P78 PRESSURE-INDEPENDENT ROLE OF THE AUTONOMIC NERVOUS SYSTEM IN THE REGULATION OF ARTERIAL STIFFNESS IN SUBJECTS WITH ESSENTIAL HYPERTENSION

Abstract

Objective: To test if arterial stiffness (AS) can be modulated by the autonomic nervous system (ANS) independently of blood pressure (BP) in hypertensive patients. Material and methods: AS was measured by carotid-femoral pulse wave velocity (cfPWV) using the SphygmoCor device (AtCor Medical, Australia). Mean arterial pressure (MAP) was obtained by pulse-wave analysis of the radial artery and ANS activity was estimated by heart rate variability (HRV) as log-ratio of low-frequency/high-frequency heart rate components (Schiller Medilog AR12plus, United States) in hypertensive subjects (n = 43, 17 female, mean ± SD age 45 ± 13 years, brachial BP 145 ± 17/87 ± 10 mmHg) at rest. All measurements were subsequently repeated during supervised device-guided paced breathing (DGB) and reduction of cardiac pre-load by lower limb venous occlusion (LVO). These interventions, which are known to decrease and increase sympathetic activity, were performed in random order. Results: DGB reduced HRV by 0.14 [0.07, 0.20] (Mean [95% confidence intervals]) and LVO increased HRV by 0.13 [0.08, 0.18] (both P<0.05). DGB reduced cfPWV by 1.3 [0.9, 1.6] m/s alongside with a reduction in MAP of 6.6 [5.1, 8.1] mmHg (both P < 0.01). By contrast, LVO increased cfPWV by 1.0 [0.6,1.4] m/s (P < 0.01), despite a fall in MAP of 1.5 [0.2,2.7] mmHg (P < 0.05). The difference between effects of DGB and LVO on cfPWV was significant whether adjusted or unadjusted for change in MAP (P < 0.05). Conclusion: Despite BP-lowering effects, DGB and LVO had opposite effects on HRV and cfPWV. This suggest that the autonomic nervous system has a pressure-independent role in the regulation of AS in hypertension.