Scientists C. Farmer and Kent Sanders decided to study the flow of air through alligator lungs because the parabronchi of these lungs were anatomically similar to those of birds. This similarity would suggest that alligators breathe in the same way that birds do which is unidirectional, or air flows one way. Mammalian breathing differed from this mode because mammals have air sacs where air flows into the alveolar sac, and then back out the same way it came in. These alveolar sacs are a type of dead end where the air must escape out the way it came in. This type of breathing is less efficient and these researchers say that uni-directional breathing is most efficient because it allows for the most oxygen to be extracted per breath.
The unidirectional breathing in alligators was studied by using false or artificial breathing of lungs that had been extracted from dead American alligator specimens. A second method they used was to surgically implant a flow meter, which is also called a thermistor, into parabronchi of these live American alligators. As a final method, the research team filled lungs that had been dissected from dead specimens with saline and florescent beads which allowed them to visually view the airflow. All of these research methods pointed to and proved that air flow in alligator lungs was indeed uni-directional.
This discovery is interesting because it shows that bellow like air sacs are not needed for uni-directional breathing as they are in birds. Through this study it was determined that hepatic ventilation was not a determinate in whether or not uni-directional breathing was possible. Hepatic ventilation is when alligators use their liver to help them breathe. Finally, this discovery showed that unidirectional breathing was present in stem archosaurs, or stem birds and reptiles. Because of the efficiency of unidirectional breathing this could also be a factor as to why dinosaurs dominated synapsids in their ability to compete for territories.
Find the entire article here: http://www.sciencemag.org/cgi/content/abstract/327/5963/338?ijkey=03a6289af67ef7ae6ba7a017416e503f373c1c51&keytype2=tf_ipsecsha