Pulmonary AV fistula & DCI

[station26]

Hi,
I have read a lot about the controversy surrounding PFO's & DCI. What's the controversy, if any, surrounding pulmonary arteriovenous fistulas. Does size matter? There aren't any medical data supporting this defect. From what I understand, a PFO is caused by an intracardiac shunt where microbubbles can pass into the arterial circulation. Pulmonary AV fistulas, however, is a intrapulmonary right-to-left shunt that bypass the capillaries in the lungs and pass into the arterial circulation. I have been told that if even just one bubble crosses, it's a risk factor for an air emboli. We're talking only microns. I was just wondering if this congenital defect also would be controversial & possibly contra-indicated as the PFO or atrial/ventricular septal defects that I've read in your site & medical journals. Thank you in advance for any information you can supply.
Regards,
Nico

 

[Saturation]

Hi,
I have read a lot about the controversy surrounding PFO's & DCI. What's the controversy, if any, surrounding pulmonary arteriovenous fistulas. Does size matter? There aren't any medical data supporting this defect. From what I understand, a PFO is caused by an intracardiac shunt where microbubbles can pass into the arterial circulation. Pulmonary AV fistulas, however, is a intrapulmonary right-to-left shunt that bypass the capillaries in the lungs and pass into the arterial circulation. I have been told that if even just one bubble crosses, it's a risk factor for an air emboli. We're talking only microns. I was just wondering if this congenital defect also would be controversial & possibly contra-indicated as the PFO or atrial/ventricular septal defects that I've read in your site & medical journals. Thank you in advance for any information you can supply.
Regards,
Nico

The controversy is mostly due to the persistence among those who subscribe to George Irvine's writing on PFOs.

Pulmonary shunts cannot be fixed, and yes, you can be born with them, but more commonly, a certain amount of blood shunts passed the lungs spontaneously ... and shunts can occur simply as a transitory thing. In many studies involving DCI in animals and humans with no PFOs, a certain amount of bubbling can be seen passing into arterial circulation, albeit not as great as in the venous side. Even if you manage to 'fix' the pulmonary shunts, bubbles can still occur spontaneously in the arterial side in severe cases of DCI.

Shunting is not a DCS phenomenon, it occurs is almost all animals and is as physiological a function as the heart pumping. Its something nearly all physiologist consider in doing studies, but in clinical medicine, is less important a phenomenon except in critically ill folks or diseases like DCS.

http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=314967

http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=11171291

The only reason to find, check, and fix a PFO is if one suffers an undeserved or unexpected DCS, and more strongly needing repair and evaluation if one suffers any symptoms of CAGE. DCS is not caused by a single bubble, but is proportionate to the volume of bubbles seen in the pumonary artery ... and its not proven to be causal but rather its a marker for the probability of getting DCS.

 

[station26]

Thank you for the prompt reply. Just a last question: If someone has a small pulmonary AV fistula, that is otherwise symptomless, would it be safe enough to go diving then? (Perhaps to depths of about 100 ft?)
Nico

The controversy is mostly due to the persistence among those who subscribe to George Irvine's writing on PFOs.

Pulmonary shunts cannot be fixed, and yes, you can be born with them, but more commonly, a certain amount of blood shunts passed the lungs spontaneously ... and shunts can occur simply as a transitory thing. In many studies involving DCI in animals and humans with no PFOs, a certain amount of bubbling can be seen passing into arterial circulation, albeit not as great as in the venous side. Even if you manage to 'fix' the pulmonary shunts, bubbles can still occur spontaneously in the arterial side in severe cases of DCI.

Shunting is not a DCS phenomenon, it occurs is almost all animals and is as physiological a function as the heart pumping. Its something nearly all physiologist consider in doing studies, but in clinical medicine, is less important a phenomenon except in critically ill folks or diseases like DCS.

http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=314967

http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=11171291

The only reason to find, check, and fix a PFO is if one suffers an undeserved or unexpected DCS, and more strongly needing repair and evaluation if one suffers any symptoms of CAGE. DCS is not caused by a single bubble, but is proportionate to the volume of bubbles seen in the pumonary artery ... and its not proven to be causal but rather its a marker for the probability of getting DCS.

 

[Saturation]

Thank you for the prompt reply. Just a last question: If someone has a small pulmonary AV fistula, that is otherwise symptomless, would it be safe enough to go diving then? (Perhaps to depths of about 100 ft?)
Nico

You're welcome. Its acceptable if a diver is without symptoms. The depth is not an issue, doing decompression dives is.

Are the risks for the AV fistula dive greater than normal folks? Yes, in theory, but there is little fixed data to quantify how much greater such risk is. for any diver, either with known or unknown shunts, its vital that good diving technique be practiced always to limit post dive bubbling to an absolute minimum: pulmonary shunts can occur spontaneously, and fix themselves as quickly too, so everyone is at risk for a shunt. About a 3rd of AGE events have no PFOs, or no known shunts. If you have no bubbles, you needn't worry about a shunt of any type.

Alas, the only way to find out the status of a fixed pulmonary AV fistula is to actually dive. As a diver gains experience, the patient-diver gradually spends more bottom time or depth, and slowly builds up increasing inert gas loads. After a dive, bubbles that form are proportionate to the gas load build up. So, patient-diver eases themselves into more and more bubbling, and see how they respond. Since all divers begin their careers in recreational no-stop diving, whatever post-dive bubbling occurs in these types of dives is the acid test of the body's response to the fistula. A shunt is a problem only when a diver manifests some symptom.

Small volumes of bubbles entering arterial circulation cause small brain emboli that manifest often as headaches, or subtle neurologic deficits ... most are transient { resolve without treatment} but alarm the diver, that often leads to a consultation with DAN. If such symptoms did occur in no-stop dives, an evaluation for further fitness to dive is needed.

 

[station26]

That was very informative. Thank you.
I will take the small risk and embark my new found passion. Though I have been informed of a few bubbles crossing as a result from an echo and sensations of tingling in my fingers every time I dive, I'm sure all of this will pass.
Take care, Nico

 

[Dr Deco]

Hello Station 26:

The Few/ The Many

As Saturation pointed out, current thinking no longer looks at decompression sickness as “a bubble” caused it. The view is one of the number of bubbles present in the tissues; this will run the gamut from a few causing subclinical problems to many resulting in very severe ones.

Prevention

The best way to prevent arterialization in any form [heart or lungs] is to limit the number of gas bubbles in the venous return. This is accomplished by bottom times that are less than the NDLs, slow ascents, safety stops, and limiting the physical exertion when boarding the boat and during the surface intervals.

Dr Deco :doctor: