Patent Foramen Ovale and Diving

As a scuba instructor, I find the physiological side of scuba diving fascinating. My personal research led me to discover Patent Foramen Ovale (PFO), a medical condition that may cause an increase in a diver's chance of decompression illness. I am not a doctor, and research into this topic is ongoing. This article is merely a summary of basic information gleaned from my research about PFOs and diving.

As a fetus, every person has a connection in his heart that runs between the left and right atriums (two chambers in the heart that are separated by tissue in adults). This passageway allows blood to circulate through a fetus's heart without passing through his lungs. As a child matures, the hole between the two sides of the heart usually seals closed with a flap of tissue, preventing blood from passing between the right and left heart chambers directly. Patent Foramen Ovale (PFO) results from the incomplete closure of this hole.

Patent Foramen Ovale (PFO) is relatively common. Studies indicate that as many as 30% of adults have a PFO. Most adults with a PFO are unaware that they have it as a PFO usually has no adverse effects on daily life. PFOs range in size from a tiny opening to opening of 10 mm or larger. Individuals with large PFOs have reported symptoms such as redness, shortness of breath, or faintness during strenuous exercise which may be indicative of a PFO and are sometimes misidentified as simply being "out of shape". In some individuals, the hole between the two sides of the heart does not close at all. This is called an Arterial Septal Defect, or ASD.

In a diver without a Patent Foramen Ovale (PFO), blood flows from the veins into the right side of the diver's heart. The right side of the diver's heart then pumps this venous blood into the lungs where it picks up oxygen. From the lungs the blood enters the left side of the diver's heart where it is pumped back into the arteries. The blood flow in a person without a PFO is: veins – right side of the heart – lungs - left side of the heart – arteries.

In a person with a Patent Foramen Ovale (PFO), normal blood flow may be disrupted. Some small amount blood may “leak” through the PFO which is basically a hole between the right and left side of the heart. In a person with a PFO, some blood might flow in the following way: veins – right side of the heart – left side of the heart – arteries. Notice the blood has skipped the lungs completely in this scenario.

One of the causes of decompression illness, or DCI, is called an arterial gas embolism (AGE). An arterial gas embolism occurs when a tiny bubble of nitrogen enters an artery. This is hazardous because the bubble can block the flow of oxygenated blood to the tissues surrounding the artery, causing cell death, numbness, pain, and a variety of other symptoms.

Divers commonly have microscopic nitrogen bubbles in their veins (not arteries) after diving. A DAN (Diver's Alert Network) study found that 91% of divers had venous nitrogen bubbles after a series of repetitive dives well within the recreational dive tables. These venous nitrogen bubbles are normally harmless because venous blood passes through a diver's lungs before circulating to the arteries. In the lungs, the bubbles in the venous blood are eliminated by routine gas exchange.

The presence of Patent Foramen Ovale (PFO) can disrupt the normal flow of blood through the heart. Venous blood with tiny, normally harmless bubbles can leak directly from the right side of a diver's heart to the left side, where it is pumped back into back into arterial circulation without passing through the lungs.

If nitrogen bubbles enter the arteries, there is now a risk of an Arterial Gas Embolism (AGE). A Patent Foramen Ovale may allow nitrogen bubble to pass from veins, where they are harmless, to arteries, where they are potentially dangerous.

Currently, a Patent Foramen Ovale is not considered a contraindication for recreational diving, but this may change in the future. Decompression illness (DCI) is relatively rare, even in divers with a PFO. However, research suggests that a PFO may increase the small chance of a diver getting DCI by as much 4-5%. In addition, some research indicates that the larger the PFO hole, the greater the risk of DCI. PFO can be a contraindication for technical diving. Concerned divers should speak with a cardiologist knowledgeable in diving medicine.

PFO has also been cited as the cause of decompression illness in cases of “undeserved bends” (cases in which a diver conservatively dived within the recreational dive tables and followed accepted safety procedures such as slow ascents and safety stops, but inexplicably contracted decompression illness). Divers who have had decompression illness for no apparent reason may want to be checked for a PFO.

A Patent Foramen Ovale (PFO) can be detected by an echocardiogram. In this test harmless microscopic bubbles are injected into the test subject's veins in a saline solution. A doctor then watches on the echocardiogram, similar to a sonogram, to see if the bubbles pass from the right to the left side of a diver's heart. If the bubbles are observed migrating to the left side of the heart, a PFO is present.

Yes. A device called an occluder can be inserted into a patient's heart though a relatively non-invasive procedure. Medical studies proving whether or not an occluder can eliminate the possible increased chance of decompression illness in divers with a Patent Foramen Ovale are not yet conclusive.

Divers should remember that any medical procedure carries with it inherent risks. Each diver must decide if the chance of adverse effects from the insertion of an occluder are worth the benefit of possibly avoiding decompression illness. If the procedure has any adverse effects, there is the chance that the patient will not be able to dive again.

Some divers who have had a PFO closed by an occluder report the elimination of “underserved bends.” However, there are no air-tight conclusive studies to prove this . . . yet.

Many divers continue to dive with a Patent Foramen Ovale (PFO) and do not get decompression illness. Remember that decompression illness is caused by nitrogen bubbles, not by the PFO itself. For divers who choose to continue to dive with a PFO, doctors have compiled the following list of suggestions to minimize the formation of venous nitrogen bubbles and reduce the risk of decompression illness.

• no decompression diving
• adopt conservative dive profiles: no deep or long dives.
• no exercise (even lifting a tank) after diving
• no valsalva maneuvers (equalizing by pinching the nose and blowing though the nose) on ascent.
• nitrox may help to reduce the formation of venous nitrogen bubbles
• make extremely slow ascents and long safety stops