Heart defect may lie behind 'bends.' (decompression sickness)

Heart defect may lie behind 'bends'

A hidden, residual defect in the heart, left over from early development in the womb, may explain many cases of decompression sickness, or the "bends," in adult scuba divers, preliminary research suggests. If confirmed in larger studies, the findings could lead to changes in the U.S. Navy's decompression tables, which spell out the maximum rate at which divers should ascend from deep dives. Or it may lead to stricter requirements for medical testing among those seeking certification for deep-water dives.

Decompression sickness results when tiny, dissolved nitrogen bubbles expand in blood before they can escape through the lungs as outside pressures decrease. Richard E. Moon and his colleagues at the Duke University Medical Center in Durham, N.C., examined the hearts of 30 patients with a history of decompression sickness. Using two-dimensional echocardiography, a technique more sensitive than traditional Doppler methods, the researchers sought evidence for a heart defect called patient foramen ovale. The defect consists of a small hole in the wall separating the left and right atria -- a hole normally present before birth that usually closes in the first hours after birth. While it appears in only 5 percent of the general population, evidence of the heart defect showed up in 37 percent of the divers. Of 18 patients with the most serious decompression symptoms, 61 percent showed the defect.

"We know that in a substantial number of divers -- sport divers and professional divers -- bubbles do form in venous blood but are ordinarily trapped by the lungs," says Moon. "But in the event of a patent foramen, theoretically some gas bubbles could pass through the left atrium [bypassing the lungs] and be distributed to the tissues. What we show here is epidemiologic evidence of that."

The researchers, who report on their work in the March 11 LANCET, plan further studies to test the findings.