OTOLITH INFLUENCES ON SYMPATHETIC ACTIVITY

这项研究验证了前庭系统耳石器官中的活动通过自主神经系统影响心血管功能并有助于维持立位耐力的假设。使用专门设计的离心机，受试者的耳石器官将被选择性地沿不同方向以线加速激活，而交感神经活动将使用新开发的微型显微神经像仪直接测量。在具体目标1中，受试者将在相对于旋转轴的不同方向上以恒定的速度进行离心，从而在广泛的方向和幅度上相对于头部和身体有重力惯性加速度(GIA)的倾斜。这将确定交感神经最大激活的平面，并测试前庭对交感神经流出的调制响应于重力惯性加速度(GIA)向量相对于头部的特定倾斜的假设。在离心过程中，将头部放置在身体上的不同角度将控制非前庭因素的潜在影响。在特定的目标中，2名受试者将以较高的频率(1至3赫兹)进行正弦平移，并以较低的频率(0.01至0.7赫兹)进行离心和平移，以确定最大限度地增加肌交感神经活动(MSNA)的线性加速度频率。将进行频谱分析，以检验自主神经流出不仅与耳石感受器沿特定方向激活有关，而且还与特定频率的激活有关的假设。特定目标3测试耳石有助于交感神经流出的增加，从而维持立位血流动力学的假设。通过沿Z轴的离心法模拟立位挑战，将诱导Legward体液移动。这将在头部处于旋转中心的情况下进行，这样耳石就不会受到线加速度的影响，或者头部在一定的速度范围内偏离旋转中心。将人体暴露在不同的速度和重力下会引起流体的渐变变化，这种变化将通过节段性身体阻抗曲线直接测量，并且阻抗和交感神经活动的变化将被关联。假设MSNA在耳石刺激下有较高的增益，从而揭示了耳石对交感神经激活的贡献。这项研究完成后，将加强对耳石对各种方向、频率和幅度上线加速度的交感反应的了解，并有助于确定耳石如何有助于维持心血管功能。

This research tests the hypothesis that activity arising in the otolith organs of the vestibular system influences cardiovascular function via the autonomic nervous system and contributes to maintenance of orthostatic tolerance. The otolith organs of human subjects will be selectively activated with linear acceleration along various directions, using a specially-designed centrifuge, while sympathetic nerve activity is directly measured, using a newly developed, miniaturized microneurography apparatus. In Specific Aim 1, subjects will be centrifuged at constant velocity in different orientations relative to the axis of rotation, so that there are tilts of gravito-inertial acceleration (GIA) relative to the head and body over a wide range of directions and magnitudes. This will determine the planes of maximal sympathetic activation and test the hypothesis that vestibular modulation of sympathetic outflow responds to specific tilts of the gravito-inertial acceleration (GIA) vector with regard to the head. Positioning the head on the body at different angles during centrifugation will control potential influences of non-vestibular factors. In Specific Aim 2 subjects will be translated sinusoidally at higher frequencies (1 to 3 Hz), and centrifuged and translated at lower frequencies (0.01 to 0.7 Hz) to determine the frequencies of linear acceleration that maximally increase muscle sympathetic nerve activity (MSNA). Spectral analyses will be done to test the hypothesis that autonomic outflow is related to activation of otolith receptors not only along specific directions, but also at specific frequencies. Specific Aim 3 tests the hypothesis that the otoliths contribute to the increase in sympathetic outflow that maintains orthostatic hemodynamics. Legward fluid shifts will be induced that simulate orthostatic challenge using centrifugation along the Z-axis. This will be done either with the head at the center of rotation, so that otoliths are not exposed to linear acceleration or with the head off the center of rotation over a range of velocities. Exposing the body to different velocities and gravitational forces will induce graded fluid shift changes, which will be directly measured via segmental body impedance profiles, and changes in impedance and sympathetic activity will be correlated. It is hypothesized that MSNA will have a higher gain in the presence of otolith stimulation, thereby revealing the contribution of the otoliths to sympathetic activation. When this research is completed, it will enhance understanding of otolith-sympathetic responses to linear acceleration over a wide range of directions, frequencies and magnitudes, and help determine how the otoliths contribute to maintenance of cardiovascular function.