Alternobaric Vertigo

Alternobaric vertigo is transient vertigo caused by unequal pressure between the two middle ears during pressure change, most often on ascent in diving or flying. It is brief, typically lasting seconds to minutes, and usually benign, but it is dangerous underwater because disorientation can cause panic and drowning.

Reported in an appreciable minority of divers and aircrew. Risk rises with unequal eustachian tube function, congestion and forceful Valsalva.

Episodes stop once pressures equalise. Persistent vertigo after the dive needs exclusion of inner ear injury.

Related conditions - Middle ear barotrauma, inner ear decompression sickness, and perilymph fistula.

Pathophysiology.

When one middle ear vents and the other does not, asymmetric pressure stimulates one vestibular organ more than the other. The brain interprets this imbalance as rotation, producing vertigo and nystagmus.

Sudden pressure changes at the round window can add inner ear stimulation. Symptoms resolve as pressures equalise.

• Brief spinning vertigo, nausea and disorientation during ascent, sometimes with ear fullness or a pressure sensation.
• Nystagmus during the episode; examination between attacks is normal.
• Short duration, usually less than 10 minutes.

Red flags.

• Vertigo persisting after surfacing or occurring with hearing loss, tinnitus or facial weakness (inner ear barotrauma, decompression sickness, stroke).
• Neurological signs or vomiting that does not settle.

• Dive history: timing on ascent, relation to equalising and congestion.
• Otoscopy, tuning fork tests, audiometry and tympanometry.
• Vestibular tests and imaging by ENT if the vertigo is recurrent, prolonged or accompanied by hearing symptoms.

Differential diagnosis. Inner ear decompression sickness, perilymph fistula, middle ear barotrauma, benign paroxysmal positional vertigo, vestibular migraine, vestibular neuritis, Meniere disease, central causes such as stroke.

• In the water: signal, stop, hold a fixed object, and descend a little if safe to ease the pressure difference, then ascend slowly while avoiding forceful Valsalva. Keep the airway secure.
• Avoid diving until the cause is clear and the diver equalises easily; no diving with symptoms of congestion.
• Treat nasal congestion: mometasone nasal spray 50 micrograms/spray, 2 sprays into each nostril once daily for 2 to 4 weeks. Maximum 200 micrograms daily. Monitor for nosebleeds. Avoid in untreated nasal infection; no renal adjustment. Avoid decongestants immediately before diving.
• Teach gentle equalising techniques early in descent, not forceful Valsalva.
• Persistent or recurrent events need ENT assessment; surgical correction of anatomical obstruction can help.

Monitoring. Review at 4 weeks; repeat otoscopy and audiometry if symptoms recur.

Referral and escalation. ENT and diving medicine physician for recurrent or atypical events; urgent assessment when vertigo persists or hearing changes.