Alternobaric Vertigo and Scuba Diving

Alternobaric vertigo is a severe, disorienting vertigo experienced by scuba divers whose ears fail to equalize pressure at the same rate. One of a diver's middle ears is filled with a greater air pressure than the other, which causes the diver's brain to go haywire and feed them confusing signals. The result is a variety of unpleasant symptoms.

Alternobaric vertigo is characterized primarily by a disabling sensation of vertigo, distinguishable from a mere "fear of heights" dizziness felt by some scuba divers when looking down in deep water. In addition, alternobaric vertigo may be accompanied by some or all of the following symptoms:

• Nausea
• Ear pain or a feeling of fullness in only one ear
• Hissing or whistling sounds, ringing, or buzzing in one ear
• Visual disturbance - it appears that the world is spinning
• Physical sensation of spinning
• Muffled hearing in one ear

The symptoms are transient and subside within seconds or minutes, not hours. Symptoms that persist after a dive are not typical of alternobaric vertigo.

Alternobaric vertigo is not dangerous in itself. The over-pressurized ear will usually equalize on its own, and symptoms should subside after a short period of time without medical attention. However, alternobaric vertigo is still dangerous for the following reasons:

• Alternobaric vertigo may cause a diver to panic. They may bolt for the surface in an uncontrolled ascent, or behave in other inappropriate ways.
• Alternobaric vertigo causes nausea, which may lead to vomiting underwater. If a diver removes their regulator, they are at risk for drowning.
• Alternobaric vertigo is a sign that one of a diver's ears has not equalized properly. Continuing to ascend or descend may cause an ear barotrauma.
• Alternobaric vertigo causes disorientation. A diver experiencing alternobaric vertigo may have trouble navigating to the surface. This condition is especially dangerous for dives that require navigation, such as wreck or cave diving.

Scuba divers experience alternobaric vertigo when ascending or descending because the pressure in a diver's air spaces changes with depth. Alternobaric vertigo most commonly occurs during ascent, when one ear equalizes normally and one does not. However, divers do occasionally experience alternobaric vertigo during descent.

Any diver, regardless of their age or experience level, can experience alternobaric vertigo.

Any condition that prevents a diver's ears from equalizing efficiently may predispose a diver to alternobaric vertigo. Some examples are:

• Diving when sick or congested
• Diving after a recent illness when a diver still has some inflammation or congestion (even if they feel recovered)
• Diving with a medical condition that predisposes a diver to alternobaric vertigo, such as a eustachian tube dysfunction, a middle ear infection (otitus media), or swimmer's ear

A diver who experiences on alternobaric vertigo during ascent should stop, descend a few feet, and stabilize themselves by grabbing a rock or the floor. The sensation will pass as soon as their ear equalizes. Attempting a Valsalva maneuver or other ear equalization technique used during descent will only exacerbate the problem, as it will add air to an already overfull ear. Instead, the diver should be patient and allow time for their ear to work the air out on its own.

While cases of alternobaric vertigo on descent are rare, logic dictates that a diver should cease their descent, ascend a few feet (using a line if possible) and hold that depth until the sensation subsides.

A diver who experiences alternobaric vertigo frequently may want to decide upon an underwater hand signal with their buddy to communicate the condition, as this is not a typical ear problem that will be solved by ascending. A diver who experiences vertigo often should also consult a diving doctor, as this may indicate a physiological problem.

Most of the measures a diver can take to avoid alternobaric vertigo are common sense. Any condition that restricts air flow through the eustachian tubes or prevents a diver's ears from equalizing can cause alternobaric vertigo. Some tips for avoiding alternobaric vertigo are:

• Do not scuba dive when sick or congested
• Do not scuba dive immediately after being sick or congested
• Ascend and descend carefully and slowly
• Take care to equalize your ears early and often on descent
• Ascend slowly. If you experience any of the symptoms of alternobaric vertigo, stop the ascent descend slightly, and allow your ears to release the pressure on their own
• Do not dive if you experience unusual difficulty clearing your ears on descent
• Check with a diving physician before diving if you have a history of eustachian tube dysfunction or middle ear infections (otitus media).

A single bout of alternobaric vertigo does not mean that you shouldn't scuba dive. Alternobaric vertigo is usually caused by transitory conditions such as illness. However, if a diver experiences alternobaric vertigo often, they should seek the advice of a scuba diving doctor.

Alternobaric vertigo is only one of many causes of vertigo and dizziness when scuba diving. Other causes of underwater vertigo include temperature differences between a diver's middle ears, a middle ear bend (a type of decompression sickness), middle ear ruptures, hyperventilation, and any condition that may make a diver nauseated on the surface, such as seasickness or a hangover.

Alternobaric vertigo is caused by dissimilar pressures in a diver's middle ears. Alternobaric vertigo is most often experienced during ascent, when one of a diver's ears does not release expanding air from the middle ear as quickly as the other. A single instance of alternobaric vertigo is not contraindicated for diving. However, frequent cases of vertigo should be investigated by a doctor. Alternobaric vertigo can cause disorientation, and in extreme cases may prevent a diver from ascending safely. This is yet another reason to follow safe diving guidelines, such as not diving when ill or congested, and always ascending with a conservative reserve of air pressure in order to have time to deal with unexpected problems.

_Sources

• _{Alternobaric Vertigo -- A Diving Hazard by CLAES E.G. Lundgren, Br Med J. 1965 August 28}
• _{Diver's Alert Network (DAN)}
• _{NOAA Diving Manual, Fourth Edition, James T. Joiner Ed., 2001}