Morning blood pressure (BP) surge is considered to be an independent risk factor for cardiovascular diseases. We tested the hypothesis that increased large-artery stiffness and impaired sympathetic baroreflex sensitivity (BRS) contribute to augmented morning surge in elderly hypertensive subjects. Morning surge was assessed as morning systolic BP averaged for 2 h just after waking up minus minimal sleeping systolic BP by using ambulatory BP monitoring (ABPM) in 40 untreated hypertensive [68 ± 1 (SE) yr] and 30 normotensive (68 ± 1 yr) subjects. Beat-by-beat finger BP and muscle sympathetic nerve activity (MSNA) were recorded in the supine position and at 60° upright tilt. We assessed arterial stiffness with carotid-to-femoral pulse wave velocity (cfPWV) and sympathetic BRS during spontaneous breathing. Awake and asleep ABPM-BPs and morning surge were higher in hypertensive than normotensive subjects (all P < 0.001). cfPWV was higher (P = 0.002) and sympathetic BRS was lower (P = 0.096) in hypertensive than normotensive subjects. Hypertensive subjects with morning surge ≥35 mmHg (median value) had higher cfPWV (11.9 ± 0.5 vs. 9.9 ± 0.4 m/s, P = 0.002) and lower sympathetic BRS (supine: -2.71 ± 0.25 vs. -3.73 ± 0.29, P = 0.011; upright: -2.62 ± 0.22 vs. -3.51 ± 0.35 bursts·100 beats(-1)·mmHg(-1), P = 0.052) than those with morning surge <35 mmHg. MSNA indices were similar between groups (all P > 0.05), while upright total peripheral resistance was higher in hypertensive subjects with greater morning surge than those with lesser morning surge (P = 0.050). Morning surge was correlated positively with cfPWV (r = 0.59, P < 0.001) and negatively with sympathetic BRS (r = 0.51, P < 0.001) in hypertensive subjects only. Thus, morning BP surge is associated with arterial stiffness and sympathetic BRS, as well as vasoreactivity during orthostasis in hypertensive seniors.
Keywords: aging; circadian rhythm; hypertension; sympathetic nerve activity.