Meeting Abstract

P1.18  Tuesday, Jan. 4  Unidirectional Airflow in the Lungs of American Alligators INGEBRETSEN, S; SCHACHNER, E; FARMER, CG*; University of Utah, Salt Lake City; University of Utah, Salt Lake City ; University of Utah, Salt Lake City cg.frmr@gmail.com

The recent observation that airflow is unidirectional in the lungs of American alligators (Alligator mississippiensis) raises the question of what specific features of the alligator lung create this pattern of flow and whether or not these features are also found in birds. To better understand the structural and functional similarities in the avian and alligator respiratory systems, we used tracer gas (He), single heated thermistors, and dual thermistor flow meters to track the pathways of flow in excised lungs of juvenile alligators. Our data indicate that airflow in the ventrocranial regions of the lungs moves in a cranial to caudal manner, whereas flow in the dorsal regions of the lungs moves in a caudal to cranial direction. There is only one major ventrobronchus that conducts the cranial to caudal flow, whereas at least four dorsobronchi conduct flow in the caudal to cranial direction. The pattern of airflow is strikingly birdlike, but the mechanism of the alligator valve is unknown. The fact that there is unidirectional flow in excised lungs rules out the possibility that muscular sphincters rectify the airflow. Although flapped-valves have not been ruled out, we have found no obvious structures that could serve this function. Furthermore, the bronchi are organized such that bird-like aerodynamic valves are a likely mechanism for the rectification. These data corroborate the hypothesis that unidirectional flow is a pleisiomorphic feature of archosaurs and that all archosaurs, including the crurotarsan lineage and the herbivorous dinosaurs.