Human Muscle Nerve Sympathetic Activity in Cardiac Arrhythmias

Microelectrode recordings of multiunit muscle nerve sympathetic activity (MSA) and intra-arterial blood pressure were made in 11 subjects with different types of cardiac arrhythmias, including sinus arrhythmia, A-V block, extrasystolic beats, and atrial fibrillation. The MSA appeared in pulse-synchronous bursts, which, after compensation for a short reflex delay, correlated closely with the pulsative blood pressure changes. The sympathetic bursts always corresponded to diastoles and were usually initiated during heart beats with low diastolic pressure. The correlation between the diastolic pressure and the percentage occurrence of the bursts was found to be described by an inverse S-shaped curve, which became approximately linear after probit transformation. The results confirm previous findings indicating strong baro-reflex control of the vascular bed of skeletal muscle and provide a method for quantitative studies of these control mechanisms in man.