Diving
In diving, the Valsalva maneuver is often used on descent to equalise the pressure in the middle ear to the ambient pressure. If the Valsalva maneuver is conducted during ascent, residual air overpressure in the middle-ear can potentially be released through the Eustachian tubes. During decompression stops at the end of a dive, if the diver unwittingly slightly descends again and makes a Valsalva to relieve his ears, there exists a non-negligible risk to transfer nitrogen bubbles from one side of the heart to the other one if the foramen membrane is permeable. If some of the inert gas-laden blood passes through the patent foramen ovale (PFO), it avoids the lungs and the inert gas is more likely to form large bubbles in the arterial blood stream, causing decompression sickness.
A Valsalva maneuver at the end of a diving must never be attempted as it can cause a decompression accident with severe neurological consequences (gas bubbles in the brain or damages to the spinal cord). Repeated Valsalva maneuvers are also suspected to increase the permeability of the foramen for divers at risk.
Read more about this topic: Valsalva Maneuver
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