RESEARCH
PFO AND DECOMPRESSION ILLNESS IN RECREATIONAL DIVERS T O P M E D I C A L R E S E A R C H E R S D E B AT E T H E R I S K S O F T H E C O N D I T I O N A N D T H E T R E AT M E N T B Y
P E TA R
D E N O B LE,
M . D . ,
D . S C .
PATENT FORAMEN OVALE (PFO) IS A RELATIVELY BENIGN CARDIAC DEFECT that creates a passage in a wall that normally separates the left and right upper chambers of the heart. PFO is found in about 25 percent of adults, most of whom will never know they have it. The passage may open in certain circumstances and enable venous blood to pass through to the arterial side of the heart; this is a unique concern for divers. If gas bubbles form after a dive, the venous bloodstream will carry them to the right side of the heart. In divers with PFO, the bubbles could pass through the opening, bypassing the lungs and theoretically putting the diver at an increased risk of decompression sickness (DCS). A number of retrospective studies have established that the incidence of PFO is two to six times greater in divers who experience a neurological DCS hit; however, these studies do not prove PFO is the cause of DCS symptoms. The only prospective study designed to measure how PFO affects the risk of DCS is ongoing. A similar association without causative relation was established for PFO and migraines as well as PFO and coronary heart disease. These conditions may be inherited in a similar way and thus may appear in the same people, but they do not necessarily cause each other. Many divers who get DCS do not have a PFO, and many divers with a PFO do not get DCS. Even if PFO is a risk factor for DCS, the risk is very small due to the low incidence of DCS. The risk can be additionally reduced by avoiding dive profiles that are likely to generate a lot of bubbles. It is reasonable to expect that closing the PFO would reduce the risk of DCS; however, there are no consensus criteria for PFO closure in divers. Divers have been undergoing transcatheter closures for years, but an evidence-based risk-benefit analysis is not available, and PFO closure as a means to prevent DCS remains controversial. Most diagnosticians recommend the procedure only in cases of repeated “undeserved” DCS — or DCS occurring without clear causative factors — involving the skin, brain or inner ear. To shed light on this poorly understood topic, we asked recognized experts to provide their opinions regarding three questions of interest for divers concerned with PFO testing and PFO closure. Should divers be tested for PFO? Dr. Alfred Bove: There is no indication for a diver to have a routine screen for a PFO. A PFO is present in 25 to 30 percent of all people. DCS is caused by excess supersaturation of inert gas with subsequent bubble formation in blood and in tissues, and not by a PFO. Bubbles in the venous blood may cross a PFO, but there are many cases of DCS in divers without a PFO, so other factors need to be considered. Several studies have shown that a PFO will increase the risk of DCS; however, the DCS risk remains miniscule even with a PFO. The most common neurological manifestation of DCS 92 |
2021 SPECIAL EDITION
