THE PHYSIOLOGY OF THE ALLIGATOR HEART: THE CARDIAC CYCLE
THE PHYSIOLOGY OF THE ALLIGATOR HEART: THE CARDIAC CYCLE
复制标题
鳄鱼心脏的生理学：心脏循环
DOI：
--
复制
发表时间：
1991
期刊：
影响因子：
--
通讯作者：
D. Jones
中科院分区：
文献类型：
--
作者：
G. Shelton;D. Jones
来自心脏和鳄鱼主要动脉的压力记录表明，左心室和右主动脉之间存在着传统的关系。在收缩期间，从脑室到主动脉的压力梯度非常小。右主动脉血流迅速上升至单峰，然后缓慢下降，直至关闭主动脉瓣。右心室既与肺动脉相连，又与左主动脉相连。右室压力显示收缩是一个两阶段的过程。最初，血液流向低阻力的肺循环，尽管整个肺流出道存在明显的压力梯度。肺流出道的活跃收缩停止了肺的射血，右室出现第二阶段的压力升高。当全身血压较高时，这种第二阶段的压力不会达到左主动脉的记录水平，左主动脉瓣膜保持关闭，以便肺和身体回路在功能上是分开的。在这些情况下，左主动脉出现血流交替，收缩时为反向血流，舒张期为正向血流。与右主动脉或肺动脉相比，血流速度极低，Panizza孔在心动周期中的意义也很小。如果全身血压较低，右室收缩的第二阶段会产生高于左主动脉的压力，左主动脉瓣膜打开，血液被排入体循环，形成从右向左的分流。这可以在不改变肺压力或流量的情况下发生。左主动脉血流不依赖于肺流出道收缩的增加，而肺流出道会继续起到开关活跃瓣的作用。在某些情况下，肺血管内的收缩在建立左主动脉血流中可能是重要的，但从目前的工作中可以清楚地看到，低体动脉压是一个至关重要的因素。
Pressure recordings from the heart and major arteries of the alligator show that a conventional relationship exists between the left ventricle and the right aorta. Pressure gradients from ventricle to aorta during systole are very small. Right aortic blood flow rises rapidly to a single peak and then falls more gradually until aortic valve closure. The right ventricle is connected both to the pulmonary arteries and to the left aorta. Right ventricular pressures show that systole is a two-stage process. Initially, blood leaves to the low-resistance lung circuit, though appreciable pressure gradients exist across the pulmonary outflow tract. Active contraction of the pulmonary outflow tract stops pulmonary ejection and a second-stage pressure rise is seen in the right ventricle. When systemic blood pressures are high, this second-stage pressure does not reach the levels recorded in the left aorta, and the left aortic valves remain closed so that lung and body circuits are functionally separate. An alternation of flow is found in the left aorta under these conditions, with reversed flow during systole and forward flow during diastole. Flow rates are extremely low, compared with those in the right aorta or pulmonary arteries, and the foramen of Panizza has very little significance in the cardiac cycle. If the systemic blood pressures are low, the second stage of systole in the right ventricle gives rise to pressures that are higher than those in the left aorta, the left aortic valves open and blood is ejected to the systemic circulation, giving a right-to-left shunt. This can occur with no changes in pulmonary pressures or flows. Left aortic flow is not dependent on increased constriction of the pulmonary outflow tract, which continues to function as an on-off active valve. Constriction within the lung vasculature may, on some occasions, be significant in establishing left aortic flow, but it is clear from the present work that low systemic blood pressure is a factor of crucial importance.