Alternobaric vertigo occurs during descent, ascent or immediately after surfacing from a dive and is caused by unequal pressure stimulation in each ear.
Mechanisms of Injury
During an ascent, the 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 a Eustachian tube may obstruct this flow of air. This obstruction causes increased pressure in the middle-ear cavity. If the obstruction is one-sided and the pressure difference is greater than about 2 feet (0.6 meters) of water, vertigo may occur as the pressure increase stimulates the vestibular apparatus. You can usually relieve it by ascending further. The increasing differential pressure in the middle-ear space forces the Eustachian tube to open and vent the excess air. Contributing factors include middle-ear barotrauma during descent, allergies, upper respiratory infections (congestion) and smoking.
Manifestations
The symptoms of alternobaric vertigo may include disorientation, nausea and vomiting. The disorienting effects of vertigo are extremely dangerous while diving. The inability to discern up from down or 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.
Prevention
- Avoid unequal pressurization of the ear by avoiding tight-fitting wetsuit hoods or earplugs.
- Maintain good ear hygiene.
- Do not dive when congested or unable to equalize.
- Learn and use proper equalization techniques.
Management
Dr. Carl Edmonds offers the following advice about how to manage alternobaric vertigo during a dive:
“If a diver encounters ear pain or vertigo during ascent, they should descend a little to minimize the pressure imbalance and attempt to open the Eustachian tube by holding the nose and swallowing (Toynbee or another 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, 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 middle-ear barotrauma during ascent (reverse squeeze). Other conditions, such as inner-ear decompression illness or caloric vertigo (when cold water suddenly enters one ear), should be ruled out.
Fitness to Dive
You can return to diving as soon as all symptoms and contributing factors have been resolved.