Comparison of head thrust test with head autorotation test reveals that the vestibulo-ocular reflex is enhanced during XXXX .

@entity1 @entity394 @entity910
OBJECTIVES: To compare 2 clinical tests of vestibular function, the head autorotation test (HART) and the head thrust test (HTT), and to determine why they give disparate results in @entity1 with known @entity394 ( @entity394 ) due to labyrinthectomy. METHODS: We used scleral coils to measure the horizontal (yaw) vestibulo-ocular reflex (VOR) in 5 healthy @entity1 subjects and in 11 @entity1 who underwent labyrinthectomy. We used 2 paradigms. Using HART, subjects visually fixated a target during self-generated, swept-frequency, sinusoidal, horizontal head rotations. Using HTT, @entity1 fixated the target during horizontal head thrusts delivered randomly in direction and time. RESULTS: In subjects without @entity394 , eye movements were almost perfectly compensatory for both paradigms. In subjects with @entity394 , VOR gain for ipsilesional head thrusts was low for both paradigms, but significantly (P<.001) higher (less abnormal) for HART (0.60 +/- 0.13) than for HTT (0.14 +/- 0.13). Contralesional gain was reduced for both, to 0.64 +/- 0.20 for HART and to 0.57 +/- 0.17 for HTT. Because ipsilesional and contralesional gains were not statistically different for HART (P =.69), comparison of VOR gains for half-cycle responses to the HART stimulus could not reliably identify the side of the known lesion. In contrast, HTT consistently identified the side of the lesion for all subjects with @entity394 . To investigate whether preprogramming contributes to the boost in VOR as measured by HART, we compared the gain and response delay of eye movements during actively self-generated and passively received head thrusts. For subjects without @entity394 , response delays were shorter for active (6 +/- 1 milliseconds) than for passive (12 +/- 1 milliseconds) HTT. For ipsilesional rotations of subjects with @entity394 , active HTT yielded a significantly higher gain (0.44 +/- 0.20) (P<.001) and a shorter delay (15 +/- 6 milliseconds) (P<.001) than did passive HTT (0.14 +/- 0.13 and 37 +/- 15 milliseconds, respectively). Contralesional test results revealed a similar performance boost for active head movements. Data are given as mean +/- SD. CONCLUSION: When comparison of half-cycle gains is used to identify the lesion side, self-generated predictable head movement paradigms, such as HART and active HTT, are less accurate than passive HTT in the characterization of @entity394 , in part because preprogramming can augment the VOR during @entity910 .
