Role of viscoelasticity in tube model of airway reopening. I. Nonnewtonian sols.

This investigation used a previously described bench-top device (Gaver et al., J. Appl. Physiol. 69: 74-85, 1990) to examine the role of nonnewtonian and viscoelastic fluids on events at reopening of a closed flexible tube. Aqueous sodium alginate solutions with and without calcium chloride and sodium dodecyl sulfate in desired concentrations provided fluids with a wide range of surface tensions, storage and loss moduli, and nonnewtonian steady shear viscosity. Dimensionless analysis, using the shear rate-dependent viscosities, was applied to reduce reopening pressure-meniscus velocity data to a master curve. With regard to fluid properties, we found that 1) fluid elasticity strongly changes the pressure-velocity relationship, causing flow instability at higher meniscus velocities; 2) decreasing surface tension gives rise to a smaller yield pressure for reopening; and 3) whereas larger tubes are easier to open, smaller tubes produce additional shear thinning of the lining fluid. These results suggest that, for both the upper (large) and lower (small) airways, nonnewtonian and viscoelastic properties of the mucosal fluid modify the time of closure and rate of reopening.