Diffusion-perfusion inhomogeneity and alveolar-arterial O2 diffusion limitation: theory

Unequal distribution of pulmonary O2 diffusing capacity (D) to pulmonary blood flow (Q) (D/Q heterogeneity) leads to decreased alveolar O2 exchange efficacy. It is shown on simple models that the effect increases with increasing amount of inequality and with increasing value of the equilibration index, D/(Q beta) (beta, increment in blood O2 content per partial pressure increment). This inhomogeneity effect, if not taken into account, leads to spurious increases of D in hypoxia and with elevated O2 uptake.