MRI scan

[DannyBoy]

A PFO is a patent foramen ovale. The foramen ovale is a tunnel in the wall separating the two top chambers of the heart (chambers=atria, wall=intra-atrial septum). During fetal life, a baby cannot use its lungs to exchange oxygen and CO2 and thus relies on its mother's blood to provide that oxygen-CO2 exchange. Mom's blood comes into the baby via the umbillical blood vessels and travels to the baby's heart. Since the lungs are non-functional, the heart passes the blood from the right side of the heart to the left side of the heart via the foramen ovale in the intra-atrial septum, thereby bypassing the lungs entirely.

Normally, the pressure on the left side of the heart is higher than the right side of the heart. However, when we are first born, the pressure on the right side of the heart is a little bit higher than the left side. This is because the resistance to blood flow in the lungs is higher than the resistance to blood flow in the systemic circulation (left side of the heart provides this flow). As the baby "learns" how to use the lungs and they begin to expand to normal size, the resistance to flow drops dramatically, allowing the pressure in the right side of the heart to drop as well. This all happens in the first few hours of life (in a normal child).

A relatively high right heart pressure is the driving force keeping the foramen ovale open (or patent, if you will). Once the right heart pressure drops below that of the left side, this tunnel closes shut and, in about 75% of people, seals off for the rest of life. In the other 25% of people, the foramen either does not close, leaving a big hole in the intra-atrial septum, or it closes without sealing shut. Babies whose foramens are left open are usually diagnosed in infancy, and a relatively simple procedure is performed through the baby's blood vessels (a catheterization), and a "plug" is inserted into the hole to close it off. As an aside, a patent foramen ovale is also known as a secundum atrial septum defect, and it should not be confused with a primum atrial septal defect, which is a completely different creature altogether. Without getting into too much detail, a patent foramen ovale is considered to be a physiologic variant with the potential to be pathologic (i.e. fetal development was normal, and the defect may or may not cause a problem later in life). A primum ASD is considered to be a congenital heart defect (i.e. something went wrong during fetal development) and is associated with other problems with the heart and development. Treatment is completely different in this case.

Babies whose foramens close but do not seal are much harder to diagnose. During normal activity, these patients have no symptoms of heart trouble, have no abnormal findings on physical exam, and routine echocardiography does not detect any obvious problems with the heart. These people can make it into adult life without any problems whatsoever. This is the patient population that is of interest to this discussion on diving and PFO.

The potential for DCI has been postulated to be higher in this patient population because of this patent foramen ovale. Remember from before I stated that it is the higher pressure on the left side of the heart that keeps this flap closed? The exception to that occurs when a patient coughs or performs a valsalva maneuver, which transiently causes the pressure to increase on the right side of the heart secondary to an increase in pulmonary resistance. This right-sided pressure can make right atrial pressure higher than left atrial pressure, which allows transient flow of blood from the right atrium to the left atrium (a right ot left shunt). Normally, the lungs filter out all the bubbles that form during decompression, but if this right-to-left shunt occurs during decompression (or off-gassing), it is possible for large, unfiltered bubbles to pass to the systemic circulation and on to the body's organs, producing decompression illness.

And that, in a nutshell, is what we are talking about when we address the issue of diving with PFO. I apologize for the long-windedness of this response, but I wasn't sure how detailed you wanted me to get.

Take care,
Dan

 

[DannyBoy]

Jeeze, John, you beat me to the punch by about 5 seconds.

 

[Dr Deco]

[sp]For the readers interested in this topic, comparisons of transesophageal echocardiography (TEE) and transcranial Doppler (TCD) ultrasonography are quite complicate but extensive. They indicate that TCD is as good as the TEE standard, but more “patient friendly.” The following is from a literature search that I performed for our NASA studies.

• Droste et al. (1999). Contrast transcranial Doppler ultrasound in the detection of right-to-left shunts. Reproducibility, comparison of 2 agents, and distribution of microemboli. Stroke 30(5):1014-8
  
  Papadopoulos et al. (1999). Contrast echocardiography and transcranial Doppler sonography for detection of a patent foramen ovale. Minerva Anestesiol;65(11):815-8
  
  Droste et al. (1999). Contrast transcranial Doppler ultrasound in the detection of right-to-left shunts: comparison of different procedures and different contrast agents. Stroke 30(9):1827-32
  
  Nygren and Jogestrand (1998). Detection of patent foramen ovale by transcranial Doppler and carotid duplex ultrasonography: a comparison with transoesophageal echocardiography. Clin Physiol; 18(4):327-30
  
  Horner (1997). Simultaneous bilateral contrast transcranial Doppler monitoring in patients with intracardiac and intrapulmonary shunts. J Neurol Sci; 150 (1): 49-57
  
  Albert et al. (1997). Optimized transcranial Doppler technique for the diagnosis of cardiac right-to-left shunts. J Neuroimaging; 7(3):159-63
  
  Zanette et al. (1996). Patent foramen ovale and transcranial Doppler. Comparison of different procedures. Stroke;27(12):2251-5
  
  Klotzsch et al. (1994). Transesophageal echocardiography and contrast-TCD in the detection of a patent foramen ovale: experiences with 111 patients. Neurology 1994 Sep;44(9):1603-6
  
  Job et al. (1994). Comparison of transcranial contrast Doppler sonography and transesophageal contrast echocardiography for the detection of patent foramen ovale in young stroke patients. Am J Cardiol;74(4):381-4
  Jauss M et al. (1994). A comparison of transesophageal echocardiography and transcranial Doppler sonography with contrast medium for detection of patent foramen ovale. Stroke;25(6):1265-7
  
  Nemec et al. (1991). Comparison of transcranial Doppler ultrasound and transesophageal contrast echocardiography in the detection of interatrial right-to-left shunts. Am J Cardiol ;68(15):1498-502

_____________
Dr Deco

 

[Dr Deco]

Dear Seawitch:

• "I now worry about the MRI ! Is there anything there that I should know? Do I just "lie back and think of Scotland"?

