10 most common reasons for fainting

There are many reasons why a person can  faint. We have listed the most common ones.

Fainting or the medical term syncope is the temporary loss of consciousness for a short period of time, after which the person recovers fully. When a person faints, they usually fall down and this may cause an injury. It is also a safety hazard if the person is driving at the time the fainting episode happened. Lack of oxygen or sugar (both provided by the blood vessels) to a part of the brain called the reticular activating system (RAS) located in the brainstem at the back of the skull is the main cause of syncope or fainting.

10 most common reasons for fainting

Here are the top ten reasons for why a person may faint.

  1. Changes in the heart rhythm: Normally, the heart beats at a steady rate; if the heart beats too fast or too slow the blood vessels may not get fully oxygenated blood. Consequently, the amount of oxygen reaching the brain is inadequate and may cause fainting.
  2. Structural changes in the heart: Structural changes in the heart walls or the valves between the chambers of the heart, if abnormal, lead to improper flow of blood through the heart. The heart then cannot do its work competently; oxygenation of blood suffers and cases syncope (brief lack of consciousness).
  3. Dehydration: In case of dehydration, the blood circulation suffers as there isn’t enough of the fluid component of blood. If the brain receives less than its share of oxygen, temporary loss of consciousness may occur.
  4. Anaemia: The iron in the blood acts as the oxygen carrier and supplies oxygen to all parts of the body. In anaemia, especially iron deficiency anaemia seen in developing countries, women lose iron after multiple pregnancies and deliveries and this is a reason why fainting is commoner is women.
  5. Drugs: Medicines like anti-hypertensive drugs which expand the blood vessels to lower the blood pressure, anti-depressants and drugs that alter the mental status like alcohol, morphine and cocaine may have syncope as a side-effect.
  6. Postural hypotension: When we change our posture from the lying down position suddenly to an upright or standing one, the blood vessels contract a little to counteract the effect of gravity and to enable optimal blood circulation. However, as a person ages, these vessels do not function as they used to and this becomes a cause of fainting in the elderly.
  7. Pregnancy: The enlarged uterus puts pressure on the inferior vena cava, one of the largest veins in the body which brings back impure blood from the lower body to the heart, this is the most likely explanation causing syncope.
  8. Vertebrobasilar insufficiency or VBI: The vertebral arteries supply the back of the brain. If these arteries undergo narrowing due to smoking, cholesterol deposition or other ailments, the oxygen reaching the brainstem which contains the RAS (reticular activating system) and other vital structures is less, this can trigger a fainting episode.
  9. Sudden cardiac death: In young athletes, parts of the heart muscle may be abnormally thickened; this condition is called hypertrophic cardiomyopathy. This defect leads to an obstruction in the blood circulation which can cause a syncope.
  10. Vasovagal syncope: This is a common cause of fainting because of stimulation of the vagus nerve, which causes the blood vessels to dilate and the heart rate to slow down. When the blood vessels dilate, less oxygen and nutrients reach the brain leading to an episode of fainting.

Written by Dr Nisreen Nakhoda, General Physician

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