Tony Brune, DO, Department of Neurology, The Johns Hopkins School of Medicine; Daniel R. Gold, DO, Departments of Neurology, Ophthalmology, Neurosurgery, Otolaryngology - Head & Neck Surgery, Emergency Medicine, and Medicine, The Johns Hopkins School of Medicine
Hyperventilation induced nystagmus is tested by asking the patient to take quick deep breaths (~1/s) for 40-60 seconds. This decreases ICP and increases CSF pH. This can be helpful in diagnosing irritative conditions of the vestibular nerve, including an acoustic neuroma (see video, https://collections.lib.utah.edu/details?id=1213447) or neurovascular compression (vestibular paroxysmia). With these irritative disorders, nystagmus is usually in an excitatory pattern with contralateral slow phases and fast phases directed toward the side of the lesion (in contrast to a paretic or inhibitory pattern where the slow phase is ipsilesional). Hyperventilation can also accentuate the nystagmus of unilateral vestibular loss due to transient central decompensation. In cerebellar disease (e.g., spinocerebellar ataxia), a downbeat nystagmus may be provoked or accentuated due to pH-induced exacerbation of cerebellar Purkinje fiber calcium channel dysfunction.
Spencer S. Eccles Health Sciences Library, University of Utah