A rigid helmet, as used in standard diving, may permit this trauma (Figure 9.3). If extra gas is not added during descent to compensate for the effects of Boyle’s Law, the suit and occupant may be forced into the helmet, thus causing fractured clavicles, bizarre injuries and death. The sequence of events may occur dramatically if the heavily weighted diver falls off his or her stage. There is a similar result when the diver loses compressed air pressure, e.g. as a result of a compressor or supply line failure. To prevent this, a non-return valve is inserted in the air supply line.
The clinical features include the following: dyspnoea and a heavy sensation in the chest; a bulging sensation in the head and eyes; swelling in the areas associated with rigid walls, e.g. the helmet, and then oedema and haemorrhages within the skin of the face, conjunctiva, neck and shoulders; and bleeding from the lungs, gastrointestinal tract, nose, ears and sinuses. These pathological changes are caused by the effects of barotrauma on the enclosed gas spaces and by a pressure gradient forcing blood from the abdomen and lower extremities into the thorax, head and neck because of the negative pressure differential in the helmet. Similarly induced haemorrhages occur in the brain, heart, respiratory mucosa and other soft tissues.