symptom of decompression sickness in 5.3% of cases by the u.s. navy as reported by powell, 2008 including isobaric decompression sickness. decompression sickness can also be caused at a constant ambient pressure when switching between gas mixtures containing different proportions of different inert gases. this is known as isobaric counterdiffusion, and presents a problem for very deep dives. for example, after using a very helium-rich trimix at the deepest part of the dive, a diver will switch to mixtures containing progressively less helium and more oxygen and nitrogen during the ascent. nitrogen diffuses into tissues 2.65 times slower than helium, but is about 4.5 times more soluble. switching between gas mixtures that have very different fractions of nitrogen and helium can result in "fast" tissues (those tissues that have a good blood supply) increasing their total inert gas loading. this is often found to provoke inner ear decompression sickness, as the ear seems particularly sensitive to this effect. stroke a stroke (either ischemic or hemorrhagic) involving the posterior fossa is a cause of central vertigo. risk factors for a stroke as a cause of vertigo include increasing age and known vascular risk factors. presentation may more often involve headache or neck pain, additionally, those who have had multiple episodes of dizziness in the months leading up to presentation are suggestive of stroke with prodromal tias. the hints exam as well as imaging studies of the brain (ct, ct angiogram, mri) are helpful in diagnosis of posterior fossa stroke. vertebrobasilar insufficiency vertebrobasilar insufficiency, notably bow hunter's syndrome, is a rare cause of positional vertigo, especially when vertigo is triggered by rotation of the head. management definitive treatment depends on the underlying cause of vertigo. people with ménière's disease have a variety of treatment options to consider when receiving treatment for vertigo and tinnitus including: a low-salt diet and intratympanic injections of the antibiotic gentamicin or surgical measures such as a shunt or ablation of the labyrinth in refractory cases. common drug treatment options for vertigo may include the following: anticholinergics such as hyoscine hydrobromide (scopolamine) anticonvulsants such as topiramate or valproic acid for vestibular migraines antihistamines such as betahistine, dimenhydrinate, or meclizine, which may have antiemetic properties beta blockers such as metoprolol for vestibular migraine corticosteroids such as methylprednisolone for inflammatory conditions such as vestibular neuritis or dexamethasone as a second-line agent for ménière's disease all cases of decompression sickness should be treated initially with 100% oxygen until hyperbaric oxygen therapy (100% oxygen delivered in a high-pressure chamber) can be provided. several treatments may be necessary, and treatment will generally be repeated until either all symptoms resolve, or no further improvement is apparent. etymology vertigo is from the latin word, vertō, which means "a whirling or spinning movement".