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Pulmonary and Critical Care Medisine Pulmonary Function Tests lndications The four PFTs commonly used to measure static lung function are spirometry flow-volume loops, lung volumes, and Dr-co. Key Tests and Patterns Spirometry is used to diagnose airflow obstruction such as asthma, COPD, and bronchiectasis. . FEVr/FVC <0.7 (or below the LLN) indicates airflow obstruction. o A>12"/n increase in either FEV, or FVC and an increase >200 mL from baseline in either parameter with bronchodilator therapy indicates reversible airway obstruction. . Equal reductions in FEV, and FVC suggest restrictive lung disease. Lung volume measures include totat lung capacity (TLC), vital capacity (VC), functional residual capacity (FRC), expiratory reserve volume (ERV), and residual volume. The TLC is normal or even increased in pure obstructive disease and decreased in restrictive diseases. Drco evaluates gas transport across the alveolar capillary membrane. $f UDY TAELE: lnterpreting DLco Finding lnterpretation J Dlco and reduced lung volumes DPLD J Dt-co and normal lung volumes Pulmonary vascular disease, anemia I Dlco and airflow obstruction COPD, bronchiectasis t or normal Drco and airflow obstruction Asthma t Dlco Pulmonary hemorrhage, left-to-right shunt, polycythemia Flow-volume loops can help localize anatomic sites of airway obstruction. Refer to the "Flow-Volume Loops" figures.

$f UDY TAELE: lnterpreting DLco Finding lnterpretation J Dlco and reduced lung volumes DPLD J Dt-co and normal lung volumes Pulmonary vascular disease, anemia I Dlco and airflow obstruction COPD, bronchiectasis t or normal Drco and airflow obstruction Asthma t Dlco Pulmonary hemorrhage, left-to-right shunt, polycythemia Flow-volume loops can help localize anatomic sites of airway obstruction. Refer to the "Flow-Volume Loops" figures. DO]II,T BE TRICKED r In patients with low lung volumes, a normal Dlco suggests an extrapulmonary cause (e.g., obesity) STUtrY TABLE: Understanding lmportant Pulmonary Tests Tests Considerations Pulse oximetry Measures percentage of oxyhemoglobin; performed at rest or during exercise Use co-oximetry when carboxyhemoglobin is suspected (e.g., smoke inhalation, carbon monoxide poisoning) Bronchial challenge testing Challenges include cold air, exercise, histamine, methacholine, and mannitol Airflow is measured before and after challenge Bronchial challenge testing is commonly used for patients with a history suggestive of bronchospastic disease but normal spirometry (Continued on the next page) 335

Pulmonary and Critical Care Medicine STU DY TAB LE : Understanding lmportant Pulmonary Tests (Co nti nue d ) Tests Considerations Cardiopulmonary exercise Performed for unexplained dyspnea, symptoms disproportionate to the measured pulmonary function testing abnormality, and other exercise-related symptoms 6-Minute walk test Usefulto assess disability, need for supplemental oxygen, and prognosis in chronic lung conditions Simple oximetry and desaturation studies are performed at rest and with exertion Fractional exhaled nitric Elevated FeNO levels correlate modestly with blood and sputum eosinophilia (inflammation)and can oxide (FeNO) predict glucocorticoid responsiveness in patients with respiratory symptoms; monitor response to anti. inflammatory therapy DOil'T BE TRICKED o Pulse oximetry is normal in patients with carbon monoxide and cyanide poisoning. . Pulse oximetry may be falsely low in patients with shock. Normal 3 o L + Volume +- Obstructive Restrictive U pper Airway Obstruction \/\/ Extrathoracic lntrathoracic Ftow-Volume toops: Flow-volume loops plot flow (Usec)as a function of volume 337