Alternobaric Vertigo

Etiology

Alternobaric vertigo is a condition caused by transient asymmetric pressure changes across the middle ear chambers. The resultant pressure differential produces unequal vestibular input. The condition is associated with alterations in ambient pressure, such as changes in altitude or underwater activities, including scuba diving. Episodes often occur during ascent or performance of the Valsalva maneuver.[4]

Epidemiology

Early literature on alternobaric vertigo reports a prevalence of 10% to 17% in at-risk populations. A recent study involving Portuguese Air Force pilots, in which 29% experienced vertiginous symptoms with changes in ambient pressure, suggests that true prevalence is likely higher. Current estimates are likely low due to underreporting, given the largely benign nature of the condition. A study suggests that as many as 25% of divers experience alternobaric vertigo at least once.[5] Regarding prevalence by sex, observational reports with relatively small sample sizes suggest higher rates in female populations compared with male populations. Other risk factors include cold-water diving, previous barotrauma, eustachian tube dysfunction, and frequent ear infections.[6] In hyperbaric medicine literature, vertigo is reported in less than 2% of patients with middle ear barotrauma and in approximately 3 per 1,000 patients undergoing hyperbaric treatment.[7]

Pathophysiology

The middle ear often becomes a functionally closed space due to obstruction or collapse of the eustachian tube. While this condition typically does not cause individual distress at home elevation, it may become problematic during altitude changes in aviation or diving. This effect is especially pronounced when the eustachian tube on one side functionally closes at a different ambient pressure than the contralateral side, producing different total air volumes within each middle ear chamber. Gas expansion or contraction within a closed middle ear during ascent or descent increases pressure differentials across the tympanic membrane and middle to inner ear interfaces, reflecting variation in baseline sea-level gas volume between chambers. A pressure differential between the left and right middle ears may produce a perceptual mismatch within the vestibular system, manifesting as vertigo. Alternobaric vertigo is expected with middle ear pressure differences greater than 60 cm H2O.[8][9][10]

History and Physical

History and physical examination findings are consistent with those seen in peripheral vertigo. Balance impairment with gait disturbance may be present. Symptoms may worsen with position, with the vertical position typically most severe. Horizontal nystagmus may be observed. A sensation of “spinning” occurs toward the ear with higher middle ear pressure. Results from head impulse testing and test of skew are usually consistent with peripheral vertigo. Neurologic examination findings are generally normal.

Evaluation

Diagnosis of alternobaric vertigo is based on history and physical examination. Eustachian tube function testing, including sonotubometry and impedance testing, often demonstrates tubal stenosis in patients with alternobaric vertigo.

Treatment / Management

The mainstay of treatment for alternobaric vertigo is reestablishing pressure equilibrium between the middle ears. Swallowing, yawning, and jaw thrusting are often the simplest methods for equalizing pressure, although these strategies may be difficult with a regulator in place. The Valsalva maneuver is a commonly taught technique that involves pinching the nostrils closed and forcibly exhaling against a closed mouth and nose. Maneuvering in this way generates nasopharyngeal pressure intended to establish patency of the eustachian tubes and facilitate equalization between the middle ear spaces and the oropharynx.

Individuals experiencing vertigo should avoid panic, as they are often in environments where impaired judgment may increase the risk of injury from other causes. Ascent or descent during diving should be stopped and position in the water maintained. Equalization may then be attempted, with gradual resolution of symptoms typically expected. The Toynbee maneuver, which involves nasal occlusion with swallowing to promote eustachian tube opening, may be used during ascent, and the Valsalva maneuver should be performed during descent. No difference in specificity of these maneuvers between diving and aviation situations has been demonstrated.[11]

Additional methods applicable to both hyperbaric and hypobaric environments include the Frenzel maneuver, in which the nostrils are pinched while a “k” sound is produced with the tongue against the palate, forcing air from the pharynx toward the eustachian tubes. The Lowry maneuver combines elements of both Valsalva and Toynbee techniques. If unilateral equalization occurs, turning the head and neck to position the affected ear toward the surface may assist by improving eustachian tube alignment during continued equalization attempts. Balloon eustachian tuboplasty and laser eustachian tuboplasty are potential options for recurrent middle ear barotrauma or alternobaric vertigo.[12][13](B3)

Differential Diagnosis

Vertigo, particularly in diving, should be taken seriously given a differential diagnosis ranging from benign to highly morbid etiologies. Causes of vertigo in settings of changing pressure may be broadly categorized according to symptom duration.

Transient vertigo, lasting less than 1 minute, is typically benign. Examples include alternobaric vertigo, resulting from differential pressure between the middle ear spaces, and caloric vertigo, which arises from temperature differences between the left and right ears.

Persistent vertigo, lasting more than 1 minute, is more concerning, as it suggests more serious conditions. Inner ear barotrauma may occur following failure of middle ear equalization, with elevated middle ear pressure causing injury to inner ear structures. Vestibular decompression sickness results from inert gas coming out of solution during ascent, with bubble formation in blood and tissues. The presentation may include associated neurologic deficits that do not necessarily follow a classic distribution pattern. The condition constitutes a medical emergency requiring immediate oxygen administration and transfer to a hyperbaric facility. Arterial gas embolism results from intravascular gas bubble formation leading to vascular occlusion and ischemia, with potential stroke-like presentation. Etiologies include gas entry into the circulation, which may arise from mechanisms like pulmonary barotrauma. The condition also requires urgent hyperbaric treatment. Cerebrovascular accident is an important alternative diagnosis in appropriate clinical contexts.

Prognosis

The prognosis of this condition is very good, with most individuals experiencing symptom resolution within seconds to minutes after reestablishing pressure equalization between the middle ears. Some cases have been reported to persist for days or weeks, necessitating further evaluation to rule out more serious causes of vertigo.

Complications

Middle ear barotrauma is often associated with eustachian tube dysfunction and alternobaric vertigo. Consequently, cumulative injury may occur in frequent divers and aviation participants. A study reported lower middle ear compliance and pressure values, as well as some hearing loss, in divers compared with non-diver control subjects.[14] However, other studies failed to demonstrate an increased risk of hearing loss in divers.[15][16]