As far as the MRI is concerned, it seems to give equivocal results. Here is a recent paper:(Schwerzmann M, Seller C, et al. (2001). Relation between directly detected patent foramen ovale and ischemic brain lesions in sport divers. Ann Intern Med. 2001 Jan 2; 134(1): 21-4.)They find:

• [1.] Divers have more ischemic brain lesions (= damaged areas) in MRI scans that do nondivers. We might expect that, but nondivers do have some MRI CNS ischemic lesions.
  
  [2.] Divers with a PFO did show a greater number of the lesions compared to divers without a PFO. The PFO was determined by transesophageal echocontrast.
  
  [3.] While lesions were more common in divers, they did not appear in the brains of those who had acquired DCS. The lesions were compartmentalized more as divers or nondivers.

This test possibly only indicates that:

[sp]- some embolic events occur in all individuals,
[sp]- that they are more common in divers,
[sp]- when associated with DCS, the ischemic event did not persist for a [sp]sufficient duration to cause tissue death. [sp]Lucky for the diver.
_____________
Dr Deco

PS. One should not come down too hard on the local physicians. It is not possible to be an expert in all fields of medicine (or all fields of any endeavor). Barophysiology is a specialty. Fortunately, divers have DAN and Scuba Source. =-x

 

[seawitch]

Thanks again Dr Deco!
I only got the PFO because I went armed with sheaves of www references to my GP.
And then the promised MRI (OK? Pete from Orlando?)because I said to Doc his analogy of Russian Roulette was unsatisfactory as far as my future diving was concerned.
I _know_ (of course I do!) that they are simply giving me the best advice they can.
It's just so da**ed hard to accept! :-(

 

[The Chairman]

Hey Seawitch & all of the Docs,

Sorry about the joke; I hope no one is offended by it ;-). But that brings to light another, possibly more insidious question. How in heck do I FIND a Barophysiologist??? They just AIN'T in the yaller pages, if you catch my drift. I have asked many in this area who a good "diving" doctor is and all I get are dumb looks... at least those are free!

BTW, NetDoc means I am a doctor for computer Networks... my slogan is "The Doctor for your Network is always in!" I am a Network consultant by trade (OK, its just a front so I can afford this diving habit!)

Oh Yeah... simply AWESOME (& not too long winded) explanations. It is so cool how our bodies work, and even cooler that we understand some of the ways they don't work too well. THANKS, for taking time to share your knowledge with us.

Pete from Orlando... (Know any good diving doctors down here???)

 

[Dr Deco]

Dear NetDoc:

Barophysiologist is the technical term for researchers in the field of pressure physiology. This might be the zoology of benthic (=deep sea) creatures, or gas uptake and bubble formation in diving or altitude work. These people are in the Undersea and Hyperbaric Medical society and/or the Aerospace Medical Association (AsMA). =-)

To find a diving physician, one could contact the Undersea and Hyperbaric Medical Society (UHMS) that maintains a web site. I am sure that the information could also come for Divers Alert Network (DAN). :doctor:

General questions can be answered from this Bulletin Board, but, as the FORUM physicians have indicated before, a diagnosis of a medical problem cannot be made by e-mail.

Dr Deco

 

[The Chairman]

Hey Dr Deco & All,

I agree with that concept wholeheartedly... One can not fully appreciate any condition, unless you are present. There are too many nuances that the senses pick up that will clue you into the REAL problem.

Please be assured, that all I ever expect or would want would be information of a general nature, and while some of that information may or may not be germaine to me, my intent is to understand as much as possible what we subject our bodies too.

 

[turnerjd]

Originally posted by DannyBoy
Of potential interest to divers concerned about the possibility of a PFO causing decompression illness is a study done by the Department of Medicine at Mass General and published last fall in the Journal of the American College of Cardiology (probably the most respected journal in that field).

J Am Coll Cardiol - the most respected journal in the field?????

How about journals like:-
Heart
Am J Cardiol

J Am Coll Cardiol is at best a second rate journal that you go to if you can't get a paper in anywhere better. Papers here have a very poor life-time, and are quite low down on the often quoted stakes.

Jon T

 

[octodiver]

Just wondering how you are and if you're still diving. We are 2 divers
who are going in for MRI's next week to check for lesions after getting
positive PFO diagnosis. We had each been getting skin/torso symptoms post
diving for years without getting a "proper" diagnosis. Then one day the
skin symptoms progressed to recognizable Type II symptoms... We would
certainly call all of our "hits" non deserved as far as table limits and
ascent rates are concerned (we are instructors with over 10,000 logged
dives between us).

Was your MRI helpful - or did it just scare you? Our physicians here
told us not to bother getting them since there is nothing that can be
done now about any damage we've received, so it would just "freak" us
out! Fortunately, we don't believe there's nothing that can be done about it
(Chinese medicine, meditation, even cross word puzzles could help improve
brain function).

Any info you could share would be helpful.