For scuba divers, the general risk of death or major injury during a dive is quite small (lower than 0.001% per dive), but decompression sickness (DCS) still remains one of the riskiest side effects. DCS is caused by nitrogen bubble formation in hypersaturated tissues during the diver’s ascent; these bubbles either cause local tissue damage or embolize through venous blood. The association between a patent foramen ovale (PFO) and DCS was first described in the 1980s, with a higher prevalence of PFO repeatedly observed in divers with the neurological or cutaneous form of DCS. A new study conducted in divers who simulated deep dives in hyperbaric chambers suggests that catheter-based closure of PFO may alleviate DCS in scuba divers by eliminating embolization of arterial bubbles.

Led by Josef Veselka, MD, PhD, of Motol University Hospital in Prague, Czech Republic, researchers looked at 47 divers who participated between February 1, 2006, and April 30, 2013, in simulated dives in a hyperbaric chamber—either to 18 meters for 80 minutes (dive A) or 50 meters for 20 minutes (dive B). Patients were further categorized according to whether they had a PFO (n = 19) or had undergone PFO closure (n = 15). All patients performed the first dive (18 meters), while a smaller number performed the second 50-meter dive: eight PFO patients and five closure patients.

In the dive A group, venous bubbles were detected in 74% of divers in the PFO group versus 80% in the closure group; arterial bubbles were detected in 32% versus 0% of divers, respectively. About one-fifth of divers with PFO and detected arterial gas bubbles had neurological symptoms of DCS (i.e., headache, unusual fatigue, and transitory visual disturbances), but none of the divers in the closure group reported these symptoms (p = 0.11).

In the dive B group, venous bubbles were detected in 88% of divers in the PFO group versus 100% of divers in the closure group; arterial bubbles were detected in 88% versus 0% of divers, respectively. One-quarter of the divers with PFO and detected arterial gas bubbles had neurological symptoms of DCS, and again, no divers in the closure group reported DCS symptoms (p = 0.49). "In our study, no difference was found in the occurrence of venous bubbles between the PFO and closure groups," the investigators noted. "However, in the closure group, no arterial bubbles were detected. It is plausible, therefore, that the presence of a PFO plays a key role in paradoxical embolization of venous bubbles after scuba dives." In addition, the results of the current study suggest that PFO occlusion might lead to a reduction of unprovoked DCS incidence in divers.

"Patent foramen ovale closure is the thing to do these days in the interventional laboratory," Alfred A. Bove, MD, PhD, of Temple University School of Medicine in Philadelphia, wrote in an accompanying editorial. Closures are performed for a variety of reasons, he continued, including strokes, migraine headaches, and postural cyanosis—and, more recently, for divers who are at risk for DCS. Importantly, though, Dr. Bove pointed out that an increased incidence of PFO in a stroke population is not equivalent to an increased incidence of stroke in a PFO population.

These data from the study by Honěk et al. are "compelling," and seem to suggest that serious divers be screened for PFO, Dr. Bove noted. From there, if a PFO is found, the decision to close the shunt should be made by the diver and physician together.

Honěk J, Srámek M, Šefc L, et al. JACC Cardiovasc Interv. 2014 March 13. [Epub ahead of print]
Bove AA. JACC Cardiovasc Interv. 2014 March 13. [Epub ahead of print]