Small airway dysfunction and flow and volume bronchodilator responsiveness in patients with chronic obstructive pulmonary disease

Background: We investigated whether a relationship between small airways dysfunction and bronchodilator responsiveness exists in patients with chronic obstructive pulmonary disease (COPD). Methods: We studied 100 (20 female; mean age: 68±10 years) patients with COPD (forced expiratory volume in 1 second [FEV<inf>1</inf>]: 55% pred ±21%; FEV<inf>1</inf>/forced vital capacity [FVC]: 53%±10%) by impulse oscillometry system. Resistance at 5 Hz and 20 Hz (R5 and R20, in kPa·s·L-1) and the fall in resistance from 5 Hz to 20 Hz (R5 – R20) were used as indices of total, proximal, and peripheral airway resistance; reactance at 5 Hz (X5, in kPa·s·L-1) was also measured. Significant response to bronchodilator (salbutamol 400 µg) was expressed as absolute (≥0.2 L) and percentage (≥12%) change relative to the prebronchodilator value of FEV<inf>1</inf> (flow responders, FRs) and FVC (volume responders, VRs). Results: Eighty out of 100 participants had R5 – R20 >0.03 kPa·s·L-1 (> upper normal limit) and, compared to patients with R5 – R20 ≤0.030 kPa·s·L-1, showed a poorer health status, lower values of FEV<inf>1</inf>, FVC, FEV<inf>1</inf>/FVC, and X5, along with higher values of residual volume/total lung capacity and R5 (P<0.05 for all comparisons). Compared to the 69 nonresponders and the 8 FRs, the 16 VRs had significantly higher R5 and R5 – R20 values (P<0.05), lower X5 values (P<0.05), and greater airflow obstruction and lung hyperinflation. Conclusion: This study shows that peripheral airway resistance is increased in the vast majority of patients with COPD, who showed worse respiratory reactance, worse spirometry results, more severe lung hyperinflation, and poorer health status. Small airway dysfunction was also associated with the bronchodilator responsiveness in terms of FVC, but not in terms of FEV<inf>1</inf>.