determined by the reduction in VCby the reduction in VCMildMild 70-80%70-80%ModerateModerate 60-70%60-70%SevereSevere <60%<60%

Normal pulmonary Normal pulmonary mechanicsmechanics

RestrictionRestriction

Algorhithim for PFT's:Algorhithim for PFT's:

yy eess nn oo

yy eess nn oo

yy eess nn oo



Interpretation Interpretation may bemay be limited by falsely low limited by falsely low FVCFVC








What do the results mean:What do the results mean: Algorhithim for PFT'sAlgorhithim for PFT's

Step 2, what is the of FEVStep 2, what is the of FEV11 /FVC?- aka FEV /FVC?- aka FEV11%%

• If it is reduced, then If it is reduced, then byby definitiondefinition there is there is airway obstructionairway obstruction– AnyAny reduction compared to the predicted value reduction compared to the predicted value

• The severity of is determined by the The severity of is determined by the FEVFEV11

– ≥≥80% is considered “normal”80% is considered “normal”

– 70-80% is considered mild70-80% is considered mild

– 60-70% is considered moderate60-70% is considered moderate

– 50-60% is considered moderately severe50-60% is considered moderately severe

– 40-50% is considered severe40-50% is considered severe

– <40% is very severe<40% is very severe

yy eess nn oo

yy eess nn oo

yy eess nn oo











Be careful before citing “restrictive deficits” in Be careful before citing “restrictive deficits” in people with obstructive lung diseasepeople with obstructive lung disease

VCFRC

RVRV

TLC

VtVt

VC

FRCRVRV

TLC

EmphysemaEmphysema NormalNormal

Algorhithim for PFT's:Algorhithim for PFT's:

Algorhithim for PFT'sAlgorhithim for PFT's If FEVIf FEV11/FVC is normal/FVC is normal

• Is FVC normal?Is FVC normal?

• If yes then the subject has “normal If yes then the subject has “normal pulmonary mechanics”pulmonary mechanics”

• If not, then is there any reason to suspect If not, then is there any reason to suspect restrictive disease?restrictive disease?– Keep in mind…a poor FEM (which affects the Keep in mind…a poor FEM (which affects the

FVC more than the FEVFVC more than the FEV11) not only ) not only underestimatesunderestimates FVC, but FVC, but overestimatesoverestimates FEVFEV11/FVC, and can lead to false negative /FVC, and can lead to false negative spirometry for airway obstructionspirometry for airway obstruction

By definition means a reduced total By definition means a reduced total lung capacitylung capacity

Reduced vital capacity can suggest restrictionReduced vital capacity can suggest restriction

Restrictive lung diseaseRestrictive lung disease

Vt

VCFRC

RV

TLC

What do the results mean: What do the results mean: Algorhithim for PFT'sAlgorhithim for PFT's

Restrictive lung diseaseRestrictive lung disease• This can only be definitively This can only be definitively

established by measurements of lung established by measurements of lung volumevolume– Gas dilution methodsGas dilution methods• Only measures gas in communication with Only measures gas in communication with

the environmentthe environment– PlethysmographyPlethysmography• Measure total thoracic gas volume, but is Measure total thoracic gas volume, but is

more cumbersomemore cumbersome• Normal FEVNormal FEV11/FVC and reduced FVC with a good /FVC and reduced FVC with a good

FEM can infer the presence of restrictive defectFEM can infer the presence of restrictive defect


Assessing severity of restrictive defectsAssessing severity of restrictive defects

• Without TLC measurement, base severity on the Without TLC measurement, base severity on the FVCFVC– ≥≥80% is considered “normal”80% is considered “normal”– 70-80% is considered mild70-80% is considered mild– 60-70%% is considered moderate60-70%% is considered moderate– 60% is considered severe60% is considered severe

• When TLC is measuredWhen TLC is measured– Gold standard to define restrictive ventilatory Gold standard to define restrictive ventilatory

defectdefect– Only order “Full PFTs” if you suspect restrictive Only order “Full PFTs” if you suspect restrictive

or interstitial lung disease (expensive!)or interstitial lung disease (expensive!)


Restrictive defects cont’dRestrictive defects cont’d

• Severity is based on the degree of Severity is based on the degree of impairment in TLCimpairment in TLC–≥≥80% is considered “normal”80% is considered “normal”

–65-80% is considered mild65-80% is considered mild

–50-65% is considered moderate50-65% is considered moderate

–<50% is considered severe<50% is considered severe

yy eess nn oo

yy eess nn oo

yy eess nn oo












What about flow-volume loops?What about flow-volume loops?

Flow

Lung Volume Time (sec)

Volume

Flow volume loop examplesFlow volume loop examples

What are these?What are these?

Inspiratory effort

Expiratory effort

What do the results mean: What do the results mean: Diffusing capacity aka DDiffusing capacity aka DLLCOCO

• Measures the ability of the lung to Measures the ability of the lung to transfer gas from the environment to transfer gas from the environment to the bloodstreamthe bloodstream

• DDLLCO=VCO=VCOCO/(P/(PACOACO-P-PaCOaCO))–Measures the volume of gas that moves Measures the volume of gas that moves

across the alveolar-capillary barrier per across the alveolar-capillary barrier per unit of time per mm Hg gradientunit of time per mm Hg gradient

What do the results mean: What do the results mean: What factors affect DLCO?What factors affect DLCO?

• Non-disease relatedNon-disease related– Age, body size, lung volume, hemoglobin concentration, Age, body size, lung volume, hemoglobin concentration,

body position, patient cooperation, altitude, tobacco body position, patient cooperation, altitude, tobacco use, etc., etc.use, etc., etc.

