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/FiO) relationships in lungs modeled with log normal distributions (LND) of inspired (V) versus expired (V) alveolar gas volumes. In lungs with normal V/Q heterogeneity, Q versus V/Q and Q versus V/Q distributions were similar with either approach, and PaO/FiO sequences remained indistinguishable. In V/Q heterogeneous lungs at high FiO, VLND generated low Q versus V/Q shoulders and some negative V units, while VLND preserved Q versus V/Q log normality by blood flow diversion from low V/Q units. We managed VLND-induced negative V units either by shunt conversion (V decreased to 0) or V redistribution simulating collateral ventilation (V increased till V = 0). Comparing oxygen transfer: VLND > VLND (redistribution) > VLND (shunt). In V/Q heterogeneous lungs VLND and VLND (redistribution) regained near optimal oxygen transfer on 100% oxygen, while impairment persisted with VLND (shunt). Unlike VLND, VLND (redistribution) produced Q versus V/Q distributions in V/Q heterogeneity compatible with multiple inert gas (MIGET) reports. VLND (redistribution) is a physiologically-based MIGET-compatible alternative to West's original VLND lung modeling approach.