Vasovagal syncope and tilt table test

[Cytarabine]

Could anyone explain why a tilt table test would elicit a response for vasovagal syncope? For orthostatic hypotension, it's obvious, but I thought the trigger in vasovagal syncope was fear, pain, etc. Why would positional changes trigger it? Or are only individuals with some form of underlying autonomic dysfunction predisposed to vasovagal syncope?

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[link2swim06]

You are comparing apples and oranges.

Orthostatic hypotension simply means there isn't enough fluid in the body to keep the BP normal when changing position.

Vasovagal syncope means passing out due to a decrease in heart rate (which could be dehydration aka orthostatic hypotension....but more commonly during a bowel movement or with extreme pain/fear).

The tilt table test is looking at the body's response to position change.

If the tilt table induces an increase HR and significant drop in BP then it might be just orthostatic hypotension.
But if it causes a drop in BP, drop in HR, and an episode of syncope then it is possibly vasovagal syncope.

 

[Priapism4tooLong]

Could anyone explain why a tilt table test would elicit a response for vasovagal syncope? For orthostatic hypotension, it's obvious, but I thought the trigger in vasovagal syncope was fear, pain, etc. Why would positional changes trigger it? Or are only individuals with some form of underlying autonomic dysfunction predisposed to vasovagal syncope?

The sympathetic system is not only just activated in fear, or pain situations. It's used also as way to regulate blood flow, which will be needed in a tilt table test.

 

[Cytarabine]

Thank you for the replies. I understand that. What I'm asking is, why would a positional change trigger a vasovagal reaction at all? Someone sees blood, they freak out, have a vasovagal response with increased vegan tone and sympatholysis, some combo of vasodilation and bradycardia occurs, they pass out. Why would these same individuals have any response to a tilt table test?

 

[link2swim06]

When you stand up your sympathetic system is suppose to engage to keep your BP up (the act of standing up is an orthostatic stressor).

If you stand up and your vagal systems engages instead then you get a drop in BP and drop in HR.

If your BP and HR drop too much, then so do you (aka vasovagal syncope).

 

[Cytarabine]

When you stand up your sympathetic system is suppose to engage to keep your BP up (the act of standing up is an orthostatic stressor).

If you stand up and your vagal systems engages instead then you get a drop in BP and drop in HR.

If your BP and HR drop too much, then so do you (aka vasovagal syncope).

Thanks for the reply. So you're saying that these individuals who pass out with pain, stress, the sight of blood, etc. have an underlying autonomic dysfunction that makes them unable to regulate their bp with positional changes? I was under the impression vasovagal syncope could happen to more or less anyone

 

[Priapism4tooLong]

Thanks for the reply. So you're saying that these individuals who pass out with pain, stress, the sight of blood, etc. have an underlying autonomic dysfunction that makes them unable to regulate their bp with positional changes? I was under the impression vasovagal syncope could happen to more or less anyone

You realize that the pain, stress, sight of blood response is sympathetic as is the positional change. its the same system. And i think vasovagal syncope can happen to anyone but its a lot more severe in some people.

 

[Cytarabine]

You realize that the pain, stress, sight of blood response is sympathetic as is the positional change. its the same system. And i think vasovagal syncope can happen to anyone but its a lot more severe in some people.

Errr, I'm coming out of a gap year, so I'm a bit rusty, but by definition vasovagal syncope is an inappropriate parasympathetic response to that pain, stress, etc., not a sympathetic one, no?

 

[Priapism4tooLong]

Errr, I'm coming out of a gap year, so I'm a bit rusty, but by definition vasovagal syncope is an inappropriate parasympathetic response to that pain, stress, etc., not a sympathetic one, no?

No you are right it is. Vasovagal syncope is due to the incorrect response of the parasympathetic system WHEN the sympathetic system should be activated. SO to trigger the sympathetic system things you can do is feel fear, pain OR change position.

 

[Cytarabine]

Right. I guess my confusion is, is there a general underlying predisposition to vasovagal syncope that would make an individual who experiences it when they see blood also more likely to experience it during pain or sudden standing? My prior understanding was that except for a select few, it was more or less specific to the situation, which is why I'm not seeing why there would be a positive tilt table test.

 

[Priapism4tooLong]

Right. I guess my confusion is, is there a general underlying predisposition to vasovagal syncope that would make an individual who experiences it when they see blood also more likely to experience it during pain or sudden standing? My prior understanding was that except for a select few, it was more or less specific to the situation, which is why I'm not seeing why there would be a positive tilt table test.

It is situational based on how the patient responds to stimuli. If he's scared of blood etc. The tilt table test doesn't give you the option of being scared, it HAS to activate your sympathetic system to regulate blood flow.

does it make sense now? or am i missing something?

 

[Cytarabine]

Sorry, I'm probably the cause of confusion/miscommunication.

