Mechanically induced pendelluft flow in a model airway bifurcation during high frequency oscillation

A single bifurcation with adjustable branch compliances, resistances and inertances was used to study the generation of pendelluft flows during ventilation at tidal volumes of 5-15 ml and frequencies of 6-26 Hz, corresponding to parent branch Reynolds numbers of 400-8000 and Womersley parameter values of 12-25. Pendelluft was quantified by the ratio of tidal volume sum in sibling branches to tidal volume in the parent branch. This tidal volume fraction being greater than one in all experiments where an asymmetry in branch mechanics was imposed, indicated that some degree of pendelluft was always present. Asymmetries in compliance and in inertance produced much greater pendelluft than an asymmetry in resistance. The largest tidal volume fraction, equal to 2.75, was recorded when inertance in both sibling branches was high, resistance was low, and compliances differed by a factor of five. Tidal volume fraction always peaked at an optimal frequency between 12-24 Hz, similar to the frequencies at which physiologic transport optima have previously been observed.