Kaufmann Horacio, Bhattacharya Kirsty
Autonomic Nervous System Laboratory, Department of Neurology, Mount Sinai School of Medicine, New York, New York 10029, USA.
Neurologist. 2002 May;8(3):175-85. doi: 10.1097/00127893-200205000-00004.
Syncope is caused by a severe but reversible reduction in blood flow to the brain stem neurons responsible for supporting consciousness (reticular activating system). Neurally mediated syncope, also referred to as vasovagal or reflex syncope, is the most frequent cause of loss of consciousness in apparently normal subjects.
Neurally mediated syncope is believed to be a reflex response with afferent, central, and efferent pathways. Characteristic autonomic changes in neurally mediated syncope are an increase in parasympathetic efferent activity causing bradycardia and a reduction in sympathetic vasoconstrictor outflow causing vasodilatation. Premonitory symptoms, such as nausea, diaphoresis, abdominal discomfort, and blurred vision, are caused by autonomic activation and are distinguishing features of neurally mediated syncope. Neurally mediated syncope frequently has a characteristic trigger, although this may not be apparent. Testing orthostatic tolerance during passive head-up tilt is the best available diagnostic procedure to evaluate patients with syncope in whom a cardiac cause has been excluded. In many cases, once the diagnosis of neurally mediated syncope is confirmed, it may suffice to reassure the patient and teach him to avoid known triggers and to recognize and act upon early warning symptoms. Because subjects with neurally mediated syncope may potentially be sodium depleted, increasing salt intake can be beneficial in improving their orthostatic intolerance.
Neurally mediated syncope is the most common form of syncope in healthy adults. The best diagnostic tools are the clinical history and passive head-up tilt. The best treatment strategies are the avoidance of triggering factors as well as intravascular volume expansion.
晕厥是由负责维持意识的脑干神经元（网状激活系统）血流严重但可逆性减少所致。神经介导性晕厥，也称为血管迷走性或反射性晕厥，是明显正常人群中意识丧失最常见的原因。
神经介导性晕厥被认为是一种具有传入、中枢和传出通路的反射反应。神经介导性晕厥的特征性自主神经变化是副交感传出活动增加导致心动过缓，以及交感缩血管神经传出减少导致血管扩张。前驱症状，如恶心、出汗、腹部不适和视力模糊，是由自主神经激活引起的，是神经介导性晕厥的显著特征。神经介导性晕厥通常有一个特征性诱因，尽管可能不明显。在被动头高位倾斜试验中测试直立耐受性是评估已排除心脏病因的晕厥患者的最佳可用诊断方法。在许多情况下，一旦确诊为神经介导性晕厥，安抚患者并教导其避免已知诱因、识别早期预警症状并采取相应行动可能就足够了。由于神经介导性晕厥患者可能存在潜在的钠缺乏，增加盐摄入量可能有助于改善其直立不耐受。
神经介导性晕厥是健康成年人中最常见的晕厥形式。最佳诊断工具是临床病史和被动头高位倾斜试验。最佳治疗策略是避免触发因素以及扩充血管内容量。
