Pulmonary function exam

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Pulmonary function exam

  1. 1. Pulmonary Function Testing
  2. 2. Goals • Indications for PFTs • Know types of studies that can be ordered • Understand how common tests are done • Interpretation of the data
  3. 3. Indications • Characterize known or suspected pulmonary disease (COPD screening) • Follow evolution of pulmonary disease • Assess effectiveness of therapy • Pre-op assessment of surgical risks • Assess need for surgical interventions • Assess impact of an occupational exposure
  4. 4. Pulmonary Function Tests • Spirometry/flow-volume loop • Lung volumes • Diffusion capacity • Arterial blood gas, shunt fraction measurement, dead space • Airway resistance • Inspiratory/expiratory muscle pressures • Airway reactivity (methacholine/exercise challenge) • Cardiopulmonary exercise test
  5. 5. Normal Lung Volumes and Capacities
  6. 6. Primary Lung Volumes • VT: tidal volume - air inhaled during quiet breathing • IRV: inspiratory reserve volume - maximal volume inhaled from quiet breathing • ERV: expiratory reserve volume - maximal volume exhaled from quiet breathing • RV: residual volume - volume remaining after maximal exhalation
  7. 7. Lung Capacities = Sum of Primary Lung Volumes • TLC: total lung capacity - sum of 4 primary volumes • VC: vital capacity - volume exhaled from maximal inspiration to maximal expiration • FRC: functional residual capacity – resting, end-expiratory volume • IC: maximal volume inhaled from FRC
  8. 8. The Spirogram
  9. 9. Spirometry and Flows FEF 25-75%: mean forced expiratory flow during middle half of FVC; sensitive to small airways disease
  10. 10. Flow/Volume Loops Includes inspiratory and expiratory flows Instantaneous flows Shape of curve restrictive vs. obstructive
  11. 11. Normal Reference • Normal standards depend upon: – Height – Gender – Age – Race • Reproducibility criteria (3 trials examined) • Rate of decline: normal fall in FEV1 with age = 20-30cc/year; in COPD = 50- 80cc/year
  12. 12. Classification of Impairment
  13. 13. Interpretation of Spirometry • Step 1: obstruction or not? – Low FEV1/FVC (<70%) = obstruction • Step 2: Interpret severity (based upon FEV1) • Restriction: FEV1 and FVC reduced in proportion (i.e. normal FEV1/FVC ratio) • Flow/Volume Loops – Obstruction – concave, scooped appearing – Restriction – decreased VC, normal shape – Upper airway obstruction: cut-off insp and/or exp limbs
  14. 14. Bronchodilator Response: • Response to inhaled bronchodilators: – Typical in asthma; some patients with COPD and CF have reversibility also – “Real response”: consists of a change in FEV1 by at least 12% (and 200cc) after inhalation of albuterol
  15. 15. Broncho-provocation testing • Reveals airway hyper-reactivity (asthma) • Useful to assess non-specific hyperrresponsiveness in a patient with symptoms c/w asthma, but without obstruction or bronchodilator reversibility (cough variant asthma, exercise-induced asthma) • Methacholine – 75% asthmatics will react • Histamine – 90-95% asthmatics will react • Decline in FEV1 by 20% at concentration of 8mg/ml or less (methacholine)
  16. 16. Flow-volume loops and upper airway obstruction • Extrathoracic obstruction – vocal cord dysfunction, goiter, cause flattening of inspiratory limb of flow/volume loop • Intrathoracic obstruction – bronchogenic cancer in right mainstem bronchus, flattening of expiratory limb of flow/volume loop
  17. 17. Intrathoracic Obstruction Extrathoracic Obstruction
  18. 18. Lung Volumes • Spirometry measures volume differences between identifiable lung capacities (TLC, FRC, RV), but cannot measure the absolute volume of these key volumes • Lung volumes measure FRC and use spirometry to calculate TLC and RV • FRC can be measured by following techniques: – Closed circuit helium dilution – Open circuit nitrogen washout – Plethysmography or body box
