The elasticity of sputum at low shear rates

Abstract

Elasticity of sputum. Elasticity of sputum has been determined using the Weissenberg rheogoniometer, by oscillatory testing, over frequencies from 0.01 to 0.8 c/s.

Sputum was from patients with either asthma, chronic bronchitis, cystic fibrosis or bronchiectasis and, macroscopically, mucoid, mucopurulent or purulent.

As in the viscosity plot over this shear rate range two Zones with a junctional region can be distinguished. In Zone 1, over the lowest shear rates, elasticity increases slowly, changes little over a “plateau” region and then, in Zone 2, increases sharply. In contrast to the viscosity plot, the plateau docs not show notching. By 0.8 c/s some samples show decreasing elasticity. Although variance between samples is wide, there is no level of elasticity characteristic of each disease or of one macroscopic appearance.

Elasticity and viscosity are correlated, most significantly at the lowest shear rates. Asthmatic and bronchiectatic sputa resemble each other in that this correlation is still significant at higher shear rates, cystic fibrosis and chronic bronchitic sputum in that it is not. Since in these last two mucous gland hypertrophy is present, it may be that the sputum has a higher mucus component.