Segregated signal averaging of sympathetic baroreflex responses in humans

The goal of this study was to merge the methods currently used to assess be at-by-beat changes in muscle sympathetic nerve activity with a signal-avera ging approach and overcome the inherent subjectivity and time-consuming nat ure of manual analysis of baroreflex-mediated sympathetic responses in huma ns. This is a retrospective study using data obtained during two prior stud ies [J. R. Halliwill, J. A. Taylor, and D. L. Eckberg. J. Physiol. (Lond.) 495: 279-288, 1996; C. T. Minson, J. R. Halliwill, T Young, and M. J. Joyne r. FASEB J. 13: A1044, 1999]. Beat-by-beat arterial pressure (Finapres devi ce) and muscle sympathetic nerve activity (microneurography) were recorded in seven healthy, nonsmoking, normotensive subjects (2 men, 5 women) betwee n the ages of 23 and 32 yr during arterial pressure changes induced by bolu s injections of nitroprusside and phenylephrine. The muscle sympathetic ner ve activity-diastolic pressure relationship was analyzed by both the tradit ional manual detection method and a novel segregated signal-averaging metho d. The results show the two analysis approaches are highly correlated acros s subjects (r = 0.914, P < 0.05) and are in close agreement [slope for manu al detection -6.17 +/- 0.91 (SE) vs, slope for segregated signal averaging -5.98 +/- 0.83 total integrated activity . beat(-1) . mmHg(-1); P = 0.60]. However, a considerable time savings is seen with the new method (min vs. h ). Segregated signal averaging as developed here provides a valid alternati ve to "by-hand" analysis of beat-by-beat changes in muscle sympathetic nerv e activity that occur during dynamic baroreflex-mediated changes in sympath etic outflow. This approach provides an objective, rapid method to analyze nerve recordings.