Mrowka Ralf, Cimponeriu Laura, Patzak Andreas, Rosenblum Michael G
Johannes-Müller Institut für Physiologie, Humboldt-Universität zu Berlin, Tucholskystrasse 2, D-10117 Berlin, Germany.
Am J Physiol Regul Integr Comp Physiol. 2003 Dec;285(6):R1395-401. doi: 10.1152/ajpregu.00373.2003. Epub 2003 Aug 7.
Activity of many physiological subsystems has a well-expressed rhythmic character. Often, a dependency between physiological rhythms is established due to interaction between the corresponding subsystems. Traditional methods of data analysis allow one to quantify the strength of interaction but not the causal interrelation that is indispensable for understanding the mechanisms of interaction. Here we present a recently developed method for quantification of coupling direction and apply it to an important problem. Namely, we study the mutual influence of respiratory and cardiovascular rhythms in healthy newborns within the first 6 mo of life in quiet and active sleep. We find an age-related change of the coupling direction: the interaction is nearly symmetric during the first days and becomes practically unidirectional (from respiration to heart rhythm) at the age of 6 mo. Next, we show that the direction of interaction is mainly determined by respiratory frequency. If the latter is less than approximately 0.6 Hz, the interaction occurs dominantly from respiration to heart. With higher respiratory frequencies that only occur at very young ages, the dominating direction is less pronounced or even abolished. The observed dependencies are not related to sleep stage, suggesting that the coupling direction is determined by system-inherent dynamical processes, rather than by functional modulations. The directional analysis may be applied to other interacting narrow band oscillatory systems, e.g., in the central nervous system. Thus it is an important step forward in revealing and understanding causal mechanisms of interactions.
许多生理子系统的活动具有明显的节律性特征。通常，由于相应子系统之间的相互作用，生理节律之间会建立起一种依赖关系。传统的数据分析方法能够量化相互作用的强度，但无法量化对于理解相互作用机制不可或缺的因果关系。在此，我们介绍一种最近开发的用于量化耦合方向的方法，并将其应用于一个重要问题。具体而言，我们研究了健康新生儿在出生后6个月内安静睡眠和主动睡眠期间呼吸节律与心血管节律的相互影响。我们发现耦合方向存在与年龄相关的变化：在出生后的头几天，相互作用几乎是对称的，而在6个月大时，实际上变为单向的（从呼吸到心律）。接下来，我们表明相互作用的方向主要由呼吸频率决定。如果呼吸频率低于约0.6赫兹，相互作用主要从呼吸到心脏发生。对于仅在非常小的年龄出现的较高呼吸频率，主导方向不太明显甚至消失。观察到的这些依赖关系与睡眠阶段无关，这表明耦合方向是由系统固有的动态过程决定的，而不是由功能调节决定的。这种方向性分析可应用于其他相互作用的窄带振荡系统，例如中枢神经系统。因此，这是在揭示和理解相互作用的因果机制方面向前迈出的重要一步。
