Fainting (cont.)
Vasovagal syncope
Vasovagal syncope is one of the most common causes of fainting. In this
situation, the balance between the chemicals adrenaline and acetylcholine is
disrupted. Adrenaline stimulates the body, including making the heart beat faster
and blood vessels narrower. Acetylcholine does the opposite. When the vagus
nerve is stimulated, excess acetylcholine is released, the heart rate slows and
the blood vessels dilate, making it harder for blood to defeat gravity and be
pumped to the brain. This temporary decrease in blood flow to the brain causes
the syncopal (fainting) episode.
Pain can stimulate the vagus nerve and is a
common cause of vasovagal syncope. Other noxious stimuli can do the same thing,
including a situational stressor. It is common for medical and nursing students to faint when observing
their first operation or autopsy. Some people pass out when they hear bad news;
others pass-out when they experience the sight of blood or needles.
Other situations commonly cause the heart rate to
temporarily slow and cause a faint. Straining with urination, bowel movement, or coughing can cause a vagal
response.
Anemia
Anemia (low red blood cell count),
whether it occurs acutely from bleeding or gradually for a variety of reasons,
can cause fainting because there aren't enough red blood cells to deliver oxygen to the brain.
Dehydration
Dehydration, or lack of water in the body can similarly cause fainting
or syncope. This
can be caused by excessive loss of water from
vomiting, diarrhea,
sweating, or
by inadequate fluid intake. Some illnesses like diabetes can cause dehydration by
excess loss of water in the urine.
Next: Orthostatic hypotension »
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