Why PFO Is Dangerous in Diving
If you dive regularly, you may have heard of PFO — Patent Foramen Ovale. It is a small opening between the right and left atria of the heart that is present in everyone before birth and normally closes shortly after we are born.
For most people, a PFO causes no symptoms and they may live their entire life without ever knowing they have one.
For divers, however, a PFO can be important because it can provide a pathway for venous blood — and potentially gas bubbles — to bypass the lungs and enter the arterial circulation.
This is why PFO is associated with an increased risk of certain types of decompression illness (DCI).
What is a PFO?
Before birth, a baby does not breathe through its lungs. Blood therefore needs a way to bypass the lungs, and the foramen ovale provides this connection between the right and left atria.
After birth, pressure changes normally push the flap closed.
In some people, the opening does not completely seal. This is called a Patent Foramen Ovale, or PFO.
Importantly, having a PFO does not necessarily mean that there is a large permanent hole. In many cases, it behaves more like a flap that can open temporarily when pressure conditions change.
Why does PFO matter to divers?
During a dive, breathing compressed gas causes additional inert gas — mainly nitrogen — to dissolve into the body's tissues and blood.
During ascent, the reduction in ambient pressure allows this dissolved gas to come out of solution and form bubbles.
Normally, venous blood returns to the right side of the heart and then travels through the lungs.
The lungs act as an important filter, trapping or eliminating many small venous gas bubbles before they can reach the arterial circulation.
With a PFO, however, bubbles can potentially cross from the right side of the heart to the left side.
This is called a right-to-left shunt.
Once on the left side of the heart, bubbles can enter the arterial circulation and travel to different parts of the body.
If they reach the brain or spinal cord, they can potentially contribute to neurological decompression illness.
How can bubbles cross a PFO?
A PFO does not necessarily allow blood to flow continuously from right to left.
The direction of blood flow depends on the pressure difference between the two sides of the heart.
Certain situations can temporarily increase pressure on the right side of the heart.
Examples include:
Straining or lifting heavy objects
Forceful coughing
Vomiting
Holding your breath and performing a Valsalva maneuver
Certain breathing or equalisation techniques
Strong physical exertion
Other situations that increase pressure inside the chest
If right atrial pressure becomes higher than left atrial pressure, the PFO can open and allow venous blood — potentially containing decompression bubbles — to cross to the arterial side.
This is one reason why the period during and shortly after ascent can be particularly relevant.
Does having a PFO mean you cannot dive?
No.
This is an important point.
A PFO is relatively common in the general population, and the majority of people with a PFO do not develop decompression illness.
Having a PFO does not automatically mean that a diver must stop diving.
The concern depends on several factors, including the characteristics of the PFO, the individual's diving history, and whether they have experienced unexplained or recurrent decompression illness.
A diver who has been diagnosed with a PFO should discuss their individual situation with a doctor experienced in diving medicine before making decisions about continuing to dive.
When should a diver be particularly concerned?
PFO becomes especially relevant when a diver experiences neurological or other decompression illness that appears disproportionate to the dive profile.
For example, medical assessment may be appropriate when a diver develops decompression illness despite apparently conservative diving and appropriate ascent procedures.
Particular attention is warranted with:
Neurological symptoms after diving
Recurrent decompression illness
DCI occurring after relatively conservative dives
DCI occurring despite apparently appropriate decompression procedures
Symptoms that suggest arterial gas embolism or neurological involvement
The presence of a PFO does not prove that it caused a particular DCI event. Other mechanisms can also be involved, so diagnosis requires proper medical assessment.
Why PFO can be different from a normal decompression problem
In a typical decompression process, venous gas bubbles are carried to the lungs.
The pulmonary circulation can eliminate or filter many of these bubbles.
With a significant right-to-left shunt, however, some bubbles can bypass this pulmonary filter.
This means that the issue is not simply how many bubbles are produced, but also where those bubbles go.
A bubble that remains in the venous circulation may be filtered by the lungs.
A bubble that crosses into the arterial circulation can potentially travel to the brain, spinal cord, or other organs.
This is one reason PFO has attracted particular attention in diving medicine.
Can divers reduce the risk?
Even when a diver has a PFO, sensible diving practices remain extremely important.
Good risk-reduction strategies include:
1. Make slow, controlled ascents
Avoid rushing to the surface.
Follow the ascent procedures appropriate for your training, dive computer and decompression model.
2. Avoid unnecessary decompression stress
Do not deliberately push your no-decompression limits simply because your computer says you can.
A conservative approach can reduce overall decompression stress.
3. Avoid breath-holding
Never hold your breath while breathing compressed gas.
Breath-holding and pressure changes can create dangerous situations for several reasons, including potentially increasing pressure differences across a PFO.
4. Be careful with heavy exertion
Avoid unnecessary strenuous exercise during and immediately after diving, particularly when it involves significant straining.
5. Stay hydrated
Good hydration supports normal circulation, although hydration alone cannot prevent decompression illness or eliminate PFO-related risk.
6. Take symptoms seriously
Neurological symptoms after diving should never be dismissed simply because the dive was "within the limits."
Symptoms such as weakness, numbness, dizziness, confusion, difficulty walking, visual disturbances or unusual neurological problems require appropriate medical evaluation.
Should every diver be tested for PFO?
Generally, routine screening of every diver for PFO is not considered necessary.
Because PFO is relatively common, finding one does not automatically mean that the diver is at high risk.
Testing is more relevant in selected situations, particularly when a diver has experienced unexplained or recurrent decompression illness.
PFO can be investigated using techniques such as contrast echocardiography ("bubble study"), usually under the guidance of a physician.
The decision to investigate should be based on the diver's individual medical and diving history.
What about closing the PFO?
In some cases, a doctor may discuss closure of the PFO.
However, closure is not automatically recommended for every diver with a PFO.
The decision involves balancing the individual's medical history, diving exposure, previous decompression illness and the characteristics of the PFO.
A cardiologist and a physician experienced in diving medicine can help determine whether closure is appropriate.
Importantly, closing a PFO does not eliminate every possible cause of decompression illness.
The most important message for divers
A PFO is not a disease that automatically makes someone an unsafe diver.
It is a relatively common anatomical feature that can become important in a specific situation: when decompression-related bubbles are able to cross from the venous circulation into the arterial circulation.
For most divers, sensible diving practices remain the foundation of decompression safety:
Plan your dive. Control your ascent. Avoid unnecessary decompression stress. Never hold your breath. Listen to your body. And never ignore neurological symptoms after diving.
If you have had unexplained or recurrent decompression illness, particularly neurological DCI, a discussion with a diving-medicine physician about PFO may be appropriate.
Understanding PFO is not about being afraid of diving.
It is about understanding your physiology, recognising potential risk factors, and making informed decisions about how you dive.
A note from Ocean Dreams Pemuteran
After more than 25 years in the diving industry, one of the most important lessons is that diving safety is not only about following a computer's numbers.
Every diver is different. Medical history, physiology, hydration, exertion, repetitive diving and individual susceptibility can all play a role.
If you have experienced unusual symptoms after diving, don't simply assume that you were "within the limits" and therefore everything is fine.
Get proper medical advice from a doctor trained in diving medicine.
