SAD was characterized by any two parameters of maximal mid-expiratory flow (MMEF)% pred, forced expiratory flow at 50% of forced vital capacity (FEF50%) pred, and forced expiratory flow at 75% of forced vital capacity (FEF75%) pred measuring <65%.

SAD was noted in 73 (60.8%) patients with CVA prior to treatment.

Findings of the study:

• Patients with SAD had a significantly longer median cough duration (p = 0.031), higher proportion of women (p = 0.029), higher mean age (p = 0.005; Table 1), and significantly lower forced expiratory volume in 1 s (FEV1%) pred, FEV1/FVC, MMEF% pred, FEF50% pred, FEF75% pred, peak expiratory flow (PEF)% pred, and PD20 (all p < 0.01), in comparison with patients without SAD.
• No significant differences were evident in cough visual analog scale (VAS), sputum eosinophil count, fractional exhaled nitric oxide (FeNO), and total immunoglobulin E (TIgE) level between patients with and without SAD (Table 1). 
• Of the 105 patients who completed 2 months of antiasthmatic treatment and repeatedly underwent spirometry measurement, 54.3% (57 patients) continued to have SAD, irrespective of significant improvement in cough VAS, sputum eosinophil count, FeNO, FEF50% pred, and PEF% pred (all p < 0.01). 
• Patients with SAD had no significant differences in the relapse rate (50.0 vs. 41.9%, p = 0.483) and wheeze development rate (10.4 vs. 0%, p = 0.063) during follow-up, in comparison with those without SAD. 

Table 1. Demographics and clinical characteristics of patients with and without SAD

Data given as % or mean ± SD or median (IQR)

SAD was noted in more than half of the patients with CVA and was still present after short-term antiasthmatic treatment.

Reference

Yi F, Jiang Z, Li H, et al. Small Airway Dysfunction in Cough Variant Asthma: Prevalence, Clinical, and Pathophysiological Features. Front Physiol. 2022 Jan 13;12:761622.