Bubbles Still Possible?

[Robert Ward]

Give me several days. I have find and contact a couple of my commercial instructors from years ago. It may not be easy. I’ll let you know.

 

[Robert Ward]

The problem was an unknown pulmonary shunt that diverted "silent bubbles" of nitrogen from a deep no-decompression dive into his arterial system rather than harmlessly screening them out on the lungs. This produced an AGE, but the bubbles were just nitrogen, not air. His congenital defect could not be diagnosed by a routine dive physical. He was injured twice. The first time it was understandably misdiagnosed as DCS. The second time was at the commercial dive school, where extensive tests finally detected the problem. I was incorrect in saying that this happened in shallow water. But, the problem did surface during no-D dives.

 

[Stirling]

"If you don't mind explaining, what, precisely, was his "unusual heart/circulation" problem?"

There are conditions that make a person more susceptible to DCS, such as PFO (which is not exactly rare).
https://www.daneurope.org/eng/cadintro.htm

"Patent Foramen Ovale is not a disease, but only a remains of the anatomy of the heart before birth (picture). Before being born, the lungs have no function in oxygenating the blood (because the fetus is immersed in water), and all the oxygen is transported via the umbilical blood vessels, from the placenta. These blood vessels, that are part of the venous blood system, lead the oxygenated blood to the right atrium of the heart."

I think it is worth noting that a couple of people in this thread have referred to somebody showing "symptoms" of DCS after shallow dives or in circumstances where you wouldn't expect DCS to occur. Symptoms are only symptoms; it is one thing to experience some of the symptoms of DCS, and it is something else entirely to have it diagnosed by a competent professional. And a person who has been bent in the past might be especially tuned in to what those symptoms feel like, and to notice them, even if they are not actually experiencing DCS again.

 

[otter-cat]

Hello mobstability:

One does not have nuclei large enough (of in sufficient quantity) to cause DCS when surfacing in a 30 foot deep swimming pool.

Dr Deco :doctor:

Dr. Deco,
Wouldn't that mean that it is impossible to get bent from any dive less than 30 ffw deep? Doesn't ascent rate play an important role? I realize that there is a very long NDL for diving to a depth of 30 feet, and most people will run out of air before that. Still, I think that perhaps I am misunderstanding what you mean there. Could you please try to clarify this for me?
Thanks!
otter-cat

 

[Dr Deco]

Hello ottercat:

Minimal Depth for DCS

It is essentially true that there is a minimal depth for DCS. This is dependent [I believe] on the maximal size of micronuclei present in the body. [The old Haldane concept would say that sufficient supersaturation does not exist for bubbles to form. ]

Micronuclei appear to be [by calculation] never bigger that about three microns. That is about one third the diameter of a red blood cell. For DCS to develop, it is necessary for these nuclei to grow to a sufficient volume. Because of surface tension effects, not all nuclei can grow with any given supersaturation. [Only those larger than the Laplace limit.] Generally, it is surmised, the microbubbles must be a sufficient number for them to grow collectively to a certain volume in a tissue.

At the same time, dissolved nitrogen is entering the blood stream and is being carried away by the blood. Thus bubble growth following a dive is a competition between diffusion into the capillaries versus diffusion into a microbubble. In general, unless there are a large number of microbubbles, the diffusion of dissolved nitrogen into the capillaries is the predominant process.

Pulmonary Barotrauma

In the above discussion, I am referring to DCS that is the result of gas phase growth. Problems from pulmonary barotrauma, that is, holding one’s breath while ascending is a different matter. Lung tissue can easily expand; it is not particularly tough. A lungful of air will expand in the lungs while the diaphragm is being pushed downward. A rupture with air being injected into the circulatory system can lead to severe problems.

This is not the same DCS we speak about when we mean the growth of bubbles in tissue (“the bends”). For pulmonary barotrauma, the limiting depth as about three feet – and it has happened!

Ascent Rate

Because of surface tension effects, ascent rate is important. Slow ascent is better than rapid ascent. The same is true with soda pop bottle. Slow release of pressure is better than rapid decrease of pressure (by quickly unscrewing the cap.) remember with soda pop, slow releasing the pressure is not the same as elimination of dissolved carbon dioxide. It is still in solution wither you open slowly or quickly. Think about it! :280:

Dr Deco :doctor:

 

[otter-cat]

Thanks for your reply, Dr. Deco!

But now I have another question....

If DCI (the bends) is so unlikely to result from diving depths of less than 30 feet, why is it that pregnant women are told that they should not even use scuba in a pool?

I understand (and agree) that with pregnancy, the guidelines should always err on the side of caution (better safe than sorry.) I always thought that hanging out weightless, in a pool would probably do a lot to relieve some of the aches and pains of pregnancy -- although I have never had a baby myself, so I am only guessing. Is there something specific that makes diving at shallow depths risky to a fetus?

It makes sense to me why a pregnant woman would not want to dive in OW, but I'm struggling with the idea of even the pool being off limits for scuba for women who are pregnant.

 

[pipedope]

There is some difference between sport diving and long term exposure.

In scuba we think of 30 as having unlimited NDL and for people doing normal things it is pretty much true.

Now if you are at 30 for many days then you probably want to do a staged ascent. DCI is still unlikely but possible.

Now I must say that I have not looked at the latest studies on this subject and my information is several years old. Dr Deco may have newer info.

 

[Dr Deco]

Hello readers:

Pregnancy

While decompression sickness is not possible from short duration in shallow, pool water, it is possible to have an embolism from breath holding. It is best to simply paddle around in the pool during pregnancy and leave the pressure breathing equipment at home.

NDLs

It is correct that the 30 foot limit is only for durations that can be accomplished with scuba gear, as pipedope states. If you are in an underwater habitat for several days, it appears that the NDL might be on the order of about twenty feet. The references are given below.


Dr Deco :doctor:



References :book3:

Eckenhoff RG, et al. Human dose-response relationship for decompression and endogenous bubble formation. J Appl Physiol. 1990 Sep;69(3):914-8.

Eckenhoff RG, et al. Direct ascent from shallow air saturation exposures. Undersea Biomed Res. 1986 Sep;13(3):305-16.