Vestibular hyperreactivity and hyperventilation.

In a group of 26 patients with a hyperventilation syndrome, 77% showed vestibular hyperreactivity of velocity step responses, mostly due to an increase in gain of the vestibulo-ocular reflex (VOR), apparent from an increase in initial velocity, but also due to an increase in the time constant. Similar effects were found among 11 normal subjects after forced hyperventilation. In another group of 44 patients whose primary complaint was dizziness and who showed vestibular hyperreactivity without having any other demonstrable abnormality, a hyperventilation syndrome was found in 75%. This suggests that the velocity step test without hyperventilation provocation is a useful test for the detection of a hyperventilation syndrome.