People love to swim in open water, with more than 3 million participating 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 stress that SIPE often happens to otherwise healthy people, making it hard for swimmers to breathe and depriving them of oxygen.
The precise cause of SIPE is not fully understood, but it happens when fluid builds up in the lungs without the person taking in water. The person usually experiences severe shortness of breath, low oxygen levels, and a wet cough.
The risk of SIPE while swimming in open water isn't well known either, but it is likely to be uncommon, report cardiologists from the Royal United Hospitals Bath and the University of Bath, UK, after treating a woman with the condition.
"First reported in 1989, its incidence is likely underreported and has been estimated between 1.1 percent and 1.8 percent", the authors write in their case report.
Once a person experiences a bout of SIPE, however, their chances of developing the condition again rise substantially.
"Recurrence is common and has been reported between 13 percent and 22 percent among scuba divers and swimmers. Episodes vary in severity and frequently do not require hospitalization; however, patients should be appropriately informed regarding the high risk of recurrence, and following an initial episode, should be assumed to have a predisposition," the authors write.
The case study reports an important finding: the heart and the lungs can be affected in SIPE, as seen in the case of a woman in her 50s who swam long distances, did triathlons, and had no major health problems in the past.
While swimming during an open-water event, she became short of breath and had to stop swimming, feeling breathless for days afterward.
The patient swam 3 kilometers (1.9 miles) with no issues the following weekend, but a week later, the breathlessness returned after 300 meters, and this time she was coughing up blood.
She had been swimming in a wetsuit at night in 17 °C (63 °F) water.
"While swimming in a quarry at a night swim, I started to hyperventilate and realized I couldn't swim any further. Luckily, I was able to call for help and got guided back to the quay by a paddleboard," the woman said after recovering.
"When I got out, I undid my wetsuit and immediately felt the sensation of my lungs filling with fluid. I started to cough and had a metallic taste in my mouth. When I got into the light, I could see my sputum was pink and frothy."
She was taken to the hospital, where her breathlessness continued, her heart rate was fast, and she had a persistent cough. During a clinical exam, small lung sounds that can indicate 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 following heart damage. An MRI indicated myocardial edema – swelling in heart muscle that can be attributed to fluid – and signs of possible fibrosis, which suggests tissue damage.
The patient's heart and lungs appeared otherwise normal, and her symptoms and heart rate settled within 2 hours of arriving at the hospital.
Four days later, the patient's troponin levels returned to normal. A clinical review showed her lung and heart functions were normal, although a small amount of fibrosis remained.
Three months after the incident, she completed an exercise test without any cause for concern.
Although this is just one case of SIPE, the team says it is the first published evidence of myocardial edema arising from swimming that has been documented using cardiac MRI. That should help doctors treating the condition know what to look for while also raising awareness amongst cold-water swimmers of what can happen.
Although more research is needed, SIPE is likely caused by changes in blood flow and a stronger response of the lung's blood vessels to cold when exercising. 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 co-authors say patients who experience breathlessness 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 mainstream globally, it is likely that more data from [immersion pulmonary edema] cases will emerge, enabling us to characterize myocardial pathology better in this under-diagnosed syndrome," the authors write.
For swimmers who experience symptoms, the researchers' advice is to leave the water immediately and seek medical help if needed. Avoiding non-steroidal anti-inflammatory drugs and swimming at a slower pace in warmer water without a tight wetsuit are other ways they suggest swimmers can minimize the risk of recurrence.
The peer-reviewed findings have been published in the journal BMJ Case Reports.