Alternobaric Vertigo

Etiology

Alternobaric vertigo is a condition caused by unequal pressures across the middle ear chambers.[4]

Epidemiology

Early literature on alternobaric vertigo holds the prevalence to be between 10 and 17% among participants in at-risk activities. A recent study involving Portuguese Air Force pilots in which 29% of the pilots experienced vertiginous symptoms with changing ambient pressure suggests that the true prevalence is likely higher. Current estimates are presumed to be low due to under-reporting, as this is largely a benign condition. Regarding prevalence among gender, observational reports with relatively small sample sizes suggest that females experience alternobaric vertigo at higher rates than males.[4]

Pathophysiology

The middle ear often becomes a functionally closed space due to obstruction or collapse of the Eustachian tube. While this typically does not cause individual distress at his or her home elevation, it may become problematic when changing altitudes during aviation or diving. This is especially true if the Eustachian tube on one side functionally closes at a different ambient pressure than the contralateral side, resulting in a larger or smaller total amount of air within the chamber as compared to the other side. As the volume of air within the closed middle ear expands or contracts with ascent or descent, relative pressure differentials across the tympanic membrane and the middle ear, as well as the middle-inner ear interfaces, are exacerbated by the expansion or contraction of the middle ear chambers as they hold different sea-level volumes of gas. If a pressure differential exists between the left and right middle ears, there becomes a difference in perception across either the vestibular system that manifests symptomatically with vertiginous symptoms. One can expect to experience alternobaric vertigo with differences in middle ear pressures of greater than 60 cm H2O.[5][6][7]

History and Physical

The history and physical exam findings should be consistent with those seen in peripheral vertigo. The patient may have balance issues with gait. Symptoms may become worse depending on the patient's position, with the vertical position typically the worst. They may have horizontal nystagmus present. The sensation of “spinning” is in the direction of the ear with the higher pressure in the middle ear. Head impulse testing and test of skew should be suggestive of peripheral vertigo. Neurologic examination should otherwise be normal.

Evaluation

Diagnosis of alternobaric vertigo is made with history and physical examination. Eustachian tube function testing, including sonotubometry and impedance testing, often shows tubal stenosis in patients who suffer from alternobaric vertigo.

Treatment / Management

The mainstay of treatment for alternobaric vertigo is re-establishing the pressure equilibrium between the two middle ears. This is typically done by pinching one's nostrils closed and forcibly attempting to exhale with a closed mouth. This is meant to establish patency within the Eustachian tubes, allowing for equalization between each middle ear space and the oropharynx. It is important that those experiencing vertigo do not panic, as they are often in situations where poor judgment could put them at risk for personal injury from other causes. When diving, the individual should stop ascending or descending and maintain his or her position in the water. At this point, the diver may attempt equalization and expect to experience a gradual resolution of their symptoms.

Differential Diagnosis

Vertigo, particularly in diving, should be taken seriously as the differential ranges from benign to highly morbid. Briefly, causes of vertigo in settings of changing pressure can be delineated according to the persistence of symptoms:

Transient

Vertigo that lasts less than one minute and typically benign.

• Alternobaric vertigo - caused by differences in pressures between the middle ear spaces
• Caloric - vertigo experienced by a difference in temperature between the left and right ears

Persistent

Vertigo that lasts more than one minute and is concerning for more serious conditions.

• Inner ear barotrauma: This can occur if there is a significant failure of equalization of the middle ear chambers. Increased pressure within the middle ear chamber causes actual damage to the inner ear. 
• Vestibular decompression sickness: This results from the formation of air bubbles in circulation and tissue as the air that became dissolved at depth reconstitutes from solution as small air bubbles. If this is the cause of vertigo, the presentation may be accompanied by other neurologic deficits that do not necessarily follow a classic distribution pattern. This is an emergency and requires immediate administration of oxygen with transfer to the nearest hyperbaric facility.
• Arterial gas embolism: Similar to decompression sickness, this is the result of an air bubble forming in circulation, preventing blood flow and essentially causing a stroke. This can be due to the reconstitution of dissolved air or secondary to another process such as lung barotrauma. This is also an emergency requiring hyperbaric treatment.

Prognosis

The prognosis of this condition is very good, with most individuals experiencing a resolution of symptoms within seconds to minutes of re-establishing equalization between the middle ears. Some cases have been reported to persist for days or weeks, and it is important to rule out more serious causes of vertigo in these scenarios.