[Quantitative analysis of head-shaking nystagmus of peripheral vestibular origin in conjunction with stimulus...

A quantitative analysis of horizontal head-shaking nystagmus (HSN) was made on 48 patients with unilateral peripheral vestibular disorders in conjunction with stimulus intensity (the number of head-shakes). Each patient underwent three head-shaking tests with 10, 30 and 50 horizontal head-shakes, with a rapidity of about 2 Hz, in random order. HSN was recorded by ENG with the eyes open in a completely dark room, and various components of nystagmus were measured manually. 1. HSN appeared in a biphasic or monophasic pattern. In some patients with biphasic HSN, the 2nd phase disappeared as the stimulus intensity diminished. 2. The maximal slow-phase eye velocity (MSV) of the 1st phase of biphasic HSN was significantly greater than that of monophasic HSN. The tendency to increase in proportion to stimulus intensity was also greater in biphasic than in monophasic HSN. The MSV values of the 2nd phase of biphasic HSN were smaller than in the 1st phase (less than one-third) at all stimulus intensities. 3. The duration and total number of HSN beats were greater in the 2nd phase of biphasic HSN and increased markedly in proportion to stimulus intensity. In contrast, in the 1st phase of biphasic HSN and in monophasic HSN, the values of these nystagmus components were smaller, there was no clear relationship with stimulus intensity, and when the stimulus intensity was high, they were instead significantly smaller in the 1st phase of biphasic HSN than in monophasic nystagmus. 4. As the stimulus intensity rose to a high level, the interval between the 1st and 2nd phases of biphasic HSN (2nd phase latency) shortened, and the 2nd phase tended to appear more quickly after head-shaking. 5. The time constant of the decline in slow-phase eye velocity was nearly constant in both the 1st phase of biphasic HSN and monophasic HSN, regardless of stimulus intensity. It was especially noteworthy that in response to an increase in stimulus intensity, both the MSV in the 1st phase and the duration of the 2nd phase of biphasic HSN increased, while the duration of the 1st phase of biphasic HSN was inversely suppressed by the 2nd phase.