Sputum viscosity is correlated with Computed Tomography (CT) mucus score in muco-obstructive lung diseases

<b>Background:</b> Our aim was to determine the variables influencing sputum rheology in patients with severe asthma, Chronic Obstructive Lung Disease (COPD) and non-CF bronchiectasis (NCFB) <b>Methods:</b> We performed a cross sectional prospective cohort study. Spontaneous sputum was collected from consecutive patients with muco-obstructive lung diseases. Sputum rheology was assessed using the Rheomuco® rheometer (Rheonova, Grenoble); the elastic modulus G’, viscous modulus G’’, and critical stress threshold σc were recorded. Chest High-Resolution CT (HRCT) were performed to assess CT mucus score (Dunican EM, et al. J Clin Invest. 2018), as well as spirometry. Patients were pooled for the analysis. Logistic regressions were performed to explain sputum rheology parameters as a function of CT mucus score and Forced Expiratory Volume in one second (FEV1 %pred). <b>Results:</b> 48 patients were included from January to August 2019. Among them, 10 had asthma, 14 COPD and 24 NCFB. Median FEV1%pred was significantly lower in the COPD group (FEV1 = 28%pred [22.75-33.25]) compared to the asthma group (FEV1 = 75%pred [57-78] (P &lt;.001)) and the non-CF bronchiectasis group (FEV1 =55.5%pred [40-79] (P &lt;.001)). For all pooled patients, CT mucus score was correlated only with viscous modulus G’’ (r² = .12 p-value=.014). FEV1 was not significantly correlated with any rheology parameters. <b>Conclusion:</b> CT mucus score is correlated with sputum viscosity, independently of the underlying muco-obstructive lung disease.