Vestibulosympathetic Reflexes in Humans

描述(申请人提供)：首席调查员的长期目标是评估调节人类心血管系统的前庭反射机制。在过去的资助期间，我们证明了耳石器官的激活介导了交感神经活动和肢体血管阻力的迅速和显著增加。这个项目的主要假设是，前庭交感神经反射通过激活人类的交感神经系统，在正位站立中发挥重要作用。据推测，前庭交感神经反射的减弱有助于人类的立位不耐受。为了验证这些假设，我们提出了以下特定目标的研究：1.确定动态俯仰旋转时的肌肉交感神经活动(MSNA)反应。从仰卧位到直立位的转换和行走动态地刺激耳石器官，因此，确定动态激活耳石器官是否会引起交感血管收缩流出增加是很重要的。我们假设MSNA的更大增长将由耳石器官的动态接触而不是静态接触引起。2.测定俯卧位、坐位和直立位MSNA对耳石器官刺激的反应。由于直立姿势最重要的是体位血压控制，因此我们将测试坐姿和站姿旋转头部时的前庭交感神经反射。我们假设，通过头向下旋转的前庭交感神经反射增加的MSNA与身体姿势无关。3.测定内脏血管对静止头低位旋转的反应。因为内脏血管收缩对体位血压调节有重要作用，我们假设前庭的激活将调节内脏血管阻力的增加。4.观察立位耐受性易感性受试者对耳石器官刺激的交感神经和血流动力学反应。我们假设，在立位耐受性受试者(即，前庭缺陷和特发性直立性低血压受试者，以及经过耐力训练的运动员)激活前庭交感神经的过程中，MSNA反应将减弱，血压降低。这些研究的设计将增加我们对前庭系统如何对人类立位血压调节做出贡献的理解。

DESCRIPTION (provided by applicant): The long-term objective of the Principal Investigator is to evaluate vestibular reflex mechanisms that regulate the cardiovascular system in humans. During the past funding period, we demonstrated that activation of the otolith organs mediated prompt and marked increases in sympathetic nerve activity and limb vascular resistance. The main hypothesis for this project is that the vestibulosympathetic reflex participates importantly in orthostasis by activating the sympathetic nervous system in humans. It is hypothesized that attenuations in the vestibulosympathetic reflex contributes to orthostatic intolerance in humans. To test these hypotheses, we propose studies with the following specific aims: 1. To determine muscle sympathetic nerve activity (MSNA) responses during dynamic pitch rotation. Transition from the supine to upright posture and ambulation dynamically stimulate the otolith organs Therefore, it is important to determine whether dynamic activation of the otolith organs elicits increases in sympathetic vasoconstrictor outflow. We hypothesize greater increases in MSNA will be elicited by dynamic rather than static engagement of the otolith organs. 2. To determine MSNA responses to otolith organ stimulation in the prone, sitting, and upright positions. Because postural blood pressure control is most important in the upright posture, we will test the vestibulosympathetic reflex during head rotations in the sitting and standing positions. We hypothesize that increases in MSNA by the vestibulosympathetic reflex via head-down rotation is independent of body posture. 3. To determine visceral vascular responses to static head-down rotation. Because visceral vascular vasoconstriction contributes importantly to postural blood pressure regulation, we hypothesize that vestibular activation will mediate increases in visceral vascular resistance. 4. To examine sympathetic and hemodynamic responses to otolith organ stimulation in subjects with a predisposition to orthostatic intolerance. We hypothesize that MSNA responses will be attenuated and blood pressure reduced during activation of the vestibulosympathetic in subjects with orthostatic intolerance (i.e., vestibular deficient and idiopathic orthostatic hypotension subjects, and endurance trained athletes). The design of these studies will increase our understanding of how the vestibular system contributes to orthostatic blood pressure regulation in humans.