PFT Interpretation and Reference Values

Transcription

1 PFT Interpretation and Reference Values September 21, 2018 Eric Wong

2 Objectives Understand the components of PFT Interpretation of PFT Clinical Patterns How to choose Reference Values

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4 3 Components Spirometry Flow Lung Volumes Capacity Diffusing Capacity Gas Exchange

5 Distribution of TLC by population:

6 PFT Interpretation (Pellegrino et al., 2005)

7 Spirometry

8 Flow FLOW-VOLUME LOOP VOLUME-TIME CURVE Peak Flow RV E Volume Volume I TLC FRC RV Tidal Breathing TLC Time

9 Flow Forced Expired Flow E Volume Definitions: PEF Peak expiratory flow FVC forced vital capacity FEV1 Forced expiratory volume in 1 sec FEF 25-75% - Mean forced expiratory flow between 25% and 75% of FVC FEF 75% - Forced expiratory flow at 75% FVC I

10 Flow THE FLOW-VOLUME LOOP IN PATIENTS WITH SMALL AIRWAY OBSTRUCTION Palv Pst E Volume Palv Pst I

11 Flow THE FLOW-VOLUME LOOP IN PATIENTS WITH EMPHYSEMA & AIRWAY OBSTRUCTION Palv Pst E Volume Palv Pst I

12 Flow THE FLOW-VOLUME LOOP IN PATIENTS WITH A FIXED EXTRATHORACIC OBSTRUCTION Palv Pst E Volume I

13 Flow THE FLOW-VOLUME LOOP IN PATIENTS WITH A VARIABLE EXTRATHORACIC OBSTRUCTION Floppy Segment P = 0 Palv Pst E Volume Forced Inspiration = (-) Forced Expiration = (+) I

14 Flow AIRWAY REVERSIBILITY E Volume I Criteria for Reversibility: > 12% and 200ml change in FEV1 or FVC Pre test Medication? If test is to determine reversibility No short-acting beta agonist within 4hrs, no long-acting within 12hr prior If test is to determine whether patient s lung function is improving w/ therapy, then patient can continue use of medication prior

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19 LUNG VOLUMES

20 MEASURING LUNG VOLUMES Gas dilution: 1. Nitrogen washout 2. Helium dilution IRV VT IC VC Body plethysmography ERV RV FRC TLC

21 C 1 V 1 = C 2 V 2 Trapped Air Ventilated Lung Dilution methods measure only the ventilated lung volume, but the Body box method measures all gas in the lungs (trapped air + ventilated lung)

22 THE LUNG VOLUME PATTERNS SEEN WITH INCREASING AIRWAY OBSTRUCTION Normal Very Severe Moderate Severe Slight ERV VC TLC FRC RV Normal TLC Normal FRC Normal RV Zero Volume

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24 DIFFUSING CAPACITY

25 DIFFUSING CAPACITY Carbon monoxide is used to measure diffusing capacity because CO is usually not present in the blood and CO is diffusion-limited. DLCO =. VCO P A CO - PcCO. VCO P A CO. The units are: ml/min VCO for each mm Hg difference between P A CO and PcCO. PcCO is usually 0, therefore: DLCO =. VCO P A CO PcCO

26 Diffusing capacity is dependent on: DLCO (V A )(Pulmonary Cap Blood Volume)([Hb]) (Alveolar-capillary membrane thickness)([cohb]) DLCO/V A seems to be a way to eliminate the effects of V A but this is not a perfect correction.

