Bubbles? PFO? Decompression Q

[Scuba-Stu]

I do not know much about decompression theory but I have a couple questions about some things Ive have read lately so excuse me if these are dumb questions. First, Some people on this board and elsewhere have stated that some degree of "bubble formation" is ok or at least tolerable. For example, I just read the following by Eric Maiken,

"Any diver who has been routinely monitored with a Doppler meter can tell of times they bubbled--even after following a conservative ascent schedule. As unnerving as the experience is, the first thing that you wonder after hearing low-grade bubbles is "why don't I feel bent?" The answer may be that the body has the ability to handle small amounts of bubbles without undue stress. There is substantial evidence that the body's tissues contain cavities and bubble nuclei before making a dive. These preexisting voids are activated into growth with the application and reduction of pressure associated with diving. Bubbles are especially prone to growth when surrounding tissue is heavily loaded with dissolved gas, such as might be expected following long, deep or repetitive dives." (Maiken, 1995)

Does any one know what keeps these "bubbles" in the tissues? Couldn't even a microscopic bubble in the blood stream could cause some kind of stroke?


Maiken, Eric. (1995). BUBBLE DECOMPRESSION STRATEGIES. Bubble Decompression Strategies


My next question has to do with PFO testing. Has any one read the following artical by Moon & Bove http://rubicon-foundation.org/dspace/bitstream/123456789/4018/1/15568413.pdf ?

What do you think about it?

 

[paddler3d]

If you're a member of DAN, you can take and online seminar, they offer it free to members, that answers a lot of your questions. Actually I think you're questions are answered over two seminars.

 

[Cave Bum]

One of the main issues here is how the body deals with bubbles.

Yes, bubble formation happens every time we dive. The lungs are the bodies' natural filtering mechanism to remove bubbles and for bubbles small in size and small in quantity, the lungs do a good job.

Enter the Patent Foramen Ovale (PFO). The foramen ovale is a shunt or bypass between the right and left side of the heart which, before birth, allows blood to bypass the lungs. After birth there is a flap of tissue that falls down and seals over the hole. In one in five of us, 20%, in the general population this flap doesn't seal completely.

For divers, if the foramen ovale remains 'patent' it allows the bubbles, which are usually filtered by the lungs to bypass the lungs and so remain in the blood stream.

A PFO is present in 80% of divers who experience type II DCS, indiso a PFO is a contraindicator to decompression diving in particular and, to a lesser extent, any kind of diving in general.

Testing to see if you have a PFO isn't usually done in the general population because it usually doesn't present a risk but isn't really that expensive and is recommended for anyone who's been treated for DCS.

I found the article you referenced at the bottom of your post interesting. Dr. Richard Moon is head of the Duke Hyperbaric research facility and was one of the educators at the Dive Medical Tech/Hyperberic Tech course I took through DAN and at Duke University in 2005. What I've posted above is what we were taught in that course. I don't think this article invalidates any of that, it just says there is more to learn and we can't say for sure that fixing a PFO eliminates all risk factors and will keep you having another bout of DCS.

Be safe and have fun in the water! Bruce

 

[netmage]

My next question has to do with PFO testing.

What was your specific question re: PFO testing....?

-Tim

PFO closed 2/14/08...

 

[Scuba-Stu]

What was your specific question re: PFO testing....?

-Tim

PFO closed 2/14/08...

Sorry about that, it is more related to the article that seems to downplay the significance of the PFO in with regards to different types of DCS. I was just curious as to what everyone though about the article.

 

[netmage]

Sorry about that, it is more related to the article that seems to downplay the significance of the PFO in with regards to different types of DCS. I was just curious as to what everyone though about the article.

It summarizes the current thinking...

There is no reason for a wholesale pre-screening of PFOs for diving... People have been diving for 50+ years, 20-30% of the population have this feature/condition...

In instances where we have unexplained/undeserved hits, I'd think of a type 2 nature, I think it warrants some investigation and discussion. Unfortunately, everyone is looking for a final answer to determine closure and eliminate all risk, and that is simply unattainable. If you dive like an unsafe diver, no amount of PFO closure will prevent you from taking a hit, and if you dive in a safe manner taking all the reasonable recreational precautions (NDL, nitrox, safety stops), statistics will say you'll do just fine... There are always wild card variables.

In my personal experiences, I had incidents following multi deco dives in a day, and general fatigue or skin bends type symptoms on heavy recreational days, like 4 dives a day using a fairly conservative computer, and always with nitrox. My TTE came back negative, pushed for a TEE which confirmed, during closure, they found three holes to close, which required an implant about the size of a quarter.

