A model for the study of diffusion and perfusion limitation.

On the basis of a very simple model for the association of diffusion and perfusion, an association common to many respiratory gas transfers, a simple equation is described that defines gas partial pressure equilibration in diffusion-perfusion-limited systems as a function of the ratio of D to beta bQ(D = diffusing capacity, beta b = blood capacitance coefficient, Q = perfusion). The equation applies to steady-state conditions and assumes D, beta b, and Q to be independent of gas partial pressures. In spite of the fact that this assumption may represent a gross simplification, the equation can be regarded as a powerful conceptual tool in the analysis of most gas exchange systems.