Abstract
Benign Paroxysmal positioning vertigo and acoustic tumors are thought to be related to the function of the vertical semicircular canal (VSCC). Therefore, we developed a new test to assess VSCC function by analyzing VSCC-induced nystagmus. We examined 11 healthy subjects, wearing goggles equipped with an infrared CCD camera and sitting on a chair designed to bilaterally stimulate the VSCCs by tilting the head backward during 45° rotation to the right on the sagital plane. The stimuli used were sinusoidal rotation with a maximal angular velocity of 100°/sec at a frequency of 0.033 Hz. The result was that the maximum slow phase eye velocity (MSPEV) of horizontal nystagmus decreased parallel to the head-tilted angle and the MSPEV of the vertical nystagmus was maximal when the head was tilted 60° or 70° backward. From the perspective of VSCC anatomy, the direction of horizontal nystagmus is reversed when head is tilted 60° backward. However, we could not observe the reverse of the direction of horizontal nystagmus even when head tilted 80° backward. We considered that vertical nystagmus was maximal when the head was tilted 60-70° backward because this position applied the optimal stimulation to the VSCC. This finding is in agreement with the position of the vertical VSCC in skull. We concluded that rotational test with respect to the VSCC can be used to analyze VSCC function.
