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Interpret spirometry results for obstructive and restrictive lung disease
FEV1: Volume exhaled in first second
FVC: Total volume exhaled (forced vital capacity)
Ratio: FEV1 ÷ FVC × 100
*Requires FEV1/FVC <70% (or <LLN) post-bronchodilator
Chronic bronchitis + emphysema. Usually irreversible. Smoking is main cause.
Reversible airflow obstruction. Variable symptoms. Responds to bronchodilators.
Chronic airway dilation with recurrent infections. May have mixed pattern.
IPF, sarcoidosis, pneumoconiosis. Reduced lung compliance.
Kyphoscoliosis, pleural effusion, obesity hypoventilation.
ALS, muscular dystrophy, myasthenia gravis. Weak respiratory muscles.
Generally ≥70%, but normal values decrease with age. Using the lower limit of normal (LLN) is more accurate than a fixed 70% cutoff, especially in elderly patients.
Significant reversibility is defined as ≥12% AND ≥200mL improvement in FEV1 after bronchodilator. Suggests asthma over COPD, though overlap exists.
In severe obstruction, air trapping can reduce FVC. This is why lung volumes (TLC) are needed to confirm true restriction vs. pseudorestriction from air trapping.
Forced expiratory flow at 25-75% of FVC. Reflects small airway function. More variable than FEV1. May be reduced in early obstruction.
Highly reliable when performed correctly. Requires patient effort and cooperation. ATS/ERS quality criteria should be met (acceptability and reproducibility).
When spirometry suggests restriction (need TLC), mixed pattern, or when diffusion capacity (DLCO) is needed for ILD, pulmonary hypertension, or unexplained dyspnea.
COPD diagnosis requires post-bronchodilator FEV1/FVC <70% (or <LLN). Pre-bronchodilator values alone are insufficient. Always document bronchodilator response.