Elam M, Macefield V
Department of Clinical Neurophysiology, Institute for Clinical Neuroscience, Sahlgren University Hospital, Göteborg, Sweden.
J Appl Physiol (1985). 2001 Aug;91(2):717-24. doi: 10.1152/jappl.2001.91.2.717.
Single vasoconstrictor nerve fibers in humans normally fire only once but have the capacity to fire as many as eight times, per cardiac interval. Our laboratory recently demonstrated that the mean firing frequency of individual vasoconstrictor fibers is more than doubled in the sympathoexcitation associated with congestive heart failure (Macefield VG, Rundqvist B, Sverrisdottir YB, Wallin BG, and Elam M. Circulation 100: 1708--1713, 1999). However, the propensity to fire only once per cardiac interval was retained. In the present retrospective study, we tested the hypothesis that vasoconstrictor fibers fire more than once per cardiac interval in response to transient sympathoexcitatory stimuli, providing one mechanism for further increase of an already augmented sympathetic discharge. Six patients with congestive heart failure (New York Heart Association functional class II--IV; left ventricular ejection range 13--37%, average 22%) were studied at rest and during premature ectopic heartbeats. Analyzed for a total of 60 premature beats, the average firing probability of 10 vasoconstrictor fibers increased from 61 to 80% in the prolonged cardiac interval (i.e., reduced diastolic pressure) after premature beats. The incidence of multiple within-burst firing increased markedly, with two spikes being more common than one. Our results illustrate two different mechanisms (increases in firing probability and multiple within-burst firing), and indirectly indicate a third mechanism (recruitment of previously silent fibers), for acute sympathoexcitatory responses.
在人类中，单一的血管收缩神经纤维通常每次心脏周期仅发放一次冲动，但每次心脏周期有能力发放多达八次冲动。我们实验室最近证明，在与充血性心力衰竭相关的交感神经兴奋时，单个血管收缩纤维的平均发放频率增加了一倍多（Macefield VG、Rundqvist B、Sverrisdottir YB、Wallin BG和Elam M.《循环》100: 1708 - 1713, 1999）。然而，每次心脏周期仅发放一次冲动的倾向仍然存在。在本项回顾性研究中，我们检验了这样一个假设，即血管收缩纤维在对短暂的交感神经兴奋刺激做出反应时，每次心脏周期发放冲动超过一次，这为已经增强的交感神经放电的进一步增加提供了一种机制。对6例充血性心力衰竭患者（纽约心脏协会心功能分级II - IV级；左心室射血分数范围为13% - 37%，平均22%）在静息状态和室性早搏期间进行了研究。在分析总共60次室性早搏时，10条血管收缩纤维在早搏后延长的心脏周期（即舒张压降低）中的平均发放概率从61%增加到了80%。爆发性多次发放的发生率显著增加，两个峰值比一个峰值更常见。我们的结果说明了急性交感神经兴奋反应的两种不同机制（发放概率增加和爆发性多次发放），并间接表明了第三种机制（募集先前沉默的纤维）。
