Aw S T, Haslwanter T, Fetter M, Heimberger J, Todd M J
Neurology Department, Royal Prince Alfred Hospital, NSW, Sydney, Australia.
Acta Otolaryngol. 1998 Sep;118(5):618-27. doi: 10.1080/00016489850183089.
Modulation of the caloric nystagmus in response to repositioning the plane of one vertical semicircular canal from gravitational horizontal to vertical during continuous caloric stimulation was used to measure the vertical canal's contribution to the nystagmus. The rationale was to examine the thermovective response from one vertical canal at a time, after a temperature gradient had been established across its two limbs. The nystagmus was measured and analysed in three dimensions using orthogonal head-referenced coordinates. The magnitude of each semicircular canal's contribution to the overall caloric response, the canal vector, was determined in non-orthogonal, contravariant semicircular canal plane coordinates. By using the canal plane reorientation technique and contravariant canal plane coordinates, we were able to measure the proportional thermovective response magnitude generated by each vertical canal during caloric stimulation. We found that the anterior canal contributed about one-third and the posterior canal about one-tenth as much as the lateral canal did to the overall caloric response magnitude when it was reoriented from horizontal to vertical. Comparison of the eye rotation axis before and after each vertical canal plane reorientation, with the geometry of the stimulated semicircular canals, also showed directional modulation of the caloric nystagmus by the vertical canal response. When one vertical canal plane was horizontal during caloric stimulation, the eye rotation axis aligned with the resultant of the other vertical canal and the lateral canal response axes. After vertical canal plane reorientation, the eye rotation axis realigned towards the resultant of the maximally stimulated vertical canal and the lateral canal, by 55.2+/-33.9 degrees (mean+/-SD) after anterior canal plane reorientation and by 32.3+/-21.2 degrees after posterior canal reorientation.
在持续热刺激过程中，通过重新定位一个垂直半规管平面，使其从重力水平方向变为垂直方向，以此调节冷热性眼震，来测量垂直半规管对眼震的贡献。其基本原理是，在一个垂直半规管的两个臂之间建立温度梯度后，每次检查来自该垂直半规管的热对流反应。使用正交头参考坐标在三维空间中测量和分析眼震。在非正交、逆变半规管平面坐标中确定每个半规管对整体冷热反应的贡献大小，即半规管矢量。通过使用半规管平面重新定向技术和逆变半规管平面坐标，我们能够测量在热刺激期间每个垂直半规管产生的成比例热对流反应大小。我们发现，当从水平方向重新定向为垂直方向时，前半规管对整体冷热反应大小的贡献约为外侧半规管的三分之一，后半规管约为十分之一。比较每个垂直半规管平面重新定向前后的眼旋转轴与受刺激半规管的几何形状，也显示了垂直半规管反应对冷热性眼震的方向调制。当在热刺激期间一个垂直半规管平面为水平时，眼旋转轴与另一个垂直半规管和外侧半规管反应轴的合力对齐。在垂直半规管平面重新定向后，眼旋转轴重新对准最大刺激垂直半规管和外侧半规管的合力，在前半规管平面重新定向后为55.2±33.9度（平均值±标准差），在后半规管重新定向后为32.3±21.2度。
