This disorder is caused by distension of enclosed gases within the middle ear, expanding with ascent. Because it may prevent ascent, it is usually more serious than middle ear barotrauma of descent, which allows an uncomplicated return to safety.
During ascent, the middle ear opens passively, with a pressure gradient of less than 50 cm H2O. If the Eustachian tube restricts release, symptoms may include sensations of pressure or pain in the affected ear (reverse squeeze) or vertigo resulting from increased middle ear pressure difference (alternobaric vertigo). Occasionally, these conditions coexist.
Middle ear barotrauma of ascent usually follows recent, but sometimes mild, middle ear barotrauma of descent and/or the use of nasal decongestants. In each case the common factor is probably congestion and therefore blockage of the Eustachian tube.
The mild vertigo is often rectified by further ascent, which may force open the less patent Eustachian tube. When the pressures in both middle ears are equalized with the ambient pressure, the stimulus to vertigo ceases. Also, subsequent opening of the tube is easier. Other divers may reach the surface while still having an asymmetry of pressure within the middle ear cavities, or residual damage from excessive middle ear pressure, and so experience vertigo following the ascent.
Most cases of vertigo from middle ear barotrauma of ascent are mild, lasting seconds or minutes. This is not always so, however, and there have been instances of temporary or permanent inner ear damage, seventh nerve palsy, severe pain during ascent and/or perforation of the tympanic membrane.
The vertigo is most pronounced when the diver assumes the vertical position and is least pronounced in the horizontal position. The spinning is toward the ear with the higher pressure. It tends to develop when the middle ear pressures differ by 60 cm H2O or more.
Otoscopic examination often reveals evidence of tympanic membrane injection or haemorrhage. Congestion of blood vessels is common but is less than with descent barotrauma. It is more pronounced around the circumference of the tympanic membrane than along the handle of the malleus. The tympanic membrane may appear to be bulging.
Hearing loss in the affected ear, if present, may be conductive and follow damage to the tympanic membrane or the middle ear structures. The tympanic membrane may rupture occasionally. Inner ear barotrauma with sensorineural hearing loss is a possible complication (see Chapter 37). Seventh nerve palsy is another possible complication.
For first aid, the diver may be able to take remedial action. A short descent may relieve symptoms and allow middle ear equalization. Occasionally, the Valsalva technique, jaw movements or performing a Toynbee manoeuvre (see earlier) will relieve the discomfort, as may sudden pressure applied to the external ear (by occluding the external ear with the tragus or middle lobe, then pushing on it and thus exerting external pressure on the water column in the external ear). Equalization may be easier if the affected ear is facing the sea bed, thereby using the pressure gradient along the now vertical Eustachian tube.
Fortunately, most effects are short-lived, and treatment should consist of prohibition of diving until clinical resolution has occurred, normal hearing and vestibular function are demonstrated and prevention of future episodes is addressed.
Rarely the diver is seen soon after the event, and if the middle ear is still distended, the first aid procedures described earlier may be satisfactory. Otherwise, the use of oxygen inhalation or minimal recompression is effective.
Antibiotics are used if there is evidence of infection, and decongestants are sometimes recommended to improve Eustachian tube patency. Usually, neither type of drugs is needed.
Decongestants, especially topical ones, are rarely of use in preventing this disorder, unless they prevent a causal middle ear barotrauma of descent. Usually, they have the opposite effect. Systemic decongestants are more effective, but they have other disadvantages, permitting the diver to descend with marginal improvement in Eustachian tube patency and inadequate autoinflation of middle ear.
Prevention is best achieved by avoiding nasal decongestants and by training the diver in correct middle ear equalization techniques during descent (see earlier). Unless descent barotrauma is prevented, ascent barotrauma is likely to recur.
Once middle ear barotrauma of ascent has been experienced, particular care should be taken to ensure that if it does recur the diver will always have adequate air to descend briefly, use the techniques described earlier and then gradually ascend. A low-on-air situation could cause extreme discomfort or danger if the diver’s ascent is restricted by symptoms.
Vestibular function has been tested experimentally during pressure changes in a recompression chamber, to replicate the sequence of events and verify the aetiology and diagnosis (see Chapter 38). This testing is not generally required.