Unidirectional pulmonary airflow, a condition where lung gases travel in the same direction through most of the airways throughout the respiratory cycle, has long been of interest to comparative physiologists. Recent work has discovered this phenomenon beyond birds and raised questions about the underlying fluid dynamical phenomena occurring in unidirectional lungs. Computational fluid dynamics, which simulates patterns of flow from prescribed boundary conditions and the laws of fluid motion, provide a powerful tool to study airflow through these complex structures. Here, computed tomography scans were segmented into a detailed computational mesh, representing the major and minor airways of monitor lizards, Varanidae. The surface of the computational meshes expanded and contracted to simulate lung motion during ventilation and provided the boundary conditions for flow. Our models show unidirectional flow in many regions of the lung and reveals airflow patterns in chambers that are too small or are inaccessible with traditional techniques.