  19. 19. Dilution Techniques • Closed circuit helium dilution – starting at FRC, patient breathes helium for 7 minutes (until equilibrium) from known volume system with known He concentration; measure helium concentration after maneuver • Open nitrogen washout – starting at FRC, begin inspiring 100% O2 and collect/measure all nitrogen exhaled from the lungs for 7 minutes (N2 essentially washed out). Given known initial concentration of nitrogen in the lungs (81%), use the measured concentration and volume of nitrogen in collected air to calculate the starting lung volume (FRC) at end of maneuver • Both techniques underestimate actual FRC if ventilation isn’t homogeneous (i.e. obstructive lung disease)
  20. 20. Helium Dilution Point A: 2 L of 10% He Point B: 5% He now present in system; FRC must be 2L!
  21. 21. Plethysmography
  22. 22. Plethysmography • Measures thoracic gas –performed at FRC • Underlying principle: Boyle’s Law – Patient sits in sealed box, patient pants against shutter that is closed at FRC – Alveolar pressure changes measured at mouth (presumes open glottis/equal pressures); – Box pressure changes measured with respiratory efforts – proportional to lung volume increases/decreases due to respiratory efforts PV = (P + P)(V + V) V = FRC
  23. 23. Lung Volume Determinants • FRC: – Lung and chest wall properties • TLC: – Lung and chest wall properties – Inspiratory muscle strength • RV: – Lung and chest wall properties – Expiratory muscle strength – Airway Closure**
  24. 24. Lung Volume Patterns TLC FRC RV ERV IC
  25. 25. Diffusion • Volume of gas transferred across alveolar/capillary membrane/per minute/mmHg of difference between the alveolar and capillary blood • Determined from CO uptake during 10 seconds of breath-holding • VCO = (Area/Thickness) x (Solubility/ MW) x (PA-PC)
  26. 26. Diffusion – use of CO • Rate of transfer of CO across respiratory membrane relates to hemoglobin affinity (240 fold higher than for O2) • CO transfer rate decreases in anemia and increases in polycythemia • DLCO is artificially low in smokers (have baseline CO in blood – i.e. concentration gradient working against CO uptake) • High altitude – increased transfer of CO
  27. 27. Diffusion Loss of membrane surface area; increase in thickness: • pneumonectomy, emphysema, interstitial disease, CHF Changes in Pulmonary Circulation • Pulmonary vascular disease Increases in DLCO • pulmonary hemorrhage, left-to-right intracardiac shunts, asthma
  28. 28. Pulmonary Gas Exchange • Evaluating Hypoxemia: • Hypoxemia with normal A-a gradient: hypoventilation • Hypoxemia with increased A-a gradient: V/Q mismatch, right-to-left shunt, diffusion impairment • P(A-a)O2 = [PiO2 –(PaCO2/R)] – PaO2 • P(A-a)O2 = [0.21(PB-47) – (PaCO2/0.8)] –PaO2 • P(A-a)O2 = 150 – (PaCO2/0.8) – PaCO2
  29. 29. Case 1 • FVC 75% pred; FEV1 60% pred; ratio 64% • TLC: 125% pred; FRC 120% pred; RV 160% • DLCO: 30% pred • ABG: 7.42/42/70 on RA
  30. 30. Case 2 • FVC 85% pred; FEV1 50% pred; ratio 55% • TLC: 95% pred; FRC 105% pred; RV 145% pred • DLCO: 85% • ABG: 7.37/48/58 on RA
  31. 31. Case 3 • FVC 65% pred; FEV1 68% pred; ratio 85%; FEF25-75% 120% pred • TLC 65% pred; FRC 65% pred; RV 70% pred • Normal flow-volume shape • DLCO 45% pred
  32. 32. Case 4 • FVC 85% pred; FEV1 71% pred; ratio 75%; FEF25-75%45% • TLC 85% pred; FRC 60% pred; RV 100% pred; ERV 10% pred • DLCO 85% pred
  33. 33. Flow-Volume Loops
  34. 34. Flow/Volume Loops in Obstruction and Restriction
  35. 35. Broncho - provocation Agents
  36. 36. Mechanics • Neuromuscular disease with MIP, MEP • Pressure/volume – elastic properties of lung • Esophageal balloon to measure changes in expiratory lung volume with changes in transpulmonary pressure • Transpulmonary pressure = alveolar pressure measured at mouth and pleural pressure measured by balloon
  37. 37. Static Compliance • volume/ pressure • Mean compliance is 260cc/cm • Interstitial lung disease – increased elastic recoil, decreased compliance, less V/ P • COPD – decreased elastic recoil, increased compliance
  38. 38. Static Compliance
  39. 39. Diffusion

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