A small dose of Viagra could save the lives of swimmers and divers who experience an abrupt and potentially life-threatening form of pulmonary edema on entering cold water, says research published in Circulation: Journal of the American Heart Association.

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SIPE can affect divers and triathletes participating in cold water swims.

Viagra, or sildenafil, is best known for treating male impotence, but it can also help in cases of pulmonary arterial hypertension.

When athletes or scuba divers make a sudden entry into cold water, they can develop a condition called swimming-induced pulmonary edema (SIPE).

When this happens, the blood vessels in the arms and legs constrict, leading to a pooling of blood in the heart and lungs. Symptoms include coughing up blood, difficulty breathing and low blood oxygen.

Although the symptoms often dissipate over 24 hours, the condition can kill. Not everyone is prone to it, and those who are tend to be unaware until they are in the water and rapidly developing symptoms. Those who experience SIPE should seek medical attention.

Small dose of sildenafil reduces pressure in lungs

Dr. Richard Moon, an anesthesiologist and medical director of the Duke Center for Hyperbaric Medicine & Environmental Physiology in Durham, NC, and colleagues studied 10 athletes who had experienced SIPE while exercising or competing in triathlons.

The team monitored the participants carefully as they exercised under conditions similar to those likely to trigger the SIPE response. They then compared the 10 athletes with 20 participants who had no history of SIPE.

None of the participants had heart abnormalities, but those who were prone to SIPE experienced higher pulmonary arterial pressure and pulmonary artery wedge pressure during the exercise.

This confirmed that SIPE is a form of pulmonary edema caused by high pressure in the blood vessels within the lungs.

The SIPE participants then repeated the exercise after taking sildenafil. This time, the pressures were reduced.

Lead author Dr. Moon explains: "During immersion in water, particularly cold water, susceptible people have an exaggerated degree of the normal redistribution of blood from the extremities to the chest area, causing increased pressure in the blood vessels of the lungs and leakage of fluid into the lungs. Some cases of SIPE appear to have been the result of cardiac problems."

Dr. Moon believes that as the blood vessels dilate in the arms and legs, there is less tendency for blood to redistribute to the thorax, and the pressure in the blood vessels of the lungs is relieved.

How one athlete controlled pulmonary edema

One of the participants is triathlete Katherine Calder-Becker, aged 51 years. Her susceptibility to SIPE threatened to end her competitive career because of debilitating shortness of breath and distress during colder open-water swims in competitions.

On coughing up blood, she was hospitalized and diagnosed with SIPE.

After participating in studies at Duke in 2011, her cardiologist prescribed her a low dose of sildenafil that she now takes shortly before competitions.

Calder-Becker says:

"I have successfully raced in 20 triathlons since I started taking sildenafil, including five ultra events that require 10-kilometer swims. I have not had an incident since then. I didn't want to give up racing. This is something my husband and I do together, and we travel together to competitions, so it has meant everything to me to continue."

The researchers would like to see larger studies to replicate the results and to learn about any potential adverse side effects of the drug. They hope that ongoing research will reveal more about what triggers SIPE and how to obtain an early diagnosis.

Medical News Today reported last year on research suggesting that Viagra increases the risk of skin cancer.