Numerical Modeling of the Effects of Congestion in Human Lungs

The human lung is a complex structure where blood is oxygenated during every breathing cycle. This study aims to understand the effects of congestion on the alveolar gas exchange by modelling the entire lung as a global, equivalent, heterogeneous porous medium of three zones of three different Permeabilities comprising 23 generations of branches. The airflow for every breathing cycle is simulated by solving mass and momentum transfer equations across the three zones of the global model. A separate local model is invoked in zone 3 to capture the oxygen exchange between the airflow in the alveoli and the incoming capillary blood by solving mass transfer equations. During every breathing cycle (5 s), 350–500 ml of air is inhaled, and the velocity with which the air reaches the last generation of zone-3 is fed as input to the local model to solve the mass exchange equations. The local model yields the percentage of oxygen transferred to the blood. Congestion is introduced in the global model by suitably altering the porous medium properties. In a parametric study, the effect of congestion on the oxygen exchange with the blood in zone 3 is determined using both the global and local models in tandem. A sample result of the velocity profiles for normal and congested human lungs is studied. When the reduced velocity values are used in the local model, a 29% reduction in blood oxygen content is observed.