Reverse Block

Pain on ascent caused by expanding air trapped in an ear, sinus, or tooth that cannot vent, forcing the diver to slow down and ascend in stages.

A reverse block is barotrauma in reverse: instead of struggling to get air into an air space on descent, the diver cannot get expanding air out of it on ascent. As ambient pressure drops, Boyle's law expands the gas trapped behind a blocked Eustachian tube, a congested sinus, or under a dental filling, and pressure builds painfully from the inside. Unlike a descent squeeze you cannot simply pinch and blow your way out of it, the air has to find its own way past the blockage.

The correct response is to stop the ascent, descend a meter or two until the pain eases, then come up much more slowly, giving the trapped gas time to bleed out. Swallowing, wiggling the jaw, and tilting the affected ear down can help open the tube. Never perform a forceful Valsalva on ascent, it adds pressure to a space that is already overpressurized. Gas supply becomes the practical limit, which is one reason to surface with a healthy reserve.

Reverse blocks are strongly linked to diving with congestion, especially when decongestants taken before the dive wear off at depth. If you needed medication to equalize on the way down, expect trouble on the way up. Skipping the dive when your head is blocked remains the only reliable prevention. For sinuses the same logic applies: slow, stepped ascents and patience, since a sinus reverse block usually resolves on its own as the trapped gas seeps past the congestion.