School of Science and Health, University of Western Sydney, Sydney, NSW, Australia.
Acta Physiol (Oxf). 2013 May;208(1):66-73. doi: 10.1111/apha.12087. Epub 2013 Mar 22.
The ability to maintain arterial blood pressure when faced with a postural challenge has implications for the occurrence of syncope and falls. It has been suggested that posture-induced declines in the mechanical component of the baroreflex response drive reductions in cardiovagal baroreflex sensitivity associated with postural stress. However, these conclusions are largely based upon spontaneous methods of baroreflex assessment, the accuracy of which has been questioned. Therefore, the aim was to engage a partially open-loop approach to explore the influence of posture on the mechanical and neural components of the baroreflex.
In nine healthy participants, we measured continuous blood pressure, heart rate, RR interval and carotid artery diameter during supine and standing postures. The modified Oxford method was used to quantify baroreflex sensitivity.
In response to falling pressures, baroreflex sensitivity was similar between postures (P = 0.798). In response to rising pressures, there was an attenuated (P = 0.042) baroreflex sensitivity (mean ± SE) in the standing position (-0.70 ± 0.11 beats min(-1) mmHg(-1)) compared with supine (-0.83 ± 0.06 beats min(-1) mmHg(-1)). This was explained by a diminished (P = 0.016) neural component whilst standing (-30.17 ± 4.16 beats min(-1) mm(-1)) compared with supine (-38.23 ± 3.31 beats min(-1) mm(-1)). These effects were consistent when baroreflex sensitivity was determined using RR interval.
Cardiovagal baroreflex sensitivity in response to rising pressures is reduced in young individuals during postural stress. Our data suggest that the mechanical component is unaffected by standing, and the reduction in baroreflex sensitivity is driven by the neural component.
在面对姿势挑战时维持动脉血压的能力与晕厥和跌倒的发生有关。有人认为，姿势引起的压力反射机械成分下降会导致与姿势应激相关的心迷走神经压力反射敏感性降低。然而，这些结论主要基于自发的压力反射评估方法，其准确性受到质疑。因此，本研究旨在采用部分开环方法探讨姿势对压力反射机械和神经成分的影响。
在 9 名健康参与者中，我们在仰卧和站立姿势下测量连续血压、心率、RR 间期和颈动脉直径。采用改良的牛津法来量化压力反射敏感性。
在血压下降时，两种姿势下的压力反射敏感性相似（P = 0.798）。在血压上升时，站立时的压力反射敏感性（站立时为-0.70 ± 0.11 次/min/mmHg，仰卧时为-0.83 ± 0.06 次/min/mmHg）减弱（P = 0.042）。这可以解释为站立时神经成分减弱（站立时为-30.17 ± 4.16 次/min/mm，仰卧时为-38.23 ± 3.31 次/min/mm），而机械成分不受影响。当使用 RR 间期确定压力反射敏感性时，也观察到了相同的结果。
在年轻个体中，姿势应激时，血压上升时的心迷走神经压力反射敏感性降低。我们的数据表明，机械成分不受站立影响，而压力反射敏感性的降低是由神经成分驱动的。
