Hopf H B, Skyschally A, Heusch G, Peters J
Institut für Klinische Anaesthesiologie, Heinrich-Heine-Universität Düsseldorf, Germany.
Anesthesiology. 1995 Mar;82(3):609-19. doi: 10.1097/00000542-199503000-00002.
Heart rate variability in the frequency domain has been proposed to reflect cardiac autonomic control. Therefore, measurement of heart rate variability may be useful to assess the effect of epidural anesthesia on cardiac autonomic tone. Accordingly, the effects of preganglionic cardiac sympathetic blockade by segmental epidural anesthesia were evaluated in humans on spectral power of heart rate variability. Specifically, the hypothesis that cardiac sympathetic blockade attenuates low-frequency spectral power, assumed to reflect cardiac sympathetic modulation, was tested.
Ten subjects were studied while supine and during a 15-min 40 degrees head-up tilt both before and after cardiac sympathetic blockade by segmental thoracic epidural anesthesia (sensory block: C6-T6). ECG, arterial pressure, and respiratory excursion (Whitney gauge) were recorded, and a fast-Fourier-transformation was applied to 512-s data segments of heart rate derived from the digitized ECG at the end of each intervention.
With cardiac sympathetic blockade alone and the subjects supine, both low-frequency (LF, 0.06-0.15 Hz) and high-frequency (HF, 0.15-0.80 Hz) spectral power remained unchanged. During tilt, epidural anesthesia attenuated the evoked increase in heart rate (+11.min-1 +/- 7 SD vs. +6 +/- 7, P = 0.024). However, while during tilt cardiac sympathetic blockade significantly decreased the LF/HF ratio (3.68 +/- 2.52 vs. 2.83 +/- 2.15, P = 0.041 vs. tilt before sympathetic blockade), a presumed marker of sympathovagal interaction, absolute and fractional LF and HF power did not change.
Although preganglionic cardiac sympathetic blockade reduced the LF/HF ratio during tilt, it did not alter spectral power in the LF band during rest or tilt. Accordingly, low-frequency spectral power is unlikely to specifically reflect cardiac sympathetic modulation in humans.
频域中的心率变异性已被认为可反映心脏自主神经控制。因此，测量心率变异性可能有助于评估硬膜外麻醉对心脏自主神经张力的影响。相应地，在人体中评估了节段性硬膜外麻醉对节前心脏交感神经阻滞对心率变异性频谱功率的影响。具体而言，测试了心脏交感神经阻滞减弱低频频谱功率（假定反映心脏交感神经调制）这一假设。
对10名受试者在仰卧位以及在节段性胸段硬膜外麻醉（感觉阻滞：C6 - T6）导致心脏交感神经阻滞前后进行15分钟40度头高位倾斜时进行研究。记录心电图、动脉压和呼吸幅度（惠特尼量表），并在每次干预结束时对从数字化心电图得出的512秒心率数据段应用快速傅里叶变换。
仅在心脏交感神经阻滞且受试者仰卧位时，低频（LF，0.06 - 0.15赫兹）和高频（HF，0.15 - 0.80赫兹）频谱功率均保持不变。在倾斜过程中，硬膜外麻醉减弱了诱发的心率增加（+11次/分钟±7标准差对 +6±7，P = 0.024）。然而，虽然在倾斜过程中心脏交感神经阻滞显著降低了LF/HF比值（3.68±2.52对2.83±2.15，与交感神经阻滞前倾斜相比P = 0.041），这是交感 - 迷走神经相互作用的一个假定标志物，但绝对和分数LF及HF功率并未改变。
尽管节前心脏交感神经阻滞在倾斜过程中降低了LF/HF比值，但在休息或倾斜期间并未改变LF频段的频谱功率。因此，低频频谱功率不太可能特异性反映人体中的心脏交感神经调制。
