MRI scan

[seawitch]

I had an undeserved DCI hit about 6 months ago followed by another 7 weeks later and was told "no more diving"
I've had the PFO test (proved negative) and am to have an MRI scan in two weeks time to ascertain whether there has been any permanent damage.
I think that if the MRI does not show any significant problems I will try to dive again.
I'm no spring chicken!
Any comments?
Am I being really foolish?

 

[Tavi]

seawitch,

Hi and welcome to the boards,

Wow! that's a tough one. I don't know what I would do. I know that when I really love something it's hard to give it up, But if those hits were undeserved what's the chances of having another? Maybe NOT breathing compressed air is better than not breathing at all.

You'll be in my thoughts and prayers,

Tavi:tree:

 

[Dr Deco]

Dear Seawitch:

That there are “deserved” and “undeserved” hits is a pious fiction. It is a holdover from the classical thought of a fine line separating “bends/no bends” regions of a dive table.

Errors in diving can result in problems even though you are "within the tables" – the classical definition of “undeserved.” Since it is not possible to view you dive day as though it were an “instant replay,” it is necessary to speak in generalities.

We perform research at NASA on altitude decompression, and all of the individuals start from sea level. That is, all have the same amount of dissolved nitrogen in their bodies. The difference in outcome of any these series is thus

[sp](1) something within the constitutional makeup of the test subject, or
[sp](2) something they did while supersaturated (in the NASA case, at altitude).

Let us examine each of these more closely.

• [*1]It is well known that individuals simply have different response to decompression. This was known during World War II when selection tests were instigated for high altitude bombing crews to ascertain who was and who was not susceptible to DCS (for a given altitude). Why this difference exists is not known, but it is real and it is reproducible. It might well be related to differences in surface tension of the body fluids or differences in biochemical constituents of the fluids (e.g., blood) that accounts for the ease of formation and lifetime of tissue gas micronuclei (the “seeds” from which decompression bubbles grow). When it comes to formation of bubbles, you might simply be an individual who is “bubbles prone."
  
  [2] If one should create a large number of tissue micronuclei, these will develop into decompression bubbles. Nuclei-generating maneuvers might include such activities as climbing ladders onto the boat with full gear, lifting heavy tanks on deck, jumping, running, or other straining maneuvers. These bubbles could pass into the arterial circulation to embolize the brain (past a PFO or through lung capillaries) if there is a rise in pulmonary artery pressure (the large vessel between the heart and the lungs). This is common when an individual performs a Valsalva maneuver. It is also possible with a Valsalva-like maneuvers. Such actions might be straining as you climb the ladder to the boat, pulling or tugging on something, all the while holding your breath for a couple of seconds. Even if you had only a small PFO, problems could arise. If the CNS DCS that you acquired was in the spine, a PFO is really not involved in the etiology (= cause).

This is is only the viewpoint from the aspect of decopression biophysics. There are other medical viewpoints that would concern, for example,the validity of the MRI test or how the PFO test was actually performed [e.g., thranthoracic (=chest) echo contrast]. Some are not as sensitive as others.

Hope that this will be of some assistance, at least as far as background information is concerned.

_________________
Dr Deco

 

[seawitch]

Hi Dr Deco,
Thanks for such a full and informative reply.

>That there are “deserved” and “undeserved” hits is a pious fiction. It is a holdover from the classical thought of a fine line separating “bends/no bends” regions of a dive table.

I said "undeserved" because there was no fast ascent which would have been the most likely trigger.
However, 1hour 40mins after a 31m dive, I had a brief (less than 2 mins - no show on computer)with a Novice who had a problem and then we went to ~11m for 20mins.

>Errors in diving can result in problems even though you are "within the tables" – the classical definition of “undeserved.” Since it is not possible to view you dive day as though it were an “instant replay,” it is necessary to speak in generalities.

See http://www.geocities.com/carolreid86/diving_belle1.html
for computer printout and indepth account of the day.


snips.....

