How the test is doneIn a tilt table study, the patient is strapped to a table, which is then mechanically tilted to an upright position. While monitoring the pulse, blood pressure, electrocardiogram, and sometimes blood oxygen saturation, the patient is left in a motionless standing position for 20 to 30 minutes. When the patient's syncope is reproduced during the test, a "positive" tilt table study is said to have occurred .
How the test worksDuring an upright tilt or for that matter while standing a person's cardiovascular system has to adjust itself in order to prevent a significant portion of the blood volume from pooling in the legs. These adjustments consist of a mild increase in heart rate, and a constriction of the blood vessels in the legs. When a normal individual is placed in an upright tilt, these cardiovascular adjustments occur very quickly, and there is no significant drop in the blood pressure.
However, in patients with two varieties of syncope orthostatic hypotension and vasovagal syncope the cardiovascular adjustment to an upright tilt does not function normally.
In orthostatic hypotension the bodys ability to adjust to an upright posture is grossly abnormal. When these individuals stand (or when they have a tilt study), their pulse increases markedly, and their blood pressure drops precipitously. These patients are simply unable to adjust to the upright position. Patients with othostatic hypotension rarely require a tilt table study for diagnosis, however doctors can easily make the diagnosis in their office simply by taking the blood pressure first while the patient is lying down, and then while standing.
The tilt table study is also frequently abnormal in people with vasovagal syncope, but in a more subtle way. In general, these patients initially adjust normally to an upright tilt, but within 20 30 minutes they have a rather sudden and marked change in vital signs their blood pressure drops dramatically; their pulse also drops, and they pass out. They recover within seconds after the table is brought back down, and they are returned to a lying-down position.
Vasovagal syncope is due to a reflex that causes sudden dilation of the blood vessels in the legs, and a slowing of the heart rate, both of which contribute to a dramatic fall in blood pressure. Numerous triggering events can initiate this so-called vasomotor reflex, including things like fear, pain, and noxious stimuli (such as the sight of blood). During the tilt table test, the upright tilt produces stress on the cardiovascular system that acts as the trigger. The tilt table study, then, tests whether a person has a hyperactive vasomotor reflex. It tests, in other words, a person's propensity to develop vasovagal syncope.
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