Stuesse S L, Wallick D W, Zieske H, Levy M N
Am J Physiol. 1981 Dec;241(6):H850-6. doi: 10.1152/ajpheart.1981.241.6.H850.
Sympathetic stimulation both shortens the cardiac cycle and potentiates the cardiac response to vagal stimulation. In the present study the effects of sympathetic stimulation on the chronotropic responses of the heart to brief bursts of vagal stimulation were determined in open-chest anesthetized dogs. The sinoatrial nodal pacemaker cells demonstrate a paradoxical response to repetitive bursts of vagal stimuli over a certain portion of the cardiac cycle. That is, the cardiac cycle length does not increase but actually decreases as the vagal stimulation frequency is raised. Background levels of sympathetic stimulation do not significantly alter the range over which this "paradoxical" response occurs. Sympathetic stimulation decreases the cardiac chronotropic response to short bursts of vagal stimuli regardless of the time in the cardiac cycle that the stimulus is given; however, it does not decrease the time from the minimum vagal chronotropic response to the subsequent atrial depolarization although the total cardiac cycle is shortened. Since sympathetic stimulation shifts the overall temporal relationship between vagal stimulation and pacemaker response, small changes in sympathetic tone may greatly alter the cardiac response to phasic vagal stimulation if the vagal stimulus is given at certain times in the cardiac cycle.
交感神经刺激既能缩短心动周期，又能增强心脏对迷走神经刺激的反应。在本研究中，在开胸麻醉犬身上确定了交感神经刺激对心脏对短暂迷走神经刺激爆发的变时反应的影响。窦房结起搏细胞在心动周期的特定时间段内对重复性迷走神经刺激爆发表现出矛盾反应。也就是说，随着迷走神经刺激频率的增加，心动周期长度不会增加反而会减少。交感神经刺激的背景水平不会显著改变这种“矛盾”反应发生的范围。无论在心动周期的何时给予刺激，交感神经刺激都会降低心脏对短暂迷走神经刺激爆发的变时反应；然而，尽管总心动周期缩短，但它不会减少从最小迷走神经变时反应到随后心房去极化的时间。由于交感神经刺激改变了迷走神经刺激与起搏细胞反应之间的整体时间关系，如果在心动周期的特定时间给予迷走神经刺激，交感神经张力的微小变化可能会极大地改变心脏对阶段性迷走神经刺激的反应。
