The majority of episodes of sinus barotrauma occur in the frontal sinuses with pain localized over the frontal area. Pressure inside the sinus increases, affecting the walls of the sinus and producing pain or epistaxis. If the outlet is blocked during ascent, the situation is reversed and "reverse squeeze" appears. The sinus will fill with fluid or blood unless the pressure differential is neutralized. The pressure differentials are directed to the center of the sinuses producing mucosal edema, transudation, and mucosal-or submucosal- hematoma, leading to further occlusion of the sinus ostium. Squeeze is produced on descent when trapped air in the sinuses contracts and produces negative pressure.
However, when the opening is obstructed due to inflammation, polyps, mucosal thickening, anatomical abnormalities, or other lesions, pressure equilibration is impossible. Normally, the sinuses drain into the nasal cavity through small ostia, which permit mucociliary clearance and ventilation that equilibrates pressure. On ascent, the air in the paranasal sinuses will expand according to Boyle's law, contracting during descent. Two types of acute barotrauma are observed: squeeze and reverse squeeze. The pathology of sinus barotrauma is directly related to Boyle's law, which states that the volume of a gas is inversely proportional to the pressure on it, when temperature is constant (P1 × V1 = P2 × V2). Neurological symptoms may affect the adjacent fifth cranial nerve and especially the infraorbital nerve. Epistaxis or serosanguineous secretion from the nose may occur. Less common is pain referred to the temporal, occipital, or retrobulbar region. This is due to pain originating from the frontal sinus, it being above the brow bones. In most cases of sinus barotrauma, localized pain to the frontal area is the predominant symptom. Ultimately fluid or blood will fill the space. The pressure difference causes the mucosal lining of the sinuses to become swollen and submucosal bleeding follows with further difficulties ventilating the sinus, especially if the orifices are involved. The pain can ultimately become disabling unless the ambient pressure is reversed. The affected person has a sudden sharp facial pain or headache during descent, which increases as the aircraft approaches ground level. Typically, sinus barotrauma is preceded by an upper respiratory tract infection or allergy.
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