Pulmonary function tests | ||
Abnormality | Interpretation | Further testing |
Airflow obstruction with complete reversibility following inhaled bronchodilator | Likely asthma: Institute therapy based on severity of obstruction according to current guidelines. | Reassess dyspnea and spirometry after treatment trial. |
Airflow obstruction that is irreversible or incompletely reversible following bronchodilator | Likely COPD, especially in smokers. Chronic/severe asthma can cause airflow limitation that is incompletely reversible with bronchodilator, but may improve over time with inhaled or oral glucocorticoid therapy. Less commonly bronchiolitis or bronchiectasis. | Reassess dyspnea and spirometry after treatment trial/pulmonary rehabilitation/smoking cessation/removal of allergen exposure. |
Bronchiolitis should be suspected in patients with poor response to therapy for asthma/COPD or with the combination of airflow limitation and impaired gas transfer, may need HRCT to look for radiographic evidence of bronchiolitis or bronchiectasis. | ||
Normal (expiratory) spirometry | Normal spirometry does not exclude asthma or upper airway obstruction. Depending on clinical suspicion:
| Positive bronchoprovocation: Asthma is likely cause of dyspnea. Reassess after treatment trial. |
Bronchoprovocation negative but flow volume loop has slowing on inspiratory phase suggesting possible upper airway obstruction; direct visualization needed to confirm. | ||
Refer to "Lung volumes normal but DLCO reduced and/or SpO2 <95% or decreases by >4% with exertion" below. | ||
Reduced FVC with normal FEV1/FVC | Evaluate for restrictive process (pleural, chest wall, or neuromuscular), interstitial lung disease, or air trapping.
| Lung volumes (FVC and TLC) confirm restrictive pattern, DLCO normal or slightly low: Consider pleural, chest wall, and neuromuscular disease.
|
Reduced DLCO and lung volumes suggest interstitial lung disease or emphysema: Consider HRCT. | ||
Increased RV or FRC suggests airtrapping (eg, due to emphysema, LAM, bronchiolitis) as a cause of low FVC. HRCT can identify emphysema, cystic changes of LAM, mosaic pattern suggestive of bronchiolitis. | ||
Lung volumes normal but DLCO reduced and/or SpO2 <95% or decreases by >4% with exertion | Possibilities include early ILD and pulmonary vascular disease: Obtain HRCT, BNP, and echocardiogram with Doppler assessment of PA pressures. | If no ILD on HRCT and BNP and echocardiogram suggest pulmonary hypertension, may need PA catheterization. |
Normal flow volume loop, lung volumes, DLCO, ambulatory SpO2, and bronchoprovocation | Increasing likelihood of nonrespiratory cause of dyspnea. | Obtain/review CXR, echocardiogram. May need CPET. |
Do you want to add Medilib to your home screen?