Freediving after Breathing on Scuba?

[ScubaSky]

I was on a dive trip recently. We had just completed our second dive of the day (3-Tank boat) we were off gassing during our surface interval. Some of the divers decided to get into the water to do some snorkeling, One of the divers did a freedive to approx. 20 ft. upon his surface the boat captain yelled "that is a good way to get Bent". Then told everyone there was to be no more freedivers.

I understand the fact that we have nitrogen in our system from the previous dives. but wouldn't it already be out of solution during your ascent on Scuba if they were going to come out of solution?

I hope I am making sense?

 

[Genesis]

What can happen is this:

Many people are bubbling some in their venous system after a scuba dive. As long as its on the venous side, and is very low-grade, its not trouble - your lungs make a great filter, and they filter them out and you exhale them through normal gas exchange.

But, there can be trouble if you do a freedive.

As you decend, the bubbles compress. If some of them now are small enough to PASS the lungs, and you ascend before they make the "round trip" in your circulatory system (~4 minutes or so) then you can end up with them on the ARTERIAL side of your circulation!

That's an instant AGE, and worse, it can be in places you REALLY don't want it, like your brain.

If you're going to freedive, do it BEFORE you scuba.

For the same reason its a bad idea to do a "bounce" to pick up something you dropped on ascent. If you're going to go back down, you need to STAY down long enough for everything to go back into solution and then do a full, second ascent, with deep and safety stops, just as you did the first time (right?)

 

[ScubaSky]

Now that makes sense. I guess I don't like being told something without an explanation, Must be the kid in me!

I also appreciate the Bounce Dive example.

Just to Clarify, would it be an overexpansion injury (Embolism) or Decompression Sickness as the captain stated ie: "Bent"?

 

[Genesis]

Which is actually worse than what people think of as "bends" (joint pain), but they're all one of the same piece (Decompression Illness) and in this case caused by the same thing (bubbles in the circulation that cut off blood flow)

 

[rmediver2002]

Just to clarify, would it be an over expansion injury (Embolism) or Decompression Sickness as the captain stated i.e.: "Bent"?

There would not be a risk of over expansion injury on the breath hold dive.

Do not be confused because of the term AGE (normally associated with P.O.I.S.) an arterial gas embolism (blockage) is an air bubble or bubbles within the arterial circulation (the supply side, oxygenated blood), the big danger being as it travel through the arterial system it is going to block or lodge in arteries of the 30-60 micron range blocking blood flow and subsequently oxygen to the tissues downstream.

Two of the first branches within the arterial system are arteries traveling upward and supplying the blood flow to the upper body / CNS. This is the big danger with AGE as in most cases the bubbles follow this route and affect the CNS...

Although the normally discussed causes in diving are related to Boyle’s law and over inflation injuries it can also be caused by:

As you descend, the bubbles compress. If some of them now are small enough to PASS the lungs, and you ascend before they make the "round trip" in your circulatory system (~4 minutes or so) then you can end up with them on the ARTERIAL side of your circulation!

As Genesis already stated, another cause could be PFO, and it has occurred as a result of bypass surgery as well...


Decompression sickness or “the bends” is bubbles within the venous system (returning lower oxygen blood) as these bubbles come out of solution in the body, if it is to rapid or the circulation is restricted in some way the bubbles can lodge and cause symptoms of decompression sickness. Type I DCS is normally less severe symptoms like pain, marbling of the skin, or swelling of the lymph nodes. Type II DCS is normally symptoms affecting the central nervous system

Although this is a very dangerous situation as well, the effects are usually not as sudden or dramatic as AGE as DCS can the blockage can occur anywhere (or in multiple places simultaneously) within the body...


Jeff Lane

 

[Dr Deco]

Dear ScubaSky:

Decompression

As I have mentioned before, “The decompression is not over when you reach the surface.” Because you still have dissolved nitrogen (or even gaseous nitrogen in bubbles) in your body for some time after reaching the surface, you can still get DCS.

Many individuals have been known to get “the bends” from swimming, playing volleyball, lifting tank and equipment, etc shortly following a dive. This is simply not a good idea. Dr Decompression promotes “extreme valet diving” where you get someone else to do all the physical work for you. (That sounds like some people’s philosophy of life in general.)

The Bends

Just a comment on the etiology (origin) of the bends. It is actually not the result of bubbles in the blood stream (as mentioned by J. Lane). It is the result of gas bubbles outside (extravascular) the circulatory system that grow in place. Doppler devices showed that gas bubbles can be present in the venous system and not result in the bends and can also not be present and the bends develop anyway. This topic concerned my first papers in the field of barophysiology. [MR Powell. Leg pain and gas bubbles in the rat following decompression from pressure: monitoring by ultrasound: Aerospace Med., 43, 168-172 (1972); MR Powell. Gas phase separation following decompression in asymptomatic rats: visual and ultrasound monitoring: Aerospace Med., 43, 1240-1244 (1972).

Dr Deco :doctor:

 

[rmediver2002]

Just a comment on the etiology (origin) of the bends. It is actually not the result of bubbles in the blood stream (as mentioned by J. Lane). It is the result of gas bubbles outside (extravascular) the circulatory system that grow in place. Doppler devices showed that gas bubbles can be present in the venous system and not result in the bends and can also not be present and the bends develop anyway. This topic concerned my first papers in the field of barophysiology. [MR Powell. Leg pain and gas bubbles in the rat following decompression from pressure: monitoring by ultrasound: Aerospace Med., 43, 168-172 (1972); MR Powell. Gas phase separation following decompression in asymptomatic rats: visual and ultrasound monitoring: Aerospace Med., 43, 1240-1244 (1972).

Re-reading my post I would agree my statement on Bends does not convey my intended meaning clearly enough.

The intent was to differentiate between injuries involving arterial circulation and injuries that occur outside the arterial system.



Unless I am misreading your statement I disagree with you that DCS injuries are:

the result of gas bubbles outside (extra vascular) the circulatory system that grow in place.

Although this is certainly true in some injuries, some decompression injuries are the result of emboli due to trapping of the bubbles that have already entered the venous system.



Jeff Lane


http://www.emedicine.com/emerg/topic121.htm

http://www.ncbi.nlm.nih.gov/entrez/...ve&db=PubMed&dopt=Abstract&list_uids=99424442

 

[Dr Deco]

Hi Jeff:

Whoops!

I had in mind that “the bends” was the result of an extravascular gas phase.

Most certainly, there are other problems of DCS associated with embolic phenomena, all of which are vascular.

Dr Deco :doctor:

 

[Charlie99]

Dr Deco promotes
“extreme valet diving” where you get someone else to do all the physical work for you. (That sounds like some people’s philosophy of life in general.)

I heartily agree with Dr Deco and gladly let the boat crew change over my tanks between dives.

When I do it myself, rather than do it right after coming up, I'll wait until just a few minutes before starting the 2nd dive before doing any heavy lifting. Something to consider .....

Charlie Allen

 

[ScubaSky]

Let me see if I understand this correctly, the risk mainly lies in the exercise (Due to increased Heart Rate?) and not as was stated before. by Genisis: "Bubbles compress and PASS the lungs" therefore ending up on the arterial side instead of the veinous?

I guess swimming / snorkeling isn't a good idea in that case also, Let alone the freediving.

The "Extreme Valet Diving" Sounds great to me, Gives me a good excuse to relax after a dive.

Thanks