Cardiopulmonary Function in Archosaurs During Hypoxic Exercise

众所周知，鸟类可以在氧气分压低到哺乳动物无法活动的高度飞行，但不知道鸟类的姐妹群鳄鱼是否有生理反应和肺部结构来支持缺氧条件下的活动。低氧条件会导致动物过度呼吸，从而降低血液中二氧化碳（CO2）的张力。 低二氧化碳压力反过来又减少了哺乳动物大脑的血流量，导致定向障碍甚至死亡。 相比之下，鸟类耐受低血液CO2水平而没有这些不良影响。 此外，鸟的肺中的空气和血液流动的模式（交叉流设计）促进了在低氧条件下血液的氧气吸收。鸟类和鳄鱼有着共同的祖先，可以追溯到中生代，与今天的大气相比，当时的环境缺氧。让鸟类在缺氧环境中发挥作用的特征是原始的祖龙特征还是它们的衍生？ 如果他们是祖先，那么在缺氧条件下运动的特殊能力可能部分解释了为什么祖龙统治了中生代的陆地动物群。 为了解决这些问题，该项目将研究空气和血液如何在美国短吻鳄的肺部移动，以及低二氧化碳压力是否会影响脑血流量。 这些研究将阐明鳄鱼和鸟类肺部系统之间的进化联系。这项研究将测试鳄鱼有一个简单的横流肺设计的假设，如果正确的话，那么只有一些小的修改将是必要的进化更复杂的禽肺。因此，这项研究将潜在地影响科学界和非科学界，因为它将深入了解祖龙为什么以及如何统治中生代，并可能为鸟类肺部的进化提供合理的解释。 这一项目还将支持对学生的培训，包括那些来自理科人数不足群体的学生。

It is well known that birds can fly at altitudes where the partial pressure of oxygen is so low that mammals cannot function, but it is not known whether the sister group of birds, the crocodilians, have the physiological responses and pulmonary structures to support activity in hypoxic conditions. Conditions of low oxygen cause animals to breathe excessively, which then reduces the tension of carbon dioxide (CO2) in their blood. Low CO2 tension in turn reduces blood flow to the brain of mammals, leading to disorientation and even death. In contrast birds tolerate low blood CO2 levels without these adverse effects. Furthermore the pattern of air and blood flow in the lungs of birds, a crosscurrent design, facilitates the absorption oxygen by blood under conditions of low oxygen. Birds and crocodilians share a common ancestor dating back to the Mesozoic, a time of environmental hypoxia compared to today's atmosphere. Are the features that allow birds to function in environmental hypoxia a primitive archosaur trait or are they derived? If they were present ancestrally, then an exceptional ability to exercise under conditions of hypoxia may partially explain why archosaurs dominated the Mesozoic terrestrial fauna. To address these questions this project will study how air and blood move in the lungs of American alligators, as well as whether low CO2 tension affects brain blood flow. These studies will shed light on the evolutionary connections between the crocodilian and avian pulmonary systems. This research will test the hypothesis that crocodilians have a simple crosscurrent lung design and, if correct, then only a few small modifications would be requisite for evolution of the more complex avian lung. Thus, this research will potentially impact both the scientific community and the lay community, because it will provide insight into why and how archosaurs dominated the Mesozoic and it may provide a plausible explanation for the evolution of the avian lung. This project will also support the training of students, including those from groups underrepresented in the sciences.