Sica Anthony L, Zhao Ning
Department of Physiology and Pharmacology, SUNY Downstate Medical Center, Brooklyn, New York 11203, USA.
BMC Physiol. 2006 Jun 16;6:5. doi: 10.1186/1472-6793-6-5.
Spectral analysis of the cardiac time series has been used as a tool for assessing levels of parasympathetic and sympathetic modulation of the sinoatrial node. In the present investigation we evaluated daily changes in heart rate variability spectra in conscious neonatal piglets that were either neurally intact (n = 5) or had undergone right stellate ganglionectomy (n = 5). The partial stellectomized animals and their intact litter mates were exposed to four days of intermittent hypoxia, each day comprising nine episodes of hypoxia alternating with nine episodes of normoxia. A time control group (n = 7) comprised animals from different litters that were not exposed to intermittent hypoxia. We hypothesized that exposure to intermittent hypoxia would increase sympathetic efferent neuronal modulation of heart rate variability spectra in neurally intact animals and in those with right stellate ganglionectomy, and that his effect would be observed in heart rate variability spectra computed from baseline recordings.
Overall, heart rate variability spectra during baseline conditions were dominated by high frequency activity, a reflection of parasympathetic efferent neuronal innervation and linkage to the ventilatory cycle manifested as respiratory sinus arrhythmia. Exposure to intermittent hypoxia did not alter daily baseline spectral features that would indicate an increase of sympathetic cardiac activity: low frequency (0.05 - 0.15 Hz) activity was unaffected and the ratio of low- to -high frequency activity remained less than unity indicating a predominance of high frequency activity. The resultant spectra were remarkably similar despite differences in cardiac sympathetic efferent neuronal innervation and experimental treatment. When spectra were computed from cardiac time series during representative hypoxic episodes, significant increases in activity across the low frequency region (0.05 - 0.15 Hz) of heart rate variability spectra were noted and were comparable in neurally intact animals and in those with right stellate ganglionectomy.
The findings of this investigation provided important information regarding sympathetic efferent neuronal innervation of the heart during the neonatal period. Both neurally intact animals and those with right stellate ganglionectomy had equivalent increases of activity in the low frequency region of heart rate variability spectra during hypoxic stimulation. Such a finding demonstrated the capability of residual cardiac sympathetic neuronal innervation to affect functionally appropriate changes in cardiac chronotropy.
心脏时间序列的频谱分析已被用作评估窦房结副交感神经和交感神经调节水平的工具。在本研究中，我们评估了清醒新生仔猪心率变异性频谱的每日变化，这些仔猪要么神经完整（n = 5），要么接受了右侧星状神经节切除术（n = 5）。部分星状神经节切除的动物及其完整的同窝仔猪暴露于四天的间歇性低氧环境中，每天包括九次低氧发作与九次常氧发作交替。一个时间对照组（n = 7）由来自不同窝的未暴露于间歇性低氧的动物组成。我们假设，暴露于间歇性低氧会增加神经完整动物和右侧星状神经节切除动物心率变异性频谱的交感神经传出神经元调节，并且这种效应会在从基线记录计算出的心率变异性频谱中观察到。
总体而言，基线条件下的心率变异性频谱以高频活动为主，这反映了副交感神经传出神经元的支配以及与呼吸周期的联系，表现为呼吸性窦性心律不齐。暴露于间歇性低氧并未改变表明交感神经心脏活动增加的每日基线频谱特征：低频（0.05 - 0.15 Hz）活动未受影响，低频与高频活动的比值仍小于1，表明高频活动占主导。尽管心脏交感神经传出神经元支配和实验处理存在差异，但所得频谱非常相似。当从代表性低氧发作期间的心脏时间序列计算频谱时，注意到心率变异性频谱的低频区域（0.05 - 0.15 Hz）的活动显著增加，并且在神经完整的动物和右侧星状神经节切除的动物中相当。
本研究的结果提供了有关新生期心脏交感神经传出神经元支配的重要信息。神经完整的动物和右侧星状神经节切除的动物在低氧刺激期间心率变异性频谱的低频区域活动均有同等程度的增加。这一发现证明了残余心脏交感神经神经元支配影响心脏变时性功能适当变化的能力。
