Diagnosis of small airway dysfunction in patients with chronic obstructive pulmonary disease

Abstract

Background: Small airway dysfunction (SAD) is a functional hallmark of chronic obstructive pulmonary disease (COPD). However, SAD prevalence and its role in COPD pathophysiology are not yet sufficiently studied.Background: Small airway dysfunction (SAD) is a functional hallmark of chronic obstructive pulmonary disease (COPD). However, SAD prevalence and its role in COPD pathophysiology are not yet sufficiently studied.Aim: To assess the prevalence of SAD in COPD patients by various functional diagnostic methods, such as spirometry, body plethysmography, and impulse oscillometry (IOS).Materials and methods: This was an cross-sectional study. Spirometry, body plethysmography and IOS were used in 132 COPD patients in remission under standard anti-COPD treatments. The presence of SAD was confirmed by at least one of the following criteria or their combination: 1) by spirometry: the difference between vital capacity (VC) and forced vital capacity (FVC) > 10%; 2) the presence of air trapping by body plethysmography; 3) identification of the frequency dependence of the resistive resistance at 5 to 20 Hz (R5 - R20 > 0.07 kPa x s/l), as assessed by IOS.Results: Mean forced expiratory volume in 1 s (FEV1) was 42.9% of predicted. Depending on the severity of the obstruction, the patients were divided into 4 groups: 7 patients (group 1) had the obstruction corresponding to GOLD 1 stage, 37 (group 2) to GOLD 2, 49 (group 3) to GOLD 3, and 39 (group 4) to GOLD 4. SAD was found in 96% of COPD patients, whereas in those with severe obstruction (GOLD 3-4), it was present in 100% of the cases. By spirometry, SAD was identified only in 67% of COPD patients, by body plethysmography in 75% of COPD patients (in those with severe obstruction (GOLD 3 and 4) in 88 and 97%, respectively). With IOS, it was possible to identify SAD in 94% of patients and in 100% of those with severe obstruction (GOLD 3-4).Conclusion: With deterioration of obstructive pulmonary ventilation abnormalities in COPD patients, there is a progressive increase in small airway dysfunction. Impulse oscillometry seems to be the most effective method for diagnosis of small airway dysfunction, as it helped to identify SAD in 94% of COPD patients and in 100% of those with severe and very severe obstruction.