Small airway dysfunction detected by oscillometry in asthma, COPD, and asthma-COPD overlap

Abstract

Background: The ATLANTIS cohort revealed that the difference between respiratory system resistance at 5 Hz and 20 Hz (R5−R20), respiratory system reactance at 5 Hz (X5), and area of reactance (AX) were strong contributors to small airway dysfunction (SAD), with high prevalence in asthma compared to other measures (Postma 2019). However, the relevance of SAD in obstructive lung diseases is unknown.

Aims: To assess the difference in these oscillometric parameters between asthma, asthma-COPD overlap (ACO), and COPD.

Methods: Subjects included patients with asthma (n = 170), ACO (n = 114), or COPD (n = 60). Oscillometry was measured and compared among the patients.

Results: R5−R20, X5, and AX values were significantly lower in ACO and COPD patients than in asthma patients. However, there was no difference between ACO and COPD patients. The median R5−R20, X5 (cmH2O/L/s), and AX (cmH2O/L) were as follows: asthma, 0.60, −0.63, 2.40; ACO, 0.81, −1.06, 5.35; and COPD, 0.81, −1.04, 5.50, respectively (Figure 1). Multinomial logistic regression analysis revealed that the odds ratio for ACO vs. asthma was R5−R20, 0.54; X5, 1.44; and AX, 0.95, and ACO vs. COPD was R5−R20, 1.06; X5, 0.90; and AX, 1.01. Based on the cutoff value of 0.07 kPa/L/s (0.714 cmH2O/L/s) for SAD (Lipworth 2014), the prevalence of patients with SAD was 70 (41%) in asthma, 62 (54%) in ACO, and 35 (58%) in COPD patients.

Conclusions: ACO and COPD patients have more severe SAD than asthma patients.