Fainting

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Definition

Fainting is loss of consciousness caused by a temporary lack of oxygen to the brain. Known by the medical term "syncope," fainting may be preceded by dizziness, nausea, or a feeling of extreme weakness.

Description

When a person faints, the loss of consciousness is brief. The person will wake up as soon as normal blood flow is restored to the brain. Blood flow is usually

restored by lying flat for a short time. This position puts the head on the same level as the heart so that blood flows more easily to the brain.

A fainting episode may be completely harmless and of no significance, but it can be a symptom of a serious underlying disorder. No matter how trivial it seems, a fainting episode should be treated as a medical emergency until the cause is determined.

— Carol A. Turkington

Syncope, or loss of consciousness owing to a sudden arrest of the blood supply to the brain, the face becoming pallid, the respiration feeble, and the heat's beat weak.

Fainting fit, a fainting or swoon; syncope. [Colloq.]

Fainting is a transient, reversible loss of consciousness due to an acute reduction in blood supply to the brain. Lack of cerebral perfusion for 2-3 sec can cause premonitory symptoms (such as light-headedness, dizziness) ; after 10 sec fainting results. Fainting is synonymous with syncope (from the Greek ‘to strike’ or ‘cut off’). Slumping in a chair or falling to the ground characteristically occurs because of loss of postural muscle tone, although occasionally there may be jerky movements, muscle spasms, or urinary incontinence as a result of transient ‘decerebration’. Fainting usually occurs when the subject is upright, and falling results in recovery of cerebral blood flow and spontaneous recovery.

Fainting does not cause damage to the nervous system, unless there is injury from the fall, but it can cause concern, embarrassment, and loss of confidence. However some of the conditions associated with fainting are potentially serious or even potentially fatal. It has been said that ‘the only difference between fainting and sudden death is that in one you wake up’ (Engel, 1978).

Maintenance of blood flow to the brain is dependent on an adequate blood pressure and on patent and responsive cerebral blood vessels. These vessels dilate to maintain flow when blood pressure falls within its normal range of variation, but a major or rapid fall can defeat this compensation. Thus, there are numerous causes of fainting.

Low blood pressure (hypotension) may occur with postural (orthostatic) change, on moving from the horizontal to the upright position such as when rising after sleep. The sympathetic nervous system normally responds to gravitational change and prevents pooling of blood in the lower limbs by an increase in its activity, which causes constriction of blood vessels. The majority of the population do not faint, as adaptive mechanisms to standing erect are well developed. However, in certain situations even the fittest can faint (such as guardsmen standing still at attention on a hot day), and there are some disease conditions, and some drugs, which impair the reflex response. Fainting caused by postural hypotension classically occurs on assumption of the head-up posture, with relief by lying flat.

Intermittent abnormal activity of the autonomic nervous system (neurally-mediated syncope) also may occur. During these episodes increased parasympathetic activity slows the heart rate whilst diminished sympathetic activity allows blood vessels to dilate, lowering blood pressure. The most common form is known as vasovagal syncope — the ‘emotional’ or ‘common’ fainting. This is often of teenage onset, in females, and with a family history.

A variety of factors, such as fear of needles, sight of blood, or pain, can precipitate this type of fainting. There is often prompt recovery on attaining the horizontal position. In the elderly, similar autonomic effects on the heart and circulation may occur, when there is hypersensitivity of the baroreceptors in the carotid sinus in the neck; tightening the collar, or moving the head whilst shaving, stimulates nerves that normally signal a rise in blood pressure. The result is a ‘correction’ of this false signal — a fall in heart rate and blood pressure. This can be a potentially serious condition, with severe injury from falls, and may require treatment with a cardiac pacemaker and drugs that maintain blood pressure.

There are other, rarer, causes of fainting mediated by the nervous system, precipitated by a range of factors such as urination, coughing, or swallowing.

