fAiNtINg…
(Fainting or syncope) (IPA: /ˈsɪnkəpi/ or /ˈsɪŋkəpi/) is a sudden (and generally momentary) loss of consciousness,
or blacking out, owing to a lack of sufficient blood and oxygen
reaching the brain. The first symptoms a person feels before fainting
are dizziness, a dimming of vision, or brown-out, tinnitus,
and feeling hot. Moments later, the person’s vision turns black and he
or she drops to the floor (or slumps if seated in a chair).
Factors that influence fainting are taking in too little food and fluids, low blood pressure, hypoglycemia, growth spurts,
physical exercise in excess of the energy reserve of the body, and lack
of sleep. Even standing up too quickly or being in too hot a room can
cause fainting. Recommended treatment is to allow the person to lie on
the ground with his or her legs a little elevated. As the dizziness and
the momentary blindness passes, the person may experience visual disturbances in the form of small bright dots (phosphene).
These will also pass within a few minutes. If fainting happens
frequently, or if there is no obvious explanation, it is important to
see a doctor about it.
More serious causes of fainting include cardiac (heart-related) causes such as an abnormal heart rhythm (an arrhythmia),
where the heart beats too slowly, too rapidly or too irregularly to
pump enough blood to the brain. Some arrhythmias can be
life-threatening. Other important cardiac conditions that can manifest
with syncope include subclavian steal syndrome and aortic stenosis.
Fainting can also be due to neurological disorders, stress, side effects of anaesthetics, etc
types
It is convenient to think of three types of fainting, or syncope.
The usual type (1) is benign and is vaso-vagal. Much less common (2) is
a pure cardiac syncope. Finally there is syncope (3) from
vertebro-basilar arterial disease. Epilepsy appearing as syncope is not
considered. (1) The vaso-vagal type can be considered in two forms: a)
Isolated episodes of loss of consciousness, unheralded by any warning
symptoms for more than a few moments. These tend to occur in the
adolescent age group, and may be associated with fasting, exercise,
abdominal straining or circumstances promoting vaso-dilatation (eg
heat, alcohol). The subject is invariably upright. The tilt-table test,
if performed, is generally negative. b) Recurrent syncope with complex
associated symptoms. This is so-called Neurally Mediated Syncope (NMS).
It is associated with any of the following: preceding or succeeding
sleepiness, preceding visual disturbance ("spots before the eyes),
sweating, light-headedness. The subject is usually but not always
upright. A pattern of background factors contributes to the attacks.
There is typically an unsuspected relatively low blood volume, for
instance, from taking a low salt diet in the absence of any
salt-retaining tendency. Heat causes vaso-dilatation and worsens the
effect of the relatively insufficient blood volume. That sets the
scene, but the next stage is the adrenergic response. If there is
underlying fear or anxiety (e.g. social circumstances), or acute fear
(e.g. acute threat, needle phobia), the Vaso-Motor Centre demands an
increased pumping action by the heart (flight or fight response). This
is set in motion via the adrenergic (Sympathetic) outflow from the
brain but the heart is unable to meet requirement because of the low
blood volume, or decreased return of blood to the heart (abdominal
straining). However, the heart’s increased Left Ventricular muscle
activity is recognised by the Vaso-Motor Centre via activity in Vagal
nerve fibres traveling from the heart to the brain. Normally, the Vagal
response would modulate this activity. However, in NMS, the abnormal
response that follows is in the exaggerated strength of the return
vagal flow, actually causing minor further peripheral vaso-dilatation
and slowing the heart decisively - to a point where fainting occurs. In
other words, an adrenalin effect causes an over-compensation by the
Vagus. Interestingly, some people faint lying in a dentist’s chair
after receiving adrenalin in a local anaesthetic, endorsing the
explanation.
The tilt-table test typically evokes the attack.
Much of this pathway was discovered in animal experiments by Bezold
(Vienna) in the 1860s. In animals, it may represent a defence mechanism
when confronted by danger ("playing possum") in which case it is a
reflex which has been carried over into some people.
The mechanism described here suggests that a practical way to
prevent attacks would be, counter-intuitively, to block the adrenergic
signal with a Beta Blocker. But simpler plan is to explain the
mechanism, discuss causes of fear, and optimise salt as well as water
intake.
2) Fainting can also occur if pressure on the carotid artery in the
neck triggers a vagal signal to the Vaso-Motor Centre, reflexly causing
a vagal response to slow the heart. A pure cardiac arrhythmia is a
serious matter that can appear as syncope but this is unusual.
3) Arterial disease in the upper spinal cord, or lower brain, causes
syncope if there is a reduction in blood supply, which may occur with
extending the neck or after drugs to lower blood pressure.
clinical symtoms
If the patient states, "I felt dizzy with blurry vision, muscle
weakness, during the fall I bumped my knee, hit my head and passed
out," then it is not syncope, it is termed pre or near-syncope.
If the patient states, "I felt dizzy, shadows came over my eyes, and
when I woke up I was lying on the floor," then it is diagnosed as
syncope.
Patients who experience syncope episode do not remember falling.
popular culture of "fainTiNg"
Intentional fainting has long been a "fad" amongst young people. It
involves cutting the oxygen supply to the brain for a period of 3-10
seconds causing a syncope. There are two common ways of inducing the
syncope. One of these is also known as the sleeper hold, or rear naked choke. The other technique involves placing the hands on either side of the rib cage before pressing and lifting.
However it is not recommended that either of these ever be used on
anyone as there are known cases of brain damage and even death.
