Control Criteria of Cardiovascular System Generating 1/f Fluctuations

在本研究中，我们探讨了心血管系统产生1/f波动的控制标准。通过对压力反射增益（BRG）的估计，研究了调节系统的状态依赖性。BRG的估计采用从血压（BP）到心率（HR）的开环假设下构建的序列方法。结果表明，站立、非快速眼动（non - REM）睡眠、快速眼动（REM）睡眠、仰卧位的BRSs较低。此外，在平头倾斜产生直立应力的情况下，矛盾地发现BRS随着倾斜角度（重力）的增加而减小。作为一种基于闭环假设估计BRS的新技术，提出了一种将序列法应用于由创新过程驱动的识别多元自回归（MAR）模型生成的时间序列的新方法，暂称“创新法”。序列法与创新法估算的BRS值没有明显的差异，说明了开环法与闭环法估算的BRS绝对值的差异。此外，发现从BP到BP的闭环脉冲响应随着直立应力的增加而加速。类似的分析也应用于脊髓损伤患者的数据。因此，上节段损伤患者的心血管系统表现出不稳定的反应。相比之下，发现低水平损伤患者与健康受试者具有相似的特征。此外，患者表现出明显的0.05Hz振荡，这为Mayer波的产生机制提供了新的信息。从血压和心率的相互依赖性分析，由于损伤导致两者分离，认为心血管系统处于不稳定状态。由于对直立应激的反应反映了外周阻力和静脉回流行为的控制，因此可以通过建模来探索心血管系统的控制标准。此外，我们构建了以心率和交感神经活动为控制变量，以血压为控制变量的心血管模型。对模型的最优控制仿真表明，HR产生1/f波动的准则是允许一定程度偏差的宽松准则，而不是不允许波动的严格准则。少

In this study, we explored the control criteria of the cardiovascular system generating 1/f fluctuations. Through estimating the baroreflex gain (BRG), state-dependency of the regulatory system was studied. BRG was estimated by the sequence method constructed under an open-loop assumption from blood pressure (BP) to heart rate (HR). As a result, the estimated BRSs were lower in order standing, non rapid eye movement (nonREM) sleep, REM sleep, supine. In addition, under the head-up tilting posing orthostatic stress, it was paradoxically found that BRS becomes reduced as the tilt angle (gravity) increases. As a novel technique estimating BRS based on the closed-loop assumption, a new method was proposed that the sequence method is applied to a time series generated by the identified multivariate autoregressive (MAR) model driven by the innovation process, tentatively called "innovation method". Comparison between the estimates obtained by the sequence and the innovation methods did not s … More how large disparity, which clears the difference in the absolute value of BRS estimated by the open- and closed-loop techniques. In addition, the closed-loop impulse response from BP to BP was found to be accelerated as the orthostatic stress became heavier. Similar analyses were applied to the data of spinal injury patients. As a result, the cardiovascular system showed unstable responses for the patients of upper level injury. In contrast, the patients of lower level injury were found to have similar characteristics to the healthy subjects. Besides, the patients showed the distinct 0.05Hz oscillation, which could provide novel information concerning generation mechanism of Mayer wave. From the analysis of inter-dependency between BP and HR, the cardiovascular system is considered to be unstabilized by the disconnection between them due to the injury. Because the response to the orthostatic stress reflects control of peripheral resistance and behavior of venous return, the control criteria of the cardiovascular system could be explored by modeling them. Additionally, we constructed the cardiovascular model which consists of HR and sympathetic activity as control variables and BP as a variable to be controlled. Simulation of optimal control on the model suggests that the criteria for generating 1/f fluctuation in HR are loose ones allowing deviations to some extent rather than rigid one not allowing fluctuations. Less