>susceptible to DCS (for a given altitude). Why this difference exists is not known, but it is real and it is reproducible. It might well be related to differences in surface tension of the body fluids or differences in biochemical constituents of the fluids (e.g., blood) that accounts for the ease of formation and lifetime of tissue gas micronuclei (the “seeds” from which decompression bubbles grow). When it comes to formation of bubbles, you might simply be an individual who is “bubbles prone."

Would this not have shown up on any of the previous 300 dives?

>[2] If one should create a large number of tissue micronuclei, these will develop into decompression bubbles. Nuclei-generating maneuvers might include such activities as climbing ladders onto the boat with full gear, lifting heavy tanks on deck, jumping, running, or other straining maneuvers. These bubbles could pass into the arterial circulation to embolize the brain (past a PFO or through lung capillaries) if there is a rise in pulmonary artery pressure (the large vessel between the heart and the lungs). This is common when an individual performs a Valsalva maneuver. It is also possible with a Valsalva-like maneuvers. Such actions might be straining as you climb the ladder to the boat, pulling or tugging on something, all the while holding your breath for a couple of seconds. Even if you had only a small PFO, problems could arise. If the CNS DCS that you acquired was in the spine, a PFO is really not involved in the etiology (= cause).[/list] This is is only the viewpoint from the aspect of decopression biophysics. There are other medical viewpoints that would concern, for example,the validity of the MRI test or how the PFO test was actually performed [e.g., thranthoracic (=chest) echo contrast]. Some are not as sensitive as others.

I was given two tests
the colour contrast echocardiogram first and then, on request, bubble contrast EEG.
But not, significantly, when performing the Valsalva.

>Hope that this will be of some assistance, at least as far as background information is concerned.


Thank you - most of it I have already gleaned from Net sources.
BUT I had not realised that the effort involved after a dive (hard physical exertion) would be so important - this may have caused the second bend 7 weeks later.
In this case, the bends were NOT undeserved.
Does this mean that if I am very careful NOT to have this type of exertion I might be safer?

 

[Dr Deco]

Dear Seawitch:

[1.]The "bubbles prone" aspect might have always occurred during your previous dives. Recreational dive tables are generally made to be so conservative that virtually everyone will be fine. When we tested the DSAT Recreational Dive Planner, there were very few Doppler-detectable gas bubbles and they were only in about five percent (5%) of the divers. It is generally only if one does something extraordinary that a problem, will arise.

Heavy physical exertion is, I believe, one overlooked area in training up to now where a scuba diver could get into trouble after reaching the surface. That is why I have emphasized in this column that one should avoid all of these vigorous activities. It is difficult to prove, however. In order to perform a prospective laboratory controlled test, it would be necessary to have divers perform only moderate surface activity and then heavy exercise in another dive. This is known in the trade as a cross over study. When speaking about neurological DCS, it would be a bad idea to provoke this problem in human subjects simply to acquire test data. Surely such a test will not be done. Simpler studies with joint pain (the bends) were done during the 1940s, and it showed that such activity was exacerbating factor in the bends. Therefore the admonition concerning neurological DCS and musculoskeletal activity is an extension of this early work. I would imagine that I am not far from the truth, though.

I do not note anything exceptional in the dive profiles that you provided - - as far as depth and time are concerned.

[2.] The tests for a PFO to which you alluded would have shown a patency (= opening). You had first a color Doppler that can detect large defects. The second was with saline bubble contrast in a transthoracic echocardiogram. [Here you said EEG which is an electroencephalogram and measures brain waves.] This will measure a so called "resting PFO" and is not common. What is also required is to have the test with the Valsalva maneuver as this will measure an "augmented PFO", more common. This is the PFO that "opens" when you hold your breath and release(the pressure gradients in the right and left atria are reverse by this means). A possibly better test is to have this test performed also with a transcranial Doppler (TCD) on the middle cerebral artery. This can then measure what is known as the "shunt volume" and reveal a hemodynamically significant PFO. We are now getting quite complicated, and I do not know where such a test is done outside of a research setting. (Others have asked me this same question, namely, where can I get this test?)

I hope that this is of some help. It does mean that avoiding exertion post dive is probably a good way to minimize the possibility of getting DCS - - both "the bends" and neurological forms. :nono:

_____________
Dr Deco

 

[John Reinertson]

Dr Deco has summarized well. There is simply no way I (or anyone) can tell you with precision what your chance of repeating DCS is.

