ACUTE MOUNTAIN SICKNESS

This is experienced by people who go up too high too quickly; some suffer at 2500m, other reach 5500m without trouble. The cause of the syndrome is unknown.

PULMONARY OVERINFLATION

This occurs in scuba divers breathing compressed air.

SHALLOW WATER BLACKOUT

Swimmers and free divers (snorkling without compressed air) may hyperventilate before submerging in order to drive off carbon di oxide and so reduce the stimulus to breathe. The raised ambient pressure maintains a high diver is eventually forced to surface. The resulting cerebral hypoxia is made worse by cerebral vaso construction induced by the low partial pressure of carbon di oxide, and can result in unconsciousness and drowning

MIDDLE EAR 'SQUEEZE'

Middle ear 'squeeze' is the commonest injury of divers. Sinus squeeze is less common.

CHRONIC MOUNTAIN SICKNESS

This is due to alveolar hypo ventilation and chronic hypoxia brought about by inappropriate polycythaemia,