ROLE OF VISCOELASTICITY IN THE TUBE MODEL OF AIRWAY REOPENING .2. NON-NEWTONIAN GELS AND AIRWAY SIMULATION

The influence of viscoelastic gels as lining fluids on the pressure-ve locity relationships in an airway tube model (Gaver et al. J. Appl. Ph ysiol. 69: 74-85, 1990) was examined. A flow instability was observed due to the occurrence of a sol-gel transition in the viscoelastic prop erties under flow conditions. We further report measurements of the vi scoelastic properties of airway secretions. Airway secretions are gels under small strains and have a yield stress of 4-7 dyn/cm(2). Secreti ons from the pharyngeal airway show lower elasticity than secretions f rom the trachea. The airway reopening process is simulated using a Wei bel lung geometry by incorporating the constitutive equations from the model gel studies and utilizing the rheological data on airway secret ions. In these simulations, a ''popping-open'' phenomenon arises from a flow instability in airway generations 8-14 when the rheological pro perties of the lining fluids are assumed to be similar to those of pha ryngeal secretions. On the basis of these studies, the elasticity of a irway secretions plays an important role in airway reopening.