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 M?ller who were the first to demonstrate a clear circadian rhythm in respiratory chemoreflex responsiveness in awake human subjects. Raschke and M?llers 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 M?llers experimental design. Raschke and M?llers 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 M?ller. 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]

參考譯文

由于閾值和(或)化學敏感性的改變，化學感受器的反應特性各有不同。Koepchen等觀察到一天當中通氣量隨時間變化。但首次在覺醒的人體中證明了晝夜節(jié)律存在于呼吸化學感受器反射體系中的是Raschke和 Moller。Raschke和M6ller的主要發(fā)現(xiàn)是在高碳酸血癥和缺氧狀態(tài)下,通氣反射在傍晚達到頂峰而在清晨降到最低。這項實驗由兩個相互獨立的小組同時進行,以排除Raschke和M6ller在實驗設計中存在的潛在干擾因素。Raschke 和M6ller的基本研究結果證實反應細節(jié)方面存在的差異(如下討論)可能與晝夜節(jié)律在調節(jié)睡眠時對呼吸穩(wěn)定性所起得作用有關。Stephenson等發(fā)現(xiàn)在高碳酸血癥逐漸加重的情況下。呼吸反射在清晨6:20達到最低,與Raschke 和Moller的研究結果類似。Stephenson等同樣證實化學感受器閥值的變化對晝夜節(jié)律有間接的調節(jié)作用。相反，Spengler等發(fā)現(xiàn)呼吸反射的晝夜節(jié)律是由化學敏感性的晝夜節(jié)律調節(jié)的而不是由闕值調節(jié),而且反應的最低值出現(xiàn)在早晨而不是晚上。這些研究差異的原因并不清楚。很有可能是由于研究方法的不同所造成的。例如，Stephenson等是惟一一個直接通過再呼吸技術來檢測化學感受器閾值的小組。更進一步說,Stephenson等在輕度觖氧狀態(tài)下通過再呼吸刺激中樞和周圍化學感受器反射,而其他研究小組則是通過高碳酸血癥誘發(fā),因而只測量了中樞化學感受器反射的情況。

                                                        [《睡眠醫(yī)學》睡眠雜志，2006;(10)1016]

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