New approaches to quantifying sympathetic nerve activity.

The importance of the sympathetic nervous system in the pathophysiology of human and experimental models of hypertension is well established. Underpinning recent advances has been direct recording from sympathetic nerves via implanted electrodes in animals or microneurography in human subjects. However, the limited life of a recording electrode and the prolonged nature of the development of hypertension bring with it the difficulty of comparing sympathetic nerve activity between groups. New developments in high-frequency radiotelemetry in animals have heralded a new age in long-term sympathetic recordings ideal for hypertension research. Standard multifiber recordings in human and animal studies have provided information about the frequency and amplitude of sympathetic bursts. Characterization of sympathetic output is now possible from new techniques of determining single-unit firing frequency, firing probability, and the number of spikes generated per cardiac interval. These have led to a better understanding of sympathoactivation in hypertension and its underlying mechanisms.