Department of Engineering Science, University of Oxford, Oxford OX1 3PJ, UK.
IEEE Trans Biomed Eng. 2010 Apr;57(4):960-8. doi: 10.1109/TBME.2009.2024265. Epub 2010 Feb 5.
The dynamic relationship between beat-to-beat mean arterial blood pressure (ABP) fluctuations and cerebral blood flow velocity (CBFV) variations have been intensively studied. The experimentally observed low coherence in the low-frequency band has previously indicated that the assumptions of linearity and/or stationarity, the preconditions of the linear transfer function analysis, are not valid in that frequency region. Latka et al. [M. Latka, M. Turalska, M. Glaubic-Latka, W. Kolodziej, D. Latka, and B. J. J. West, "Phase dynamics in cerebral autoregulation," Amer. J. Physiol. Heart Circ. Physiol., vol. 289 pp. H2272-H2279, Jul. 2005] used a wavelet phase synchronization method to identify the instantaneous phase difference between ABP and CBFV, and low values of synchronization index were found in the low-frequency range, seeming to provide further evidence that the cerebral autoregulation system is nonstationary. Here, we focus on another possible factor corresponding for this low synchronization index-unmeasured variability. We demonstrate analytically and with a physiologically based cerebral hemodynamic model that, in the case of multiple inputs, the phase difference between one input, ABP, and the output, CBFV, will be distorted by an additional input, end-tidal CO(2) (P(ETCO(2))), and no longer accurately represent the true ABP-CBFV system phase shift. We also prove that this phase distortion can be corrected if the transfer functions for ABP-CBFV and P(ETCO(2))-CBFV are known or can be estimated. A significantly increased value of synchronization index in the low-frequency band is found by using the CO(2) correction term with experimental data on 13 subjects. This essentially indicates that the lack of synchronization between ABP and CBFV previously identified by Latka et al. [M. Latka, M. Turalska, M. Glaubic-Latka, W. Kolodziej, D. Latka, and B. J. J. West, "Phase dynamics in cerebral autoregulation," Amer. J. Physiol. Heart Circ. Physiol., vol. 289, pp. H2272-H2279, Jul. 2005] can be partly attributed to unmeasured variability.
人们对逐搏平均动脉血压（ABP）波动与脑血流速度（CBFV）变化之间的动态关系进行了深入研究。低频段中观察到的低相干性表明，线性和/或平稳性的假设，即线性传递函数分析的前提条件，在该频率范围内并不成立。Latka 等人[M. Latka、M. Turalska、M. Glaubic-Latka、W. Kolodziej、D. Latka 和 B. J. J. West，“脑自动调节中的相位动力学”，《美国生理学杂志：心脏循环生理学》，第 289 卷，第 H2272-H2279 页，2005 年 7 月]使用了一种基于小波的相位同步方法来识别 ABP 和 CBFV 之间的瞬时相位差，并在低频范围内发现了低同步指数值，这似乎进一步证明了脑自动调节系统是非平稳的。在这里，我们关注的是另一个可能对应于低同步指数的因素——未测量的变异性。我们通过分析和基于生理的脑血液动力学模型证明，在存在多个输入的情况下，一个输入 ABP 和输出 CBFV 之间的相位差将被另一个输入，即呼气末二氧化碳（P(ETCO(2)))所扭曲，且不再准确代表真正的 ABP-CBFV 系统相位偏移。我们还证明，如果 ABP-CBFV 和 P(ETCO(2))-CBFV 的传递函数已知或可以估计，则可以纠正这种相位失真。我们对 13 名受试者的实验数据使用 CO(2)校正项，发现低频段的同步指数值显著增加。这实质上表明，Latka 等人先前识别的 ABP 和 CBFV 之间缺乏同步性[M. Latka、M. Turalska、M. Glaubic-Latka、W. Kolodziej、D. Latka 和 B. J. J. West，“脑自动调节中的相位动力学”，《美国生理学杂志：心脏循环生理学》，第 289 卷，第 H2272-H2279 页，2005 年 7 月]可以部分归因于未测量的变异性。
