Positional Envelope as a Response Parameter in Caloric Testing

Bithermal caloric testing was carried out in 57 normal subjects and 374 patients presenting with subjective complaints of vertigo over a 4-year period from December 1984 to December 1988. Responses were quantitatively assessed using a DEC PDP 11/73 laboratory minicomputer. Patients were classified as normal and abnormal according to caloric responses based on standard methods of calculating unilateral hypoexcitability and directional preponderance using the maximum slow component velocity. Results obtained from the slow component velocity for unilateral hypoexcitability and directional preponderance were compared to the same values obtained from the overall positional envelope calculated by an integration of the slow component velocity vs. time curve. Although duration of nystagmus varies extensively in normal subjects and has not proven clinically useful in identifying abnormalities, the integral of response amplitude over time gives a more complete description of the vestibular response. However, when compared to the maximum slow component velocity in abnormal patients, the positional envelope identified only 94 of the total 119 abnormalities (79%). Therefore, maximum slow component velocity is the more sensitive response parameter in identifying vestibular pathology.