27 D L CO (% value at normal TLC) D L CO/V A (% value at normal TLC) EFFECTS OF LUNG VOLUME ON DLCO and DLCO/V A D L CO/V A overcorrects when V A is low D L CO D L CO/V A Alveolar Volume (% Predicted TLC)

28 PFT Diffusion Capacity Pure airway disease asthma, chronic bronchitis normal Restrictive Disease with normal lung parenchyma and pulmonary vasculature Neuromuscular disease, obesity Low DLCO DLCO / VA normal to high

29 PFT Diffusion Capacity Low DLCO Alveolar disease emphysema, alveolitis, pulm edema Thickened Interstitium Pulm fibrosis Pulmonary vascular disease Pulm hypertension Anemia High carboxyhemoglobin just after smoking, CO poisoning Low cardiac output cardiogenic shock

30 DLCO

31 PFT Interpretation

32 PFT Interpretation (Pellegrino et al., 2005)

33 Spirometry

34 INTERPRETING PFTs Spirometry Is FVC normal? >LLN Is there evidence for airway obstruction? FEV1/VC < LLN - more sensitive than FEV1/FVC to detect obstruction - FVC more dependent on flow - take largest of VC, FVC, Slow VC, Insp VC Is there any change after bronchodilator? FEV 1 or FVC >12% and 200 ml (Adapted from Pellegrino et al., 2005)

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36 Global Strategy for Diagnosis, Management and Prevention of COPD Classification of Severity of Airflow Limitation in COPD* In patients with FEV 1 /FVC < 0.70: GOLD 1: Mild GOLD 2: Moderate GOLD 3: Severe GOLD 4: Very Severe FEV 1 > 80% predicted 50% < FEV 1 < 80% predicted 30% < FEV 1 < 50% predicted FEV 1 < 30% predicted *Based on Post-Bronchodilator FEV Global Initiative for Chronic Obstructive Lung Disease

37 Classification of Severity (Pellegrino et al., 2005) For obstruction FEV1/VC previously determined to be <LLN

38 Lung Volumes

39 Lung Volumes Is there evidence for a restrictive defect? TLC < LLN Are the lungs hyperinflated? TLC > ULN Is there a high RV or FRC? RV or FRC > ULN Is there evidence for air trapping? RV / TLC > ULN

40 Diffusing Capacity

41 Diffusing Capacity Are DLCO or DLCO / VA decreased? < LLN Are DLCO or DLCO / VA increased? > ULN (Pellegrino et al., 2005)

42 Patterns

43 THE LUNG VOLUME PATTERNS SEEN WITH INCREASING AIRWAY OBSTRUCTION Normal Very Severe Moderate Severe Slight ERV VC TLC FRC RV Normal TLC Normal FRC Normal RV Zero Volume

44 LUNG VOLUME PATTERNS SEEN IN PATIENTS WITH AIRWAY OBSTRUCTION Degree of Obstruction TLC VC FRC RV/TLC RV Slight Moderate Severe Very Severe N N N N N N N N N N N

45 LUNG VOLUME PATTERNS SEEN IN PATIENTS WITH RESTRICTIVE DISEASE Causes of Restriction TLC VC FRC RV/TLC RV Obesity Chest wall mechanics Parenchyma Pleural space disease Weak chest muscles N N N N N N N N N N N

46 TYPICAL LUNG FUNCTION PATTERNS Abnormality FEV 1 FVC VC TLC RV RV TLC FRC DLCO Asthma N N N Chronic Bronchitis N N Emphysema N Pulmonary Fibrosis N N N Chest wall or Obesity N N N N N N Muscle Weakness N N N

47 PFT Interpretation (Pellegrino et al., 2005)

48 PFT Interpretation Algorithm Legend PV pulmonary vascular CW chest wall NM neuromuscular ILD interstitial lung diseases CB chronic bronchitis

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50 Reference Values

51 Ideal Reference Values Find healthy people and do PFT on them Based on the results, develop equations Test equations on other normal and patients with diseases

52 Realistic Approach Find reference set best fit to your population Adopt their standard deviation if your population has similar distribution Use one equation if possible to fit full age range

53 Global Lung Function Initiative From European Respiratory Societ Clinical Research Group Submission of lung function results from > 70 groups

54 GLI 2012 Spirometry reference set 2017 DLCO reference set? Lung Volumes reference set

55 Reference Sets Canadian Thoracic Society Spirometry Lung volumes & DLCO GLI NHANES GLI Gutierrez / Peds Gutierrez / Peds

56 Summary ATS approach to PFT interpretation Poor quality test can lead to misdiagnosis Reference Values awaiting GLI