Vasovagal syncope is the common faint that may be experienced by normal persons with no evidence of heart disease.
The vagus nerve is the nerve of the muscle in the throat and the larynx, and is the nerve that slows the rate of the heartbeat and supplies the parasympathetic nerves to the lungs, the stomach, the esophagus, and other abdominal organs.
Arasympathetic means the nerves pertaining to the autonomic nervous system; the system which is concerned with control of involuntary bodily functions.
Stimulating the parasympathetic nerves generally produces vasodilation of the part supplied; in general, it slows the heart rate, decreases the blood pressure; contracts the pupils; causes copious secretion of the saliva; and increases gastrointestinal activity.
Stimulation of the vagus causes slowing of the heart rate and, if sufficient, can cause fainting or even cardiac arrest. Usually, when this happens, the heart's ventricles start beating on their own despite continued vagal stimulation.
In the moment-to-moment regulation of heart rate at rest, the vagal influence is dominant and, particularly in athletes with low resting heart rates, this 'vagal tone' can be considerable.
Hypotension, or low blood pressure, is associated with increased nervous system activation and increased heart rate, but one type, hypovolemic hypotension, occurring after hemorrhage or certain drugs, induces a decrease in heart rate. Both effects result from abnormal excitation of the vagus nerve, and hence, the term used to describe the loss of consciousness that may result is vasovagal syncope.
Syncope (fainting) or presyncope (faintness or feeling faint before fainting) is usually brought about by low blood pressure with reduction of blood flow to the brain.
Vasovagal syncope is frequently recurrent and tends to take place during emotional stress (especially in a warm, crowded room), after an injurious, shocking accident, and during pain. Mild blood loss, poor physical condition, prolonged bed rest, anemia, fever, organic heart disease, and fasting are other factors which increase the possibility of fainting in susceptible individuals.
In most instances, hypotension and fainting are relatively benign. If you feel all right, you do not have to do anything. Treatment depends on the initiating mechanisms. Your doctor should look first for those causes that constitute an emergency or serious condition.
If fainting is involved, then lying down with elevation of the legs and removal of the offending stimulus will rapidly restore consciousness.
If there are no contraindications, a diet with more salt may be beneficial.