The effect of carotid sinus nerve stimulation on muscle and skin nerve sympathetic activity in man.

Microelectrode recordings of multi-unit sympathetic activity were made in the right peroneal nerve of 4 awake human subjects during carotid sinus nerve stimulation. 36 periods of CSN-stimulation gave in all cases an inhibition of the muscle nerve sympathetic activity and there was good temporal agreement between this effect and the reduction of heart rate and blood pressure. The neural inhibition was marked during the first part of the stimulation but with continued stimulation the sympathetic activity reappeared, in most cases with reduced strength. In contrast, 20 periods of CSN-stimulation had no reproducible effect on skin nerve sympathetic activity. In most cases, the neural activity remained unchanged but both increases and decreases could occur. The results demonstrate that stimulation of carotid sinus baroreceptors in man has different effects on sympathetic outflow to different regions: a clear inhibition of the outflow to the muscles but no discernable effect on impulses destined to the skin.