Rheological and Low Field NMR Characterisation of Cystic Fibrosis Patient’s Sputum

G. Staltari, A. Biasin, L. Grassi, F. Gerin, M. Maschio, M. Confalonieri, G. Grassi, M. Grassi and M. Abrami

Abstract
The shear modulus G of the sputum obtained by expectoration from cystic fibrosis patients is fundamental to determine the mesh size of the polymeric network pervading the sputum, a parameter related to lung functionality. The Akaike criterion revealed that in 55.2 % of the examined samples, the best approach (among those considered) to determine G relied on the mechanical spectrum fitting by the generalised Maxwell model with relaxation times scaled by a factor 10. Thus, this approach was adopted to evaluate the mesh size distribution combining G knowledge with the determination of the average magnetic relaxation time (T2m) of sputum. As G and T2m determination can be negatively affected by sputum contamination by saliva, whose presence increases T2m and depresses G, we developed a proper “decontamination” procedure to obtain more reliable T2m and G estimations (necessary in 21 % of the samples). This procedure allowed to strengthen the T2m correlation with lung functionality evaluated by FEV1 (normalised air volume emitted in the first second during a spirometry test).

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Keywords
rheology, low field NMR, cystic fibrosis, shear modulus, mesh size, saliva contamination