Fractal analysis of lung fluid flow

The human lung brings a continuous flow of blood into close proximity with a cyclic flow of air so that respiratory gases can readily diffuse between these two fluids. Nature has created an intricate arrangement of spaces to accomplish this task. A 3-dimensional cylinder of venous blood leaving the right ventricle is transformed into a nearly 2-dimensional film of blood by the time it arrives at the alveolus. At the same time, a bolus of inhaled air is divided into smaller streams and pockets until its surface area approaches 100 m2. Both processes distribute a fluid through a repeatedly bifurcating network. The configuration of these networks as well as their relative sizes have been difficult to summarize using the conventional language of Euclidean geometry [7].