 

[DocVikingo]

Enter the Patent Foramen Ovale (PFO). The foramen ovale is a shunt or bypass between the right and left side of the heart which, before birth, allows blood to bypass the lungs. After birth there is a flap of tissue that falls down and seals over the hole. In one in five of us, 20%, in the general population this flap doesn't seal completely.

Hi Cave Bum,

This isn't accurate. The percentage in the general population and in divers is reported to be higher than this, e.g.,:

Diving Medicine: A Review of Current Evidence
James H. Lynch, MD, MS and Alfred A. Bove, MD, PhD (The Journal of the American Board of Family Medicine 22 (4): 399-407 (2009)
DOI: 10.3122/jabfm.2009.04.080099
Diving Medicine: A Review of Current Evidence -- Lynch and Bove 22 (4): 399 -- The Journal of the American Board of Family Medicine


- Risk of decompression illness among 230 divers in relation to the presence and size of patent foramen ovale
Sandra Rea Torti, Michael Billinger, Markus Schwerzmann, Rolf Vogel, Rainer Zbinden, Stephan Windecker and Christian Seiler (European Heart Journal 2004 25(12):1014-1020; doi:10.1016/j.ehj.2004.04.028
Copyright © 2004 by the European Society of Cardiology.)
Risk of decompression illness among 230 divers in relation to the presence and size of patent foramen ovale -- Torti et al. 25 (12): 1014 -- European Heart Journal

Regards,

DocVikingo

 

[DocVikingo]

There is no reason for a wholesale pre-screening of PFOs for diving....

This is consistent with the very recent conclusions of recognized diving medicine experts James Lynch and Alfred Bove (Diving Medicine: A Review of Current Evidence -- Lynch and Bove 22 (4): 399 -- The Journal of the American Board of Family Medicine) that, "Evidence supports that the average recreational sport diver need not be screened for PFO."

Regards,

DocVikingo

 

[Cave Bum]

Hi Cave Bum,

This isn't accurate. The percentage in the general population and in divers is reported to be higher than this, e.g.,:

Diving Medicine: A Review of Current Evidence
James H. Lynch, MD, MS and Alfred A. Bove, MD, PhD (The Journal of the American Board of Family Medicine 22 (4): 399-407
(2009)

As I stated, my information was based on statistics presented in the November 2005 DMT course at DAN/Duke University by Dr. Richard Moon, Dr. Jake Freiberger and Dr. Peter Bennett, the lead researchers in the field and experts I respect and trust. If subsequent research has proven differently, I accept that and appreciate the update. I've seen figures of '20-30%' but not the studies that they came from so I quoted what I was taught.

The main point I was trying to make was the disparity between the incidence of PFO's in the general population and of PFO's in divers having been treated for type II DCS. Whether it's 20% or 30% or whatever in the general population, the percentage is much higher in those having been treated for type II DCS, making it a contraindictor for diving at that level or perhaps diving period. I did state that testing was only indicated if someone had been treated for DCS.

Would you agree with those two points? Higher risk and testing only if you had a DCS hit?

I don't think we should get bogged down in the minutia of the details. The issue is to educate divers to the mechanics of the risk so they can correctly evaluate their own situation -ie- incidence in general population vs. incidence in divers exhibiting DCS.

CaveBum (Bruce Bosshardt)

 

[DocVikingo]

I was trying to make was the disparity between the incidence of PFO's in the general population and of PFO's in divers having been treated for type II DCS. Whether it's 20% or 30% or whatever in the general population, the percentage is much higher in those having been treated for type II DCS, making it a contraindictor for diving at that level or perhaps diving period. I did state that testing was only indicated if someone had been treated for DCS.

Would you agree with those two points? Higher risk and testing only if you had a DCS hit?anics of the risk so they can correctly evaluate their own situation -ie- incidence in general population vs. incidence in divers exhibiting DCS.

The research does support that the risk of neurological DCS is higher in those diagnosed as having PFO.

However, I can't agree that "...testing was only indicated if someone had been treated for DCS" as it depends upon the individual circumstances. A diver who is treated for a lone event DCS (Type II or otherwise) following a dive profile(s) that clearly and recklessly ignored common safety practices (e.g., obligated deco stops, slow ascents, safety hangs, adequate surface intervals, proper hydration) arguably is not a candidate for evaluation of PFO. On the other hand, a diver who conservatively follows all safety recommendations and still sustains Type II DCS, and especially if more than one event, very probably should undergo such assessment.

Helpful?

Regards,

DocVikingo