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Pulmonary Function Tests Jonathan Kass

Pulmonary Function Tests Jonathan Kass. Cooper University Hospital Robert Wood Johnson School of Medicine UMDNJ at Camden. PFTs. Spirometry, Flow Volume Loop, MVV Lung Volumes Diffusing Capacity Challenge Testing Respiratory Muscle Testing Airways Resistance. What do PFTs Measure.

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Pulmonary Function Tests Jonathan Kass

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  1. Pulmonary Function TestsJonathan Kass Cooper University Hospital Robert Wood Johnson School of Medicine UMDNJ at Camden

  2. PFTs • Spirometry, Flow Volume Loop, MVV • Lung Volumes • Diffusing Capacity • Challenge Testing • Respiratory Muscle Testing • Airways Resistance

  3. What do PFTs Measure • How much air the lung can hold • How well the air moves through the airways • How well the oxygen penetrates the lung tissue in order to enter the blood stream • Respiratory muscle strength & endurance

  4. History of PFTs • 1718 Jurin: TV and FVC • 1800 Davy: gasometer TV,VC,RV • 1846 Hutchinson spirometer (height) • 1854 Wintrich spirometer (ht,wt,age) • 1868 Bert: body plethys in animals • 1959 Wright: peak flow meter • 1969 Dubois: body plethys in humans

  5. Davy Gasometer

  6. Hutchinson Spirometer

  7. Lung Volume Sub-Divisions

  8. Poor (Man’s) PFT

  9. Match Test • Extinguish a match from 6 inches away from the open mouth • Correlated with FEV1 >1.5L and MVV > 60 L/Min • Reverse less correlated (some with good function could not blow out the match) • Dines DE. Minn Med 1968; 51:33-36

  10. Spirometers • Pneumotachygraphs: Flow signal is integrated to obtain volume & is calibrated for air only • Rolling-seal • Water-seal: inaccurate with high flows or MVV

  11. Rolling Seal Spirometer

  12. Spirometric Maneuvers • Maximum expiration made as rapidly as possible after a maximum inspiration (Forced Vital Capacity) • Maximum expiration made slowly after a maximum inspiration (Slow VC)

  13. Spirometric Measurements

  14. Volume Time Curve

  15. Forced Vital Capacity • Maximum volume of air which can be exhaled or inspired during a forced maneuver (at least 6-12 seconds) • Most effort independent PFT w/ least variabilty

  16. Etiologies of a Decreased Forced Vital Capacity • Obstruction • Restriction • Sub-optimal effort

  17. Slow Vital Capacity (SVC)

  18. Slow Vital Capacity • SVC is always > FVC • The greater the airways obstruction the greater the difference btw FVC & SVC

  19. Peak Expiratory Flow Rate • Assesses maximal effort • Effort dependent • Strength of expiratory muscles • Large airways (trachea & main bronchi)

  20. FEV1 • Less effort dependence than Peak Flow • Assessment of degree of airway obstruction when present • Assessment of bronchodilator response

  21. FEV1/FVC • When decreased best indicator of airway obstruction • When normal does not exclude airway obstruction if values are decreased in parallel

  22. FEF25-75% • Small airways obstruction • Effort Independent • Dependent on FVC and high variability limiting its clinical utility • Epidemiological studies

  23. Maximum Spirometic Values • Maximum values of 3 technically satisfactory tests provided the 2nd best test is within 100ml or 5% • Best FVC and FEV1 can be from separate maneuvers • Alternative: Mean of 3 best tests

  24. Assessment of Presence of Airway Obstruction • Low FEV1/FVC • Flow volume loop • Evidence for air trapping from SVC-FVC difference, bronchodilator improvement, or from increased RV/TLC (especially in children)

  25. FEV1/FVC Ratio • Inversely related to age and height • Can be decreased in athletes, deep sea divers, miners, tall people

  26. Variables Affecting Spirometry Becklake MR. Am J Med 1986:80:1158-63

  27. Assessment of Severity of Airway Obstruction Based on % Predicted FEV1 if the FEV1/FVC is Below the Normal Range • Mild: 70-100% • Moderate: 60-70% • Moderate to Severe: 50-60% • Severe: 34-50% • Very Severe: < 34% • ATS: ARRD 1991; 144: 1202-1218:

  28. Assessment of Bronchodilator Response • Increase in FEV1 of 12% & 200cc • Increase in FVC of 12% & 200cc but ? due to improved effort or decreased air trapping (ATS: ARRD 1991; 144: 1202-1218) • > 15% increase (ACCP Chest 1974; 65: 552-553)

  29. Flow Volume Loops

  30. Flow Volume Loops

  31. Flow Volume Loops

  32. Flow Volume Loops

  33. Maximum Voluntary Ventilation (MVV) • The volume of gas that can be breathed in 12-15 seconds extrapolated to 1 minute. • Usually 35-40 X the FEV1 • Optimal MVV with RR 120/min and TV 30% of VC (Resp Physiol 1968; 5: 118-129)

  34. Maximum Voluntary Ventilation (MVV) • Indicator of respiratory muscle strength and endurance • Weaning and Pre-op assessment • Decreased in obstruction in proportion to the FEV1 • Not usually decreased in ILD

  35. Maximum Sustained Ventilation(MSV) • 100% of MVV < 1 minute • 5% of MVV indefinitely • Energy supply to respiratory muscles adequate to sustain ventilation at about 55% of MVV in normals (Resp Physiol 1968; 5: 187-201)

  36. Conditions associated with MVV/FEV1 < 30 • Poor Effort • Neuromuscular, musculoskeletal, fibrothorax, abdominal distention • Fixed and variable extrathoracic airway obstruction (< 20) • Owens GR. Spirometric diagnosis of UAO. Arch Int Med 198; 143:1331-34

  37. Conditions associated with MVV/FEV1 > 50 • Interstitial Lung Disease • Supra-effort

  38. Spirometry Interpretation

  39. Spirometry Interpretation

  40. Indications/Ordering of PFTs • ASTHMA: Methacholine Challenge • COPD/ABNL X-RAY: Full PFT • DYSPNEA: Full PFT with Methacholine challenge • PRE-OP: Spirometry w/ MVV • DRUG EFFECT: Spirometry and DLCO

  41. Equine PFTs

  42. PFT Quiz • 3 causes of a decreased FVC? • What is the best PFT indicator of airway obstruction? • What is the most reproducible PFT measurement? • What is the best PFT test to see UAO?

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