People love swimming in open water, with more than 3million taking part in England in 2021. But a new study warns there is evidence linking the sport to a lung condition called swimming-induced pulmonary edema (SIPE).
Age, long swims, cold water, being female, and high blood pressure or heart disease are risk factors. Doctors point out that SIPE often happens to otherwise healthy people, making it difficult for swimmers to breathe and depriving them of oxygen.
The precise cause of SIPE is not fully understood, but it occurs when fluid builds up in the lungs without the person taking in water. The person usually suffers from severe shortness of breath, low oxygen levels and a wet cough.
The risk of SIPE while swimming in open water is also not well known, but is likely to be rare, report cardiologists from Royal United Hospitals Bath and the University of Bath, UK, after treating a woman with the disease.
“First reported in 1989, its incidence is likely underreported and has been estimated at 1.1% to 1.8%,” the authors write in their case report.
However, once a person experiences an episode of SIPE, their chances of developing the disease again increase dramatically.
“Recurrence is common and has been reported at 13% to 22% in divers and swimmers. Episodes vary in severity and often do not require hospitalization; however, patients should be properly informed of the high risk of recurrence and , after an initial episode, should be assumed to have a predisposition,” the authors write.
The case study reports an important finding: the heart and lungs can be affected in SIPE, as seen in the case of a woman in her 50s who swam long distances, triathlons and had no major health issues in the past.
While swimming in an open water event, she became short of breath and had to stop swimming, feeling short of breath for days afterwards.
The patient swam 3 kilometers (1.9 miles) with no problem the following weekend, but a week later the shortness of breath returned after 300 meters, and this time she was coughing up blood.
She had swum in a wetsuit at night in 17°C (63°F) water.
“While swimming in a quarry during a night swim, I started to hyperventilate and realized I couldn’t swim anymore. Fortunately, I was able to call for help and was guided to the dock by a paddleboard,” the woman said after recovering.
“When I came out, I undid my suit and immediately felt my lungs fill with fluid. I started coughing and had a metallic taste in my mouth. When I walked into the light, I saw that my sputum was pink and frothy.”
She was taken to hospital, where her shortness of breath continued, her heartbeat was rapid, and she had a persistent cough. During a clinical examination, small lung sounds that could indicate the presence of fluid in the lungs were observed, and a chest X-ray confirmed the presence of fluid.
Blood tests revealed higher than usual levels of troponin, a protein found in muscle that can be released into the blood after heart damage. An MRI showed myocardial edema – swelling of the heart muscle that could be attributed to fluid – and signs of possible fibrosis, suggesting tissue damage.
The patient’s heart and lungs appeared otherwise normal, and her symptoms and heart rhythm subsided within 2 hours of arriving at the hospital.
Four days later, the patient’s troponin levels returned to normal. A clinical examination showed that his lung and heart functions were normal, although a small amount of fibrosis remained.
Three months after the incident, she performed a stress test without any cause for concern.
Although this is just one case of SIPE, the team say this is the first published evidence of myocardial edema resulting from swimming that has been documented using a cardiac MRI. This should help doctors treating the condition know what to look for while also making cold water swimmers aware of what can happen.
Although more research is needed, SIPE is likely caused by changes in blood flow and a stronger response of blood vessels in the lungs to cold during exercise. People with thickening of the wall of their heart’s main pumping chamber, structural heart disease, or high blood pressure are more likely to get SIPE.
Cardiologist James Oldman and his co-authors say patients who experience shortness of breath while swimming should be tested for SIPE. They also recommend doctors undertake a thorough investigation of the circulatory system to look for any heart problems that should resolve within a few days, like other symptoms.
“As cardiac MRI becomes more widespread globally, it is likely that more data from [immersion pulmonary edema] cases will emerge, allowing us to better characterize myocardial pathology in this underdiagnosed syndrome,” the authors write.
For swimmers who show symptoms, the researchers advise leaving the water immediately and seeking medical attention if necessary. Avoiding nonsteroidal anti-inflammatory drugs and swimming at a slower pace in warmer water without a drysuit are other ways they suggest swimmers. minimize the risk of recurrence.
The peer-reviewed results have been published in the journal BMJ case Reports.