Relationship between spontaneous variations of muscle sympathetic activity and succeeding changes of blood pressure in man.

Pulse-synchronous bursts of sympathetic vasoconstrictor impulses in peroneal muscle nerve fascicles were recorded together with intra-arterial blood pressure and ECG in 24 healthy subjects resting in the supine position. A statistical procedure similar to spike-triggered averaging was used to calculate mean changes of blood pressure and pulse interval following a burst of sympathetic impulses. In all subjects the result was a transient increase of blood pressure and a transient shortening of pulse interval with maxima occurring on the average 5.5 and 2.9s, respectively, after the burst. It is suggested that the same baroreceptor events that relate to a burst of sympathetic impulses in muscle nerves also change cardiac autonomic outflow to cause transient cardioacceleration. Presumably, the transient blood pressure increase following the burst is due to the combined effects of cardioacceleration and peripheral vasoconstriction.