Meeting Abstract
Almost nothing is known about the flow of gases very close to and within the gas exchange parenchyma of any reptile, yet this flow is a crucial determinant of gas-exchange capacity. The parenchyma is diverse, ranging from simple trabecule, where branching structures form a polygonal network along the lung wall, to faveoli, with a honeycomb appearance. Our recent work on gross patterns of airflow within the lungs of a variety of reptiles suggests that much of the flow is unidirectional and laminar, which could increase the thickness of boundary layers and impede gas exchange. To better understand the relative contribution of diffusion and advection to gas exchange at the microscale level, we have: (1) developed physical models of the lung walls; (2) simulated gas exchange. The physical models were created using micro-CT of a green iguana to generate a surface file, which was scaled to maintain dynamic similarity when water flowed over the surface at steady state (Re ≈ 8-12), and 3D printed with PLA filament, or laser cured resin. Polyamid seeding particles (50 μm ø) were visualized using Flocoach™ model B1. The gas-exchange simulations were generated for a series of 2D wells, with geometries typical of reptilian respiratory parenchyma, using Fluent and Peclet # <<1. Our results indicate the faveoli are an impediment to convection and suggest thick boundary layers impede gas-exchange with flow at steady state. We found little evidence of vortices developing within the faveoli. These results point to the importance of cardiac pulsations of the vasculature or smooth muscle for improving mass transport. Funded by NSF IOS CAREER-1055080, NSF 1256065, NSF ACI-1238993, and Enterprise Ireland.
