Postrotatory nystagmus was analyzed by a 2nd order system model in 15 healthy nomal subjects. In postrotatory nystagmus the input into the semicircular canal is the impulse, so the model was
Y (t) =A/T
1-T
2× (e
-t/T1-e
-t/T2)
y (t) : slow phase velocity
T
1 : short time constant
T
2 : long time constant
A : amplitude
By means of the least square method, the variables T
1, T
2 and A were calculated with the aid of a microcomputer.
The subject was seated in the dark on a rotating chair which was stopped at 80/sec
2, 120/sec
2 and 160/sec
2. The slow phase of the electro-nystagmogram on DC ENG recording was calculated every 2 minutes and its values were used to calculate the variables of the model.
T
1 (short time constant) at 80, 120 and 160/sec
2 was 0.37, 0.5 and 0.67sec and T
2 (long time constaant) was 12.8, 12.19 and 11.13sec, respectively.
These values could be converted into the frequency range of postrotatory nystagmus by the equation : f=1/2T.
The frequency range corresponding to the above values is 0.01 to 0.4Hz, which is considered to be the normal frequency range in postrotatory nystagmus testing.
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