If the DCS you had shows no major Central Nervous System residual (and no major spinal cord residual) then some people would choose never to dive again and some would choose to take the risk.

Anyone can reduce risk by reducing tissue saturation. There are some reasonably good but imprecise observations that conclude that those of us who aren't spring chickens and that aren't at an "ideal" body mass index have increased risk, and reasonable suggestions that reducing nitrogen loading and slower ascent rates will reduce this risk.

This is info not from huge studies, but the observed occurrences from Navy Chiefs and Navy diving officers.

Peter Bennett of DAN fame suggests that many hits are from relatively "fast" tissue compartments and slower ascents are needed, not only from fifteen feet to surface but also from 60 feet to 15 feet.

As Dr Deco points out, precise info isn't available.

As one who is 53, mildly overweight, and somewhat risk averse, I use nitrox between fifty feet and a hundred, don't go below a hundred without a good reason and a very prolonged ascent, and stay on the conservative side of the computers routinely.
Deco risk is not zero on one side of the tables and 100 % on the other side. It is a continuum affected by many factors, and previous hits ought to weigh heavily in the decision as to degree of conservatism employed.

It's your body and brain and your decision. I'd personally be exceptionally careful but still dive. Other rational people would never dive again.

(how's that for waffling?)

Dive low risk,
John

 

[DannyBoy]

Seawitch,
I would only add to this conversation that transthoracic echocardiogram is NOT the best way to diagnose patients with a patent foramen ovale. The gold standard has, for years, been the transesophageal echocardiogram, which involves passing a transducer probe down the patient's throat in order to view the intra-atrial septum while bubbled saline is injected into the patient's veins.

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). The study compared the detection sensitivity of TTE with that of TEE and transmitral doppler/TTE. The results showed that 2D TTE (what you had done) had a relatively low ability to detect patients with PFO, while TEE and TTE/TMD had a much higher ability to detect these defects. TTE/TMD is a relatively non-invasive test (when compared to the more invasive TEE) that, as more clinicians adopt this procedure, may prove to be just as effective at diagnosing PFO as TEE, without the discomfort of having a 2cm probe jammed down your throat.
Food for thought,
Dan

Reference: J Am Coll Cardiol 2000 Nov 15;36(6):1959-66

 

[seawitch]

Thankyou, both DannyBoy and Dr Deco, for your knowledgable information on this subject.
It does rather upset me to know that there were things I should have known (and the Drs involved SHOULD have known) when testing me for the PFO.
I now worry about the MRI!
Is there anything there that_I_ should know?
Do I just "lie back and think of Scotland"?

 

[The Chairman]

Hey All,

I can mostly follow everything said, but will someone define PFO??? That would make the whole discussion clear to me.

Pete from Orlando...

 

[John Reinertson]

PFO stands for Patent Foramen Ovale. The Foramen Ovale is a "hole" between the right and left upper chambers of the heart that is critical before birth to allow circulation to bypass the lungs.
It usually closes up after birth.

In a certain percentage of people (varies with the studies) the " hole " remains open and can pass blood from right to left. People who have a Patent Foramen Ovale have a somewhat (again a matter of controversy as to exactly how much) higher chance of DCS.
This is presumed because bubbles on the right or venous side of the heart can pass thru the foramen and be carried out directly in the arterial circulation to the tissues, especially those of the spinal cord and brain. Thus people with one or more hits that can't be easily explained by a major violation of the tables or other risk factors often get an ultrasound study.
There are tricks to getting the most precise echo study that are not universally known among all physicians, but are usually known to Diving docs.
The precise pros and cons of each person's PFO study have to be carefully decided by the patient and their physician. If your docs aren't familiar with diving medicine, DAN consult might be in order.

If they are familiar, they should be able to give you fairly precise advice as to diving risk and let you choose.

PFO's are only significant if there is venous bubbling to start with, so "if there are no bubbles there are no troubles." (hence my advice for major conservatism above)
You have to decide what risks you are willing to accept.

Dive safe and bubble-free

John Reinertson