Clinical significance of small airway obstruction markers in patients with asthma

Summary Background The role of small airway obstruction in the clinical expression of asthma is incompletely understood. Objective We tested the hypotheses that markers of small airway obstruction are associated with (i) increased asthma severity, (ii) impaired asthma control and quality of life and (iii) frequent exacerbations. Methods Seventy‐four adults with asthma and 18 healthy control subjects underwent impulse oscillometry (IOS), multiple breath inert gas washout (MBW), body plethysmography, single‐breath determination of carbon monoxide uptake and spirometry. Patients completed the six‐point Asthma Control Questionnaire (ACQ‐6) and standardized Asthma Quality of Life Questionnaire [AQLQ(S)]. Asthma severity was classified according to the Global Initiative for Asthma (GINA) treatment steps. Results The putative small airway obstruction markers Sacin, resistance at 5 Hz minus resistance at 20 Hz (R5‐R20) and reactance area (AX) were not independently associated with asthma severity, control, quality of life or exacerbations. In contrast, markers of total (R5) and mean airway resistance of large and small airways (R20) were significantly higher in the severe asthma group compared with the mild–moderate group (0.47 vs. 0.37, P