Efficiency of Alveolar Ventilation During High-Frequency Modes in Piglets: Effects of Airway and Tissue Heterogeneity

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BACKGROUND: Oscillatory high-frequency ventilation modalities, including high-frequency oscillatory, percussive, and jet ventilation, are commonly used during anesthesia and critical care to improve oxygenation or facilitate airway surgery. These techniques rely on rapid, small-amplitude pressure oscillations to sustain gas exchange while minimizing baro- or volutrauma. However, how effectively such oscillations transmit through the conducting airways to the alveoli in mechanically heterogeneous lungs remains poorly understood, particularly under perioperative conditions associated with atelectasis, airway narrowing, or altered chest wall mechanics. METHODS: We combined in vivo measurements in anesthetized, mechanically ventilated piglets with computational simulations to quantify pressure transmission and ventilation heterogeneity across controlled variations in airway and tissue mechanical properties. Airway opening, tracheal, and alveolar capsule pressures (n = 16) were recorded with miniature pressure transducers during multifrequency (0.5-20.75 Hz) oscillations at positive end-expiratory pressures (PEEP) of 5 and 10 cmH2O. The experimental data informed a simulation model comprising heterogeneous airway and tissue compartments to identify determinants of alveolar ventilation during oscillatory modes. RESULTS: The in vivo measurements revealed that the endotracheal tube accounted for most of the total flow resistance and inertance, whereas the chest wall contributed approximately two-thirds of tissue damping and elastance. Only 29% (95% confidence interval [CI], 22%-36%) to 43% (95% CI, 32%-54%) of tracheal oscillatory pressure reached the alveoli, showing strong frequency-dependent attenuation that was not significantly influenced by PEEP. Simulation results validated against measured pressure transfer functions indicated that airway heterogeneity dominated regional disparities in pressure and tidal volume, causing up to 250% differences in local volumes at high net resistance. Tissue heterogeneity exerted smaller (<100%) but distinct effects on pressure-volume relationships. CONCLUSIONS: Airway heterogeneity, common in perioperative atelectasis, bronchospasm, and acute lung injury, profoundly limits the efficiency of oscillatory ventilation. Understanding how airway and tissue properties modulate oscillatory pressure transmission provides a mechanistic basis for tailoring high-frequency ventilation to individual patients. These insights may inform more rational ventilation strategies to optimize gas exchange while minimizing regional overdistension and collapse.

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