Development and Understanding of Caloric Responses; An Overview of the First Hundred Years

In 1906 Robert Barany published his original research on the caloric test and his convection theory to explain the direction of nystagmus. Subsequent publications by others suggested different explanations, including the effect of temperature on the vestibular nerves, pressure changes in the ampulla related to temperature expansion, but also the possibility of otolith modulation of the response. Technical developments have allowed quantitative measurement of the caloric response using electronystagmography; caloric assessment consists of measuring the slow phase velocity of nystagmus and uses the Jongkees-Phillipszoon equation (difference over sum) to detect pathology. The caloric test has become an entrenched assessment in the evaluation of patients with vestibular complaints. Barany’s convection theory was accepted as the explanation for the fact that with the lateral semicircular canal at right angles to horizontal (30 degrees head up) the response to caloric irrigation was greater with the patient supine (face up) than prone (face down). The convection theory was questioned when caloric responses in the appropriate direction were documented during space flight. It seems that there are many factors affecting the underlying convection caloric response that has been advanced for the last century.