MORNING BLOOD PRESSURE SURGE IS NOT RELATED TO MUSCLE SYMPATHETIC NERVE ACTIVITY IN HYPERTENSION: 9C.04

Abstract

Objective: Blood pressure rise on awakening (the morning surge) might be a predictor of hypertension-related cardiovascular complications. Previous studies indicated that the autonomic nervous system may contribute to the diurnal blood pressure rhythm. We tested the hypothesis that direct measures of intraneural sympathetic nerve activity taken at rest may be related to blood pressure morning surge in hypertension. Design and Methods: We measured muscle sympathetic nerve activity (MSNA), heart rate (HR) and blood pressure (BP) during undisturbed supine rest in 68 hypertensive patients (53 males, age 40 ± 3 years, BMI 27 ± 1 kg/m2, mean ± SEM). Patients were newly diagnosed, never treated for hypertension and were free of any other known diseases. All hypertensives underwent 24-hour ambulatory blood pressure monitoring. Morning surge was defined as the difference between the morning BP (the average BP during the 2 h after waking up) and the pre-awake BP (the average BP during the 2 h before waking up). Results: SBP averaged 143 ± 3 mmHg for daytime and 126 ± 2 mmHg for night time. Mean HR was 81 ± 2 bpm for daytime and 69 ± 2 bpm for night time. Average MSNA was 32 ± 2 bursts/min., SBP morning surge 19 ± 2 mmHg, and HR morning surge 14 ± 2 bpm. In univariate analysis, MSNA was related to daytime SBP (r = 0.28; P = 0.02), nighttime SBP (r = 0.26; P = 0.03), daytime HR (r = 0.28; P = 0.02), night time HR (r = 0.26; P = 0.03). Multivariate analysis, taking into consideration age, BMI and gender, revealed that MSNA was independently related to both daytime (P = 0.006) and nighttime HR (P = 0.02), but to ambulatory SBP. MSNA was not linked to morning surge of SBP (r = 0.01) or HR (r = 0.07). Conclusions: In patients with essential hypertension, muscle sympathetic nerve activity is related to both daytime and night time heart rate, but not to morning blood pressure surge.