As the diver continues to ascend, one of the sinus walls can burst into an adjacent sinus that did vent correctly (the point of least resistance), effectively relieving the excess pressure. If a sinus fails to vent during ascent, the increasing pressure can apply significant tension to the mucosal lining and bony walls of the sinus. However, mild swelling and inflammation of the mucous membranes (as caused by a cold or by seasonal allergies) can compromise the narrow passages through which air escapes, trapping gas, mucus and blood. Equalisation of ears and sinuses during ascent is usually a passive event, which means active attempts should not be necessary. Sinus barotrauma can also happen during ascent, known as a reverse block. The bleeding can increase if you are taking blood thinners that include aspirin or other nonsteroidal anti-inflammatory drugs (NSAIDs).
These barotraumas usually manifest as postnasal drip or bloody discharge from the nose, depending on the sinuses involved. While ascending, any remaining gas within the sinus expands and forces out this blood and mucus. At this point the pain usually resolves or diminishes, and the diver continues the dive. The capillary vessels of the mucous membranes lining the sinuses engorge and burst, likely filling the sinuses with blood until the negative pressure is equalised. The first sign of this type of sinus barotrauma is generally a sharp pain. The mechanisms of injury of sinus barotraumas depend on whether it happened during descent or ascent.įailure to equalise pressures on paranasal sinuses while descending keeps these cavities at atmospheric pressure, which results in a relative negative pressure (vacuum) as you descend to depth. While ascending, the increasing volume usually vents itself passively. While descending, it is imperative that divers actively or passively equalise all enclosed air-filled spaces to avoid injury. As the ambient pressure decreases while ascending, the volume of the gas increases proportionately. According to Boyle’s Law, as the ambient pressure increases while descending, the volume of the gas in an enclosed space decreases proportionately. The pressure diminishes by the same amount on ascent. Ostia blockage can impair drainage and make both descents and ascents troublesome.Įvery foot of descent in water adds approximately one-half pound of pressure on each square inch of tissue.
The ostia can easily be blocked by inflammatory processes, like colds or allergies, and in divers by improper attempts at equalization. The paranasal sinuses communicate with the nasal cavity via small orifices called ostia (singular: ostium). The maxillary sinuses (area four) are located within the maxillary bone below your eyes and lateral to your nose and are the largest pair of paranasal sinuses.The sphenoidal sinuses (area three) are centrally located behind the nasal cavity and vary in size and shape.The ethmoid cells (area two) are located within the ethmoid bone between your eyes and nose and are formed by a variable number of connected individual cells.