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.