LAUSR

The video-head-impulse test (vHIT) [1] and bithermal caloric irrigation (CI) [2] are routinely used for examining unilateral vestibular hypofunction of the horizontal vestibular-ocular reflex (VOR). Passive whole body rotation of the subject around an earth vertical axis on a rotatory chair is another method which not only tests the peripheral VOR, but also the central processing. The test depends on the velocity profile, the disease itself, the stage of the disease and on the cooperation and alertness of the patients. This kind of test has been applied for years, but the sensitivity to identify unilateral vestibular failure is low [3, 4]. These results are based on fitting the data using a single exponential (i.e. a first-order model), which provides an inaccurate description of the data [5]. We report here a first step to better describe the responses to the ‘rotatory intensity damping test’ (RIDT) with multiple parameters using a model of the VOR. This retrospective study included patients referred to our inand outpatient clinic with vertigo and dizziness for whom vHIT, CI and RIDT were performed on the same day. Patients underwent a detailed clinical history and clinical examination [2], they were diagnosed according to the cited criteria [6–8] and tested as previously described [2]. As rotatory test, the RIDT [9] was used (Vestlab 7.1®, GN-Otometrics, Taastrup, Denmark) in complete darkness. The head of the patient was pitched 30° forward and carefully aligned so that the earth vertical rotatory axis was centered between the two labyrinths. The test started with a step-like acceleration of 3°/s2 (perrotatory) until 90°/s was reached and stopped (postrotatory) after 180 s. The stimulus was applied in the rightand leftward direction in sequence. The perand postrotatory responses of the desaccaded slow phase velocities were analyzed separately by fits. To better quantify the data, we performed optimizations with a model of vestibular processing, based on a model published by Furman and colleagues [10] and physiological value ranges [5] (Fig. 1a). This included the time constant of the semicircular canals with a gain (k1) and a high-pass filter of the form sT c1