Posted by danf on October 27, 2000, at 11:11:38
In reply to Re: vasovagal fainting, posted by noa on October 27, 2000, at 6:36:39
It is an interesting question.
anaemia & hypoglycemia lower the threshold for fainting, but the mechanism is usually not vasovagal.
For anaemia to have a significant effect, it must be severe & this tends to be a positional /change of position effect where blood flow rates are high from the anaemia & do not compensate. AS in, peripheral vessela are dilated & one stands up & faints... 'orthostatic fainting'
hypoglycemia is similar but is driven by glucose supply to the brain. As blood glucose falls, neurologic function starts to fail, this includes all levels, conscious & autonomic plus the body pumps out adrenaline to keep blood glucose levels up ( the jittery feeling some people get that warns them the glucose level is falling ). Then as glucose stores are used, glucose levels quickly fall & fainting occurs.
Then for meds. since vasovagal is triggered by a cholinergic episode ( heart slowing), any med that increases cholinergic tone has the theoritical potential to lower the threshold for vasovagal fainting ( gagging & retching increases this tone, by the way).
most SSRIs & ADs fall into this catagory. However, they do not in practice, seem to have this side effect.
Many other meds may have fainting as a side effect. beta blockers, High BP meds of all classes, Heart meds, angina meds, etc... however most of these cause fainting by affecting BP control, or peripheral resistance, etc, not by affecting vagal tone.
I know when I started celexa, that I yawned like crazy for a couple of weeks. I also coughed & gagged. there was some light-headed-ness with the coughing /gagging, but never a full faint.
I think it is possible for an AD med to lower the VV threshold, but unless it happenes more than once it will be difficult to trace the cause. Most would consider this to be an idiosyncratic reaction, if present.
poster:danf
thread:47237
URL: http://www.dr-bob.org/babble/20001022/msgs/47508.html