Vertigo when diving is not a rare phenomenon and can have various causes. This blog post sheds light on a phenomenon that may be more common than assumed.
Case vignette
A healthy young man undertook a training dive with compressed air accompanied by an instructor. In the 5th minute at a depth of 20 m, he felt acute dizziness and disorientation, which he reported to the instructor. The instructor noticed apathy and eye shaking and initiated a controlled ascent to 10 m, whereupon the symptoms disappeared completely. The dive was continued there and ended without any problems. The initial diagnosis was rapture of the deep.
After a 70-minute surface interval, a second dive followed (17 m, 25 minutes), which went just as smoothly as two further dives in the following days at maximum depths of 16 m.
During the next training dive, acute dizziness, disorientation and an abrupt sinking occurred again after 5 minutes at approx. 20 m, so that the diving instructor had to intervene and initiate an assisted ascent. On the surface, the symptoms disappeared completely. All dives took place in Swiss lakes at 8-9 °C water temperature, without any additional complaints such as pressure equalization problems or hearing loss. An ENT examination was unremarkable and the diver was fit and cold-free on all dives. He had never had middle ear problems in the past. The person concerned has a one-star certification (CMAS) and a current diving fitness certificate.
What could be the cause of the vertigo?
Analysis
The symptoms do not indicate a nitrogen narcosis, as the depth was too shallow (maximum nitrogen partial pressure 2.4 bar). Barotrauma is also unlikely in the absence of pain or pressure equalization problems. What is striking, however, is the repeated occurrence of discomfort at 20 m, combined with eye shaking (nystagmus), which disappeared immediately on ascent. This, in combination with the low water temperatures and the unremarkable ENT examination, suggests caloric nystagmus as the cause.
Nystagmus is an involuntary, rhythmic eye movement with a slow drift in one direction and a rapid correction in the other direction. This is exactly what the diving instructor observed underwater. It is the result of a malfunction of the inner ear in the area of the semicircular canals or a disturbance of the balance system at the level of the brain.
Caloric (temperature-induced) nystagmus is a phenomenon observed when testing the vestibular system: When an ear canal is rinsed with warm or cold water, the difference in temperature stimulates the endolymph (the fluid) in the semicircular canals. This creates a flow in the semicircular canal similar to a head movement. As a result, nystagmus and vertigo occur. It is easy to imagine that this also happens when diving in cold water if the ear canals are not exposed to the water to the same extent, for example if the hood does not fit equally on both sides.
Sometimes, vertigo that occurs during diving seems to be explainable only by the assumption of a caloric reaction of the inner ear, especially if, as in the case of our diver, no abnormalities are found in the specialist medical examination and there are no other reasons for the vertigo such as barotrauma, rapture of the deep or decompression sickness. The symptoms typically occur within the first 5 minutes of the dive after a smooth descent and tend to recur on similar dives under similar conditions (1). A side-differentiated sensitivity of the vestibular organ to external stimuli is also conceivable. This would be difficult to determine and would require specialized medical examinations.
Recommendation
The diver was advised to dive only with experienced guides and in easy conditions. Night dives, poor visibility and greater depths should be avoided, and further training will only be continued in spring when conditions are warmer.
1) Edmonds C. et al. Diving and Subaquatic Medicine (p.445). CRC Press. Kindle-Version.
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