Influence of canal paresis and compensation on gain and time constant of nystagmus slow-phase velocity to yaw-axis rotation

In order to assess the influence of canal paresis and compensation on the y aw-axis rotatory chair test parameters gain and time constant, a study was conducted in 435 patients diagnosed with unilateral peripheral vestibulopat hy. Patients were grouped according to the amount of canal paresis found in the caloric test and by the result of a bedside examination of the vestibu lo-ocular reflex (VOR). The time constant of the VOR diminishes as canal pa resis increases and, when using a high-velocity sinusoidal test, there is a similar reduction in gain. Mean time constant was reduced when rotations w ere to the side of the lesion (ipsilesional) and to the normal (contralesio nal) and differences between both rotations were found for 21-80%. canal pa resis. Ipsilesional gain was significantly less than contralesional gain, w hich had a normal result independent of the amount of canal paresis; differ ences between them were significant when canal paresis was > 41%. Spontaneo us nystagmus significantly influenced the appearance of asymmetries in gain and time constant in the tests performed while, with high-velocity sinusoi dal rotation, gain was found to be significantly different for ipsilesional and contralesional rotations in non-acute symptomatic patients.