Single-Unit Sympathetic Discharge

Abstract

Background —Reports demonstrating sympathetic hyperactivity in hypertension with the use of microneurography have been inconsistent. One possible reason is that previous studies have assessed muscle sympathetic nerve activity (MSNA) from integrated voltage waves (“bursts”) recorded from multiunit discharges. We studied single units with defined vasoconstrictor properties (s-MSNA) to further characterize sympathetic output in hypertensive disease. Methods and Results —We examined 74 subjects with a wide range of arterial blood pressure that were considered to be either normal (NT), high normal (HN), or stages 1 to 3 essential hypertension (EHT-1, EHT-2/3). All had their peripheral sympathetic activity measured from both multiunit bursts and single-unit vasoconstrictor impulses. There was a significant correlation between s-MSNA and MSNA, and results of variability studies were similar. The EHT-1 and EHT-2/3 groups had greater s-MSNA and MSNA than did the matched NT group (always P <0.01). The HN group also had greater s-MSNA and MSNA than did the NT group (mean±SEM; 43±5 vs 29±2 impulses/100 beats, P <0.05; 36±4 vs 24±2 bursts/100 beats, P <0.05). In addition, the EHT-1 group had significantly greater s-MSNA than did the EHT-2/3 group (63±6 vs 51±3 impulses/100 beats, P <0.05), which could not be demonstrated with MSNA bursts. Conclusions —Quantification from single vasoconstrictor units has provided additional evidence in established essential hypertension of increased central sympathetic output. Furthermore, in the mild or early stages of hypertension, this technique has provided new evidence of augmented sympathetic output compared with more severe hypertension.