title: Model analysis of intra-acinar gas exchange.
abstract: A previously described multibranch-point model, incorporating branching asymmetry within an acinus, has been extended to include gas exchange at the alveolar surface. Using a transport equation for simultaneous convection and diffusion within the gas phase and independent perfusion of all nodes, we obtained steady-state solutions for the temporal and spatial distributions of O2 and CO2 tensions within an acinus during a respiratory cycle. Results for conditions corresponding to both rest and moderate exercise indicated a significant inhomogeneity of gas concentrations within a single acinus. The coefficient of variation of PACO2 at end-inspiration during exercise reached 11.3%. Despite this non-uniformity the computation of a negligible PAO2 - PAO2 difference indicated no impairment in gas exchange. The simulations are consistent with the hypothesis that in the normal lung the whole acinus acts functionally as a gas exchanging unit and ventilation-perfusion inequality has an interacinar basis.
mesh_terms: D002245:Carbon Dioxide / Q000032:analysis; D008954:Models, Biological; D010100:Oxygen / Q000032:analysis; D010101:Oxygen Consumption; D010313:Partial Pressure; D011650:Pulmonary Alveoli / Q000378:metabolism; D011659:Pulmonary Gas Exchange
chemical_list: D002245:Carbon Dioxide; D010100:Oxygen