Another cause of fainting is a change in cardiac rhythm, when the heart beats too fast or too slowly, resulting in a poor cardiac output and inadequate blood flow to the brain. The best known is the Stokes-Adams attack, when the ventricles of the heart fail to beat because of heart block.

There are also more direct — mechanical or hydraulic — causes of low blood pressure; these include depletion of the circulating blood volume due to haemorrhage or plasma loss, and inadequate fluid intake or excessive fluid loss due to vomiting or diarrhoea, or from the kidneys in some abnormal conditions. Excessive dilatation of blood vessels, due to drugs (such as glyceryl trinitrate used in angina, or from excessive alcohol ingestion), circulating vasodilator substances, or venous disorders (extensive varicose veins), may be contributory.

Finally, constriction of the cerebral blood vessels may contribute to fainting. For example, during hyperventilation, even in healthy people, low carbon dioxide in the blood causes constriction of the blood vessels. Or when a major vessel supplying the brain is partly or severely occluded in carotid artery stenosis, even small decreases in blood pressure or changes in cardiac rhythm threaten the blood supply.

In summary, fainting may occur in any individual, from the young (vasovagal syncope), to the elderly (carotid sinus hypersensitivity). It is estimated to occur at some time in 3% of the adult population, and sometimes in extremely healthy and fit people (oarsmen, athletes, and in particular weightlifters). There may be an occupational hazard — as in trumpet players. Fainting is usually involuntary, but it may be deliberately induced, as in the so-called ‘fainting lark’: a combination of squatting, overbreathing, forceful expiration, and standing up suddenly. The ‘Mess trick’ is a variation of this.

Fainting can sometimes be ominous, especially in those with an untreated cardiac rhythm disorder, consistent with ancient observations that ‘those who suffer from frequent and severe fainting without cause often die suddenly’ (Hippocrates, Aphorisms 2.41). But in many other conditions, such as vasovagal syncope, the prognosis is excellent.

— C. J. Mathias

See also autonomic nervous system; blood pressure.

Loss of consciousness because of an insufficient blood supply to the brain. Fainting may occur in an otherwise healthy person because of emotional shock, overheating, or because of a sudden reduction in blood pressure on standing up quickly (postural hypotension). It may also result from severe injury or loss of blood.

Fainting during exercise is a classic warning of heart disease. It may indicate that the heart is not pumping enough oxygen-rich blood to meet the demands of active muscles. Fainting can occur in healthy, fit people when they are relaxing after strenuous exercise. This is due to pooling of blood in the legs.

It has been suggested that Central Ischaemic Response be merged into this article or section. (Discuss)

For the Linkin Park song, see Faint (song).

Name of Symptom/Sign:
Fainting
Classifications and external resources

ICD-10	R55.
ICD-9	780.2
DiseasesDB	27303
eMedicine	med/3385  ped/2188 emerg/876
MeSH	D013575

Fainting, also called syncope (IPA: [ˈsɪnkəpi] and [ˈsɪŋkəpi]), is a sudden, and generally momentary, loss of consciousness, or blacking out caused by the Central Ischaemic Response, because of a lack of sufficient blood and oxygen in the brain. The first symptoms a person feels before fainting are dizziness; a dimming of vision, or brownout; 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). If the person is unable to slump from the position to a near horizontal position, he or she risks dying of the Suspension trauma effect.

Causes

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, emotional distress, 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 slightly 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 cardio-vascular conditions that can be manifested by syncope include subclavian steal syndrome and aortic stenosis.

Types

Vasovagal (situational) syncope, one of the most common types, may occur in scary or embarrassing situations or during blood drawing, coughing, or urinating. Other types include postural syncope (caused by a changing in body posture), cardiac syncope (due to heart-related conditions), and neurological syncope (due to neurological conditions). There are many other causes of syncope including low blood sugar levels and lung disease such as emphysema and a pulmonary embolus. The cause of the fainting can be determined by a doctor using a complete history, physical, and various diagnostic tests.

