Single-unit sympathetic discharge - Quantitative assessment in human hypertensive disease

Background-Reports demonstrating sympathetic hyperactivity in hypertension with the use of microneurography have been inconsistent. One possible reaso n is that previous studies have assessed muscle sympathetic nerve activity (MSNA) from integrated voltage waves ("bursts") recorded from multiunit dis charges. 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 b lood pressure that were considered to be either normal (NT), high normal (H N), or stages 1 to 3 essential hypertension (EHT-1, EHT-2/3). All had their peripheral sympathetic activity measured from both multiunit bursts and si ngle-unit vasoconstrictor impulses. There was a significant correlation bet ween 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 N T 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 h ad 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 bu rsts. Conclusions-Quantification from single vasoconstrictor units has provided a dditional evidence in established essential hypertension of increased centr al sympathetic output. Furthermore, in the mild or early stages of hyperten sion, this technique has provided new evidence of augmented sympathetic out put compared with more severe hypertension.