Rotary Chair Nydiag 200
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Maximum acceleration is 100°/S² and must never exceed this value.
Like in the sinusoidal test, the various parameters of the triangular test are difficult to test objectively.
Apart from the number of cycles that can be counted, only subjective assessment is possible:
1.
Velocity: does the chair move faster with increasing values for velocity? Compare values
20°/s with 60°/s
–
with Acceleration change and Velocity Change dv = 1
2.
Acceleration: Check that low values (such as 10°/s²) produce soft acceleration and that high
values (such as 50°/s²) produce abrupt acceleration.
3.
Acceleration change: Does the chair accelerate faster from one cycle to another with values
>1 entered in the acceleration change box?
4.
Velocity Change dv: values >1 produce faster movements whereas values >1 produce slower
movements
5.
Cycles: check that the chair rotates the number of cycles ordered. One cycle is half the
pendular movement; i.e. from zero, acceleration phase and then deceleration into zero again.
6.6 Trapeze test
(Also referred to as Step-Rotation test or Velocity-Step Test)
Purpose of Trapeze Test: Measurement of perrotatory and postrotatory nystagmus response in
terms of
o
Response Gain, which is the ratio of peak eye velocity to head velocity
o
Response Time Constant, which is the time, in seconds, for the response to decline to 37%
of its peak value
Stimulus: Acceleration up to peak velocity (typically 100 °/s) which is then kept for a certain period
(typically 60 seconds) followed by de-acceleration - this is the Perrotatory Period.
The postrotatory period which is a pause before next cycle is initiated.
Relevant VNG test protocol: Data from “Set Velocity” can be recorded and analyzed i
n the
StepRotation test
The figure above shows a typical velocity-step test setup. The chair accelerates slowly at 2°/s² until the
final
Velocity v
of 100°/s is reached. This velocity is kept for 60 seconds with
Stable time t1
set at
60
–
then the chair decelerates with 60°/s². The deceleration is the stimulus for the patient.