Regulation of Intracardiac Shunting in Chelonians

龟类动物表现出长时间不呼吸而生存的非凡能力。例如，在水生海龟潜水时，观察到1至2小时的呼吸。心脏是海龟潜水时非凡的呼吸能力中起关键作用的器官。海龟的心脏只有3个腔室（与哺乳动物和人类的4个腔室相比）。这种独特的解剖结构使得血液从体内回流，要么通过肺部循环，要么绕过肺部。当血液绕过肺部时，它被称为右至左心内分流。先前的科学研究报告称，绕过肺部的血液量通常与呼吸模式有关，在呼吸过程中，从右到左的分流增加。相反，在呼吸过程中，循环到肺部的血液量增加，右至左分流减少。虽然从右到左的大分流会对哺乳动物和人类产生有害的结果，但爬行动物绕过肺部的能力可能在呼吸过程中发挥了几个重要作用。这些措施包括减少心脏的能量消耗，“计量”肺中的氧气（类似于水肺），以及维持肺和血液之间的液体平衡。然而，海龟心脏完成不同程度血液分流的精确过程一直存在争议，也没有得到很好的理解。Hicks博士提出的这项研究将结合复杂的放射技术、血流测量和注射示踪气体来对心脏进行成像，并确定在各种生理条件下心脏的血流模式。Hicks博士提案中概述的这些技术和实验将确定血液分流过程是由心脏外部因素（即肺的调节）还是心脏内在因素引起的，从而了解脊椎动物心血管系统的进化发展。他对爬行动物血液分流机制的阐述将有助于回答血液分流在这一古老但重要的动物群体中扮演什么功能角色的问题。

Turtles (chelonians) exhibit the remarkable ability to survive long periods without breathing. For example during diving in aquatic turtles, breatholds for 1 to 2 hours have been observed. The organ that plays a critical role in the turtles remarkable breatholding ability during diving is the heart. The heart of the turtle is comprised of only 3 chambers (as compared to the 4 chambers of mammals and humans). The unique anatomy results in the potential for the blood returning from the body to either circulate through the lungs or to bypass the lungs. When the blood bypasses the lungs it is referred to as a right-to-left intracardiac shunt. Previous scientific investigations have reported that the amount of blood bypassing the lung is often coupled with ventilatory patterns, with the right-to-left shunt increasing during breatholding. In contrast, during breathing the amount of blood circulating to the lungs increases and the right- to-left shunt is reduced. While a large right-to-left shunt would produce harmful results in mammals and humans, the ability of reptiles to bypass the lungs may play several important roles during breatholding. These include reducing the energy expenditure of the heart, the "metering" of oxygen from the lung (analogous to a scuba tank) and maintaining the balance of fluids between the lung and blood. However, the precise process by which the heart of turtles can accomplish varying levels of blood shunting have been controversial and not well understood. The study proposed by Dr. Hicks will utilize a combination of sophisticated radiological techniques, blood flow measurements and injections of tracer gases to image the heart and determine blood flow patterns through the heart during a variety of physiological conditions. These techniques and the experiments outlined in Dr. Hicks' proposal will determine if the process of blood shunting results either from factors external to the heart (i.e. regulation by the lung) or factors intrinsic to the heart to understanding the evolutionary development of the cardiovascular system in vertebrate animals. His elucidation of the mechanism of blood shunting in reptiles will help to answer the question of what functional role blood shunting plays in this ancient but important group of animals.