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

比较生物学家早在150多年前就知道，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)。心脏分流可定义为从右到左(R-L贫血绕肺)或从左到右(L-R富氧血液通过肺循环)。在几种爬行动物身上，R-L心脏分流会在潜水过程中发生，导致血氧水平迅速下降。这种类型的心血管调节的生理益处仍然是难以捉摸和推测的。希克斯博士提出的这项研究将调查这样一种假设，即R-L心脏分流术后血氧水平降低会引发新陈代谢减少。新陈代谢的降低被称为“低代谢状态”，可能有几种生理益处，特别是在长时间潜水时。这项拟议的研究将通过研究心脏分流对淡水海龟、Trachemys Scripta、美洲鳄、扬子鳄和绿色鬣蜥代谢的影响来检验这一假说的普遍性。这些物种具有使它们成为很好的实验模型的几个特征，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逸行为中的；2)所有物种都很容易获得；3)它们足够大，足以支持所需的生理仪器。这项拟议的研究将在实验上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.