Effects of oscillating air flow on the rheological properties and clearability of mucous gel simulants.

This in vitro study addressed the question of clearance-related changes in the physical properties of mucous gel simulants (MGS) subjected to oscillating air flow. Delineating some of the possible mechanisms of action for the reported beneficial effects of high-frequency chest compression (HFCC) therapy constituted the rationale. The rheological variables measured were spinnability by filancemeter and viscoelasticity (mechanical impedance, G*, and loss tangent, tan delta) by magnetic microrheometry. Two derivative parameters, mucociliary clearability index (MCI) and cough clearability index (CCI), were computed from the rheological variables, based on relationships established from model studies of clearance. Two ranges of air flow oscillation frequencies used previously in animal and clinical studies, i.e., 12-13 Hz or 22-23 Hz, were applied. The measurements were made after application of oscillating air flow for 15, 30 and 60 minutes, and compared with those at baseline and negative control. A significant decrease in log G* with administration of oscillations was observed (p = 0.06 at 30 minutes, p < 0.01 at 60 minutes, for G* measured at 1 rad/s). Spinnability also decreased by 19.3% and 30.7% after 15 minutes; 32.9% and 41.1% after 30 minutes; 36.4% and 50.5% after 60 minutes, for 12 Hz and 22 Hz, respectively (all significantly different from baseline). There was a positive correlation between viscoelasticity and spinnability, and a negative correlation between spinnability and CCI, but no correlation between spinnability and MCI. Oscillating air flow seemed to act as a physical "mucolytic" that affected mostly the cough clearability of the mucus simulant.