Pulmonary function tests Goals Don’t memorize! Try to understand… What are you measuring and why? How are you measuring it? What do the results mean? (aka How to interpret PFTs and impress your friends)

Pulmonary Function Tests Practical goals Basics about measurements What do your measurements reflect Two broad categories of disease Obstruction (Definition and grading of severity) Restriction (Definition, severity, when to suspect it)

Lung Cancer ARDS Inside the mind of a pulmonologist?? Pneumonia Autoimmune/Vasculitis ARDS Environmental/Occupational TB and other Mycobacterial disease Pulmonary vascular disease Inside the mind of a pulmonologist?? Sleep apnea Obstructive Lung Diseases Restrictive Golf, Cubs, College basketball Pneumonia

Why measure PFTs? Why do any test? To look for disease To evaluate severity of disease To determine response to treatment To prevent disease

What measurements should you make? To know what to lung function to measure you need to know... What does the lung normally do How does it do it What can cause this to go wrong

What measurements: Normal lung To understand lung function think in terms of anatomy Airflow Gets the gas to the blood and back again Gas exchange Lots of air Really close to the capillaries

Normal anatomy Medium airways…. Small airways…. Alveoli…gas exchange units

Large airways and chest wall

What measurements? Airflow (Obstructive diseases) How fast (Forced exhaled volume) FEV1, and FEV1% (actually FEV1/FVC) and Flow volume loop (FVL) Gas Exchange (Restrictive diseases) How much Forced Vital Capacity, Total Lung Capacity (FVC, TLC) Diffusion capacity (Diffusion capacity of the lung for carbon monoxide) DLCO

ERV/IRV Expiratory/Inspiratory reserve volume Vt Tidal volume VC Vital Capacity ERV/IRV Expiratory/Inspiratory reserve volume These are all measured easily with spirometers FRC Functional residual capacity RV residual volume TLC Total lung capacity (RV + VC) Measuring these requires more specialized equipment

TLC RV ERV IC TLC VC Vt VC FRC RV RV Normal

Vital capacity is reduced in both obstructive and restrictive diseases VC VC VC RV RV RV Obstructive Normal Restrictive

What are “PFT?s”? Spirometry is just the measure of dynamic lung mechanics FEV1 and FVC, and the FEV1/FVC ratio Lung volume measurements Usually measured as part of “Full PFTs” or “Complete PFTs” Involves more sophisticated (aka expensive) equipment and technician time Diffusion capacity or DLCO

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

How are the measurements made? Spirometry Most “PFTs” mean simple spirometry, which is all most patients need to accomplish the goals of obtaining “PFT’s” in the first place

How are measurements made? Measuring lung volumes Some patients also require “Full PFT’s” or lung volume measurements in addition to spirometry These are usually the patients in whom restrictive lung disease is suspected Gas dilution method of measuring FRC May underestimate TLC if the patient has emphysema C1=N/Vbox C2=N/(Vbox+FRC)

Body plethysmograph

Plungx Vlung=P’lungx V’lung Plethysmography- measures total thoracic gas volume, but is more cumbersome. Uses Boyle’s law to calculate RV. Pbox x Vbox= P’box x V’box V’box =Vbox+∆V P’box =Pbox+∆P Plung Vlung Plungx Vlung=P’lungx V’lung V’lung = Vlung +∆V P’lung =Plung+∆P Pbox x Vbox

Why measure residual volume Why measure residual volume? Look at two people with identical vital capacity TLC TLC Vt Vt VC FRC VC RV FRC RV

Summary What we measure Why we measure it How we measure Airflow, and gas exchange Why we measure it Diagnose, follow treatment, prognosticate How we measure 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) Remember the question you want to answer in the first place To look for disease To evaluate severity of disease To determine response to treatment To prevent disease For most of these you need a “normal” value for comparison

What are normal values? You don’t have to worry about memorizing normal values! (woohoo) All modern PFT labs have a set of nomograms which they use to predict normal values What you should know Normals are derived just like any normal lab value There are limitations to these estimates Predicted values are only as good as the population in which they were measured The patient should be from the population from which the normals are calculated

