Department of Internal Medicine, Tampere School of Public Health, University of Tampere, Tampere, Finland.
Br J Clin Pharmacol. 2011 Jan;71(1):41-51. doi: 10.1111/j.1365-2125.2010.03794.x.
Nitrates may facilitate syncope through various pathways, but the precise mechanism of nitrate-induced syncope is still under debate. The purpose of the present study was to compare the underlying haemodynamic mechanisms in subjects without and with presyncopal symptoms during a nitroglycerin-stimulated tilt-table test.
A major decrease in systemic vascular resistance was documented in subjects with presyncope during 0.25 mg nitroglycerin-stimulated tilt-table test, in the absence of changes in cardiac output. These findings indicated that even a small dose of nitroglycerin significantly decreased arterial resistance and cardiac afterload. AIMS The mechanism of nitrate-induced syncope remains controversial. We examined the haemodynamic changes in healthy volunteers during nitroglycerin-stimulated tilt-table test.
Continuous radial pulse wave analysis, whole-body impedance cardiography and plethysmographic finger blood pressure were recorded in a supine position and during head-up tilt in 21 subjects with presyncopal symptoms (6 male/15 female, age 43 ± 3 years) after 0.25 mg sublingual nitroglycerin and 21 control subjects (6 male/15 female, age 43 ± 2 years). The drug was administered in the supine position and a passive head-up tilt followed 5 min later. Additionally, nitroglycerin was only administered during head-up tilt in 19 subjects and the haemodynamics were recorded.
Supine and upright haemodynamics were similar before nitroglycerin administration in the two groups. During the nitroglycerin-stimulated tilt test, aortic and radial mean blood pressure decreased significantly more in the presyncope group when compared with the controls (P= 0.0006 and P= 0.0004, respectively). The decreases in systemic vascular resistance (P= 0.0008) and heart rate (P= 0.002), and increase in aortic reflection time (P= 0.0002) were greater in the presyncope group, while the change in cardiac index was not different between the groups (P= 0.14). If nitroglycerin was administered during the upright tilt and not in supine position, the haemodynamic changes were quite corresponding.
Presyncopal symptoms during nitrate-stimulated tilt test were explained by decreased systemic vascular resistance and increased aortic reflection time, while cardiac output remained unchanged. These findings indicated reduced arterial resistance in nitroglycerin-induced presyncope.
硝酸盐可能通过多种途径促进晕厥，但硝酸盐引起晕厥的确切机制仍存在争议。本研究的目的是比较在硝酸甘油刺激倾斜试验中无先兆晕厥和有先兆晕厥患者的潜在血流动力学机制。
在 0.25 毫克硝酸甘油刺激倾斜试验中，有先兆晕厥的患者记录到全身血管阻力明显下降，而心输出量没有变化。这些发现表明，即使是小剂量的硝酸甘油也会显著降低动脉阻力和心脏后负荷。目的：硝酸盐引起的晕厥的机制仍存在争议。我们在硝酸甘油刺激倾斜试验中检查了健康志愿者的血流动力学变化。
21 名有先兆晕厥症状的受试者（6 名男性/15 名女性，年龄 43 ± 3 岁）和 21 名对照受试者（6 名男性/15 名女性，年龄 43 ± 2 岁）在舌下含服 0.25 毫克硝酸甘油后，分别在仰卧位和头高位倾斜位记录连续桡动脉脉搏波分析、全身阻抗心动图和容积描记手指血压。药物在仰卧位给予，5 分钟后进行被动头高位倾斜。此外，在 19 名受试者中仅在头高位倾斜时给予硝酸甘油，并记录血流动力学。
两组在硝酸甘油给药前的仰卧位和直立位血流动力学相似。在硝酸甘油刺激倾斜试验中，与对照组相比，先兆晕厥组的主动脉和桡动脉平均血压显著下降（P=0.0006 和 P=0.0004）。全身血管阻力（P=0.0008）和心率（P=0.002）下降，主动脉反射时间增加（P=0.0002）在先兆晕厥组更大，而心输出量在两组之间无差异（P=0.14）。如果硝酸甘油在直立倾斜时而不是仰卧位给予，血流动力学变化相当。
硝酸甘油刺激倾斜试验中的先兆晕厥症状可解释为全身血管阻力降低和主动脉反射时间增加，而心输出量保持不变。这些发现表明，在硝酸甘油引起的先兆晕厥中，动脉阻力降低。
