DAN Medical Frequently Asked Questions
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>Alternobaric vertigo occurs during descent, ascent or immediately after surfacing from a dive and is caused by unequal pressure stimulation in each ear.
>According to various sources, up to 25 percent of divers experience alternobaric vertigo at some time.During ascent, air in the middle-ear space expands, relative pressure increases, the Eustachian tubes open passively, and gas escapes through the Eustachian tubes into the nasopharynx. Occasionally the Eustachian tube may obstruct this flow of air, with subsequent air distension and increased pressure sensation in the middle-ear cavity during ascent. If the obstruction is one-sided and the pressure difference is greater than 60 centimeters of water, vertigo may occur as the pressure increase stimulates the vestibular apparatus. Usually it is relieved by further ascent, because the increasing differential pressure in the middle-ear space forces open the Eustachian tube and vents the excess air. Contributing factors include middle-ear barotrauma during descent, allergies, upper respiratory infections (congestion) and smoking.The symptoms of alertnobaric vertigo may include disorientation, nausea and vomiting.
>Note: The disorienting effects of vertigo while diving are extremely dangerous. The inability to discern up from down, follow safe ascent procedures, and the risks associated with vomiting pose a significant hazard to the diver as well as other divers in the water.Advice provided by Dr. Carl Edmonds about how to manage alternobaric vertigo during a dive:
>"If a diver encounters ear pain or vertigo during ascent, he should descend a little to minimize the pressure imbalance and attempt to open the Eustachian tube by holding the nose and swallowing (Toynbee or other equalization maneuver). If successful, this equalizes the middle ear by opening it up to the throat and relieves the distension in the affected middle ear.
>"Occluding the external ear by pressing in the tragus (the small fold of cartilage in front of the ear canal) and suddenly pressing the enclosed water inward may occasionally force open the Eustachian tube. If this fails, then try any of the other techniques of equalization described previously, and attempt a slow ascent."
>Uncomplicated cases resolve quickly within minutes upon surfacing. If symptoms persist, see your primary care physician or an ENT specialist. Do not dive if you have equalization problems.
>Associated injuries include middle-ear barotrauma and inner-ear barotrauma; alternobaric vertigo may occur during descent or ascent, but is commonly associated with a middle-ear barotrauma of ascent (reverse squeeze). Other conditions such as inner-ear DCS or caloric vertigo (when cold water suddenly enters one ear) should be ruled out.As soon as all symptoms and contributing factors have been resolved, a diver may return to diving.Take measures for the prevention of ear barotraumas. Avoid the unequal pressurization of the ear by avoiding tight-fitting wetsuit hoods or earplugs. Maintain good aural hygiene. Do not dive when congested or unable to equalize.