Fuente Mora Cristina, Palma Jose-Alberto, Kaufmann Horacio, Norcliffe-Kaufmann Lucy
Department of Neurology, New York University School of Medicine, New York, USA.
J Cereb Blood Flow Metab. 2017 Jul;37(7):2414-2422. doi: 10.1177/0271678X16667524. Epub 2016 Jan 1.
Familial dysautonomia is an inherited autonomic disorder with afferent baroreflex failure. We questioned why despite low blood pressure standing, surprisingly few familial dysautonomia patients complain of symptomatic hypotension or have syncope. Using transcranial Doppler ultrasonography of the middle cerebral artery, we measured flow velocity (mean, peak systolic, and diastolic), area under the curve, pulsatility index, and height of the dictrotic notch in 25 patients with familial dysautonomia and 15 controls. In patients, changing from sitting to a standing position, decreased BP from 124 ± 4/64 ± 3 to 82 ± 3/37 ± 2 mmHg (p < 0.0001, for both). Despite low BP, all patients denied orthostatic symptoms. Middle cerebral artery velocity fell minimally, and the magnitude of the reductions were similar to those observed in healthy controls, in whom BP upright did not fall. While standing, patients had a greater fall in cerebrovascular resistance (p < 0.0001), an increase in pulsatility (p < 0.0001), and a deepening of the dicrotic notch (p = 0.0010), findings all consistent with low cerebrovascular resistance. No significant changes occurred in controls. Patients born with baroreflex deafferentation retain the ability to buffer wide fluctuations in BP and auto-regulate cerebral blood flow. This explains how they can tolerate extremely low BPs standing that would otherwise induce syncope.
家族性自主神经功能障碍是一种伴有传入性压力反射衰竭的遗传性自主神经疾病。我们不禁要问，为什么尽管家族性自主神经功能障碍患者站立时血压较低，但令人惊讶的是，很少有患者主诉有症状性低血压或晕厥。我们使用经颅多普勒超声检查大脑中动脉，测量了25例家族性自主神经功能障碍患者和15名对照者的血流速度（平均、收缩期峰值和舒张期）、曲线下面积、搏动指数和重搏波切迹高度。在患者中，从坐位变为站立位时，血压从124±4/64±3降至82±3/37±2 mmHg（两者p均<0.0001）。尽管血压较低，但所有患者均否认有体位性症状。大脑中动脉速度下降极小，下降幅度与健康对照者相似，而健康对照者站立时血压并未下降。站立时，患者的脑血管阻力下降幅度更大（p<0.0001），搏动性增加（p<0.0001），重搏波切迹加深（p=0.0010），所有这些结果均与脑血管阻力降低一致。对照者未发生显著变化。出生时即存在压力反射传入障碍的患者仍保留缓冲血压大幅波动和自动调节脑血流量的能力。这就解释了他们如何能够耐受站立时极低的血压，否则这种血压会诱发晕厥。
