The Interaction of Cardiac Shunting and Metabolic Rate: Triggering Hypometabolism During Diving

150多年前，比较生物学家就已经知道，爬行动物心脏的解剖结构可能导致心脏分流（贫氧和富氧血液的混合）。心脏分流可以定义为右至左（左至左缺氧血液绕过肺）或左至右（左至右富氧血液通过肺循环）。在一些爬行动物中，在潜水期间会发生R-L心脏分流，导致血氧水平迅速降低。这种类型的心血管调节的生理益处仍然难以捉摸和推测。希克斯博士提出的这项研究将调查一种假设，即由左心室分流引起的血氧水平降低会引发新陈代谢的减少。新陈代谢的减少被称为“低代谢状态”，可以有几个生理上的好处，特别是在长时间潜水期间。本研究将通过研究心脏分流对淡水龟、美洲鳄、密西西比鳄和绿鬣蜥代谢的影响来验证这一假设的普遍性。这些物种具有几个特征，使它们成为很好的实验模型，包括；1)所有物种都表现出潜水行为，无论是自愿的还是在逃避行为中；2)所有物种都很容易获得；3)它们足够大，可以支持所需的生理仪器。拟议的研究将通过实验测试爬行动物独特的心血管“设计”所产生的潜在生理功能，并将为保留心脏分流能力的功能后果提供见解。

Comparative biologists have known for more than 150 years that the anatomy of the reptilian heart results in the potential for cardiac shunts (mixing of oxygen poor and oxygen rich blood). Cardiac shunts can be defined as right-to-left (R-L oxygen poor blood bypasses the lung) or left-to-right (L-R oxygen rich blood recirculates through the lung). In several reptiles an R-L cardiac shunt can develop during diving resulting in a rapid reduction of the blood oxygen levels. The physiological benefits of this type of cardiovascular regulation have remained elusive and speculative. The proposed research by Dr. Hicks will investigate the hypothesis that reductions in blood oxygen levels, resulting from the development of a R-L cardiac shunt, triggers a reduction in metabolism. The reduction in metabolism is referred to as a "hypometabolic state" and can have several physiological benefits, particularly during prolonged diving. The proposed research will test the generality of the hypothesis by investigating the effects of cardiac shunting on metabolism in the freshwater turtle, Trachemys scripta, American Alligator, Alligator mississippiensis and green iguana, Iguana iguana. These species possess several characters that make them good experimental models that include; 1) all exhibit diving behavior, either voluntarily or during escape behavior, 2) all species are readily available and 3) they are large enough to support the required physiological instrumentation. The proposed research will experimentally test a potential physiological function that results from the unique cardiovascular "design" of reptiles and will provide insights into the functional consequences of retaining the capacity for cardiac shunting.