Single-unit sympathetic discharge pattern in pathological conditions associated with elevated cardiovascular risk.

1. Although measuring the rate of firing of multi-unit muscle sympathetic nerve activity (MSNA) has provided important information in many aspects of cardiovascular medicine, measuring single-unit vasoconstrictor activity provides a better understanding of the possible mechanisms underlying disturbed sympathetic nervous system activity. 2. Detailed firing patterns of sympathetic vasoconstrictor neurons have been recorded in conditions associated with sympathoexcitation such as heart failure, obstructive sleep apnoea syndrome, hypertension and obesity; conditions in which cardiovascular morbidity and mortality are demonstrably elevated. 3. Moreover, in conditions such as anxiety disorders and depression, in which elevated cardiovascular risk has recently been established, single-unit analysis has highlighted a disturbed sympathetic firing pattern, which could not be identified on multi-unit MSNA recording. This disturbed sympathetic nerve firing pattern, characterized by increased incidence of multiple firing within a sympathetic burst, has deleterious consequences on the cardiovascular system. 4. Single-unit methodology may represent a major step forward in the understanding of the link between disturbed sympathetic nerve firing and associated cardiovascular risk.