Physical properties of sputum—VI: Physical–chemical factors in sputum rheology 1

The viscoelasticity of reconstituted sputum was found to vary as a function of the solid concentration, pH, ionic strength and temperature. At a given solid concentration, the highest viscosity and elastic modulus occurred at pH = 6.0 and decreased with higher or lower pH. This effect is theorized to be mainly the result of electrostatic interactions. The addition of sodium chloride acted to shorten the Newtonian viscosity area. Both the elastic modulus and viscosity were increased with increasing solid concentration. A slight, 4°C increase in experimental temperature reduced the elastic modulus by 19.3% and the Newtonian viscosity by 80.3% at pH 7.9. Whenever rheological changes occurred, both viscosity and elastic modulus changed in the same direction: an increase in viscosity correlated with a decrease in elastic recoil (increased modulus) and vice versa.