Last Updated: 2003-06-23 16:00:23 -0400 (Reuters Health)

NEW YORK (Reuters Health) - Long airplane flights may increase the risk of stroke in people with a relatively common heart defect called patent foramen ovale, although such strokes are rare, French doctors announced Monday.

In patent foramen ovale, a tiny opening between the heart's two upper chambers that normally closes during fetal development remains open. Up to 30 percent of the population may have the heart defect.

Long flights are also thought to increase the risk of developing blood clots in the legs, or deep vein thrombosis (DVT). These clots can break free and travel to the lungs, leading to a potentially life-threatening condition called pulmonary embolism. These conditions are sometimes called "economy class syndrome," although any type of immobility -- such as bedrest after an operation -- can increase the risk of clot formation.

Previous research has suggested that people with a patent foramen ovale may be at greater risk of stroke after many hours spent in an airplane. The opening between their heart's two chambers may, in some cases, allow a blood clot to enter the arteries of the brain, thereby causing stroke.

In the new study, reported in the June 24th issue of the journal Neurology, Dr. Frederic Lapostolle of the Hopital Avicenne in Bobigny and colleagues looked at air travelers with a pulmonary embolism who arrived at Roissy Charles de Gaulle Airport in Paris over an eight-year period. Sixty-five individuals with the blood clots were transported to a hospital in that time.

Four of these airplane travelers experienced a stroke during or immediately following a flight lasting between eight and 12 hours. All the patients were in their 50s or 60s. Two of the individuals had no previous medical history of heart problems, another was a very heavy smoker and the fourth had a history of blood clots.

Further analysis revealed that all four had a patent foramen ovale, according to the report.

Although stroke after a long flight is rare, a considerable percentage of people who experience a pulmonary embolism and have patent foramen ovale may be at risk of a stroke, according to Lapostolle and his colleagues.

"If the patent foramen ovale was the key for the development of stroke in the four patients, as seems reasonable, the risk for stroke in the patients with pulmonary embolism and patent foramen ovale would be ... approximately 15 percent to 21 percent," the authors write.

"Although this figure is based on speculation, it is a substantial percentage," they add.

Physicians must be aware of this association, the authors conclude.

To reduce risk of blood clots during flight, experts advise passengers to drink fluids, avoid alcohol, wear loose clothing, avoid crossing their legs, wear elastic support stockings and engage in minor physical activity during flight, such as walking or moving their legs.