Study of ventilation testing with electronystagmography.

Provocation tests such as head shaking and positional tests, as well as hyperventilation, have been used routinely by many laboratories to elicit nystagmus during an electronystagmogram. We added oxygen testing to this routine battery and compared the results with hyperventilation and other forms of provocative testing. Hyperventilation and oxygen testing are unique in that they probably affect the vestibular system by changing the levels of oxygen and carbon dioxide supplied. Hyperventilation in theory would decrease available oxygen, while oxygen testing would cause an increase. In a study of two groups totaling over 700 patients, we found that oxygen testing is only occasionally positive (2.5%) and is of little practical value. Hyperventilation testing is positive 8% of the time but rarely alone, and has no localizing value. When hyperventilation and oxygen tests are both positive, the nystagmus may be in opposite directions. In 6 of 18 patients with acoustic neurinomas, hyperventilation produced transitory direction-changing nystagmus.