BAROREFLEX HYSTERESIS AND ARTERIAL STIFFNESS

这项研究将从机制上描述动脉压力反射控制的一个鲜为人知的方面，它可以影响全身动脉压的调节。动脉压与心脏周期的关系不是简单地描述乙状窦，而是表现出一种迟滞。也就是说，心期反应取决于压力变化的方向；在任何压力下，心率下降时比上升时慢。动脉气压反射的这一特征可能具有重要的临床意义，特别是在了解低血压综合征方面。这项工作将检查压力反射滞后的可能关键成分-压力感觉血管扩张性。较小的膨胀率不仅会改变气压反射的灵敏度，而且会增加气压反射的滞后。如果迟滞因动脉硬化而被夸大，仅这一点就会对低血压刺激产生不一致的心率反应，导致脑血流量减少和晕厥。快速药物诱导的动脉压力变化将被用来通过整个反射范围来表征自主压力反射滞后。自主反应和压力变化将与颈动脉压力感觉血管拉伸的同时测量有关，以检查压力反射滞后的粘弹性成分。由于主要的拉伸决定了压力感觉血管的扩张性，因此在两种不同拉伸水平的情况下（仰卧和45度倾斜），将表现为迟滞。由于颈动脉僵硬度较高的个体可能表现出不适应的夸张迟滞，因此这些关系不仅将在血压正常者中进行研究，而且还将在先前已显示颈动脉僵硬度较高的中年高血压患者中进行研究。这项工作可能为理解有序高血压和高血压个体中动脉压力失调的高患病率提供关键见解。

This research will mechanistically describe a poorly understood aspect of arterial baroreflex control which can impact the regulation of systemic arterial pressure. The arterial pressure - heart period relation does not simply describe a sigmoid, but demonstrates a hysteresis. That is, heart period responses depend on the direction of pressure change; at any pressure, heart rates are slower during falls than during rises. This characteristic of the arterial baro-reflex may have significant clinical import especially in understanding hypotensive syndromes. This work will examine the likely key component of baroreflex hysteresis -- barosensory vessel distensibility. Lesser distensibility may not only alter baroreflex sensitivity, but also augment baroreflex hysteresis. If hysteresis is exaggerated by arterial stiffening, this alone could produce discordant heart rate responses to hypotensive stimuli, leading to reduced cerebral blood flow and syncope. Rapid pharmacologically induced arterial pressure changes will be used to characterize autonomic baroreflex hysteresis through the full reflex range. The autonomic responses and pressure changes will be related to concurrent measures of carotid barosensory vessel stretch to examine the viscoelastic component of baroreflex hysteresis. Since the prevailing stretch determines barosensory vessel distensibility, hysteresis will be characterized under two conditions to vary the level of stretch (supine and 45 tilt). Since individuals with greater carotid stiffness may demonstrate a maladaptive exaggerated hysteresis, these relationships will be examined not only in normotensives but also in middle aged hypertensives who have been shown previously to have greater carotid stiffness. This work may provide key insight to understand the high prevalence of arterial pressure dysregulation in order and hypertensive individuals.