Pathophysiology of Evolution of Small Airways Disease to Overt COPD

ABSTRACT

Background: The slope of phase III (single breath nitrogen test), an index of ventilation inhomogeneity, has been used for early detection of COPD. Tidal airway closure (cyclic opening and closure of the peripheral airways during tidal breathing; AC_T) and expiratory flow limitation (attainment of maximal expiratory flow during tidal expiration; EFL_T) cause small airways disease (SAD). The relationships of these indices with COPD severity may reflect the progress from SAD to overt COPD. Methods: In this cross-sectional study we have assessed for the first time the phase III slope, AC_T and EFL_T in 10 smokers with normal spirometry (group O) and 40 COPD patients with GOLD scores from I to IV. Results: In most group O smokers the phase III slope was increased, and further increased with GOLD severity (up to 800%pred in GOLD IV). A close correlation was found of slope with GOLD (r = 0.77). AC_T was absent in smokers with normal spirometry and in most patients with mild COPD. EFL_T first appeared in GOLD II patients and its prevalence progressively increased in GOLD III and IV patients. Conclusions: Most group O smokers exhibit increased phase III. With overt COPD there is a progressive increase in phase III and reduction of FEV₁/FVC ratio from GOLD I to IV. A reduction of FEV₁ occurs from GOLD stage II. As the disease progresses from moderate to severe, there is an increasing presence of AC_T. Tidal EFL, with dynamic hyperinflation and severe dyspnea is present only in GOLD III and IV.

Keywords: :

• COPD
• small airways disease
• airway closure
• GOLD
• expiratory flow-limitation