What Are The Causes Of Fainting

Fainting (syncope) is a temporary loss of consciousness, which occurs suddenly, resulting from decreased blood flow to the brain, often due to hypotension.

  • Abnormalities in the brain’s function cause fainting.
  • Prior to fainting, symptoms such as light-headedness and giddiness may occur.
  • Heart function testing and tilt-table testing are done to detect the cause.\
  • Soon after fainting, consciousness may be restored by lying down and resting for a short while, but the cause of the fainting episode needs to be investigated and treated.

Fainting occurs due to insufficient blood supply to the brain, most often resulting from blood pressure which is too low to pump the blood all the way up to the brain. Since the head is much higher than the heart, blood has to reach the brain against the force of gravity. The blood pressure in the arteries is responsible for the flow of blood upwards and in to the brain. Hence, it is the first organ to be affected by low blood pressure.

Causes Of Fainting

People lose consciousness when brain function is disrupted, usually due to reduced flow of blood to the brain, often resulting from hypotension. Hypotension may have developed due to various reasons, including disorders of the heart such as heart failure, heart attack, arrhythmias that are too fast, too slow or irregular. Severe blood loss also can cause low blood pressure resulting in fainting. If flow of blood to the brain is impaired due to a blood vessel disorder, it may cause fainting. Loss of consciousness due to seizures, which result from abnormal electrical activity in the brain, is not considered as fainting even though fainting and seizures are very similar outwardly and it is difficult to distinguish one from the other.

Problems with the Heart’s Pumping: Heart’s blood pumping capacity may be impaired due to many reasons. If the heart is not able to pump sufficient quantity of blood to meet the demand for oxygen and nutrients by the body, it is termed heart failure. Heart failure may occur due to valve disorders or abnormal heart rhythms; and people with heart failure may not feel any difficulty while resting. But, when the demand for blood supply is increased due to any exertion, the heart’s insufficiency becomes apparent and the person feels light headed or actually faints, because enough blood is not reaching the brain. This condition is called exertional fainting or effort syncope.

Instead of fainting during exercise, some people faint after they stop exercising. This may seem peculiar, but there is a valid reason for that. During exercise, the heart rate increases to enhance the cardiac output to meet the additional requirement, due to which the blood pressure remains high enough to prevent fainting. But as soon as the person stops exercising, the heart rate returns to normal, but the arterioles which had become dilated to supply extra amount of glucose and oxygen to the working muscles during the exercise, remain dilated for some more time to help with tissue repair and removal of waste materials produced during muscle activity. Since more blood remains in dilated arterioles even after the exercise, this continued demand in the muscles, combined with the reduced heart output, results in low blood pressure and less blood being available to the brain, causing fainting.

 Hypertrophic cardiomyopathy, which is a disorder of the heart muscle, can also be a reason for fainting during exercise. Aortic valve stenosis, when severe, also causes fainting. Disorders such as these are not limited to any age group, but they often occur in people who have high blood pressure. Without proper treatment they can be fatal.

Low Volume of Blood:  If the circulating volume of blood becomes too low due to excessive bleeding and severe dehydration, low blood pressure may develop. Dehydration may be due to copious sweating and urination, Addison’s disease, severe diarrhea and use of diuretics combined with insufficient rehydration, especially during summer.  Older people with reduced mobility and those who suffer from dementia often fail to drink enough water to maintain adequate fluid levels in the body, resulting in fainting.

Vagus Nerve Stimulation:  The vagus nerve which enervates chest, neck and intestine slows down the heart rate when stimulated. Vagus nerve stimulation results in nausea and skin that feels cold and clammy to touch; if the heart rate becomes too low, it may result in fainting which is termed vasovagal syncope.  Emotional stress such as fear and distressing sights as well as physical stress from strained bowel movements, urination or vomiting may stimulate the vagus nerve, resulting in fainting. Swallowing vigorously also may have the same effect. Micturition syncope is one such condition, in which fainting occurs during urination or immediately after.

