Viscoelastic characteristics of spontaneous sputum obtained from patients with chronic productive cough in comparison to bronchial asthma.

BACKGROUND

Chronic respiratory diseases are known to be associated with alterations in mucus rheology, but limited information is available regarding chronic cough. The aim of this study was to determine the sputum rheology in chronic productive cough (CPC) in comparison to bronchial asthma (BA).

METHODS

The viscoelasticity profiles of spontaneous sputum obtained from 26 patients with CPC (10 sinobronchial syndrome [SBS], 16 non-SBS) and 25 patients with BA (12 mild-persistent, 7 moderate, and 6 severe) were analyzed by rheometry in a single center. The non-SBS group included fungus-associated chronic cough, post-COVID-19 cough, bronchorrhea, and unexplained chronic cough.

RESULTS

Viscoelastic modulus (G∗) and viscous modulus (G″) of the SBS group were similar to those of the total BA group. Although critical strain (γC) and critical stress (σC) tended to be larger in the BA group, and the former was comparable between the non-SBS group and the moderate or severe BA group. In the non-SBS group, G″ was closely correlated with FeNO, and γC was inversely correlated with respiratory function, as in the BA group, but no such correlations were observed in the SBS group.

CONCLUSIONS

Quantitative rheological analysis revealed unique viscoelastic characteristics of spontaneous sputum and altered association with clinical biomarkers in the non-SBS group, in which the profile was more similar to BA than SBS in CPC. This new rheometer can identify features of sputum in patients with CPC that cannot be detected by conventional methods. Further investigations of sputum rheology in CPC are warranted to understand its pathogenesis.