| Understanding the pulmonary gas transport process is a fundamental requirement for prevention, diagnostics and therapy of many respiratory and cardiopulmonary diseases (e.g., hypoxemia, pulmonary sarcoidosis, fibrosis, cancer, asthma, and emphysema). Predicting the physiological operation of the lungs is also important for designing artificial lungs, as well as discovering further applications for BioMEMS.; The effects of blood velocity on the gas transport within a lung capillary (and on the lung diffusing capacity, DL) have for many years been regarded as negligible. However, simple scale analysis of the blood flow within an alveolar capillary predicts gas transport process within an alveolar capillary to be convection dominated for the practical range of physiologic parameters normally considered in the literature. This contradiction is resolved in the present study using realistic mathematical modeling for simulating numerically the alveolar gas exchange of carbon-monoxide under blood flow through a lung capillary.; Model equations, with appropriate boundary conditions and physical properties, are presented for the gas exchange process in a lung capillary. The consistency and accuracy of the numerical predictions are established against published numerical results for simpler configurations, vis-a-vis the blood speed, and against morphometric based experimental measurements of fixed lungs (no blood flow).; Two- and three-dimensional simulations of the convection-diffusion phenomena within a lung capillary are performed. The effects of blood speed (RBC and plasma movement), RBC shape (circular, parachute, disk) and alveolar capillary dimensions (gap between RBC and capillary membrane) on the lung diffusing capacity are investigated.; In a preliminary effort, the effect of plasma mixing and RBC movement for circular shaped RBCs in a two-dimensional domain, for different hematocrit, reveals that RBC movement can be very important at low hematocrit, even at moderate blood speed affecting DL by as much as 60%. One of the most important findings is the determination of plasma gas-storage effects on the value of the lung diffusing capacity, believed to be partially responsible for this increase in DL.; The conclusions of the previous effort are extended for the more realistic case of parachute-shaped RBCs, also in a two-dimensional domain.; The importance of the gap (distance) between the RBC surface and the capillary wall in the gas transport process under blood flow is also thoroughly investigated. (Abstract shortened by UMI.)... |
