Normal Routine Spirometry Can Mask COPD/Emphysema in Symptomatic Smokers

Area of Science:

• Pulmonary Medicine
• Respiratory Physiology

Background:

• Chronic Obstructive Pulmonary Disease (COPD) diagnosis is often delayed in symptomatic smokers with normal spirometry.
• Early COPD pathology begins in small peripheral airways, which are not adequately assessed by standard spirometry.
• Standard spirometry may miss early signs of small airway disease and emphysema.

Purpose of the Study:

• To investigate the utility of expiratory airflow measurements at low lung volumes for detecting early COPD in smokers with normal spirometry.
• To correlate lung function tests with CT scans and lung pathology.

Main Methods:

• Evaluated post-bronchodilator expiratory airflow at high and low lung volumes in 16 symptomatic smokers with normal spirometry.
• Correlated airflow measurements with lung CT scans and pathological data from 6 patients.
• Utilized data from Knudson et al, Hankinson et al NHAMES III, Quanjer et al, and the Global Lung Function Initiative.

Main Results:

• All 16 patients showed abnormal forced expiratory flow at 75% of FVC (FEF75), indicating small airway obstruction or emphysema despite normal spirometry.
• FEF75 was more sensitive in detecting small airway obstruction than FEF50, MEF25-75, RV, or RV/TLC ratio.
• Lung CT and pathology confirmed the absence of emphysema in cases where it was suspected.

Conclusions:

• Analysis of expiratory airflow at low lung volumes, particularly FEF75, is crucial for detecting small airway obstruction and emphysema in symptomatic smokers with normal spirometry.
• Relying solely on routine spirometry can lead to delayed diagnosis and treatment of COPD in this patient group.
• FEF75 measurements offer a valuable tool for earlier identification of early COPD.