Regulation of Intracardiac Shunting in Chelonians

海龟(海龟)表现出在没有呼吸的情况下长时间存活的非凡能力。例如，在水生海龟潜水时，可以观察到1到2个小时的呼吸声。在潜水过程中，对海龟非凡的屏气能力起关键作用的器官是心脏。海龟的心脏只有3个腔(与哺乳动物和人类的4个腔相比)。独特的解剖结构导致了血液从体内返回的可能性，要么通过肺部循环，要么绕过肺部。当血液绕过肺部时，它被称为从右向左的心内分流。此前的科学研究报告称，绕过肺的血量往往与呼吸模式有关，屏气时从右向左的分流会增加。相反，在呼吸过程中，循环到肺部的血量增加，从右向左的分流减少。虽然从右向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在屏气过程中可能扮演着几个重要的角色。这些措施包括减少心脏的能量消耗，从肺中“计量”氧气(类似于水肺水箱)，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确切过程一直存在争议，也没有被很好地理解。希克斯博士提出的这项研究将结合使用尖端的放射学技术、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通过心脏的血流模式。这些技术和希克斯博士提案中概述的实验将确定血液分流过程是由心脏外部因素(即肺的调节)还是心脏内在因素造成的，以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明将有助于回答血液分流在这一古老而重要的动物群体中扮演的功能角色的问题。

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.