By Fred Bove, M.D., Ph.D.

A diver with a full wetsuit is diving in cold water. When he pulls the hood out from his ear to relieve a pressure difference, he notices the surface tilting and his buddies see that he is spinning in the water. The spinning sensation caused by the cold water entering his ear canal disappears in about three minutes.

Another diver is descending to about 10 feet and having difficulty clearing her left ear. After a forceful Valsalva maneuver, she develops a sudden sensation of dizziness with a feeling of spinning and a loud buzzing sound in the ear. She ascends but the feeling of dizziness persists and she breaks out in a sweat, becomes nauseated and she can't hear in her left ear.

A third diver has some difficulty clearing his ears on descent but gets to the bottom at 60 feet feeling normal. At 15 feet during his ascent, however, he develops a feeling of nausea, the surface begins to turn and, when he reaches the surface, he vomits, turns pale and breaks out in a cold sweat. To be comfortable he must lie still on the boat deck for a hour, until all the symptoms disappear.

All of these divers experienced an episode of vertigo, owing to a pressure effect on the middle ear. The first diver created a temperature difference between the two inner ear balance organs, thus causing a sensation of imbalance. The brain's effort to correct the misperceived imbalance caused vertigo. When the water in the ear canal warmed up to body temperature, the confusing imbalance disappeared and sensation returned to normal.

The second diver caused the round window in the inner ear to rupture by performing a forceful Valsalva maneuver. When the pressure in the middle ear is below ambient pressure (the eustachian tube is blocked), a Valsalva maneuver will raise the pressure withing the inner ear fluid and cause the round window to rupture. The loss of inner ear fluid through the torn round window caused a sensation of imbalance and the brain attempted to oppose the sensation of falling.

The third diver was a victim of alternobaric vertigo. This occurs when the two middle ears do not ventilate equally on ascent. The pressure imbalance produces an unequal stimulation of the balance mechanism, a sensation of imbalance and an effort to correct it by motion of the body. Imbalance of the vestibular organs of the inner ear causes the feeling of motion. Abnormal stimulation of these organs by erratic motion of the head will cause motion sickness. When these organs are abnormally stimulated while diving, they will produce nausea and a cold sweat along with dizziness or spinning.

None of these scenarios require recompression but injury to the nerves of the vestibular organ (eighth cranial nerve) owing to decompression sickness can also cause vertigo and would require recompression treatment.

A diver attempting to walk while vertigo is still present after a dive will often have an unsteady gait and may fall; he may look as if he's had too much to drink. When vertigo is present, visual clues can be used to improve balance; when the eyes are closed, the vertigo may become more severe. Visual information on body position usually overrides the false sensation of motion that occurs with vertigo. Sailors are taught to fix their vision on a landbased marker to avoid motion sickness.

The inner ear is made up of the organs that detect sound (the cochlea) and the organs that detect motion and position of the body (utricle, saccule, semicircular canals). These organs are susceptible to injury from barotrauma and from decompression sickness. Injury to areas of the brain involved with the sensations of position and balance can also cause vertigo. Infection of the inner ear from a virus will cause severe vertigo, often associated with vomiting. This viral illness (acute labrinthitis) is one of the most unpleasant, causing total disability for several days owing to the need to remain absolutely motionless until it is over.

Pressure effects on the inner ear, particularly the balance organs, are a common cause of vertigo. These problems have plagued aviators, astronauts and divers for many years. In addition, many millions of people are susceptible to motion sickness in automobiles, airplanes or boats. Because vertigo and its associated symptoms of nausea, sweating and pale skin are common in diving, this disorder is often considered a manifestation of decompression sickness and leads to treatment in a hyperbaric chamber. However, most of the vertigo associated with diving is not caused by decompression sickness and is more likely owing to benign causes such as thermal stimulation or alternobaric vertigo. Divers with previous disorders of the inner ear, such as acute labrinthitis, may have increased sensitivity to pressure or motion and are prone to vertigo during or after diving.

Treatment of vertigo associated with diving should be based on an understanding of its cause. A ruptured round window should be evaluated by an ear, nose and throat specialist, while most causes of benign vertigo can be treated with an antihistamine. Vertigo caused by decompression sickness, although rare, should be treated by recompression therapy. Vertigo caused by thermal imbalance on the ears is usually transient and should disappear in a few minutes.

When vertigo occurs in the water, there may be severe nausea and vomiting. Divers should be prepared to use visual clues (bubbles, surface, other divers) or tactile clues (holding on to a fixed structure) to overcome the feeling of vertigo. They should also be prepared to handle a bout of vomiting underwater.

Some forethought and understanding will prevent a serious accident should you experience vertigo underwater.

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