Elastic contributions dominate the viscoelastic properties of sputum from cystic fibrosis patients

Sputum samples from cystic fibrosis (CF) patients were investigated by oscillators,, creep and steady shear rheological technique, over a range of time scales from 10(-3) to 10(6) s. The viscoelastic changes obtained by mixing sputa with the actin-filament-severing protein gelsolin and with the thiol-reducing agent dithiothreitol (DTT) were also investigated. At small strains sputum behaves like a viscoelastic solid rather than a liquid. A nearly constant steady shear viscosity at low shear rates is only observed after long shearing times which cause irreversible changes in the samples. Creep-recovery tests confirm that sputa exhibit viscoelastic proper-ties. with a significant elastic recovery. The results suggest that measurements of elastic moduli, rather than viscosities are more closely related to the mechanical properties of sputum in situ. Severing of actin filaments lowers the elastic modulus by 30-40%. but maintains viscoelastic integrity. while reduction of thiols in the glycoproteins nearly completely fluidizes the samples. (C) 2004 Elsevier B.V. All rights reserved.