REGIONAL GAS TRANSPORT IN THE HETEROGENEOUS LUNG DURING OSCILLATORY VENTILATION

Regional ventilation in the injured lung is heterogeneous and frequency-dependent, making it difficult to predict how an oscillatory flow waveform at a specified frequency will be distributed throughout the periphery. To predict the impact of mechanical heterogeneity on regional ventilation distribution and gas transport, we developed a computational model of distributed gas flow and CO₂ elimination during oscillatory ventilation from 0.1 to 30 Hz. The model consists of a three dimensional airway network of a canine lung, with heterogeneous parenchymal tissues to mimic effects of gravity and injury. Model CO₂ elimination during single frequency oscillation was validated against previously published experimental data (Venegas et al., J. Appl. Physiol. 60:1025-1030, 1986). Simulations of gas transport demonstrated a critical transition in flow distribution at the resonant frequency, where the reactive components of mechanical impedance due to airway inertia and parenchymal elastance were equal. For frequencies above resonance, the distribution of ventilation became spatially clustered and frequency-dependent. These results indicate that regional distribution of ventilation and gas exchange, in addition to global CO₂ elimination, should be important factors for determining the appropriate frequency settings during oscillatory ventilation in the heterogeneous lung.

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