Relative contribution of central and peripheral input to cardiovascular regulation during exercise

为探讨运动时中枢指令和反射控制肌交感神经活动（MSNA）对心血管调节的相对贡献，我们用显微神经摄影技术记录了运动时MSNA和心血管参数。1）等长收缩使MSNA增加，但运动时MSNA增加的开始时间延迟，运动后收缩肌缺血时MSNA仍保持较高水平。MSNA的增加可能主要与肌肉代谢反射有关，而不是与中央命令有关。MSNA反应的大小也取决于收缩的肌肉群。2）在最大随意肌肉收缩期间，MSNA上升的开始也延迟，如在等长肌肉收缩中所见，因此表明中枢命令对MSNA的影响较小。3）由于低强度循环由于持续几分钟的循环（>最大氧摄取的40%）没有激活MSNA，我们测试了MSNA是否在持续30分钟的延长的循环期间增加。运动开始后15分钟，MSNA和体温升高，血乳酸浓度无任何增加。这些结果表明，在长时间下肢运动中，代谢反射以外的其他反射机制对心血管系统的控制比中枢指令更为重要。4）分级蹬车运动中，心率变异性和MSNA估计的心交感神经活动增加。认为心率的增加和交感神经活动对骨骼肌血管的供应可能至少部分具有相同的反射机制，因此，本研究将证明反射机制在运动中比中枢指令更重要地控制心血管适应。这些反射机制受运动强度和持续时间以及运动肌群的调节。

In order to determine the relative contribution of central command and reflex control of muscle sympathetic nerve activity (MSNA) to cardiovascular regulation during exercise, we recorded the MSNA using microneurographic technique and the cardiovascular parameters.1) Isometric muscle contraction increased MSNA but the onset of increase in MSNA was delyaed during exercise and the higher MSNA was persisted during ischemia of contracting muscle following exercise. The increase in MSNA may be related predominantly to the muscle metaboreflex rather than the central command. The magnitude of MSNA response was also depended on the contracting muscle groups.2) During maximal voluntary muscle contraction, the onset of MSNA rise was also delayd as seen in isometric muscle contraction and thus indicated a lesser effect of the central command on MSNA.3) Since low intensity cycling (>40% of maximal oxygen uptake) performed for several minutes did not activate MSNA,we tested whether the MSNA increased during prolonged cycling for 30 minutes. The MSNA and body temperature were increased 15 minutes after the commencement of cycling without any increse in blood lactate concentration. These results suggest that the other reflex mechanism besides the metaboreflex is more important than the central command to control cardiovascular system during prolong leg exercise.4) The cardiac sympathetic activity estimated by heart rate variability and MSNA were increased concomitantly during graded cycling. It is considered that the increase in heart rate and sympathetic nerve activity supplying skeletal muscle vasculature might at least in part have the same reflex mechanism.In conclusion, this study will demonstrate that the reflex mechanisms have a more important role to control cardiovascular adaptation during exercise rather than the central command. These reflex mechanisms are modulated by the by the intensity and the duration of exercise, and also the exercising muscle groups.