High-normal blood pressure is associated with increased resting sympathetic activity but normal responses to stress tests

Objective. High-normal blood pressure (BP) increases the risk of cardiovascular (CV) disease. The mechanisms underlying this increased risk are not clear. Sympathetic activation appears to be a potential mechanism linking high-normal BP to CV disease. This study examined whether high-normal BP compared with optimal BP is linked to sympathoexcitation at rest and/or during laboratory stressors. Methods. Heart rate (HR), BP and muscle sympathetic nerve activity (MSNA) were obtained at rest and during stress tests (sustained handgrip and mental stress) in 18 subjects (15 males and three females) with high-normal BP (systolic BP of 130-139 mmHg, diastolic BP of 85-89 mmHg, or both) and in 12 subjects (10 males and two females) with optimal BP (< 120/80 mmHg) matched for age (34 ± 3 years in both groups) and body mass index (25 ± 2 kg/m² in both groups). Results. Despite the higher resting BP levels, MSNA was higher in subjects with high-normal BP than in the optimal BP group (26 ± 3 vs 18 ± 2 bursts/min, p< 0.05). During sustained handgrip, MSNA increased by 37 ± 14% in high-normal BP group compared with an increase of 49 ± 15% in optimal BP group (p = 0.55). Changes during mental stress were 50 ± 28% and 37 ± 12%, respectively (p = 0.73). There were no significant differences in SBP responses to handgrip and mental stress between the high-normal and optimal BP groups. Baseline HR and chronotropic responses to stress tests were comparable between the two groups. Conclusion. In comparison with optimal BP, high-normal BP is associated with increased resting MSNA, but normal neural and circulatory responses to stress tests. These findings suggest that tonic activation of the sympathetic nervous system may precede overt arterial hypertension and contribute to an excess risk of CV disease in subjects with high-normal BP.