New approach to caloric stimulation of the vestibular receptor

A new caloric testing method is described. During continuous aural irrigation, fluid is switched between hot and cold values at times computed according to a mathematical model of heat conduction in the labyrinth area. As a result, the induced temperature difference across the lateral semicircular canal describes an approximately sinusoidal time course, reaching peak values of equal magnitude but opposite sign. The magnitude of the caloric stimulus may be selected by choosing appropriate irrigation durations from a graph or table. Application of the test to clinical subjects demonstrated that the heat conduction model and analysis used in timing the sequence of thermal pulses was accurate. The new procedure causes less patient discomfort and requires less time to complete than does the conventional Fitzgerald-Hallpike test.