Editing Reflex syncope (section)

==Pathophysiology==
Regardless of the trigger, the mechanism of syncope is similar in the various vasovagal syncope syndromes. The [[nucleus tractus solitarii]] of the [[brainstem]] is activated directly or indirectly by the triggering stimulus, resulting in simultaneous enhancement of [[parasympathetic nervous system]] ([[vagal]]) tone and withdrawal of [[sympathetic nervous system]] tone.{{citation needed|date=April 2021}}

This results in a spectrum of hemodynamic responses:{{cn|date=May 2024}}
# On one end of the spectrum is the cardioinhibitory response, characterized by a drop in heart rate (negative [[chronotropic]] effect) and in contractility (negative [[inotropic]] effect) leading to a decrease in cardiac output that is significant enough to result in a loss of consciousness. It is thought that this response results primarily from enhancement in [[parasympathetic tone]].
# On the other end of the spectrum is the vasodepressor response, caused by a drop in blood pressure (to as low as 80/20) without much change in heart rate. This phenomenon occurs due to [[vasodilation|dilation of the blood vessels]], probably as a result of withdrawal of [[sympathetic nervous system]] tone.
# The majority of people with vasovagal syncope have a mixed response somewhere between these two ends of the spectrum.

One account for these physiological responses is the [[Bezold-Jarisch reflex]].

Vasovagal syncope may be part of an evolved response, specifically, the [[fight-or-flight response]].<ref>{{cite journal |title=Vasovagal syncope in humans and protective reactions in animals|date=2015|vauthors=Blanc JJ, Alboni P, Benditt DG|pmid=25662986|doi=10.1093/europace/euu367|volume=17|issue=3|journal=Europace|pages=345–9|doi-access=free}}</ref><ref>{{cite journal |title=Vasovagal Syncope As A Manifestation Of An Evolutionary Selected Trait|journal=Journal of Atrial Fibrillation|date=2014|vauthors=Alboni P, Alboni M|pmc=5135249|pmid=27957092|doi=10.4022/jafib.1035|volume=7|issue=2|page=1035|doi-broken-date=1 November 2024}}</ref>