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Syncope - A spontaneous loss of consciousness caused by an insufficient blood supply to the brain

There are many causes of syncope, some common and some rare. Reflex Syncope is the most common cause of blackouts. However, many people, including medical professionals, are unaware that some everyday activities can be the cause of many reported fainting attacks.

Situational syncope

Dr P Boon Lim, Consultant Cardiologist & Clinical Lead for the Syncope Diagnostic Unit at Hammersmith Hospital, London, discusses the diagnosis and treatment of situational syncope.

Brushing Syncope:

Hair grooming syncope most commonly occurs in young women who experience nausea, light headedness, sweating, and visual disturbances before fainting. Research suggests that the pulling of the hair or scalp has an effect on a particular nerve in the head that triggers the faint.

Carotid Sinus Hypersensitivity (CSH):

CSH is common in older adults and increases in prevalence with age. It is more common in men who have high blood pressure or coronary heart disease. The Carotid Sinus is a part of the major artery supplying blood to the head. Any manoeuvre that causes stimulation of the area, i.e. turning the head, looking up or even a tight collar can cause syncope in people who have CSH. Simple techniques such loosening your collar and avoiding turning your head or neck too far will help reduce your chance of syncope.

Cough Syncope:

In Cough Syncope, sudden syncope occurs due to heavy coughing. A burning or tingling of the larynx may precede the cough. Straining when you cough can raise the pressure in your chest area. This may lower the amount of blood being returned from your legs to your heart. In some people the reduced blood return to the heart leads to a fall in blood pressure and increases your chance of fainting.

Heat Syncope:

A warm environment may increase your chance of fainting. Heat expands blood vessels, causing them to hold more blood. The reduced return of blood to the heart can cause low blood pressure. Hot weather, a warm room or a hot shower or bath may dilate vessels and decrease blood pressure. It is advised to wear loose clothing in warm weather, keep well hydrated and seek shelter in hot weather.

Orthostatic Hypotension syncope:

Orthostatic Hypotension is an excessive lowering of blood pressure when moving to an upright position. Some people may experience symptoms of syncope when they stand up from a sitting position or when they sit up from a lying position. Fainting is caused by the change of posture and becoming upright, where gravity pulls blood down towards your lower body and legs. As a result there is a lack of blood supply to the brain which results in loss of consciousness. To prevent Orthostatic syncope ensure that if you have been sitting or lying for long periods of time stand up slowly, particularly in the morning when your blood pressure is likely to be lower.

Postprandial Syncope:

Postprandial syncope simply means ‘after a meal’. In some people, eating will cause a fall in blood pressure after finishing a meal. Postprandial Hypotension occurs due to the inability of the nervous system to adjust for the concentration of blood around the digestive organs after a meal. Symptoms of Postural Hypotension may be subtle with a slight dizziness or weakness when standing after eating. If syncope occurs after a meal it is advised to eat small regular meals and avoid large carbohydrate meals. Sitting with legs slightly raised after a meal will also avoid blood pooling in the legs and increase blood pressure.

Stretch Syncope:

Stretch Syncope occurs through stretching and bending the neck as far back as possible. The patient will first experience lightheadedness and visual disturbances and then passes out. These attacks can be prevented by remembering not to extend the neck backwards when having a good stretch!

Micturition Syncope

Dr P Boon Lim, Consultant Cardiologist & Clinical Lead for the Syncope Diagnostic Unit at Hammersmith Hospital, London, discusses the diagnosis and treatment of micturition syncope.

Micturition syncope is a form of Neurocardiogenic Syncope that occurs in response to urination or emptying of one’s bowels. It is caused by a sudden drop in blood pressure during these functions that reduces the supply of blood to the brain resulting in syncope. If syncope occurs while emptying one’s bowels it is advised to use laxatives to treat constipation. If syncope occurs while urinating, men are advised to urinate in the sitting position.

Swallow Syncope:

Swallow Syncope is rare. Patients who have Swallow Syncope may experience a drop in blood pressure and lowered heart rate in response to the action of hot food/fluids passing from the throat to the stomach. The autonomic nervous system is not able to compensate for this increase in pressure, which decreases the flow of blood to the heart.

Reflex Anoxic Seizures (RAS)

RAS occurs mainly in young children and is the result of an unexpected stimulus, such as pain, shock or fright, which causes the heart and breathing to stop temporarily; the body to stiffen and the complexion to become white and blue around lips. The patient will regain consciousness after a few minutes. See Reflex Anoxic Seizures section for further information.

Reflex Syncope

Reflex Syncope is the most common form of syncope and is also known as Vasovagal Syncope and Neurocardiogenic Syncope. A variety of situations (distress, fear, prolonged standing) stimulate the vagus nerve (receptors that respond to being stretched in the heart), which leads to a slowing of the heart rate and dilation of the body’s blood vessels. With a slow heart rate and dilated blood vessels, less blood gets to the brain and causing fainting. See Reflex Syncope section for further information.