Posted by danf on October 26, 2000, at 14:42:44
In reply to Re: Hypoglycemia, posted by dove on October 25, 2000, at 14:45:44
some help with vasovagal stuff.
vaso vagal faints are by definition, neurogenic in nature.
some stimulus causes the heart rate to slow down & bp falls. In some, part of the event is mediated by peripheral dilation of the extremities so that blood pools in the extremities & does not go back to the heart quick enough to be pumped out.
Not enough blood goes to the brain & we faint. a short warning of a few seconds is present. While not impossible, one will usually not faint if lying down as adequate blood returns to the heart to keep some perfusion (blood flow) to the brain.
after the BP / HR control 'escapes' from the slow HR, the BP & HR both go 'high' for a short while ( few minutes). this sequence is easy to see if another person is present to monitor BP & HR.
IT can be induced if some one has a sensitive carotid sinus ( 'sensitive carotid sinus syndrome' ) in the neck & is wearing a tight collar for instance, or has the neck massaged.
a mechanism present in some people is putting the head under water ( a variation of the 'diving reflex' ). A deep yawn may trigger a variation of this same reflex pathway.
An interesting sister reflex, is initiation of a sneeze when a bright light is shined in the eyes, or by walking from a shaded room to bright sunlight.
It is unknown why some people have these reflexes activated in a powerful way at times. All people have the reflexes, but they are rarely triggered in such a powerful way. Perhaps some neurologic meds have an influence.
Anything which causes peripheral dilation may cause blood to pool in the extremities & possible fainting. A hot shower or bath are examples. some meds, like aldomet, partially paralize the bodys ability to respond to postural changes.
However these other mechanisms are not vasovagal, by definition.
poster:danf
thread:47237
URL: http://www.dr-bob.org/babble/20001022/msgs/47426.html