• Disease related-Disease related-anything that affects the anything that affects the lung parenchyma or hemoglobin in the lung parenchyma or hemoglobin in the lungslungs– EmphysemaEmphysema (Very sensitive), (Very sensitive), but but notnot asthma or chronic bronchitis asthma or chronic bronchitis– Pulmonary vascular disease Pulmonary vascular disease – Infiltrative/interstitial lung diseasesInfiltrative/interstitial lung diseases (Very sensitive) (Very sensitive)

• Sarcoid, IPF, BOOP, hypersensitivity pneumonitisSarcoid, IPF, BOOP, hypersensitivity pneumonitis• Others..CHF (Increased?), pulmonary hemorrhage (increased)Others..CHF (Increased?), pulmonary hemorrhage (increased)

What do the results mean: What do the results mean: DLCO?DLCO?

• Because of the number of factors affecting Because of the number of factors affecting the test there is a wider variationthe test there is a wider variation

–Normal is considered ≥75%Normal is considered ≥75%– Less than 75% is “reduced”Less than 75% is “reduced”

–Less than 40% is commonly associated Less than 40% is commonly associated with resting or exercise induced with resting or exercise induced hypoxemia and should prompt you to hypoxemia and should prompt you to evaluate the patient for supplemental evaluate the patient for supplemental oxygenoxygen

What can PFTs tell you about What can PFTs tell you about the patientthe patient

• Normal or abnormalNormal or abnormal

• What diseases can you diagnose?What diseases can you diagnose?– OnlyOnly asthma is defined by its PFTs asthma is defined by its PFTs

• Estimation of impairment, or severity Estimation of impairment, or severity of diseaseof disease

• Response to therapyResponse to therapy

• Occupational surveillanceOccupational surveillance

What PFTs cannot tell youWhat PFTs cannot tell you

• Does the degree of abnormality Does the degree of abnormality explain the patients symptoms?explain the patients symptoms?

• ““Normality” does not exclude the Normality” does not exclude the presence of diseasepresence of disease

• Abnormal test may not reflect loss of Abnormal test may not reflect loss of lung functionlung function

BASELINE BASELINE

LUNG MECHANICSLUNG MECHANICS ActualActual %Pred%Pred

FVCFVC liters liters 5.03 5.03 98% 98%

FEV1FEV1 liters liters 3.77 3.77 97% 97%

FEV1/FVCFEV1/FVC % % 75% 75% 76%76%

LUNG VOLUMESLUNG VOLUMES ActualActual %Pred%Pred

RV plethRV pleth liters liters 1.81 1.81 87% 87%

TLC plethTLC pleth liters liters 6.96 6.96 97% 97%

RV/TLC plethRV/TLC pleth % % 26% 26%

49 year old man with aplastic 49 year old man with aplastic anemia, awaiting BMT; May 1997anemia, awaiting BMT; May 1997

One month after BMTOne month after BMT

LUNG MECHANICSLUNG MECHANICS ActualActual PredPred %Pred%Pred

FVCFVC liters liters 2.98 2.98 5.12 5.12 58% 58%

FEV1FEV1 liters liters 2.31 2.31 3.90 3.90 59% 59%

FEV1/FVCFEV1/FVC % % 78% 78% 76% 76% 102% 102%

DIFFUSIONDIFFUSION ActualActual PredPred %Pred%Pred

HgbHgb mg/dl mg/dl 12.00 12.00 14.60 14.60 82% 82%

COHgbCOHgb % % 2.30 2.30

MUSCLE FORCESMUSCLE FORCES ActualActual PredPred %Pred%Pred

PemaxPemax cmH2O cmH2O 150.00 150.00 216 +/- 45 216 +/- 45

PimaxPimax mcH2O mcH2O -60 -60 -127 +/- 28 -127 +/- 28

SUPINE SUPINE ActualActual %Pred%Pred %Chg%Chg1.31 1.31 26% 26% -56% -56% 0.85 0.85 22% 22% -63% -63% 65% 65% 85% 85% -16% -16%

FVCFVC

FEV1FEV1

FEV1/FVCFEV1/FVC




FEV1/FVCFEV1/FVC % % 70% 70% 76% 76% 92% 92%

49 year old man with aplastic anemia, 8 49 year old man with aplastic anemia, 8 months after BMT; February 1998months after BMT; February 1998




FEV1/FVCFEV1/FVC % % 67% 67% 68% 68% 100% 100%

71 year old man with 2 year 71 year old man with 2 year history of dyspnea; June 2002history of dyspnea; June 2002




FEV1/FVCFEV1/FVC % % 77% 77% 68% 68% 115% 115%

71 year old man with 2 year 71 year old man with 2 year history of dyspnea; August 2002history of dyspnea; August 2002

Extrathoracic/upper airway Extrathoracic/upper airway obstruction (stridor)obstruction (stridor)

Fixed upper airway obstructionFixed upper airway obstruction

PFT summaryPFT summary

• Check the FEM to make sure it is adequateCheck the FEM to make sure it is adequate

• Obstructive ventilatory defects are defined Obstructive ventilatory defects are defined by FEVby FEV11/FVC less than predicted/FVC less than predicted– Severity graded by degreee of impairment in FEV1Severity graded by degreee of impairment in FEV1

• Restrictive ventilatory defect is defined by Restrictive ventilatory defect is defined by reduced TLCreduced TLC– Reduced FVC with no obstruction and a good FEM Reduced FVC with no obstruction and a good FEM

suggests the presence of a restrictive deficitsuggests the presence of a restrictive deficit

• DLCO is abnormal in almost all DLCO is abnormal in almost all parenchymal lung diseasesparenchymal lung diseases

pulmonary function tests goalsgoals –don’t memorize! try to understand… what are you measuring...

Documents

disease slide

lung function

normal lung

collegebasketball slide

dlco slide

wrong slide

total lung capacity

chest wall slide