What do the results mean: Algorhithim for PFT's Is the FEM adequate? y e s n o Is the FEV1/FVC lower than predicted? Interpretation may be limited by falsely low FVC y e s n o This is the definition of obstruction Mild FEV1 >70% Moderate FEV1 60-70% Mod severe FEV1 50-60% Severe FEV1 <50% Very severe FEV1 <40% Is FVC reduced? y e s n o Restriction may be present; Need TLC to definitively diagnose restriction Normal pulmonary mechanics Restriction Spirometry: Lung volumes: Severity is determined Severity determined by by the reduction in VC the reduction in TLC Mild 70-80% Mild 65-80% Moderate 60-70% Moderate 50-65% Severe <60% Severe <50%

Algorhithim for PFT's:

What do the results mean: Algorhithim for PFT's Is the FEM adequate? y e s n o Is the FEV1/FVC lower than predicted? Interpretation may be limited by falsely low FVC y e s n o This is the definition of obstruction Mild FEV1 >70% Moderate FEV1 60-70% Mod severe FEV1 50-60% Severe FEV1 <50% Very severe FEV1 <40% Is FVC reduced? y e s n o Restriction may be present; Need TLC to definitively diagnose restriction Normal pulmonary mechanics Restriction Spirometry: Lung volumes: Severity is determined Severity determined by by the reduction in VC the reduction in TLC Mild 70-80% Mild 65-80% Moderate 60-70% Moderate 50-65% Severe <60% Severe <50%

What do the results mean: Algorhithim for PFT's Step 2, what is the of FEV1 /FVC?- aka FEV1% If it is reduced, then by definition there is airway obstruction Any reduction compared to the predicted value The severity of is determined by the FEV1 ≥80% is considered “normal” 70-80% is considered mild 60-70% is considered moderate 50-60% is considered moderately severe 40-50% is considered severe <40% is very severe

What do the results mean: Algorhithim for PFT's Is the FEM adequate? y e s n o Is the FEV1/FVC lower than predicted? Interpretation may be limited by falsely low FVC y e s n o This is the definition of obstruction Mild FEV1 >70% Moderate FEV1 60-70% Mod severe FEV1 50-60% Severe FEV1 <50% Very severe FEV1 <40% Is FVC reduced? y e s n o Restriction may be present; Need TLC to definitively diagnose restriction Normal pulmonary mechanics Restriction Spirometry: Lung volumes: Severity is determined Severity determined by by the reduction in VC the reduction in TLC Mild 70-80% Mild 65-80% Moderate 60-70% Moderate 50-65% Severe <60% Severe <50%

RV RV TLC TLC Vt Vt VC FRC VC FRC Be careful before citing “restrictive deficits” in people with obstructive lung disease TLC TLC Vt Vt VC FRC VC RV FRC RV Emphysema Normal

Algorhithim for PFT's:

Algorhithim for PFT's If FEV1/FVC is normal Is FVC normal? If yes then the subject has “normal pulmonary mechanics” If not, then is there any reason to suspect restrictive disease? Keep in mind…a poor FEM (which affects the FVC more than the FEV1) not only underestimates FVC, but overestimates FEV1/FVC, and can lead to false negative spirometry for airway obstruction

Restrictive lung disease By definition means a reduced total lung capacity Reduced vital capacity can suggest restriction TLC V t VC FRC RV

What do the results mean: Algorhithim for PFT's Restrictive lung disease This can only be definitively established by measurements of lung volume Gas dilution methods Only measures gas in communication with the environment Plethysmography Measure total thoracic gas volume, but is more cumbersome Normal FEV1/FVC and reduced FVC with a good FEM can infer the presence of restrictive defect

What do the results mean: Algorhithim for PFT's Assessing severity of restrictive defects Without TLC measurement, base severity on the FVC ≥80% is considered “normal” 70-80% is considered mild 60-70%% is considered moderate 60% is considered severe When TLC is measured Gold standard to define restrictive ventilatory defect Only order “Full PFTs” if you suspect restrictive or interstitial lung disease (expensive!)