I agree with

It is situational based on how the patient responds to stimuli. If he's scared of blood etc. The tilt table test doesn't give you the option of being scared, it HAS to activate your sympathetic system to regulate blood flow.

Where I'm confused is that step up to medicine says (under vasovagal syncope) "Tilt-table study can reproduce the symptoms in susceptible people." If the vasovagal response is situation specific in these individuals, why would it also be triggered by the positional change in a tilt-table study?

 

[Priapism4tooLong]

Sorry, I'm probably the cause of confusion/miscommunication.

I agree with



Where I'm confused is that step up to medicine says (under vasovagal syncope) "Tilt-table study can reproduce the symptoms in susceptible people." If the vasovagal response is situation specific in these individuals, why would it also be triggered by the positional change in a tilt-table study?

Ok i think you are over thinking this lol. By situation specific it just means that whatever triggers that person sympathetic system the most is going to cause syncope, for instance the guy is scared of blood but not spiders. If he see's blood he's going to faint right. But if he see's spiders he's fine, he doesn't faint. But what does seeing the blood actually do?? its supposed to trigger a sympathetic response but instead triggers a serious parasympathetic response and causes him to faint. I know you understand that.

So before doing any test there has to be a reason. We want to see what happens if we activate this guys sympathetic system, does he faint?. If he faints then its most likely vasovagal syncope. You are activating the sympathetic system with the tilt table test, its that simple. It's not like just because he faints seeing blood absolutely NOTHING else is going to make him faint. Anything that will cause an increase sympathetic stimulation will make him faint. I don't know in-depth details about the pathophys of the disease though and what exactly happens.

Also not everyone with vasovagal syncope will have a (+) tilt table test.

 

[Cytarabine]

What I mean by specific situation is, it's typically certain things that make people freak out - e.g. needles. I was under the impression for vasovagal syncope, it typically takes an inordinate sympathetic response to trigger the vagal tone. That's why someone might pass out when they get stuck with a needle, but they're not passing out when they get out of bed. Or are these the same people (or is there a subset of these people) who risk or come close to passing out when they get out of bed? Because that isn't what I understood to be the case.

Thanks for bearing with me

 

[link2swim06]

What I mean by specific situation is, it's typically certain things that make people freak out - e.g. needles. I was under the impression for vasovagal syncope, it typically takes an inordinate sympathetic response to trigger the vagal tone. That's why someone might pass out when they get stuck with a needle, but they're not passing out when they get out of bed. Or are these the same people (or is there a subset of these people) who risk or come close to passing out when they get out of bed? Because that isn't what I understood to be the case.

Thanks for bearing with me

First, realize a tilt table isn't an amazing test. It is simply trying to activate the sympathetic system (or the parasympathetic in the case of vasovagal syncope). It is very possibly it might not get the same response as a fear of something. However, it is an easy standardized test to run. You cannot really keep live spiders (snakes, bears, etc.) in the hospital and show them to patients and try to get them to pass out. We give the test because we know that the sympathetic/parasympathetic systems have the same response more or less regardless of the stimuli. This is one of the many ways to try to trigger the mis-wiring where the parasymp fires up when the symp was suppose to.

Just memorize:
Orthostatic Hypotension = Drop in BP + Increase in HR
Vasovagal Syncope = Drop in BP + Drop in HR + Syncope

You can have orthostatic syncope or vasovagal syncope....that is determined how your body responded to the stimuli (did HR go up or down?).

 

[Priapism4tooLong]

What I mean by specific situation is, it's typically certain things that make people freak out - e.g. needles. I was under the impression for vasovagal syncope, it typically takes an inordinate sympathetic response to trigger the vagal tone. That's why someone might pass out when they get stuck with a needle, but they're not passing out when they get out of bed. Or are these the same people (or is there a subset of these people) who risk or come close to passing out when they get out of bed? Because that isn't what I understood to be the case.

Thanks for bearing with me

Getting out of bed will not stimulate the sympathetic as much as being jabbed with a needle. But they may get light headed getting out of bed but they may not faint because of it.....or they may be totally asymptomatic. Anything is possible in medicine lol.

haha np, i hope you understand it a bit better.

 

[Priapism4tooLong]

if you still don't understand it, forget everything you knew about vasovagal syncope and re read this whole thread.

 

[Kahreek]

he asks too many questions.
Vasovagal triggered by fear is of psychogenic nature and thus very hard to deliniate.
What we know is there is parodoxal response to stress, by cardioinhibition and vasodepression wich leads to fainting especially if you are in upright position. People with autonomic neuropathy have a similar response because their nerves are messed by diabetes for example.
People that pass out while getting out of the bed are probably the latter with organic autonomic neuropathy.
People that pass out seeing blood are probably the ones with psychogenic autonomic pathology (if we can agree to call it that). (triggered by thalamus probably)