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正常活动的高度飞行，但我们不知道鸟类的姐妹类鳄鱼是否具有在缺氧条件下支持活动的生理反应和肺结构。低氧环境会导致动物过度呼吸，从而降低血液中的二氧化碳浓度。低二氧化碳浓度反过来会减少哺乳动物大脑的血流量，导致迷失方向甚至死亡。相比之下，鸟类可以忍受血液中的低二氧化碳水平，而不会产生这些副作用。此外，鸟类肺部的空气和血液流动模式是一种交叉流设计，有助于血液在低氧条件下吸收氧气。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。让鸟类在环境缺氧中发挥作用的特征是原始祖龙的特征还是衍生出来的？如果它们在祖先时期就存在，那么在缺氧条件下的特殊运动能力可能部分解释了为什么祖龙在中生代陆生动物群中占主导地位。为了解决这些问题，这个项目将研究空气和血液如何在美国短吻鳄的肺部运动，以及低二氧化碳浓度是否会影响脑血流量。这些研究将阐明鳄鱼和鸟类肺系统之间的进化联系。这项研究将验证鳄鱼具有简单的交叉流肺设计的假设，如果正确的话，那么对于更复杂的鸟类肺的进化只需要一些小的修改。因此，这项研究将对科学界和非专业人士产生潜在的影响，因为它将深入了解祖龙为什么和如何统治中生代，并可能为鸟类肺的进化提供一个合理的解释。该项目还将支持培训学生，包括来自科学领域代表性不足群体的学生。

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.