Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Science, University of British Columbia, Kelowna, Canada;
Cardiovascular Stress Response Laboratory, School of Kinesiology and Health Studies, Queen's University, Kingston, Ontario, Canada.
J Appl Physiol (1985). 2017 Nov 1;123(5):1386-1396. doi: 10.1152/japplphysiol.00583.2017. Epub 2017 Aug 31.
Evidence indicates that increases in sympathetic nervous activity (SNA), and acclimatization to high altitude (HA), may reduce endothelial function as assessed by brachial artery flow-mediated dilatation (FMD); however, it is unclear whether such changes in FMD are due to direct vascular constraint, or consequential altered hemodynamics (e.g., shear stress) associated with increased SNA as a consequence of exposure to HA. We hypothesized that ) at rest, SNA would be elevated and FMD would be reduced at HA compared with sea-level (SL); and ) at SL and HA, FMD would be reduced when SNA was acutely increased, and elevated when SNA was acutely decreased. Using a novel, randomized experimental design, brachial artery FMD was assessed at SL (344 m) and HA (5,050 m) in 14 participants during mild lower-body negative pressure (LBNP; -10 mmHg) and lower-body positive pressure (LBPP; +10 mmHg). Blood pressure (finger photoplethysmography), heart rate (electrocardiogram), oxygen saturation (pulse oximetry), and brachial artery blood flow and shear rate (Duplex ultrasound) were recorded during LBNP, control, and LBPP trials. Muscle SNA was recorded (via microneurography) in a subset of participants ( = 5). Our findings were ) at rest, SNA was elevated ( < 0.01), and absolute FMD was reduced ( = 0.024), but relative FMD remained unaltered ( = 0.061), at HA compared with SL; and ) despite significantly altering SNA with LBNP (+60.3 ± 25.5%) and LBPP (-37.2 ± 12.7%) ( < 0.01), FMD was unaltered at SL ( = 0.448) and HA ( = 0.537). These data indicate that acute and mild changes in SNA do not directly influence brachial artery FMD at SL or HA. The role of the sympathetic nervous system on endothelial function remains unclear. We used lower-body negative and positive pressure to manipulate sympathetic nervous activity at sea level and high altitude and measured brachial endothelial function via flow-mediated dilation. We found that acutely altering sympathetic nervous activity had no effect on endothelial function.
证据表明，交感神经活动（SNA）的增加和对高海拔（HA）的适应可能会降低通过肱动脉血流介导的扩张（FMD）评估的内皮功能；然而，尚不清楚 FMD 的这种变化是由于直接的血管限制，还是由于 SNA 增加导致的相关血流动力学改变（例如，剪切力），这是由于暴露于 HA 所致。我们假设）在休息时，与海平面（SL）相比，HA 时 SNA 升高，FMD 降低；并且）在 SL 和 HA 时，当 SNA 急性升高时，FMD 会降低，而当 SNA 急性降低时，FMD 会升高。使用一种新颖的随机实验设计，在 14 名参与者中，在轻度下体负压（LBNP；-10mmHg）和下体正压（LBPP；+10mmHg）下，在 SL（344m）和 HA（5050m）评估肱动脉 FMD。在 LBNP、对照和 LBPP 试验期间记录血压（手指光电容积描记法）、心率（心电图）、血氧饱和度（脉搏血氧饱和度）以及肱动脉血流量和剪切率（双功能超声）。在一部分参与者中（=5）记录肌肉 SNA（通过微神经记录）。我们的发现是）在休息时，与 SL 相比，SNA 升高（<0.01），绝对 FMD 降低（=0.024），但相对 FMD 保持不变（=0.061），在 HA；并且）尽管 LBNP（+60.3±25.5%）和 LBPP（-37.2±12.7%）显著改变了 SNA（<0.01），但 SL（=0.448）和 HA（=0.537）的 FMD 仍未改变。这些数据表明，SL 和 HA 时，急性和轻度 SNA 变化不会直接影响肱动脉 FMD。交感神经系统对内皮功能的作用仍不清楚。我们使用下体负压和正压在海平面和高海拔调节交感神经活动，并通过血流介导的扩张测量肱动脉内皮功能。我们发现，急性改变交感神经活动对内皮功能没有影响。
