Multi-compartment V/Q lung modeling: Log normal distributions of inspired or expired alveolar gas?

Using a 50-compartment Python-coded mathematical lung model, we compared mixed venous blood flow (Q) distributions and arterial oxygen tension/inspired oxygen fraction (PaO ₂ /FiO ₂ ) relationships in lungs modeled with log normal distributions (LND) of inspired (V _I ) versus expired (V _A ) alveolar gas volumes. In lungs with normal V/Q heterogeneity, Q versus V _A /Q and Q versus V _I /Q distributions were similar with either approach, and PaO ₂ /FiO ₂ sequences remained indistinguishable. In V/Q heterogeneous lungs at high FiO ₂ , V _I LND generated low Q versus V _A /Q shoulders and some negative V _A units, while V _A LND preserved Q versus V _A /Q log normality by blood flow diversion from low V _I /Q units. We managed V _I LND-induced negative V _A units either by shunt conversion (V _I decreased to 0) or V _I redistribution simulating collateral ventilation (V _I increased till V _A  = 0). Comparing oxygen transfer: V _A LND > V _I LND (redistribution) > V _I LND (shunt). In V/Q heterogeneous lungs V _A LND and V _I LND (redistribution) regained near optimal oxygen transfer on 100% oxygen, while impairment persisted with V _I LND (shunt). Unlike V _A LND, V _I LND (redistribution) produced Q versus V _A /Q distributions in V/Q heterogeneity compatible with multiple inert gas (MIGET) reports. V _I LND (redistribution) is a physiologically-based MIGET-compatible alternative to West's original V _A LND lung modeling approach.
(© 2024 The Author(s). Physiological Reports published by Wiley Periodicals LLC on behalf of The Physiological Society and the American Physiological Society.)