Reduced Blood Flow: Cough syncope, is fainting due to the strain of coughing, because the blood flow back into the heart becomes reduced. Weight lifters’ syncope, due to the strain of lifting heavy weights without proper breathing, is also due to the reduction of blood flow into the heart. Micturition syncope in older people may result from having to strain too much to pass urine, due to the enlargement of prostate gland, in addition to vagus nerve stimulation.

 Problems with Blood Pressure: Orthostatic syncope or postural syncope is a type of fainting that occurs when people suddenly change their body posture, for instance, quickly getting up from a sitting position or vice versa. This disorder, mainly occurring in older people, results from orthostatic hypotension. It is due to the slow response of body’s compensatory mechanism to restore to normal, the low blood pressure in the arteries because gravity has caused blood to accumulate in the legs. Parade ground syncope is a similar occurrence when the blood accumulated in the legs does not return to the heart because of the inactivity of the leg muscles, causing hypotension and fainting. Postprandial hypotension, occurring usually in older people after a meal, also may cause fainting.

Other Problems: Hyperventilation or very fast breathing, possibly due to anxiety or severe emotional distress, may result in hyperventilation syncope. Rapid breathing lowers the level of carbon dioxide in the body, which results in the constriction of arterioles in the brain, causing giddiness or fainting.

Fainting may be caused by a mild stroke, when the blood flow is decreased to certain areas of the brain, but it is seldom seen in younger people. Anemia may cause fainting due to the inadequate amount of the oxygen carrying molecule, hemoglobin, in the blood. Lung disorders, which affect the oxygenation of blood in the lungs, reduce the amount of oxygen made available to the tissues, leading to fainting due to oxygen starvation in the brain. Hypoglycemia or less than normal levels of blood sugar in people with diabetes, often caused by antidiabetic drugs, can also result in fainting.

Some of the drugs used for the treatment of heart failure, angina and high blood pressure can cause hypotension that may lead to fainting. Hence, it is very important to adjust the dosage of such drugs, especially that of antihypertensive drugs.


Prior to fainting, warning signs such as a light-headed or dizzy feeling may be felt, particularly if the person is already standing or has suddenly got up. When the person falls down due to fainting, the head may come to the same level as the heart, and blood flow to the brain may improve enough for him to regain consciousness in a short while. There may be a temporary improvement in the blood pressure but if the person tries to get up, again he may lose consciousness.

Fainting due to arrhythmia happens suddenly, without the usual warning signs, and disappears just as suddenly. But palpitations due to fast arrhythmias may be felt before the person faints.

Vasovagal syncope usually has many warning signals such as sweating, pale, cold and clammy skin, blurred vision, yawning and nausea. Very slow pulse resulting from the effect of vagus nerve stimulation significantly reduces blood supply to the skin, making the person look deathly pale.

Fainting due to hypoglycemia sets in slowly and the recovery is also just as slow. Hypocapnia or low levels of carbon dioxide, also leads to fainting that sets in slowly, following a sensation of pins- and- needles felt in the area surrounding the lips as well as in the tips of fingers, which may be considered a warning signal.

Diagnosis Of fainting

The cause of fainting has to be detected as soon as possible, since some of the causes are extremely dangerous conditions that require immediate medical intervention. Fainting due to arrhythmias, aortic valve stenosis, heart failure and heart attack are potentially fatal, while some other causes of fainting require only minimal medical care or even just a period of rest and relaxation.

The descriptions provided by those who have witnessed the person fainting, may help the doctor assess whether physical or emotional stress could have caused the fainting. Medical history of the patient, details of the medications taken and the symptoms such as chest pain, palpitations or shortness of breath which may have preceded the episode, may help the doctor with diagnosis. If fainting seems to have occurred due to some disorders of the cardiovascular or nervous systems, further tests are conducted to detect the exact cause, and to start immediate remedial action.

