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目的：探讨神经介导的反射性晕厥低血压的发生机制。方法56例直立倾斜试验阳性的神经介导的反射性晕厥患者入选该回顾性研究，分为二组：常规组27例患者(无药物激发的60°头高位倾斜试验阳性)、药物激发组29例患者(0.4mg 硝酸甘油舌下含服激发的60°头高位倾斜试验阳性)。对比二组患者倾斜试验中无创血流动力学参数的变化过程。结果硝酸甘油的药物激发没有改变血管迷走反应的模式；晕厥发生过程中系统血管阻力未出现明显降低，晕厥的低血压主要由于心排量的严重突然下降所致。结论在直立倾斜试验中，心排量的骤然下降是导致反射性晕厥低血压的决定性因素；倾斜试验中，硝酸甘油的激发并不能改变晕厥发生过程中血流动力学的变化模式。“,”Objective To assess the determinants of hypotension during drug - free and Nitroglycerine (NTG)induced syncope in routine tilt table testing.Methods A total of 56 patients with neurally media-ted syncope and a positive tilt test were selected in this retrospective study.Syncope was provoked by 0.4 mg sublingual NTG in 29 patients,administered in the 60°head-up tilt position,while syncope was pro-voked by passive tilt alone in other 27 patients.No invasive finger arterial pressure was monitored continu-ously and hemodynamic parameters were computed from the pressure pulsations.Results The use of NTG did not affect circulatory patterns precipitating a vasovagal response.Hypotension during syncope was me-diated by a marked drop in cardiac output,while systemic vascular resistance was well maintained.Conclu-sion In routine tilt testing,hypotension is cardiac output-mediated the mechanism of which appears inde-pendent on the use of sublingual NTG.