Initially , a reduction in cardiac output leads to unloading of baroreceptor reflex that , in turn , increases heart rate through vago - sympathetic mechanisms and total peripheral resistance via an increase in sympathetic outflow to vascular beds 心输出量降低首先引起动脉压力感受性反射失负荷，进而通过迷走-交感机制加快心率；同时，支配血管床的交感传出活动增加，进而增加总外周阻力。
