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Definition of Fainting (syncope)

Fainting (syncope) definition - medical term

Syncope is due to a temporary reduction in blood flow and therefore a shortage of oxygen to the brain. This leads to lightheadedness or a "black out" episode, a loss of consciousness. Temporary impairment of the blood supply to the brain can be caused by heart conditions and by conditions that do not directly involve the heart:

Non-cardiac causes

• Postural (orthostatic) hypotension: Drop in blood pressure due to changing body position to a more vertical position after lying or sitting;
• Dehydration causing a decrease in blood volume.
• Blood pressure medications leading to low blood pressure.
• Diseases of the nerves to the legs in older people (especially with diabetes or Parkinson's disease) when poor tone of the nerves of the legs draws blood into the legs from the brain.
• High altitude.
• Brain stroke or "near-stroke" (transient ischemic attack).
• A migraine attack.
• Fainting after certain situations (situational syncope) such as:
  • Blood drawing,
  • Urinating (micturition syncope),
  • Defecating (defecation syncope),
  • Swallowing (swallowing syncope), or
  • Coughing (cough syncope)
  that trigger a reflex of the involuntary nervous system (the vasovagal reaction) that slows the heart and dilates blood vessels in the legs and cause one to feel nausea, sweating, or weakness just before losing fainting.

Cardiac causes

• Abnormal heart rhythms (heart beating too fast or too slow).
• Abnormalities of the heart valves (aortic stenosis or pulmonic valve stenosis).
• High blood pressure in the arteries supplying the lungs (pulmonary artery hypertension).
• Tears in the aorta (aortic dissection).
• Widespread disease of the heart muscle (cardiomyopathy).

To be sure, many of the causes of temporary loss of consciousness can be detected by a careful history. Dizziness after standing up in an older person suggests postural hypotension. Temporary loss of consciousness after urinating, defecating, or coughing suggests situational syncope. Cardiac causes of temporary loss of consciousness such as aortic stenosis or cardiomyopathy are suggested by the occurrence of the event during exercise. Signs of weakness localized to certain areas of the body with temporary loss of consciousness suggest stroke.

The blood pressure and pulse are tested in the lying, sitting, and standing positions. Unequal blood pressures in each arm is a sign of aortic dissection. The heart is examined with a stethoscope to listen for sounds that can indicate valve abnormalities. The nervous system is tested for sensation, reflexes, and motor function to detect conditions of the nerves and brain. An EKG is done to check for abnormal heart rhythms. Other tests may include echocardiograms, rhythm monitoring tests (heart event recorders), and electrophysiologic testing for abnormalities of the heart's electrical system.

When heart conditions are not suspected, tilt-table testing can be used to detect causes of temporary loss of consciousness. Tilt-table testing involves placing the patient on a table with a foot-support. The table is tilted upward and blood pressure and pulse is measured while symptoms are recorded in various positions.

No treatment is needed for many non-cardiac causes of syncope (such as postural hypotension, vasovagal reaction, and situational syncope). The person regains consciousness by simply sitting or lying down. The person is thereafter advised to avoid trigger situations, to not strain while eliminating, to sit when coughing, to lie down for blood drawing, etc.

Older people should have their medications reviewed and caution is advised to slow the process of changing positions from lying to standing. This simple technique can allow the body to adjust to the new position (as the nerves to circulation of the legs adjust slower in older persons).