Pathophysiology of neurally-mediated syncope.
BACKGROUND
Neurally-mediated syncope (NMS) is defined as a transient loss of consciousness due to an abrupt and intermittent drop in blood pressure (BP).


OBJECTIVE
This study describes the putative pathophysiological mechanisms giving rise to NMS, the role of baroreflex (BR), and the interaction of its main haemodynamic variables: heart rate (HR) and BP.


METHODS
Episodic dysregulation affects control over the haemodynamic variables (HR and BP) mediated by baroreflex mechanisms. During active standing, individuals experience a profound transient drop in systolic BP due to the effect of gravity on the column of blood and probably also because of reflex vasodilation. Abnormalities in the BR in NMS could be due to a more profound drop in BP upon standing, or to delayed or incomplete vasoconstriction resulting from inhibited or delayed sympathetic activity.


CONCLUSIONS
Sympathetic hyperactivity is present in patients with NMS at rest and before syncope. During active standing or passive tilting, excessive tachycardia may be followed by bradycardia and profound hypotension. Recovery of systolic BP is delayed or incomplete.
Departamento de Neurología y Psiquiatría, Laboratorio de Neurofisiología Clínica, Instituto Nacional de Ciencias Médicas y Nutrición «Salvador Zubirán», México, D.F. Electronic address: caroline.malamud@gmail.com.
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Malamud-Kessler
Departamento de Neurología y Psiquiatría, Laboratorio de Neurofisiología Clínica, Instituto Nacional de Ciencias Médicas y Nutrición «Salvador Zubirán», México, D.F.
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Bruno
Departamento de Neurología y Psiquiatría, Instituto Nacional de Ciencias Médicas y Nutrición «Salvador Zubirán», México, D.F.
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Chiquete
Departamento de Neurología y Psiquiatría, Laboratorio de Neurofisiología Clínica, Instituto Nacional de Ciencias Médicas y Nutrición «Salvador Zubirán», México, D.F.
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Sentíes-Madrid
Departamento de Ciencias Exactas, Universidad Peruana Cayetano Heredia, Lima, Perú.
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Campos-Sánchez
D001341:Autonomic Nervous System / Q000503:physiopathology; D017704:Baroreflex; D001794:Blood Pressure; D006339:Heart Rate; D006801:Humans; D011187:Posture; D012018:Reflex; D013575:Syncope / Q000503:physiopathology*
Active Standing; Baroreflex; Barorreflejo; Neurally-mediated syncope; Ortostatismo activo; Prueba de inclinación; Síncope neuralmente mediado; Tilt test