Syncope is the proper medical terminology for a sudden loss of consciousness, or fainting. While the underlying causes for syncope vary, the phenomenon is relatively common. Chances are that every person will experience an episode of passing out with little or no warning at some point during his or her life.
Fainting is a defense mechanism used by the brain. If the supply of blood and oxygen to the brain becomes too low, the brain will immediately take any available blood and oxygen from the rest of the body at the expense of other bodily functions.
Your breathing rate will be increased (hyperventilation) as your brain tries to increase its supply of oxygen. Your heart rate will also increase, to pump more blood from the rest of your body to your brain.
The increase in heart rate will lead to a loss of blood pressure in the rest of your body (hypotension) as blood is diverted to your brain. The combination of hyperventilation and hypotension can then lead to a temporary loss of consciousness and muscle weakness, resulting in fainting.
The trigger for syncope can be something as simple as a sudden scare or a shock. It is not unusual for someone to faint upon hearing of some unexpected event, such as the death of a loved one. Syncope may also occur when the mind and body sense some type of impending danger or threat, and the individual is unable to escape the situation.
In terms of how syncope affects the body, the condition is brought on by a change of the blood flow to the brain. There is often a substantial change in blood pressure that results in the brain not receiving a normal amount of blood into and out of the organ. This interruption in blood flow causes the individual to lose consciousness for a short period of time. When syncope is not due to some ongoing medical condition, it is usually easy to revive the individual within a short period of time.
Because syncope does not have to be tied to some underlying illness, the phenomenon may be experienced by just about anyone. Persons of all ages and genders may experience a fainting episode. Generally, the actual faint is preceded by a momentary stiffening of the body posture before the person loses consciousness. The eyes may appear to roll back in the head just as the eyelids close and the body becomes limp.
Syncope is usually harmless and requires no treatment. However, you can injure yourself during a syncope episode. Syncope can also be a symptom of some type of medical condition, such as low blood pressure or even an extreme anxiety disorder. When an episode of syncope takes place, it is important to see a doctor as soon as possible to rule out more serious causes of fainting, such as heart disorders. While syncope is often a one-time event that is triggered by some unexpected stimuli, a complete physical checkup will help to ensure the event was not a precursor to something more serious.
There are different types of fainting which are caused by the blood supply to the brain being interrupted for different reasons. The different types of fainting are explained below.
Neurally mediated syncope is also called reflex syncope. Neurally means that it is related to the nervous system, which is made up of your brain, nerves and spinal cord. There are three types of neurally mediated syncope. They are:
vasovagal syncope
situational syncope
carotid sinus syndrome
These are explained in more detail below.
Vasovagal syncope occurs when something triggers a temporary malfunction in your autonomic nervous system. The autonomic nervous system is the part of the nervous system responsible for regulating many of the body's automatic functions, such as heartbeat and blood pressure.
The malfunction in the autonomic nervous system causes a drop in your blood pressure and a reduction in your heartbeat. This leads to a temporary interruption to your brain's blood supply.
Vasovagal syncope may be caused by:
sudden exposure to an unpleasant sight or experience, such as the sight of blood
standing for long periods of time
spending a long time in hot or stuffy environments
a sudden intense episode of stress, emotional upset, fear or anxiety
a sudden feeling of pain
Situational syncope is also a type of fainting related to the nervous system. It occurs when a bodily function or activity places a sudden strain on your autonomic nervous system. Possible causes of situational syncope include:
coughing
sneezing
swallowing
laughing
passing stools
urinating
some physical activities, such as weightlifting, although this could also be a sign of an underlying heart problem (see cardiac syncope, below)
Situational syncope may also occur after eating a meal or exercising.
The carotid sinus is a collection of sensors in the carotid artery. The carotid artery is located in your neck and is the main artery that supplies blood to your brain. The carotid sinus helps to regulate the flow of blood through the carotid artery into your brain.
Some people can develop a hypersensitive carotid sinus. This means that any physical stimulation of the carotid sinus can cause the sensors suddenly to trigger a drop in blood pressure, resulting in fainting. This condition is known as carotid sinus syndrome.
Examples of physical stimulation that may affect your carotid sinus include:
turning your head to one side
wearing a tight collar
shaving over the part of your neck that contains the carotid sinus
Carotid sinus syndrome is very rare in people who are under 40 years of age. It is most common among older men.