If symptoms such as sweating or nausea, accompanied by pale, cold and clammy skin were felt prior to fainting, it may be a vasovagal syncope, which is not serious and require no further investigation or treatment. People who have fainted due to emotional stress will also recover without further intervention.

An ECG or electrocardiogram can record the heart’s electrical activity, to detect heart disorders that may have caused the fainting. A portable ECG machine called Holter monitor is worn by the patient, for continuous monitoring of the heart’s electrical activity over a period of time, as the patient goes about his routine activities, to see if fainting is due to exertion.

The structural as well as the functional abnormalities of the heart can be detected by echocardiography which produces ultrasound images of the heart. Hypoglycemia and anemia can be detected by blood tests. Re-creating a fainting episode artificially, in a safe, monitored environment, often helps to confirm whether the suspected cause. Pressing the carotid sinus, to produce a false sensation of high blood pressure in the arteries, may trigger the body’s blood pressure controlling mechanism to lower the blood pressure. Fainting may result, and during this time the heart function is closely monitored through ECG, to establish the connection, if any, between heart’s function and fainting. Patient is also made to inhale and exhale deeply, in quick succession, to determine if the fainting was caused by hyperventilation due to emotional stress.

In tilt table testing, which helps detect the cause of fainting, the patient strapped to a motorizes tilt table is tilted into an upright position for about 45 minutes, while the heart rate and blood pressure are monitored for any decease in blood pressure. Using isoproterenol to stimulate the heart, before doing this test, gives a more accurate result.

 A seizure due to abnormal electrical activity in the brain may cause loss of consciousness, but it is considered to be different from fainting, and the treatments also differ. Slower recovery following an episode of unconsciousness, and persistent drowsiness even after recovery, are characteristic features of seizure. EEG or electroencephalography, which is a test that records brain’s electrical activity, may help in diagnosis.


If the reason for fainting is not a very serious condition, allowing the patient to rest for some time in a horizontal position, preferably with the legs at a slightly higher plane, may be all that is necessary to restore consciousness. Even after recovery, the person should not be made to sit up nor should be carried in sitting position, as recurrence is likely, if the blood flow to the brain is again reduced due to the upright position.

Arrhythmias can be corrected by various means; an implantable pacemaker helps to correct slow heart rate, beta blockers such as metoprolol or asatenolol can reduce a fast heart rate, an implantable defibrillator can change an irregular arrhythmia to normal heart rhythm. Heart valve disorders can be corrected surgically.

Fainting due to hypoglycemia in people who are diabetic can be avoided, by adjusting the antidiabetic medication, taking meals at regular intervals and carrying some sweets to restore glucose levels when the symptoms of hypoglycemia appear. Anemia can be avoided by taking balanced meals or can be treated with iron supplements. Intravenous administration of fluids helps to restore blood volume, if fainting has occurred due to blood loss.

Share and Enjoy

  • Facebook
  • Twitter
  • Delicious
  • LinkedIn
  • StumbleUpon
  • Add to favorites
  • Email
  • RSS

Yasser Elnahas

MD, PHD, Professor Of CardioVascular Surgery
Dr. Yasser Elnahas, Is an associate Professor of Cardiovascular Surgery. Dr. Elnahas was trained as a fellow At Texas Heart Institute And Mayo Clinic Foundation.Dr. Elnahas is dedicated to educating the general public about different disease conditions and simplifying the medical knowledge in an easy to understand terminology.

Latest posts by Yasser Elnahas (see all)

Leave a Reply

Your email address will not be published. Required fields are marked *


You may use these HTML tags and attributes: <a href="" title=""> <abbr title=""> <acronym title=""> <b> <blockquote cite=""> <cite> <code> <del datetime=""> <em> <i> <q cite=""> <strike> <strong>

You might also likeclose
WP Socializer Aakash Web