Caloric test

Abstract

The caloric test has been used worldwide for many years. It is a clinical test that is performed to evaluate the function of the lateral semicircular canal, by irrigation of the external auditory canal with warm or cold water. This irrigation generates a convective flow in a duct of the lateral semicircular canal, stimulating or suppressing the canal, and inducing nystagmus and vertigo. Robert Bárány termed the neurologic response to the irrigation of water of different temperatures, the "caloric response." The duration or the maximum angular velocity of the slow phase of the nystagmus is used as the evaluation index. Caloric stimulation is the only test in which the right ear and the left ear can be stimulated separately. When the caloric response is weak, canal paresis is diagnosed. The caloric test was established by Bárány, who was awarded the 1914 Nobel Prize in Physiology/Medicine for it. To obtain a strong response, the recording must be done while the subject is in complete darkness. During the caloric test, a visual suppression test is also performed to check the activity of the central vestibular system. During the caloric response, the subject looks at a visual target for 10 seconds in light. The slow phase eye velocity of the caloric nystagmus should reduce, and the reduction ratio is used as the evaluation index in the visual suppression test. In this review, the history, basic neurophysiological findings, recording methods, data interpretation, and future of the caloric and visual suppression tests are described.