Orthostatic hypotension is a condition in which your blood pressure falls suddenly when you stand up, which can cause fainting. It is more common in older people, and is the reason for fainting in 1 person in 10 aged 60 years or over who faint.
When you stand up after sitting or lying down, gravity naturally draws your blood down into your legs, reducing your blood pressure. Usually, the nervous system counteracts this effect by making your heart beat faster and narrowing your blood vessels, both of which will stabilize your blood pressure.
However, in cases of orthostatic hypotension, something interrupts the process of stabilization. This means that if you stand up suddenly, the blood supply to your brain is interrupted, causing you to faint.
Some possible causes of orthostatic hypotension are explained below.
Dehydration (low blood volume). If you become severely dehydrated (where the normal water content of your body is reduced), the amount of fluid in your blood will reduce along with your blood pressure. This will make it much harder for your nervous system to stabilize your blood pressure, increasing your chances of fainting. This can be caused by heavy bleeding, vomiting or diarrhea.
Diabetes. Untreated diabetes (a condition where there is too much glucose in the blood) causes frequent urination, which can lead to dehydration. Excess glucose in the blood can also damage the nerves that help to regulate your blood pressure.
Medication. Some medicines can cause orthostatic hypotension in some people. These include diuretics, which increase the production and flow of urine from the body, beta-blockers and some types of antidepressants.
Neurological conditions. Some health conditions that affect the nervous system, such as Parkinson's disease, can trigger orthostatic hypotension in some people.
Cardiac syncope is where the blood supply to the brain is interrupted due to an underlying problem with your heart. Possible causes of cardiac syncope include:
abnormal heart rhythms (arrhythmias)
narrowing of the heart valves (stenosis)
a heart attack, which is a medical emergency when the blood supply to the heart is suddenly blocked
Cardiac syncope becomes more common as people get older. For example, it is estimated that a third of people aged 60 years or over who have fainted may have fainted as a result of a heart problem.
When you faint, you will feel weak and unsteady before passing out for a short period of time, usually only a few seconds. Fainting can happen when you are sitting down, standing up or when you get up too quickly.
Just before losing consciousness, you may experience the following symptoms:
yawning
a sudden, clammy sweat
nausea (feeling sick)
fast, deep breathing
confusion
feeling lightheaded
blurred vision or spots in front of your eyes
ringing in your ears
This is followed by a loss of strength and a loss of consciousness. It only takes a few seconds to run through these symptoms, and there may be very little warning before you collapse. In some cases, there may be no other symptoms to warn you that you are about to faint.
When you collapse to the ground, your head and heart are on the same level. This means that your heart does not have to work as hard to push blood up to your brain. You should return to consciousness after about 20 seconds. In rare cases, you may remain unconscious for longer, perhaps several minutes.
Before fainting, the person may feel light-headed and shaky and experience blurred vision.
The person may "see spots in front of their eyes."
During this time, observers note paleness, dilated pupils, and sweating.
While unconscious, the person may have low pulse rate (less than 60 beats/minute).
The person should quickly regain consciousness.
Many people have no warning signs before a syncopal episode.
Consciousness returns when the situation is over, usually very quickly.
The person may have noted a blood loss (black stools, heavy menstrual periods) or fluid loss (vomiting, diarrhea, fever).
The person may have experienced light-headedness when sitting or standing.
Observers may note paleness, sweating, or signs of dehydration (dry lips and tongue).
The person may report palpitations (awareness of pounding, fast, or abnormal heartbeat), chest pain, or shortness of breath.
Observers may note a weak, abnormal pulse, paleness, or sweating.
Syncope often occurs without warning or following exertion.
The person may have a headache, loss of balance, slurred speech, double vision, or vertigo (a feeling that the room is spinning).
Observers note a strong pulse during the unconscious period and normal skin color.
After fainting, you may feel confused and weak for about 20 to 30 minutes. You may also feel tired. Sometimes, older people may not be able to remember what they were doing just before they fainted.
Treatment for fainting (syncope) will depend on whether there is an underlying cause. See Fainting - causes above for more information about the possible causes of fainting.
