Cardiac rhythmicity of skin sympathetic activity recorded from peripheral nerves in man

In previous microelectrode recordings of sympathetic impulse activity in human peripheral nerves a marked cardiac rhythmicity has been found in the spontaneous firing of vasoconstrictor neurones supplying the vascular bed of skeletal muscles. Evidence has been presented that this rhythmicity depends on a potent baroreflex control of these neurones which are significantly involved in blood pressure regulation. In contrast, no cardiac rhythmicity has previously been seen in the spontaneous firing of sympathetic fibres supplying vessels and sweat glands in the human skin. The present study shows that when strong sudomotor activity is induced in skin nerves by a rise in ambient temperature, the sudomotor impulses tend to occur in volleys time-locked to the cardiac cycle. A similar cardiac rhythmicity is not exhibited by the skin vasoconstrictor fibres which can be activated by lowering of the ambient temperature. Induced falls in blood pressure do not produce any baroreflex modulations of the sudomotor outflow, suggesting that the cardiac rhythmicity of the sudomotor impulses is mot dependent on the action of this reflex.