From the US Naval Flight Surgeon's Manual...
http://www.iiimef.usmc.mil/medical/F...an/FS_TOC.html
Physiological Effects of Rapid Decompression
The occupants' primary concerns are hypoxia, gas expansion, decompression sickness, and hypothermia.
Lungs.
The lungs are potentially the most vulnerable part of the body during a rapid decompression. Whenever a rapid decompression is faster than the inherent capability of the lungs to decompress, a transient positive pressure will temporarily build up in the lungs. If the escape of air from the lungs is blocked or seriously impeded during a sudden drop in cabin pressure, intrapulmonary pressure can build up high enough to cause tearing and rupture of the lung tissues and capillaries. If the expanding gas is free to escape from the lungs through an open airway, the risk of lung damage is nonexistent. Momentary breath-holding, such as swallowing or yawning will not cause excessively high intrapulmonary pressure and over expansion of lung tissue.
Ears and Sinuses.
Decompression of a pressurized cabin is unlikely to cause symptoms in the middle ear and paranasal sinuses. It is more likely, however, that individuals will develop pain in the middle ear and paranasal sinuses during the subsequent emergency descent as they will be exposed to a large and rapid increase of cabin pressure.
Gastrointestinal Tract.
One of the potential dangers during a rapid decompression is the expansion of trapped gases within the gastrointestinal tract causing abdominal distress. Abdominal distention, if it does occur, may have several important effects. The diaphragm is displaced upward by the expansion of the trapped gas in the stomach which can retard respiratory movements. Distention of the abdominal organs may also stimulate the abdominal branches of the vagus nerve, resulting in cardiovascular depression, and if severe enough, cause a reduction in blood pressure, unconsciousness and shock.
Hypoxia.
Of all the physiological hazards associated with the loss of pressure, hypoxia is the most important. The rapid reduction of ambient pressure produces a corresponding drop in the partial pressure of oxygen and reduces the alveolar oxygen tension. A twofold to threefold performance decrement occurs regardless of altitude. The reduced tolerance to hypoxia after decompression is due to (1) a reversal in the direction of oxygen flow in the lung; (2) diminished respiratory activity at the time of decompression; (3) decreased cardiac activity at the time of decompression.
Decompression Sickness.
In general, decompression sickness does not occur until cabin altitudes of 18,000 feet are reached. The incidence of decompression sickness is small unless the cabin altitude reaches 25,000 to 30,000 feet. As the duration of exposure to the unpressurized environment increases, so does the incidence of decompression sickness. The incidence of decompression sickness following a rapid decompression appears to be only slightly greater than after a slow decompression to the same altitude.
Hypothermia.
When cabin temperatures drop because of a decompression, it is likely that injuries such as frostbite and hypothermia will exist. Again, the extent and severity will be dependent on the altitude and the type of protective clothing worn during the decompression.