Originally, IPE was thought to occur almost exclusively in cold water. While this condition seems to be more common in cold water, it has also been reported in warm waters.
During immersion in water, blood is redistributed from the legs to the heart and blood vessels in the lungs. Usually the heart and lungs compensate for this, but sometimes the resulting increased pressure within the blood vessels in the lungs causes fluid to traverse the small vessels (capillaries) and enter the gascontaining spaces of the lungs.
Sometimes this is caused by an underwater myocardial infarction (heart attack), abnormalities of the heart muscle or heart valves or hypertension. Usually there is no obvious cause.
Cold water may be a predisposing factor because immersion can cause the small arteries to constrict, increasing the resistance to the flow of blood.
Vasoconstriction in response to cold can be exaggerated in people with hypertension or those likely to develop it. But some people who experience IPE are young and healthy, even military recruits.
Immediate treatment should include breathing oxygen while in transit to a hospital. Some IPE cases have been fatal, although most cases resolve on their own during observation in a hospital. A closer examination may reveal hypertension, a heart attack, cardiac valve disease or impaired contraction of the heart.
Divers who have experienced IPE are concerned with the likelihood it will recur. Unfortunately, that likelihood is not known, so many physicians recommend that people with a history of IPE not return to diving. Still others recommend taking an antihypertensive medication before each dive. Before considering a return to diving after IPE, DAN recommends the diver consult with a doctor knowledgeable about the condition.