Normal Routine Spirometry Can Mask COPD and Emphysema in Symptomatic Smokers

Abstract

BACKGROUND: Recent studies have emphasized the difficulty of early detection of COPD in symptomatic smokers with normal routine spirometry. This includes post bronchodilator normal FEV1 (L) ≥,80% predicted, FVC (L) ≥,80% predicted, and FEV1/FVC ≥ 70% or greater than age corrected LLN. However, in COPD the pathologic site of small airway obstruction and emphysema begins in the small peripheral airways ≤2mm id which normally contribute < 20% of total airway resistance. METHODS:. Expiratory airflow at high and low lung volumes post bronchodilator were measured and correlated with lung CT and lung pathology (6 patients) in 16 symptomatic, treated smokers, and all with normal routine spirometry. RESULTS: Despite normal routine spirometry, all 16 patients had isolated abnormal FEF75%. using data from Knudson et al, Hankinson et al NHAMES III, and Quanjer et al. GLI. This reflects isolated detection of small airways obstruction and or emphysema. Measuring airflow at FEF50% detected only 8 of 16 patients, MEF25-75% only 4 of 16, RV 4 of 16, and RV/TLC% only 2 of 16. There was excellent correlation between limited lung pathology and lung CT for absence of emphysema. CONCLUSIONS: This study confirms our earlier observations that detection of small airways obstruction and or emphysema, in symptomatic smokers with normal routine spirometry, requires analysis of expiratory airflow at low lung volumes, including FEF75%. Dependence upon normal routine spirometry may result in clinical and physiologic delay in the diagnosis and treatment in symptomatic smokers with emphysema and small airways obstruction.