[Indaemed_Freelist.Org] Vaso-Vagal-Syncope [was Syncope evaluation [was Re: Re: NMS]]
- From: USM Bish <bish@xxxxxxxxxxx>
- To: indaemed@xxxxxxxxxxxxx
- Date: Mon, 22 Mar 2004 00:19:08 +0530
On Sun, Mar 21, 2004 at 01:39:22PM +0530, SS Mishra wrote:
>
> First of all, VVS is not essentially a baroreceptor induced
> phenomenon !!!!!!!
>
I am not certain what the latest journals say on the subject,
but as I understand VVS is not a primary entitly, it is merely
a response phenomenon (which has neuro-vascular components).
> Today, more and more evidence is gathering for it to be a
> centrally mediated process.
It was no different when I did my I MBBS over 30 years ago !
The live example of VVS (explained by our Prof) was the
fainting spell one girl in our batch had on the sight of blood
being drawn from her veins ! Surely, the origin was central
(psychological), but the manifestation was through ANS/
baro-receptor based physiology. He explained the whole process,
and I remember it clean as being baro-receptor mediated. Things
may have changed now, but frankly, I am quite unaware of these
recent changes in the explanation process.
I tried to find out over the internet, but could not find any-
thing in this regard. To the contrary, a search for vaso vagal
syncope on google threw out 957 links. One of the first was
from the Univ of Columbia, Neurology Dept. This is aimed at lay
audience (Patient information, as they call it).
This are the first three paras:
------------------------<snip>---------------------------------
What is vaso-vagal syncope?
Vaso-vagal syncope is the medical term for a common cause of
fainting. In this disorder, the nervous reflexes which control
heart rate and blood pressure behave abnormally causing a drop
in blood pressure and a fainting spell.
The nerves which control the heart rate and blood pressure are
regulated through pressure sensors in the arteries and veins
called the baroreceptors. The baroreceptors detect changes in
blood pressure. These baroreceptors detect a fall in blood
pressure and send signals via the nerves to increase the heart
rate and constrict blood vessels bringing the blood pressure
back to normal. Conversely, baroreceptors detect abnormally
elevated blood pressure and send signals to slow heart rate and
relax blood vessels to lower blood pressure back to normal.
These reflexes are called the baroreflexes.
Vaso-vagal syncope results from an abnormality in the
baroreflexes. When you stand up, the force of gravity causes
some of the blood from your heart and your chest cavity to pool
in your legs. This produces a slight drop in blood pressure
which is detected by the baroreceptors and is adjusted through
the baroreflexes. In patients with vaso-vagal syncope, after a
period of standing in the upright position, baroreflex
adjustments fail and blood pressure and heart rate decrease
causing fainting.
[ Rest snipped ... goes to other examples and tilt table ]
-------------------------</snip>-------------------------------
And this is from heartdisease.about.com:
------------------------<snip>---------------------------------
[ First portion pertaining to vasomotor syncope excluded]
Vasovagal syncope (also known as cardioneurogenic syncope) is
the most common cause of syncope, probably accounting for more
than 80% of all syncopal episodes. Since vasovagal syncope is
simply an exaggeration of a normal neurological reflex, most
individuals will experience at least one vasovagal episode in
their lifetimes.
The reflex responsible for vasovagal syncope works like this: A
person is exposed to some stimulus (such as a needle stick)
that initiates the reflex. The "stimulated" nerves (the nerves
of the stuck finger, for instance) send an electrical signal to
the vasomotor center in the brainstem. (The vasomotor center
determines the body's vascular "tone.") The vasomotor center,
in turn, signals the blood vessels in the legs to dilate,
causing the blood to pool in the legs, and producing syncope.
This same reflex also causes a drop in the heart rate, but
usually it is the pooling of blood in the legs - and not the
slow heart rate - that produces loss of consciousness.
The "stimulus" that triggers a vasovagal episode can be any one
of hundreds of things. As already noted, pain is a common cause
of fainting. Other common triggering events include the sight
of blood, receiving upsetting news, or standing motionless for
long periods (such as with soldiers standing at parade rest).
Anyone can have vasovagal syncope given an adequate triggering
event, but many people are particularly prone to these
episodes, and often with relatively mild triggers. These
individuals tend to relate histories of syncope dating back to
adolescence, and frequently will describe several different of
triggering events. While, as noted, there are scores of
possible triggering events for vasovagal syncope, some are
quite characteristic and almost always point to vasovagal
syncope. Syncope occurring after urinating, defecating,
coughing or swallowing, or syncope associated with pain,
fright, the sight of blood, or other noxious stimuli, is almost
always vasovagal.
In these and other ways, vasovagal syncope tends to be highly
situational. It is more likely to occur after a viral illness,
after exercise, after a warm shower, or early in the morning -
any time that relative dehydration is present, and dilation of
the blood vessels in the legs would be more likely to produce a
significant drop in blood pressure. Furthermore, vasovagal
syncope is often preceded by a few seconds or a few minutes of
warning symptoms. Often, these symptoms include
lightheadedness, ringing in the ears, visual disturbances,
sweating and/or nausea. Because of such "warning symptoms,"
people who have had one or two episodes of syncope are
frequently able to tell when an event is about to occur. And
importantly, if they recognize the warning symptoms, they are
able to abort the blackout simply by lying down and elevating
the legs. ("Aborting" syncope is not possible with most other
forms of syncope.)
Given these characteristic features and the situational nature
of this condition, doctors can make the correct diagnosis in
the vast majority of patients with vasovagal syncope simply by
asking right questions and listening carefully to the answers.
------------------------</snip>--------------------------------
The fact remains, that my understanding on the subject, is
perhaps more detailed than what is stated above, but definitely
in line with these. If things have changed drastically from the
above, it is time to re-educate ourselves. Could we have the
references (if readily available), or anything on the net ? Or
could you post a "recent thinking" type of discourse on this
list ?
Ready to receive the next Shoib delivery ....
Bish
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