Vertical semicircular canal function: a study in patients with benign paroxysmal positional vertigo.

A pendular rotation test in a head-tilted position (60 degrees backwards and rotated 45 degrees to either the right or left) was performed in 7 patients with benign paroxysmal positional vertigo (BPPV). Patients were rotated 360 degrees at a frequency of 0.1 Hz (maximum speed 114 degrees/s). The excitability of vertical semicircular canals was evaluated using this test procedure. Using an infrared CCD camera and a PC, evoked nystagmus was analyzed in order to determine the morbidity of BPPV. A statistically significant difference (p < 0.05) was found in the maximal slow-phase eye velocity between nystagmus from the anterior semicircular canal and nystagmus from the posterior semicircular canal. The excitability of the posterior semicircular canal in the affected ear was lower than that of the anterior semicircular canal. However, when vertigo and nystagmus disappeared, the difference in excitability was improved. The present results indicate some functional deterioration of the posterior semicircular canal in BPPV cases, suggesting the participation of both mechanical (dumping by mass) and organic (peripheral end organ) factors in causing morbidity.