Hi Scubanimal,
The following an updated and expanded piece from my "Ask RSD" column in "Rodale's Scuba Diving":
What is patent foramen ovale (PFO)?
PFO, a type of atrial septal defect, is an abnormal opening between the right and left upper chambers of the heart.
It is normal for blood to flow through a small opening between these two chambers during fetal development when the lungs are inoperative and blood is oxygenated by the mother. At the moment of birth, however, changes in chamber pressures cause this membranous opening to close, shunting blood to the now functioning lungs. While usually permanently sealed by the 3rd month of life, this does not always occur; about one in every four persons has an incomplete closure of varying size. Without complete closure, blood can flow from the right to the left side of the heart without passing through the lungs. This causes a decrease in the amount of oxygen reaching the body and may limit exercise tolerance, sometimes severely.
In the absence of shifts in the pressure gradient in these upper chambers of the heart, however, the majority of otherwise healthy persons with PFO, many with only small openings, are unaware they have the condition. It typically requires no treatment in the adult.
Of significance to divers with PFO is the increase in right chamber pressure which occurs with common equalization techniques like the Valsalva maneuver. Under this condition, nitrogen bubbles that form in the venous bloodstream during normal decompression can pass directly into the arteries without the filtering action of the lungs. When this occurs divers can develop decompression illness (DCI) ranging from relatively harmless skin rashes to serious neurological problems such as loss of consciousness or paralysis. Bubbles passing into the brain and obstructing blood vessels also can result in "silent" lesions of various size.
Studies have shown that a high percentage of divers who had otherwise unexplained incidents of DCI turned out to have PFO. In addition, the risk of severe decompression sickness (DCS) appears to be about three to five times greater in those with PFO as compared to the general diving population, although the relationship is much weaker for only small openings. However, a relatively recent study in the American Journal of Cardiology showed that the size of a PFO in some divers increased over time. While this finding needs replication, it is potentially disturbing.
Despite research findings of increased risk of DCI in divers with PFO, the risk still is quite low. Most dive medicine experts do not recommend echocardiogram as a routine procedure in healthy recreational divers.
The presence and nature of a PFO is best established by transesophageal echocardiogram (TEE) with bubble contrast. This allows bubbles passing from the right to the left to side of the heart to be observed. Even a small number of bubbles are a matter of concern. The basic procedure is described here---->
http://en.wikipedia.org/wiki/Echocardiography.
If repair is indicated, the procedure selected depends upon a number of factors including the size of the opening. There are several approaches, including suturing of the defect or placing a tissue patch over it, although preferred where possible is the non-surgical placement of a blocking device such as the Amplatzer PFO Occluder described here---->
http://www.fda.gov/cdrh/mda/docs/p000039.html
In cases where a repair is performed, at some point TEE with bubble contrast likely will be repeated. Armed with these findings and other information regarding fitness to dive, the diver and his physician can decide on the best course of action. Given an uncomplicated and successful closure in an otherwise fit individual, return to diving typically can be expected within 6-12 weeks.
Helpful?
DocVikingo
