vasovagal syncope

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aioo

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Hallo,

I have some basic question about vasovagal syncope. But i cant find the answer anywhere.

Why is it that you get an increased vagal tone when you see blood or get scared and things like that. Which lead to vasodilation and or bradycardia which leads to the syncope?

Wouldnt you expect the opposite, so that you would get an increased symphatetic tone? I have never heard a clear explenation how this works.

thanks

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Here's an interesting article on the topic: Resting Vagal Tone and Vagal Response to Stress: Associations with Anxiety, Aggression and Perceived Anxiety Control among Youth

It helps to consider that there is resting neurogenic tone in both the sympathetic and parasympathetic systems. Emotional or physical stressors can have a differential or temporally dispersed effect on the two systems -- hence why some people get an initial parasympathetic surge over idiosyncratic emotional stressors like the sight of blood, which is unopposed by an increase in sympathetic tone. As a result you get transient nausea, bradycardia, and sometimes syncope. If you wait a little longer, there may be a sympathetic tone increase as well, but by then the damage is done.

Other stresses can invoke an initial sympathetic response, like public speaking makes some people sweaty, clammy, and tachycardic. Exercises to increase parasympathetic tone, such as deep slow breathing, meditation, etc. counteract this response through an increase in parasympathetic tone.

While I've seen hand-waving hypotheses about the nature of the stressor playing a role, with "other-directed" stressors (i.e. an empathic experience of someone else's situation) provoking parasympathetic responses and "self-directed" stressors (i.e. existential threats to the self) provoking sympathetic responses, I'm not personally aware of any science behind that. I sort of get the idea of it, though. Seeing someone else bleeding is kind of different than seeing yourself bleeding. Maybe that's all there is to it.
 
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