If your doctor finds an underlying cause for your fainting, treating it should help prevent further fainting episodes. For example, if you are diagnosed with type 2 diabetes (where there is too much glucose in the blood) you may be advised to take regular exercise and eat a healthy diet.
If you are diagnosed with a heart condition, you may need to have further tests and treatment. For example, there are several different medicines that can be used to treat heart disease, which is where your heart's blood supply is blocked by a build-up of fatty substances in the main blood vessels.
Neurally mediated syncope, also called reflex syncope, includes:
vasovagal syncope
situational syncope
carotid sinus syndrome
Treatment for neurally mediated syncope involves avoiding any possible triggers. If you are not sure what caused your fainting episode, your doctor may suggest that you keep a diary of any symptoms you experience and what you were doing at the time that you fainted, to help identify possible causes.
There are also steps that you can take to avoid losing consciousness if you think that you may be about to faint. See "If someone is about to faint" below for more information.
Vasovagal syncope occurs when something triggers a temporary malfunction in your autonomic nervous system. This is the part of the nervous system that is responsible for regulating many of the body's automatic functions, such as heartbeat and blood pressure.
In most cases of vasovagal syncope, further treatment is not required. However, you may find it useful to avoid potential triggers, such as:
spending a long time on your feet
hot and stuffy environments
If you know that injections or medical procedures (such as blood tests) make you feel faint, you should tell the doctor or nurse beforehand. They will then be able to make sure you are lying down during the procedure.
Situational syncope is caused by a bodily function or activity that places a sudden strain on your autonomic nervous system, such as sneezing or laughing. There is no specific treatment, but avoiding the triggers may help. For example, if coughing has caused you to faint, it may be possible to suppress your urge to cough and therefore avoid fainting.
Carotid sinus syndrome is where pressure on your carotid sinus causes you to faint. Your carotid sinus is a collection of sensors in the carotid artery, which is the main artery in your neck that supplies blood to your brain. You can avoid fainting by not putting any pressure on your carotid sinus, for example, by not wearing shirts with tight collars.
In some people, carotid sinus syndrome can be treated by having a pacemaker fitted. A pacemaker is a small, battery-operated device that is inserted into your chest to help your heart beat regularly.
Orthostatic hypotension is a type of fainting that occurs when you stand up suddenly. This is because your nervous system does not stabilize your blood pressure quickly enough. By avoiding anything that lowers your blood pressure you should be able to prevent fainting. For example, you should:
make sure you do not get dehydrated, for example, by limiting how much alcohol you drink
avoid medication that can lower your blood pressure, but do not stop taking a prescribed medication unless you are advised to do so by your doctor or another qualified healthcare professional who is responsible for your care
Several different medications have been tested for the treatment of fainting. Guidelines for treating fainting from the European Society of Cardiology found that most medications had disappointing results.
The data suggested that taking medication long term for occasional fainting is not effective. However, taking a single dose of a medication before an activity that is known to trigger fainting might work. For example, taking a dose of medicine an hour before you know you will be standing for a long period of time may prevent you from fainting.
If you know or suspect that someone is going to faint, you should help the person to lie down, preferably in a position where their head is low and their legs are raised.
If it is not possible for the person who is feeling faint to lie down, sit them down with their head between their knees. Gently, but firmly, push their head down while they try to push their head upwards. This will encourage the blood to flow to their brain, reducing their symptoms and helping them to recover more quickly.
Physical counterpressure manoeuvres are movements that are designed to raise your blood pressure and prevent you losing consciousness. One study found that just under a third of people who fainted regularly who were trained in physical counterpressure manoeuvres fainted within a year, compared with half of those who were not trained in using these measures.
Physical counterpressure manoeuvres include:
crossing your legs
clenching the muscles in your lower body
squeezing your hands into a fist
tensing your arm muscles
You need to be trained in how to carry out these movements correctly. You can then carry them out if you experience any symptoms that suggest you are about to faint, such as feeling lightheaded.
If a person faints and does not regain consciousness within one or two minutes, you should put them into the recovery position. To do this, you should:
place the person on their side so they are supported by one leg and one arm
open their airway by tilting their head back and lifting their chin
monitor their breathing and pulse continuously
You should then dial 911 to request an ambulance and stay with the person until medical help arrives.