Alternobaric vertigo is a benign condition that affects individuals traveling in environments with changing ambient pressures, such as SCUBA diving or aviation, though has also been reported in patients utilizing positive airway pressure breathing assistance. It is the direct result of an incongruency in middle ear pressures caused by incomplete or insufficient equalization, typically while moving from an area of higher pressure to one of lower pressure. Numerous factors may increase the likelihood of experiencing this phenomenon, including recent upper respiratory infections, use of decongestants or abnormal eustachian tube morphology. The vertigo is typically considered mild and usually resolves with further ascent and with the use of equalization techniques to restore similar pressures between the two chambers, though has been reported to persist for days or weeks.
Alternobaric vertigo is a condition caused by unequal pressures across the middle ear chambers.
Early literature on alternobaric vertigo holds the prevalence to be between 10% and 17% amongst 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 underreporting, 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.
The middle ear often becomes a functionally closed space due to obstruction or collapse of the Eustachian tube. While this typically does not cause an individual distress at his or her home elevation, it may become problematic when changing altitudes during aviation or diving. This is especially true if a 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 vestibular system that manifests symptomatically with vertiginous symptoms. One can expect to experience alternobaric vertigo with differences in middle ear pressures of greater than 60cm H2O.
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. He or she 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.
Diagnosis of alternobaric vertigo is done 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.
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 should expect to experience a gradual resolution of his or her symptoms.
Vertigo, particularly in diving, should be taken seriously as the differential ranges from the benign to the highly morbid. Briefly, causes of vertigo in settings of changing pressure can be delineated according to the persistence of symptoms:
Vertigo that lasts less than one minute and typically benign.
Vertigo that lasts more than one minute and is concerning for more serious conditions.
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.
Alternobaric vertigo is a benign condition caused by disequilibrium between middle ear pressures that results in a difference in perception in the vestibular system.