de Boer Roel W, Karemaker John M
Department of Medical Biology, Section Systems Physiology, Amsterdam University Medical Centers, Location AMC, Amsterdam, Netherlands.
Front Neurosci. 2019 Jul 9;13:694. doi: 10.3389/fnins.2019.00694. eCollection 2019.
Baroreflex sensitivity (BRS) is often presented as a single number, but it is actually a frequency-dependent phenomenon whose value changes constantly due to internal and external stimuli. The standing posture, for instance, necessitates a changeover from vagal to sympathetic predominance for cardiovascular control. We present a wavelet cross-spectral analysis of blood pressure (BP) and interbeat interval (IBI) recordings in the search for variations in gain and phase between these signals. Additionally, we show how the lag in sympathetic response dictates BP-to-IBI phase relations.
Recordings in supine and head-up tilted (HUT) position, obtained earlier in 10 healthy subjects (4f/6m, aged 27-47 years) were used. BP and IBI were measured from the continuous finger pressure (by Finometer). The cross-wavelet analysis produced time- and frequency dependent gain (wBRS, wavelet derived BRS) and phase, using the MATLAB wavelet toolbox. We also applied the wBRS method to model-generated BP- and IBI-data with known interrelations to test the results of this analysis technique. Finally, wBRS values were compared with the xBRS-approach, which is a time domain method for continuous BRS estimation in a sliding 10-s window.
In resting supine conditions, wBRS fluctuates; more at respiratory frequencies than in the 0.1 Hz band. After HUT, wBRS at the respiratory frequency decreases from average 22.7 to 8.5 ms/mmHg, phase between BP and IBI increases from -30° to -54°; in the sympathetic 0.1 Hz range these numbers are 13.3→6.3 ms/mmHg and -54°→-59°. The values found by xBRS are intermediate between wBRS-resp and wBRS-0.1 Hz. The Appendix shows that for the simulated data the BRS and phase values as found by the wavelet technique can be explained from vector additions of vagal and sympathetic BRS contributions.
During supine rest parasympathetic control of heart rate dominates BRS; after HUT this is diminished and less effective. Due to the reaction times of the autonomic effectors, the phase relations between the signals depend on the relative contribution of the sympathetics, which explains the larger phase shift.
Cross wavelet analysis allows to follow fast BRS changes in time and frequency, while the computed phase relations help understand sympathetic participation.
压力反射敏感性（BRS）通常以单一数值呈现，但实际上它是一种频率依赖性现象，其值会因内部和外部刺激而不断变化。例如，站立姿势需要从迷走神经占主导转变为交感神经占主导来进行心血管控制。我们对血压（BP）和心动周期间期（IBI）记录进行小波交叉谱分析，以寻找这些信号之间增益和相位的变化。此外，我们展示了交感神经反应的延迟如何决定血压与心动周期间期的相位关系。
使用10名健康受试者（4名女性/6名男性，年龄27 - 47岁）之前在仰卧位和头高位倾斜（HUT）姿势下获得的记录。通过连续手指压力（使用Finometer）测量血压和心动周期间期。使用MATLAB小波工具箱进行交叉小波分析，得出时间和频率依赖性增益（小波衍生的BRS，wBRS）和相位。我们还将wBRS方法应用于具有已知相互关系的模型生成的血压和心动周期间期数据，以测试这种分析技术的结果。最后，将wBRS值与xBRS方法进行比较，xBRS方法是一种在滑动10秒窗口中连续估计BRS的时域方法。
在静息仰卧位条件下，wBRS波动；在呼吸频率下比在0.1Hz频段波动更大。头高位倾斜后，呼吸频率下的wBRS从平均2２.7降至8.5毫秒/毫米汞柱，血压与心动周期间期之间的相位从 - 30°增加到 - 54°；在交感神经0.1Hz范围内，这些数值分别为13.3→6.3毫秒/毫米汞柱和 - 54°→ - 59°。xBRS方法得到的值介于wBRS - 呼吸频率和wBRS - 0.1Hz之间。附录表明，对于模拟数据，小波技术得出的BRS和相位值可以通过迷走神经和交感神经BRS贡献的矢量相加来解释。
在仰卧位休息时，副交感神经对心率的控制主导BRS；头高位倾斜后，这种控制减弱且效果降低。由于自主效应器的反应时间，信号之间的相位关系取决于交感神经的相对贡献，这解释了更大的相位偏移。
交叉小波分析能够追踪BRS在时间和频率上的快速变化，而计算出的相位关系有助于理解交感神经的参与情况。
