Effects of interstimulus interval on slow phase velocity to ipsilateral warm air caloric stimulation in normal subjects.

This study investigated the effects of interstimulus interval on slow phase velocity (SPV) to ipsilateral warm air caloric stimulation in normal subjects. Results suggest that about 3 minutes should intervene between the offset of one irrigation and the onset of the second irrigation. This finding supports the hypothesis that carryover effects are likely only when nystagmus from the preceding irrigation overlaps the subsequent irrigation. If correct, clinicians do not have to wait a fixed time period between stimuli, but can initiate caloric stimulation as soon as nystagmus has ceased from the preceding irrigation. This recommendation compensates for individual and procedural differences. Test-retest reliability also was investigated. Findings suggest that when immediate test-retest differences exceed approximately 6 degrees/second (95% confidence interval), the examiner should administer additional trials until stability is ascertained. Moreover, unusual or significant findings should be verified with repeat testing.