Abstract
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.