Chemoreflex response characteristics can vary due to a change in threshold and/or a change in chemosensitivity (slope of the chemoreflex response curve). Koepchen et al. observed an apparent variation of ventilatory control with time of day, but it was Raschke and Möller who were the first to demonstrate a clear circadian rhythm in respiratory chemoreflex responsiveness in awake human subjects. Raschke and Möllers mainfinding was that ventilatory responsiveness to hypercapnia and hypoxia reached a peak in late afternoon and decreased to a minimum in early morning. This question was revisited independently and concurrently by two research groups employing the constant routine protocol to exclude potential confounds in Raschke and Möllers experimental design. Raschke and Möllers basic results were corroborated,although there were differences in some of the detailed response and,as is discussed later,these differences may be relevant to the possible role of circadian rhythms in modulating the propensity for respiratory instability during sleep. Stephenson et al. observed a significant circadian rhythm in respiratory responsiveness to progressive hypercapnia with a minimun at 6:20 a. m., similar to that of the subjects studied by Raschke and Möller. The study by Stephenson et al. also confirmed that the circadian rhythm was mediated mainly by changes in chemoreflex threshold. In contrast, Spengler et al. found that the circadian rhythm in respiratory responsiveness was mediated by a circadian rhythm in chemosensitivity (slope)rather than estimated threshold (x-intercept), and the minimum of the response was at the beginning rather than near the end of the subjective night. The reasons for these discrepancies between studies are not clear but likely derive from methodological differences. For example,the study by Stephenson et al. was the only one to measure chemoreflex threshold directly through the use of a rebreathing technique specifically modified for that purpose. Further more, Stephenson et al. included mild hypoxia in the rebreathing test to stimulate both central and peripheral chemoreflexes, whereas the other studies used hyperoxia and thereby measured only the central chemoreflex.

                                   [《Sleep Medicine).j.sleep,2006;(10)1016]

参考译文

由于阈值和(或)化学敏感性的改变，化学感受器的反应特性各有不同。Koepchen等观察到一天当中通气量随时间变化。但首次在觉醒的人体中证明了昼夜节律存在于呼吸化学感受器反射体系中的是Raschke和 Moller。Raschke和M6ller的主要发现是在高碳酸血症和缺氧状态下,通气反射在傍晚达到顶峰而在清晨降到最低。这项实验由两个相互独立的小组同时进行,以排除Raschke和M6ller在实验设计中存在的潜在干扰因素。Raschke 和M6ller的基本研究结果证实反应细节方面存在的差异(如下讨论)可能与昼夜节律在调节睡眠时对呼吸稳定性所起得作用有关。Stephenson等发现在高碳酸血症逐渐加重的情况下。呼吸反射在清晨6:20达到最低,与Raschke 和Moller的研究结果类似。Stephenson等同样证实化学感受器阀值的变化对昼夜节律有间接的调节作用。相反，Spengler等发现呼吸反射的昼夜节律是由化学敏感性的昼夜节律调节的而不是由阙值调节,而且反应的最低值出现在早晨而不是晚上。这些研究差异的原因并不清楚。很有可能是由于研究方法的不同所造成的。例如，Stephenson等是惟一一个直接通过再呼吸技术来检测化学感受器阈值的小组。更进一步说,Stephenson等在轻度觖氧状态下通过再呼吸刺激中枢和周围化学感受器反射,而其他研究小组则是通过高碳酸血症诱发,因而只测量了中枢化学感受器反射的情况。

                                                        [《睡眠医学》睡眠杂志，2006;(10)1016]

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