Department of Physiology, New York Medical College, Valhalla, New York 10532, USA.
Am J Physiol Heart Circ Physiol. 2011 Sep;301(3):H1033-42. doi: 10.1152/ajpheart.00018.2011. Epub 2011 May 27.
Low flow postural tachycardia syndrome (LFP) is associated with vasoconstriction, reduced cardiac output, increased plasma angiotensin II, reduced bioavailable nitric oxide (NO), and oxidative stress. We tested whether ascorbate would improve cutaneous NO and reduce vasoconstriction when delivered systemically. We used local cutaneous heating to 42°C and laser Doppler flowmetry to assess NO-dependent conductance (%CVC(max)) to sodium ascorbate and the systemic hemodynamic response to ascorbic acid in 11 LFP patients and in 8 control subjects (aged 23 ± 2 yr). We perfused intradermal microdialysis catheters with sodium ascorbate (10 mM) or Ringer solution. Predrug heat response was reduced in LFP, particularly the NO-dependent plateau phase (56 ± 6 vs. 88 ± 7%CVC(max)). Ascorbate increased baseline skin flow in LFP and control subjects and increased the LFP plateau response (82 ± 6 vs. 92 ± 6 control). Systemic infusion experiments used Finometer and ModelFlow to estimate relative cardiac index (CI) and forearm and calf venous occlusion plethysmography to estimate blood flows, peripheral arterial and venous resistances, and capacitance before and after infusing ascorbic acid. CI increased 40% after ascorbate as did peripheral flows. Peripheral resistances were increased (nearly double control) and decreased by nearly 50% after ascorbate. Calf capacitance and venous resistance were decreased compared with control but normalized with ascorbate. These data provide experimental support for the concept that oxidative stress and reduced NO possibly contribute to vasoconstriction and venoconstriction of LFP.
低流量体位性心动过速综合征（LFP）与血管收缩、心输出量减少、血浆血管紧张素 II 增加、生物可利用的一氧化氮（NO）减少和氧化应激有关。我们测试了全身性给予抗坏血酸是否会改善皮肤 NO 并减少血管收缩。我们使用局部皮肤加热至 42°C 和激光多普勒流量测量法来评估对钠抗坏血酸的 NO 依赖性传导（%CVC(max)）以及抗坏血酸对 11 名 LFP 患者和 8 名对照者的全身血流动力学反应（年龄 23 ± 2 岁）。我们用 10 mM 抗坏血酸钠或林格溶液灌注皮内微透析导管。LFP 患者的药物预处理热反应降低，尤其是 NO 依赖性平台期（56 ± 6%比 88 ± 7%CVC(max)）。抗坏血酸增加了 LFP 和对照组的基础皮肤血流量，并增加了 LFP 平台反应（82 ± 6%比 92 ± 6%对照组）。系统输注实验使用 Finometer 和 ModelFlow 来估计相对心指数（CI），使用前臂和小腿静脉闭塞容积描记术来估计血流量、外周动脉和静脉阻力以及输注抗坏血酸前后的电容。抗坏血酸输注后 CI 增加了 40%，外周血流量也增加了。抗坏血酸输注后外周阻力增加（接近对照组的两倍），降低了近 50%。与对照组相比，小腿电容和静脉阻力降低，但用抗坏血酸后正常化。这些数据为氧化应激和 NO 减少可能导致 LFP 的血管收缩和静脉收缩的概念提供了实验支持。
