Late Breaking Abstract - Biological Determinants of Sputum Rheology in Chronic Airway Diseases

Background: Mucus hyperproduction and mucus plugs are key pathophysiological features of chronic airway diseases. Objectives: To determine biological and clinical variables influencing sputum rheology. Methods: We performed a non-interventional clinical study. Spontaneous sputum was collected from consecutive asthma, COPD, and non-CF bronchiectasis patients. Patients answered the Cough and Sputum Assessment Questionnaire (CASA-Q). Sputum rheology was assessed using the Rheomuco® rheometer (Rheonova, Grenoble); the elastic modulus G’, viscous modulus G’’, and critical stress τC were recorded. Key quantitative and qualitative biological sputum components were determined by cytology, nucleic acid amplification tests and mass spectrometry. Results: 48 patients were included from January to August 2019. Among them, 10 had asthma, 14 COPD and 24 non-CF bronchiectasis. G’ and G’’ were significantly different in asthma patients (G’=14.49[7.18-25.26]Pa, G’’=3.0[2.16-5.38]Pa) compared to COPD (G’=5.01[2.94-6.48]Pa, G’’=1.45[1.16-1.94]Pa, p<0.05) and to non-CF bronchiectasis (G’=4.99[1.49-10.49]Pa, G’’=1.46[0.71-2.47]Pa, p<0.05). G’ and G’’ were positively correlated with MUC5AC protein concentration ((r²=0. 77, p<.001) and (r²=0.819, p<.001) respectively). τC was positively correlated with sputum eosinophilia (r²=0.826, p=0.032), MUC5AC (r²=0.826, p=<.001) and MUC5B (r²=0.826, p=0.025) protein concentrations. CASA-Q was poorly but significantly correlated with τC (r²=0.131, p=0.03). Conclusion Sputum rheology assessment is routinely feasible and simple in patients with chronic airway diseases and is better correlated with mucin concentrations and sputum eosinophilia than with symptoms regardless of the underlying disease.