Vestibular tests

In the caloric test, each ear will be stimulated with hot (44ºC) and cold (30ºC) water, individually and alternately.

In this test, which is one of the most important, a jet of approximately 200 cc of water at the above mentioned temperatures is directed through the external auditory canal.

Its mission is to cause a temperature difference along the entire temporal bone where the inner ear is housed. This determines a displacement of the liquids of the internal ear through the semicircular canals which triggers a transitory vertigo reaction and an involuntary nystagmus or eye movement in shakes.

Warm water stimulation of one ear produces a nystagmus in a different direction than cold water stimulation. For this reason, by stimulating both ears with the two temperatures (a total of four irrigations are performed in the test) we can obtain a precise idea of the relative function between the two.

The sensation of dizziness that accompanies this test is normal, that is, any normal subject to whom this test is performed suffers from vertigo and nystagmus is recorded. The duration of this sensation after each stimulation does not last more than 2 minutes.

In this case the eye reflex movement is studied as in the tests described above. The patient sits in a chair whose movement is programmed from a computer that generates a precise movement.

The movements are similar to those the patient makes throughout his or her daily activities, and the patient's positioning is precise and safe in order to avoid head movements during rotations that could invalidate the results.

The tests take place in a booth or room in the dark, although the patient is in contact with the person performing the tests by means of a microphone and headphones between the two; a camera records what happens in the booth and this is constantly monitored by the person performing the tests.

The movements that the chair makes are sinusoidal, back and forth, at different speeds and frequencies, not exceeding 50º per second of maximum speed.

This test is complemented by another in which the rotation is performed identically but in this case keeping the eye fixed on one point to analyze the absence of nystagmus. The same test is also performed but with lights on or with the simultaneous projection of some lights on the wall to analyze the contribution that vision has with the vestibular system in the gaze stabilization reflexes.

The ability to maintain balance depends not only on sight and the vestibular system but also on the information the brain receives from the muscles and joints. This information provides the brain with certain clues such as the direction in which the head moves, the type of road surface on which it wanders, the slope of the ground, etc.

Dynamic Posturography allows us to analyze the interrelationship between the three parts of the balance system (eyes, vestibular system, muscles and joints). It allows to determine if one of them is abnormal in its functioning or if it is incapable of analyzing and considering the anti-physiological or balance altering stimuli.

The patient stands on a platform, barefoot and held by a harness that prevents falls in case of loss of balance. Changes in position and therefore in weight distribution on the support platform that occur during the maintenance of balance are the object of the platform recording.

In response to movements, the platform or the visual environment in which the patient is standing may also shift, and on occasion the patient will also be asked to keep his or her balance with his or her eyes closed.