Background: A relationship between the severity of bronchial asthma (BA) and mucus plug formation has been reported. Rheological measurement of sputum is considered important to evaluate characteristics of mucus plugs although current methods are so complicated.

Objective: To measure the viscoelasticity of sputum in patients with BA and chronic cough (CC) quantitatively and analyze its relationship with biomarkers, pulmonary function and hematological findings.

Methods: Seventeen patients with CC (F:11 M:6, age median 65.0 (36-79)) and 16 patients with BA (F:9, M 7, age 75.0 (48-91), x9 mild, x4 moderate, x3 severe) were enrolled (Ethics Committee Kasuga 2022-01). Spontaneous sputum was applied to the rheometer (Rheomuco®: Rheonova, Grenoble) to evaluate 11 rheological parameters.

Results: There was a good reproducibility in most of rheological markers on fresh samples, although the characteristics were not maintained for 3 hrs after collection. Elastic modulus (G') and critical stress (?C), typical parameters for sputum viscoelasticity, were 18.2 Pa (SD 7.6), 16.5 Pa (14.1) in CC, 16.3 (6.8), 34.3 (50.5) in mild BA, 34.4.(29.4), 56.1 (25.9) in moderate BA, and 9.8 (2.8), 14.9 (10.2) for severe BA, respectively. In addition, peripheral blood eosinophil counts correlated with Viscoelastic modulu (G*), G?, Viscous modulus (G??), Limit linear strain (?L) and Limit linear stress (?L) in BA, FeNO values correlated with ?L in CC.

Conclusion: Quantitative measurement of sputum rheological parameters by Rheomco revealed their abnormalities in CC and BA. More work is needed to understand the abnormalities in different diseases, and usefulness of the parameters in clinical practice.