Time-Dependent Diffusion in the Alveolar Region of the Lungs: Effect of Moving Red Blood Cells

Results from a preliminary numerical simulation of alveolar gas diffusion with moving capillary red blood cells (RBCs) are presented. The alveolar region is modeled with four basic constituents, namely the alveolus (or gas region), the tissue (a region lumping the alveolar and capillary membranes, and the interstitial fluid), the blood plasma (a liquid region) and the RBCs. A single, straight capillary with equally spaced RBCs moving together with the blood plasma is considered in this preliminary study. The numerical simulation attempts also to mimic the time-varying gas concentration in the alveolus region due to respiration. Realistic physical parameters (e.g., dimensions, diffusivities and RBCs speed) are used for simulating CO diffusion, in accordance to clinical tests for determining the lung diffusing capacity. Results are compared to published results obtained when the RBCs are fix in place (stationary). The RBCs moving effect, relevant at high hematocrit, is to increase the resulting lung diffusing capacity.