Regulation of arterial blood pressure: effects of arterial stiffness and respiration

Background. Baroreceptors (arterial stretch receptors) regulate blood pressure (BP). Arterial stiffness increases with age, leading to decreased baroreflex sensitivity (BRS) and altered autonomic nervous system (ANS) feedback. Slow breathing, through stretch receptor activation and BRS and ANS feedback, is said to lower BP. This study aimed (i) to confirm relationships between BRS, ANS, and arterial stiffness, and (ii) to quantify haemodynamic changes with slow breathing. Methods. In 30 healthy subjects (20-66 years, 15 female), arterial stiffness was determined by carotid-femoral pulse wave velocity (cfPWV) and aortic augmentation index (aAIx), measured non-invasively. R-R interval and finger BP was continuously measured during 10 minutes each free breathing, and 0.1Hz breathing rate with 50% and 70% inspiration. BRS was estimated from spontaneous changes in systolic BP and corresponding interbeat interval (sequence technique). ANS (sympathetic and parasympathetic) input was measured through low and high frequency components of heart rate variability normalized to total power. Results. BRS was not significantly correlated with cfPWV (R²=0.06, p=0.223) but was with aAIx (R²=0.15, p=0.036) and sympathetic activity (R²=0.05, p=0.042). BP did not change with slow breathing (brachial systolic BP, free breathing: 117±13 mmHg, 0.1Hz/50% inspiration: 117±13 mmHg, 0.1Hz/70% inspiration: 118±13 mmHg, p=0.817), nor did BRS (p=0.103) but sympathetic activity increased (0.27±0.11, 0.41±0.19, 0.39±0.18 respectively, p˂0.001). Conclusion. BRS was correlated with aAIx but not with aortic stiffness as measured by cfPWV. Slow breathing increased sympathetic activity but did not alter BP. It is proposed that compensatory effects (sympathetic activity) overrides the BP reduction effects of slow breathing.