Effects of Vestibular Loss on Orthostatic Mechanisms

当直立时，保持稳定的血压受到直立（流体静力）柱延长的挑战。我们假设前庭耳石器官提供短潜伏期的方向信息，有助于在姿势变化过程中的自主心肺调节。该假设将通过首先比较从不同方向直立倾斜期间的血压和循环的非侵入性测量来进行测试，这些方向提供相同的立位应力但对耳石提供不同的刺激。我们预测，由于对耳石的不同刺激，健康受试者对直立倾斜的早期心肺反应将取决于倾斜的方向而不同，而在直立倾斜的后期部分期间的反应将是相似的，而不管倾斜的方向如何，这是由于其他心肺（例如，压力反射）机制。其次，我们将通过比较已知双侧前庭缺陷受试者的倾斜数据与年龄和性别匹配的健康个体的相应数据，评估前庭损失对直立机制的影响。我们预测，无论倾斜方向如何，前庭功能丧失患者对直立倾斜的早期心肺反应都会受到影响。将在一个阶段期间测试12名双侧前庭功能丧失的受试者和12名健康受试者，该阶段包括四次10分钟的倾斜，眼睛从水平方向闭合到80度直立（仰卧-俯仰倾斜、俯卧-俯仰倾斜、右耳下滚倾斜和左耳下滚倾斜）.在倾斜刺激期间将测量动脉血压、心率、每搏输出量、外周血管阻力、呼气末CO2、呼吸速率和呼吸量、脑血流速度和脑血管阻力的调节。在第二组实验中，将评估耳石对立位反应的贡献，因为受试者以不同的频率围绕地球水平轴连续旋转，头部朝向正前方或转向侧面。我们预测，在健康受试者中，心肺反应将被调制为相对于重力和频率的头部方向的函数，但在双侧前庭缺陷的受试者中则不然。这项研究将提供新的信息，前庭损失如何可能增加直立不耐受的易感性，并将提供新的见解耳石自主人类受试者。

When standing upright, the maintenance of stable blood pressure is challenged by the lengthening of the orthostatic (hydrostatic) column. We hypothesize that the vestibular otolith organs provide short-latency orientation information that contributes to autonomic cardio-respiratory regulation during changes in posture. This hypothesis will be tested by first comparing non-invasive measurements of blood pressure and circulation during upright tilts from different orientations that provide the same orthostatic stress but different stimuli to the otoliths. We predict that due to varying stimuli to the otoliths, the early cardio- respiratory responses to upright tilt in healthy subjects will differ depending on the direction of tilt whereas responses during the later portions of upright tilt will be similar regardless of the direction of tilt due to activation of other cardio-respiratory (e.g., baroreflex) mechanisms. Second, we will assess the effects of vestibular loss on orthostatic mechanisms by comparing tilt data from subjects with known bilateral vestibular deficiency to corresponding data from healthy individuals matched for age and gender. We predict the early cardio-respiratory responses to upright tilt in patients with vestibular loss will be compromised regardless of the direction of tilt. Twelve subjects with bilateral loss of vestibular function and twelve healthy subjects will be tested during one session consisting of four 10 min tilts performed with eyes closed from a horizontal orientation to 80 deg upright (supine - pitch tilt, prone - pitch tilt, right ear down - roll tilt and left ear down - roll tilt). Modulation of arterial blood pressure, heart rate, stroke volume, peripheral vascular resistance, end-tidal C02, respiratory rate and volume, cerebral blood flow velocity and cerebrovascular resistance will be measured during the tilt stimuli. During a second set of experiments, the contribution of the otoliths to orthostatic responses will be assessed as subjects are continuously rotated about an earth horizontal axis at varying frequencies with head facing straight ahead or turned to the side. We predict that cardio- respiratory responses will be modulated as a function of head orientation relative to gravity and frequency in healthy subjects but not in subjects with bilateral vestibular deficiency. This study will provide new information on how vestibular loss might increase susceptibility for orthostatic intolerance, and will provide new insights on otolith- autonomic human subjects.