Quantitative computed tomography: what does airway obstruction look-like?

Both COPD and asthma are heterogeneous diseases, characterized by airway obstruction and chronic airway inflammation (1). Small airway obstruction is present in both diseases, although there is a lack of accurate and reproducible measures of small airway function suitable to be used in clinical practice (1,2). Spirometry is the most widely used non-invasive test of pulmonary function and provides an assessment of lung function and an objective method for following disease progression or improvement and therapeutic response over time (3). However, FEV₁ mainly assesses large airways, providing only limited information regarding airway remodeling, small airway obstruction, air trapping and emphysema (4). Although the presence of a post-bronchodilator FEV₁/FVC <0.70 confirms the presence of airflow limitation (5) it does not assess all aspects of obstructive diseases. Tests that are often accessible to most respiratory departments such as the measurement of RV/TLC via body plethysmography and FEF 25−75% via spirometry are only moderately sensitive to detect air trapping and small airway involvement respectively in asthma and COPD (2).