Barotrauma is defined as the tissue damage caused by expansion or contraction of enclosed gas spaces, according to Boyle’s Law and its pressure-volume changes.
The volume change in gas spaces with depth is proportionally greatest near the surface, and so it is in this zone that ear barotrauma is more frequently experienced. It is probably the most common occupational disease of divers, experienced to some degree by most.
Ear (also called otological or aural) barotrauma may affect any of the following:
- External ear (when a sealed gas space exists).
- Middle ear (which incorporates an enclosed gas space).
- Inner ear (which adjoins a gas space) (Figure 7.1).
Middle ear barotrauma is the most common form. Barotrauma problems may contribute to panic and diving deaths in novice divers or to permanent disability – tinnitus, balance and hearing loss.
In the earlier literature on caisson workers’ and divers’ disorders, otological barotrauma symptoms were hopelessly confused with decompression sickness symptoms. This confusion still exists in many clinical reports today.
Barotrauma refers to damage to tissues resulting from changes in volume of gas spaces, which in turn are caused by the changes in environmental pressure with descent and ascent (Boyle’s Law).
Barotrauma of descent is a result of a failure or an inability to equalize pressures within the ear cavities as the volume of contained gas decreases. Because enclosed cavities are surrounded by cartilage and bone, tissue distortion is limited, and the contracting space may be taken up by engorgement of the mucous membrane, oedema and haemorrhage. This, together with the enclosed compressed gas, assists in equalizing the pressure imbalance. It is commonly called a ‘squeeze’ by divers.
Barotrauma of ascent is the result of the distension of tissues around the expanding gas within the ear, when environmental pressures are reduced, i.e. on ascent. Divers use the misnomer ‘reverse squeeze’ to describe it.
Middle ear barotrauma of descent is the most common disorder encountered by divers.
Similar problems are encountered with aviation and space exposure, in hypobaric or hyperbaric chambers and by caisson workers (who work under increased pressure).
Barotrauma is classified according to its anatomical sites and whether it is caused by ascent or descent. It may occur in any combination in the external, middle, or inner ear.
Breathing helium-oxygen gases when diving makes equalization of pressures (‘autoinflation’) in middle ear and sinus cavities easier, and so barotrauma is less.
General information on the ear in diving, including many references to barotrauma, is included in Chapters 35 to 38.