Meeting Abstract
Understanding the biomechanical basis of avian unidirectional pulmonary airflow, a condition where lung gases travel in the same direction through most of the airways and throughout the respiratory cycle, has long been of interest to scientists. Recent work has revealed a wide phylogenetic distribution of this trait, beyond the confines of Aves, to include crocodilians, green iguanas, and monitor lizards, and has raised new questions about the underlying fluid dynamical phenomena occurring in unidirectional lungs. Advances in computational fluid dynamics, a technique where patterns of flow are simulated from prescribed boundary conditions by laws of fluid motions, provide a powerful tool to study airflow through these complex and fascinating structures. In this study, computed tomography scans were segmented into a detailed computational mesh, representing the major and minor airways of the savannah monitor, Varanus exanthematicus. Flow was simulated through these airways in two ways: 1) in a dynamic simulation, where air flowed into and out of the lung domain through a static tracheal inlet that was driven by expansion and contraction of the lung domain. 2) steady state flow with the caudal part of the lung serving as an outlet or inlet respectively. Simulations were carried out in open-source software on an 80-processor computing cluster. The model shows unidirectional pulmonary airflow in many regions of the lung, and reveals airflow patterns in chambers that are too small or are inaccessible to empirical study. The results of this study indicate that many aspects of the flow are similar between the dynamic and static models. Further computational modeling can be used to test hypotheses regarding unidirectional flow, such as the role of internal lung partitions and the pattern of lung motion during ventilation.
