Effect of changes in blood pressure on per-rotational nystagmus in guinea pigs with obliterated endolymphatic sac.

The effect of blood pressure (BP) changes on per-rotational nystagmus (PRN) was compared between normal guinea pigs and guinea pigs with unilaterally obliterated endolymphatic sac. Eye movements were recorded 3 months postoperatively. When the animal was rotated sinusoidally, asymmetry of PRN was minimal in the control animals. In the operated guinea pigs, however, nystagmus oscillating toward the operated side was largely suppressed when BP was decreased (30-40 mmHg). Thus, directional preponderance of PRN toward the nonoperated side was established. Oxygen tension (pO2) was measured in the perilymphatic space of the lateral semicircular canal to investigate the mechanisms underlying the PRN asymmetry. When BP was reduced below normal, pO2 on the operated side decreased much more than that on the intact side. It is suggested that obliteration of the endolymphatic sac results in an autoregulatory dysfunction in the semicircular canal. Asymmetry of the vestibulo-oculomotor reflex at low BP may be the result of decreased blood flow to the semicircular canal.