Simulation of Central Airway Gas Flow Dynamics During Conventional and Multifrequency Ventilation

Patients with acute respiratory failure often require supportive mechanical ventilation to maintain adequate gas exchange. Recent studies have shown that multifrequency ventilation (MFV), the technique of presenting multiple simultaneous frequencies in flow or pressure at the airway opening, may provide more uniform ventilation distribution and parenchymal strain throughout the mechanically heterogeneous lung. In this study, we simulated gas flow within a porcine central airway tree, from the trachea to the fifth generation, with dynamic boundary conditions (BCs) during volume-controlled conventional mechanical ventilation (CMV) cycled at 0.27 Hz (16.2 min-1), as well as MFV waveforms comprised of two fast sinusoidal components (i.e., 3.5 Hz and 7.0 Hz) superimposed on the 0.27 Hz CMV waveform. By using forced gas flows at the airway opening of the computational lung model, dynamic pressures at various airway segments were predicted, based on the interactions of internal flow with the downstream elastances and peripheral resistances. Internal airflows were simulated and analyzed in both time- and frequency-domains. The results indicate that MFV resulted in stronger asymmetric flow (i.e., "pendelluft") at end-inspiration and end-expiration. MFV also appeared to augment inlet-outlet phase differences for both pressure and flow compared with CMV, suggesting that MFV may enhance gas mixing, thus facilitating more efficient ventilation.