Relationship between sympathetic baroreflex sensitivity and arterial stiffness in elderly men and women

Abstract

Previous human studies have shown that large-artery stiffness contributes to an age-related decrease in cardiovagal baroreflex sensitivity. Whether this is also true with sympathetic baroreflex sensitivity is unknown. We tested the hypothesis that sympathetic baroreflex sensitivity is associated with the stiffness of baroreceptor segments (the carotid artery and the aorta) in elderly individuals and that sex affects this relationship. Sympathetic baroreflex sensitivity was assessed from the spontaneous changes in beat-by-beat diastolic pressure and corresponding muscle sympathetic nerve activity (microneurography) during supine rest in 30 men (mean±SEM: 69±1 years) and 31 women (68±1 years). Carotid artery stiffness (B-mode ultrasonography) and aortic stiffness (MRI) were also determined. We found that elderly women had lower sympathetic baroreflex sensitivity than elderly men (-2.33±0.25 versus -3.32±0.25 bursts · 100 beats(-1) · mm Hg(-1); P=0.007). β-Stiffness indices of the carotid artery and the aorta were greater in elderly women than in men (6.68±0.48 versus 5.10±0.50 and 4.03±0.47 versus 2.68±0.42; both P<0.050). Sympathetic baroreflex sensitivity was inversely correlated with carotid artery stiffness in both men and women (r=0.49 and 0.50; both P<0.05), whereas this relation was shifted in parallel upward (toward a reduced sensitivity) in women with no changes in the slope (0.26 versus 0.24 arbitrary units). Sympathetic baroreflex sensitivity and aortic stiffness showed similar trends. Thus, barosensory artery stiffness seems to be one independent determinant of sympathetic baroreflex sensitivity in elderly men and women. The lower sympathetic baroreflex sensitivity in elderly women may predispose them to an increased prevalence of hypertension.

Figure 1

Sympathetic baroreflex sensitivity (BRS) calculated from burst incidence (A) and total MSNA (B) during spontaneous breathing in the supine position, and cardiovagal BRS assessed during phase II (C) and phase IV (D) of the Valsalva maneuver in elderly men and women. Values are means±SEM.

Figure 2

β-stiffness indices of the carotid artery assessed using ultrasonography (A) and the aorta assessed using magnetic resonance images with the aortic pressure computed by transfer function from radial artery and with the carotid artery pressure directly measured by tonometory (calibrated by brachial BP) (B) in elderly men and women. Values are means±SEM.

Figure 3

Linear regression analysis of the inter-individual relationship between sympathetic BRS and β-stiffness of the carotid artery (A; 30 men, 31 women) and the aorta (28 and 29) calculated with aortic pressure derived from transfer function analysis (B) and carotid artery pressure (C) in all subjects and in elderly men (○) and women (●), separately.