Abstract
Objective: It is well established that essential hypertension is characterized by increased adrenergic tone in different districts. Aim of the study is to examine the correlation between different measures of cardiovascular autonomic regulation, muscle sympathetic nerve activity (MSNA) and spectral analysis of RR interval variability, and their possible relation with plasma markers of renin-angiotensin system and endothelin activity. Design and Methods: 35 untreated essential hypertensive patients (HT) and 14 normotensive subjects (NT), age-and gender-matched, were included. MSNA was recorded by microneurography of the peroneal nerve, together with beat-to-beat BP and ECG for heart rate (HR) evaluation. Fast Fourier Transform spectral analysis of RR interval variability was applied to obtain normalized high and low frequency (nHF and nLF respectively) power density, and their ratio. Plasma norepinephrine (NE), renin activity (PRA) and endothelin-1 (ET-1) were also measured. Log-transformation was applied for correlation of not normally distributed variables. Results: HT showed higher MSNA (51.5 vs 41.4 bursts/100 heart beats, p < 0.001), NE (342 vs 269 pg/ml, p = 0.03), and LF/HF (3.4 vs 1.9, p = 0.04) as compared to NT. MSNA and LF/HF showed a significant correlation in the HT group (r = 0.36,p = 0.04), but not in the NT group (r = 0.20,p = ns). MSNA was also inversely related to nHF (r = -0.48,p = 0.004) in HT. MSNA and LF/HF were not significantly related to HR or NE in both HT and NT groups. In HT patients, but not in NT, nLF was related to NE (r = 0.43,p = 0.03) and ET-1 (r = -0.69,p = 0.01), while LF/HF was related to ET-1 (r = -0.70,p = 0.02). MSNA was not related to any of these humoral parameters in HT and NT. Conclusions: MSNA increase and sympatho-vagal unbalance in HR modulation are associated in essential hypertension. Spectral components of RR interval variability, but not MSNA, seem to be influenced by endothelin system in HT.
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