Crescendo Time for Per-Rotatorily Elicited Nystagmus

Abstract

Forty-four clinically healthy subjects were accelerated at 1, 2, 4 and 8°/sec². Both clockwise and counterclockwise acceleration was used alternately. In each acceleration how the nystagmus increased to maximal intensity was studied. The stimulation time required for this was called the crescendo time. At 1°/sec² acceleration this crescendo time was fully 15 sec and, subsequently, for increasing strengths of stimulation it became shorter and shorter. The mean values were about 7.5 sec at 8°/sec².

There were wide individual variations. At l°/sec² the times measured were between 0–29 sec, and the higher value became throughout increasingly lower when the strength of acceleration was increased, whereas the lower value remained unchanged.

On calculating the differences between the crescendo times for clockwise and counterclockwise accelerations, values were obtained whose mean was the same for different acceleration strengths, but varied within a wider time range for the weaker accelerations.

Since repeated tests were made for each strength of acceleration it was possible to assess reproducibility. This was the same for different acceleration strengths, but a tendency to increasingly shorter crescendo times was observed at l°/sec² when the tests were repeated. For iterated identical accelerations the crescendo time could be longest for either clockwise acceleration or counterclockwise acceleration, and only in a few cases was the condition throughout the same. Statistical analyses of the borderline values were made in such a way that variations in normal persons could bz assessed.