ABSTRACT

Animal and human studies demonstrate anatomical and functional links between the vestibular nuclei and the circadian timing system. This promotes the hypothesis of a circadian rhythm of vestibular function. The objective of this study was to evaluate the vestibular function through the vestibulo-ocular reflex using a rotatory chair at different times of the day to assess circadian rhythmicity of vestibular function. Two identical studies evaluating temporal variation of the vestibulo-ocular reflex (VOR) were performed, the first in young adults (age: 22.4 ± 1.5 y), and the second in older adults (70.7 ± 4.7 y). The slow phase velocity and time constant of the VOR were evaluated in six separate test sessions, i.e., 02:00, 06:00, 10:00, 14:00, 18:00, and 22:00 h. In both studies, markers of circadian rhythmicity (temperature, fatigue, and sleepiness) displayed expected usual temporal variation. In young adults, the time constant of the VOR showed variation throughout the day (p < .005), being maximum 12:25 h (06:00 h test session) before the acrophase of temperature circadian rhythm. In older adults, the slow phase velocity and time constant also displayed temporal variation (p < .05). Maximum values were recorded at 10:35 h (06:00 h test session) before the acrophase of temperature circadian rhythm. The present study demonstrates that vestibular function is not constant throughout the day. The implication of the temporal variation in vestibular system in equilibrium potentially exposes the elderly, in particular, to differential risk during the 24 h of losing balance and falling.

摘要

动物和人类研究证明了前庭神经核和昼夜节律计时系统之间的解剖和功能联系。这促进了前庭功能昼夜节律的假设。本研究的目的是在一天中的不同时间使用旋转椅通过前庭眼反射来评估前庭功能，以评估前庭功能的昼夜节律性。进行了两项相同的评估前庭眼反射 (VOR) 时间变化的研究，第一项是年轻人（年龄：22.4 ± 1.5 岁），第二项是老年人（70.7 ± 4.7 岁）。VOR 的慢相速度和时间常数在六个单独的测试阶段进行评估，即 02:00、06:00、10:00、14:00、18:00 和 22:00 h。在这两项研究中，昼夜节律的标志物（温度、疲劳、和困倦）显示出预期的通常时间变化。在年轻人中，VOR 的时间常数在一天中表现出变化（p < .005)，在体温昼夜节律的高峰期之前的最大 12:25 小时（06:00 小时测试时段）。在老年人中，慢相速度和时间常数也显示出时间变化 ( p < .05)。在温度昼夜节律的顶点之前的 10:35 小时（06:00 小时测试时段）记录了最大值。本研究表明，前庭功能并非全天恒定。平衡中前庭系统的时间变化的含义可能使老年人，特别是在失去平衡和跌倒的 24 小时内面临不同的风险。