Vasovagal syncope

Main article: Vasovagal syncope

The vasovagal type can be considered in two forms:

• 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.
• 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. The tilt-table test, if performed, is generally positive.

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. The high (ineffective) sympathetic activity is always modulated by vagal outflow, in these cases leading to excessive slowing of heart rate. The abnormality lies in this excessive vagal response. 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"). This reflex occurs in only some people and may be similar to that described in animals.

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.

Pure cardiac syncope

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. Severe narrowing of the Aortic Valve leading to syncope is included for completeness.

Syncope from vertebro-basilar arterial disease

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 symptoms

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 a syncoptic episode do not remember falling.

See also

• Orthostatic hypotension blackout after rising
• Shallow water blackout for the special case of fainting arising from hypocapnia
• Deep water blackout for the special case of fainting arising from latent hypoxia

External links

• 2004 European Society of Cardiology Guidelines on Management (Diagnosis and Treatment) of Syncope.
• http://www.syncope.us
• Dysautonomia Information Network
• Dysautonomia Youth Network of America, Inc.
• Dysautonomia Support Network Corp.
• Tilt table test
• Choking Game in the News
• Archive of Fainting Experiences
• WebMD Fainting First Aid

Symptoms and signs (R00-R69, 780-789)
Circulatory and respiratory systems	Tachycardia - Bradycardia - Palpitation - Heart murmur - Epistaxis - Hemoptysis - Cough - abnormalities of breathing (Dyspnea, Orthopnoea, Stridor, Wheeze, Cheyne-Stokes respiration, Hyperventilation, Mouth breathing, Hiccup, Bradypnea, Hypoventilation) - Chest pain - Asphyxia - Pleurisy - Respiratory arrest - Sputum - Bruit/Carotid bruit - Rales
Digestive system and abdomen	Abdominal pain - Acute abdomen - Nausea - Vomiting - Heartburn - Dysphagia - Flatulence - Burping - Fecal incontinence - Encopresis - Hepatomegaly - Splenomegaly - Hepatosplenomegaly - Jaundice - Ascites - Fecal occult blood - Halitosis
Skin and subcutaneous tissue	disturbances of skin sensation (Hypoesthesia, Paresthesia, Hyperesthesia) - Rash - Cyanosis - Pallor - Flushing - Petechia - Desquamation - Induration - Diaphoresis
Nervous and musculoskeletal systems	abnormal involuntary movements (Tremor, Spasm, Fasciculation, Athetosis) - Gait abnormality - lack of coordination (Ataxia, Dysmetria, Dysdiadochokinesia, Hypotonia) - Tetany - Meningism - Hyperreflexia
Urinary system	Dysuria - Vesical tenesmus - Urinary incontinence - Urinary retention - Oliguria - Polyuria - Nocturia
Cognition, perception, emotional state and behaviour	Anxiety - Somnolence - Coma - Amnesia (Anterograde amnesia, Retrograde amnesia) - Dizziness/Vertigo - smell and taste (Anosmia, Ageusia, Parosmia, Parageusia)
Speech and voice	speech disturbances (Dysphasia, Aphasia, Dysarthria) - symbolic dysfunctions (Dyslexia, Alexia, Agnosia, Apraxia, Acalculia, Agraphia) - voice disturbances (Dysphonia, Aphonia)
General symptoms and signs	Fever (Hyperpyrexia) - Headache - Chronic pain - Malaise - Fatigue - Fainting (Vasovagal syncope) - Febrile seizure - Shock (Cardiogenic shock) - Lymphadenopathy - Edema (Peripheral edema, Anasarca) - Hyperhidrosis (Sleep hyperhidrosis) - Delayed milestone - Failure to thrive - food and fluid intake (Anorexia, Polydipsia, Polyphagia) - Cachexia - Xerostomia - Clubbing

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