Physiological Role of Intracardiac Shunting in Chelonians

海龟表现出间歇性通气模式，在短暂的通气期间穿插着不同持续时间的呼吸暂停。与这种通气模式相关的是肺和全身血流的循环变化。由于心脏的解剖结构，这些血流变化可能与右至左（R-L；肺旁路）和左至右（L-R；肺再循环）心内分流有关。这些心血管变化可影响肺部气体交换，影响CO2和O2的运输。心内分流的功能意义仍然主要是推测性的。本研究将确定间歇通气期间海龟心内分流的生理作用。具体来说，这项研究将确定；1)通气和呼吸暂停期间肺回路和全身回路（即R-L和L-R分流）之间的流量比；2)胆碱能和肾上腺素能阻断对心内分流的方向和大小的影响，以及这些影响与通气模式、肺气体交换和血气运输的变化之间的关系。研究将在25摄氏度的活体龟（pseudomyscripta）中进行。所有的目标都将在长期使用仪器，自由潜水，自然通气的动物中完成。连续测量肺部和全身血流、通气、气体交换、肺气体和血气。结果将在几个当前假设的背景下进行分析，以解决心脏内分流的呼吸“益处”。提出的假设不一定是新颖的，然而，本提案中概述的实验将首次专门研究这种独特类型的心血管调节的功能意义。

Turtles exhibit intermittent ventilatory patterns in which brief periods of ventilation are interspersed with apneas of variable duration. Associated with this ventilatory pattern are cyclic changes in pulmonary and systemic blood flow. Due to the anatomy of the heart, these changes in blood flow may be associated with both right-to-left (R-L; pulmonary bypass) and left-to-right (L-R; pulmonary recirculation) intracardiac shunting. These cardiovascular changes can influence pulmonary gas exchange, affecting both CO2 and O2 transport. The functional significance of intracardiac shunting has remained primarily speculative. This study will determine the physiological role of intracardiac shunting during intermittent ventilation in turtles. Specifically the study will determine; 1) the flow ratios between the pulmonary and systemic circuits (i.e. R-L and L-R shunts) during ventilation and apnea and 2) the effects of cholinergic and adrenergic blockade on the direction and magnitude of intracardiac shunt and correlate these effects with changes in ventilatory patterns, pulmonary gas exchanged and blood gas transport. Studies will be conducted in the turtle, Pseudemys scripta, in vivo at 25oC. All objectives will be accomplished in chronically instrumented, freely diving, spontaneously ventilating animals. Continuous measurements of pulmonary and systemic blood flows, ventilation, gas exchange, lung gases and blood gases will be made. The results will be analyzed within the context of several current hypotheses addressing the respiratory "benefits" of intracardiac shunting. The hypotheses presented are not necessarily novel, however, the experiments outlined in this proposal will for the first time specifically examine the functional significance of this distinctive type of cardiovascular regulation.