Severity is based on the degree of impairment in TLC What do the results mean: Algorhithim for PFT's Restrictive defects cont’d Severity is based on the degree of impairment in TLC ≥80% is considered “normal” 65-80% is considered mild 50-65% is considered moderate <50% is considered severe

What do the results mean: Algorhithim for PFT's Is the FEM adequate? y e s n o Is the FEV1/FVC lower than predicted? Interpretation may be limited by falsely low FVC y e s n o This is the definition of obstruction Mild FEV1 >70% Moderate FEV1 60-70% Mod severe FEV1 50-60% Severe FEV1 <50% Very severe FEV1 <40% Is FVC reduced? y e s n o Restriction may be present; Need TLC to definitively diagnose restriction Normal pulmonary mechanics Restriction Spirometry: Lung volumes: Severity is determined Severity determined by by the reduction in VC the reduction in TLC Mild 70-80% Mild 65-80% Moderate 60-70% Moderate 50-65% Severe <60% Severe <50%

What do the results mean: Algorhithim for PFT's What about flow-volume loops? Lung Volume Time (sec)

Flow volume loop examples

What are these?

Inspiratory effort Expiratory effort

What do the results mean: Diffusing capacity aka DLCO Measures the ability of the lung to transfer gas from the environment to the bloodstream DLCO=VCO/(PACO-PaCO) Measures the volume of gas that moves across the alveolar-capillary barrier per unit of time per mm Hg gradient

What do the results mean: What factors affect DLCO? Non-disease related Age, body size, lung volume, hemoglobin concentration, body position, patient cooperation, altitude, tobacco use, etc., etc. Disease related-anything that affects the lung parenchyma or hemoglobin in the lungs Emphysema (Very sensitive), but not asthma or chronic bronchitis Pulmonary vascular disease Infiltrative/interstitial lung diseases (Very sensitive) Sarcoid, IPF, BOOP, hypersensitivity pneumonitis Others..CHF (Increased?), pulmonary hemorrhage (increased)

What do the results mean: DLCO? Because of the number of factors affecting the test there is a wider variation Normal is considered ≥75% Less than 75% is “reduced” Less than 40% is commonly associated with resting or exercise induced hypoxemia and should prompt you to evaluate the patient for supplemental oxygen

What can PFTs tell you about the patient Normal or abnormal What diseases can you diagnose? Only asthma is defined by its PFTs Estimation of impairment, or severity of disease Response to therapy Occupational surveillance

What PFTs cannot tell you Does the degree of abnormality explain the patients symptoms? “Normality” does not exclude the presence of disease Abnormal test may not reflect loss of lung function

49 year old man with aplastic anemia, awaiting BMT; May 1997   BASELINE  LUNG MECHANICS Actual %Pred FVC liters  5.03   98%  FEV1 3.77   97%  FEV1/FVC %  75%  76%  LUNG VOLUMES RV pleth 1.81   87%  TLC pleth 6.96   RV/TLC pleth 26% 

One month after BMT LUNG MECHANICS Actual Pred %Pred FVC liters 2.98 2.98   5.12   58%  FEV1 2.31   3.90   59%  FEV1/FVC %  78%  76%  102%  DIFFUSION Hgb mg/dl  12.00   14.60   82%  COHgb 2.30   MUSCLE FORCES Actual Pred %Pred Pemax cmH2O  150.00   216 +/- 45  Pimax mcH2O  -60   -127 +/- 28  SUPINE  Actual %Pred %Chg 1.31   26%  -56%  0.85   22%  -63%  65%  85%  -16%  FVC FEV1 FEV1/FVC

49 year old man with aplastic anemia, 8 months after BMT; February 1998 LUNG MECHANICS Actual Pred %Pred FVC liters  3.71   5.12   72%  FEV1 2.59   3.90   66%  FEV1/FVC %  70%  76%  92% 

71 year old man with 2 year history of dyspnea; June 2002 LUNG MECHANICS Actual Pred %Pred FVC liters  1.30  4.09  32%  FEV1 0.82  2.72  30%  FEV1/FVC %  67%  68%  100% 

71 year old man with 2 year history of dyspnea; August 2002 LUNG MECHANICS Actual Pred %Pred FVC liters  2.71  4.02  67%  FEV1 2.09  2.69  78%  FEV1/FVC %  77%  68%  115% 

Extrathoracic/upper airway obstruction (stridor)

Fixed upper airway obstruction

PFT summary Check the FEM to make sure it is adequate Obstructive ventilatory defects are defined by FEV1/FVC less than predicted Severity graded by degreee of impairment in FEV1 Restrictive ventilatory defect is defined by reduced TLC Reduced FVC with no obstruction and a good FEM suggests the presence of a restrictive deficit DLCO is abnormal in almost all parenchymal lung diseases