Department of Physiology, Comenius University, Jessenius Faculty of Medicine, Martin, Slovak Republic.
Physiol Meas. 2012 Oct;33(10):1747-56. doi: 10.1088/0967-3334/33/10/1747. Epub 2012 Sep 26.
Time irreversibility is a characteristic feature of non-equilibrium, complex systems such as the cardiovascular control mediated by the autonomic nervous system (ANS). Time irreversibility analysis of heart rate variability (HRV) and blood pressure variability (BPV) represents a new approach to assess cardiovascular regulatory mechanisms. The aim of this paper was to assess the changes in HRV and BPV irreversibility during the active orthostatic test (a balance of ANS shifted towards sympathetic predominance) in 28 healthy young subjects. We used three different time irreversibility indices-Porta's, Guzik's and Ehler's indices (P%, G% and E, respectively) derived from data segments containing 1000 beat-to-beat intervals on four timescales. We observed an increase in the HRV and a decrease in the BPV irreversibility during standing compared to the supine position. The postural change in irreversibility was confirmed by surrogate data analysis. The differences were more evident in G% and E than P% and for higher scale factors. Statistical analysis showed a close relationship between G% and E. Contrary to this, the association between P% and G% and P% and E was not proven. We conclude that time irreversibility of beat-to-beat HRV and BPV is significantly altered during orthostasis, implicating involvement of the autonomous nervous system in its generation.
时间不可逆性是心血管自主神经调节等非平衡、复杂系统的特征。心率变异性（HRV）和血压变异性（BPV）的时间不可逆性分析代表了评估心血管调节机制的一种新方法。本文旨在评估 28 名健康年轻受试者在主动直立测试期间（自主神经平衡向交感神经优势转移）HRV 和 BPV 不可逆性的变化。我们使用了三种不同的时间不可逆性指数——Porta 指数、Guzik 指数和 Ehler 指数（分别为 P%、G%和 E），这些指数是从四个时间尺度上包含 1000 个心跳到心跳间隔的数据段中得出的。与仰卧位相比，直立位时 HRV 增加，BPV 不可逆性降低。替代数据分析证实了体位变化的不可逆性。与 P%相比，G%和 E 的差异更明显，而且在较高的尺度因素下差异更明显。统计分析表明 G%和 E 之间存在密切关系。与此相反，P%和 G%之间以及 P%和 E 之间的关联并未得到证实。我们得出结论，在直立位期间，心率和血压的逐拍时间不可逆性发生了显著变化，这表明自主神经系统参与了其产生。
