Meeting Abstract
Varanids are a remarkable group of lizards that exhibit great variation in body mass, ecological niche, and aerobic capacity but retain a conserved body plan. Their lungs also vary and are an ideal group in which to investigate the functional and ecological significance of pulmonary traits. Our group reported unidirectional flow in the larger chambers of Varanus exanthematicus but detailed flow patterns and how these patterns vary among species remains unknown. Studying airflow in varanid lungs is difficult because much of the lung is dense parenchyma that cannot be accessed with flow probes. Computational fluid dynamics (CFD) can overcome these difficulties by generating simulations of pulmonary airflow based on computed tomography (CT) data that can be validated on real lungs. Airways were segmented and made into surface files in Avizo. Surface models were meshed into a computational meshes using the unstructured mesh generation utility, snappyHexMesh. CFD simulations were run using a custom PIMPLE-based dynamic solver in OpenFOAM. Varanid lungs consist of an intrapulmonary bronchus (IPB) that ends in a caudal bronchus, branches cranially into a hilar-cranial bronchus (HCB), and opens throughout into secondary bronchi that interconnect via perforations. Smaller species have fewer but larger caudal chambers and relatively thicker IPBs. Flow in V. exanthematicus is net-unidirectional: the IPB moves air net caudally, the secondary bronchi move air net cranially, and the HCB is tidal. In V. spenceri, which has a has a thin IPB, the dorsal aspects of secondary chambers carry net caudal flow and the ventral aspects carry net cranial flow. These results show that pulmonary airflow patterns in varanids vary with life-history traits and varanid lungs contain a mix of unidirectional and tidal lung traits.
