Age-related changes in muscle sympathetic nerve activity in essential hypertension

To investigate the pathophysiological role of the sympathetic nervous system in essential hypertension, this study recorded the muscle sympathetic nerve activity (MSNA) of the tibial nerve and examined the age-related changes in patients with essential hypertension and in normotensive persons. There were 43 normotensive subjects (16-69 years old) and 63 patients with essential hypertension (18-67 years old) in the study. The MSNA at rest, recorded by microneurography, was evaluated by burst rate (bursts/min), burst incidence (bursts/100 heart beats), and spike frequency (spikes/min). The MSNA recording showed a high reproducibility with a correlation coefficient of 0.86 (p less than 0.01) in repeated studies. The MSNA was significantly greater in the hypertensive patients than in the normotensive subjects, irrespective of activity units (p less than 0.01), and this finding was consistent in the young (30 years old or less), middle-aged (31-50 years old), and old groups (51 years old or more). Furthermore, MSNA showed a significant positive correlation with age both in the normotensive subjects (r = 0.43, p less than 0.01 for burst rate; r = 0.49, p less than 0.01 for burst incidence; and r = 0.50, p less than 0.01 for spike frequency) and in the hypertensive patients (r = 0.40, p less than 0.01 for burst rate; r = 0.44, p less than 0.01 for burst incidence; and r = 0.40, p less than 0.01 for spike frequency).(ABSTRACT TRUNCATED AT 250 WORDS)