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Syncope: Physiology, Pathophysiology and Aeromedical Implications
Published in Anthony N. Nicholson, The Neurosciences and the Practice of Aviation Medicine, 2017
David A. Low, Christopher J. Mathias
Autonomic (neurally or reflex) mediated syncope is the most frequent cause of syncope. Autonomic (neurally) mediated syncope traditionally refers to a heterogeneous group of conditions in which the cardiovascular reflexes that are normally useful in controlling the circulation become intermittently inappropriate, in response to a trigger, resulting in vasodilatation through sympathetic nerve activity withdrawal and/or bradycardia via increased vagal activity and thereby a fall in arterial blood pressure and global cerebral perfusion. There are three major forms of autonomic (neurally) mediated syncope: vasovagal syncope, carotid sinus hypersensitivity and situational syncope. Vasovagal syncope is the most common form and is also referred to as common faints or emotional syncope as provoking factors include fear, pain and psychological factors. Nausea and other gastrointestinal upsets, probably through activation of visceral afferents, may also be causative.
Tests for the identification of reflex syncope mechanism
Published in Expert Review of Medical Devices, 2023
Michele Brignole, Giulia Rivasi, Artur Fedorowski, Marcus Ståhlberg, Antonella Groppelli, Andrea Ungar
The diagnosis of reflex (vasovagal) syncope requires reproduction of syncope along with the characteristic hemodynamic pattern of reflex hypotension/bradycardia [2,13]. At some moment after tilt-up, BP starts to decrease slowly and slightly for several minutes. At this stage HR increases slightly, indicating the activation of compensatory baroreflex mechanisms to orthostatic stress. HR then decreases, indicating the onset of cardioinhibition. Some degree of bradycardia is always present at the time of reflex syncope and indicates the activation of the vagal phase of the reflex. According to the magnitude of bradycardia, positive responses to TT are classified as VD (minimal heart rate decrease, i.e. less than 10%), mixed (heart rate decrease >10% but without asystolic pause >3 s) or CI (one or more asystolic pause >3 s) [50].