Vaso-vagal syncope is the medical term for a common cause of fainting. In this disorder, the nervous reflexes which control heart rate and blood pressure behave abnormally causing a drop in blood pressure and a fainting spell.
The nerves which control the heart rate and blood pressure are regulated through pressure sensors in the arteries and veins called the baroreceptors. The baroreceptors detect changes in blood pressure. These baroreceptors detect a fall in blood pressure and send signals via the nerves to increase the heart rate and constrict blood vessels bringing the blood pressure back to normal. Conversely, baroreceptors detect abnormally elevated blood pressure and send signals to slow heart rate and relax blood vessels to lower blood pressure back to normal. These reflexes are called the baroreflexes.
Vaso-vagal syncope results from an abnormality in the baroreflexes. When you stand up, the force of gravity causes some of the blood from your heart and your chest cavity to pool in your legs. This produces a slight drop in blood pressure which is detected by the baroreceptors and is adjusted through the baroreflexes. In patients with vaso-vagal syncope, after a period of standing in the upright position, baroreflex adjustments fail and blood pressure and heart rate decrease causing fainting.
Vaso-vagal syncope can be diagnosed by tilt table testing and can be prevented by treatment.
― Ganbare Goemon (ex machina), Thursday, 30 December 2004 17:00 (twenty-one years ago)
What is a tilt table test?
A tilt table test is a diagnostic test which is designed to evaluate fainting in patients who are susceptible to vaso-vagal syncope. When a patient tells a doctor about a fainting spell, the doctor considers a long list of causes of fainting spells and tries to determine which of those causes was responsible for the patient's fainting spell. Sometimes, the diagnosis is evident from the patient's description of the fainting spell, or from the patient's physical examination. Laboratory tests such as blood tests and an electro-cardiogram (ECG) may also help the doctor determine the cause. More often, however, the doctor is left considering a few possibilities. In this case, further testing is performed. The tilt table test is a commonly used test to determine if a patient's fainting spell was caused by vaso-vagal syncope.
A tilt table test is simple. The patient is placed on a table, and intravenous line in placed into one of the veins in the arms. An intravenous line is a small tube attached to a needle placed into one of the veins. The patient is connected to a machine which records the electrocardiogram (ECG) and to a machine that measures blood pressure using a cuff wrapped around one of the fingers. The lights in the room are dimmed and the patient is asked to relax.
After a 15-minute period of rest, the table begins to tilt the patient head-up (the table includes a foot board for the patient to stand on). The patient is tilted head-up to 30o for a few minutes and then up to 600 which is nearly standing. The patient then remains in the position for up to 60 minutes. There is a doctor and/or a nurse in the room at all times and the electrocardiogram and blood pressure are continuously monitored. When a patient begins to feel symptoms of any kind, the doctor or the nurse will check the patient. Often, there are changes in the heart rate and blood pressure that indicate the cause of the patient's symptoms and the cause of the patient's fainting spells. For example, patients who are susceptible to vaso-vagal syncope will develop a characteristic decrease in heart rate and decrease in blood pressure and they may begin to faint. Once the mechanism is clear and if the patient begins to faint, then the table is lowered back to the horizontal position which restores heart rate and blood pressure within a few seconds. Sometimes a medication called isopro-terenol (which is like adrenaline) is infused during the tilt table test.
At the Syncope Center, we have performed more than 500 tilt table tests over the past few years. The tilt table test is safe. Patients who faint return to normal within a few seconds and are able to leave the laboratory and return to their normal activities 15 to 30 minutes after the test.
― Ganbare Goemon (ex machina), Thursday, 30 December 2004 17:01 (twenty-one years ago)