Breathing physiology... whats best for off-gassing

[Uncle Pug]

Originally posted by neil

It's academic at this point, anyway.
Neil

It was academic to begin with....

Anyway.... the point of the quote was that the blood pooling due to gravity does not exist in the water because of hydrostatic pressure. Therefore circulation from the extremities is better in the water when vertical than out of the water when vertical. Nothing said about vertical in the water being better than horizontal in the water.

 

[The Chairman]

There is too much going on in the human body to be able to predict variances accurately. No matter what analogies or models you use, there are incredible amounts of mitigating circumstances that these CANNOT account for. There is no empirical data to support the claim of better off-gassing while you are horizontal.

While everyone wants to claim a "victory" from what Dr Deco said, I believe that I will still hover smugly at my safety stop, knowing what I said first is correct... That the initial "theory" that was proposed had basic flaws in it, and that there is no problem with off gassing in the vertical position. Personally, I do not think that there is a "victory" to claim or a point that "has" to be given, as LONG as we all learn something from our lengthy discussion. Not only did I glean a lot about physiology, but also about human nature. A philosopher once wrote "to err is human". I know for a fact that I will stop making mistakes only when I die, so I guess I will opt to continue making -AND ADMITTING- my many myriad of mistakes. Only fools believe that they are perfect!

 

[mking1]

Let me jump in and make a statement:

Your body in either an atmosphere of increased or decreased pressure acts as a closed incompressible vessel and only the air space inside the lungs (or other small areas) are exposed to the average of the pressure exerted against your body. So there is no differential pressure between the top and bottom of your lungs, except for that small difference in the density of the air.


Miles.

 

[mking1]

As long as I here I might as well add a little more about pressure on the body and hopefully not alienate anyone.

Blood flow is not alerted by increased or decreased pressure on the body. Our bodies are basically a closed incompressible vessel and only air spaces inside our bodies are affected, anyway by pressures we would experience as living terrestrials. Our bodies are still influenced by gravity even in or under the water. It is the increased density of the water that gives us the impression of weightlessness. Remember that if you are over weighted with weights you will sink. That’s gravity at work.

Cold temperatures do affect blood flow. The colder we are the less blood flow there is to our extremities. This is our bodies way of conserving heat. Hope this clears up some thing for you guys.

Miles.

 

[Uncle Pug]

Originally posted by NetDoc

While everyone wants to claim a "victory" from what Dr Deco said, I believe that I will still hover smugly at my safety stop,

Nah....
No Jihad here....
Neither victory nor defeat....
Nor is there humiliation....
In humility....

 

[Dr Deco]

Dear mking1:

Your comment about pressure not altering blood flow is correct except in the condition of immersion. In air, the blood will “pool” in the legs on an erect individual. When immersed, the water pressure will counteract this pooling and blood return in the veins to the heart will be improved.

When individuals have a distension of the veins in their legs and “incompetent” (= non-functioning) valves, improvement can be obtained by wrapping the legs in bandages or wearing support stockings. This is the same principle.

Dr Deco :doctor:

 

[The Iceni]

I knew Americans could talk!

Let me add a new slant. This thread, which I have studied in the greatest of detail(of course!), is concerned with the relative benefits of vertical or horizontal positioning for stops.

Firstly may I comment of the sponge analogy? This fails because the "sponge" is held in a rigid container. What happens when you put your sponge in a selaed coffee jar and submerge it? It retains its shape.

I agree that for maximum gas exchange, one wants the ventilation/perfusion ratio to be equal throughout the lung. When vertical, this is only achieved in the mid zone (so called, "Zone 2"). The tops of the lungs ("Zone 1") have a higher ventilation to perfusion ratio, and the bases ("Zone 3") have a lower ratio.
:
:If horizontal, the conditions in the entire lung approximate "Zone 2" of the vertical individual (ie a 1:1 ratio).
:
Hence the vertical posture is theoretically, at least, less effective for gas exchange.

Turning now to breathing work, the pressure within the thoracic cage will be the same as at the regulator so there will be additional work to inhale when verticall, but this will be offset by the easier exhalation, surely?

However, I understood the limiting factor for deco is not gaseous exchange in the lungs but gaseous exchange at the periphery, particularly in the slower tissues?

As you know the entire cardiac output (mixed venous blood) passes through the lungs in the pulmonary bed. However the brain, kidneys and exercising muscle proportionately take the lion's share of the corporeal circulation, gut, bone and resting muscle receiving proportionately less. These represent the slower tissue compartments when it comes to off-gassing.

The effectiveness of decompression requires both an adequate circulation of the tissues concerned together with an adequate but not excessive pressure gradient to facilitate off-gassing from those tissues.

The problem with vertical hangs, as I see it, is the very real difference in hydrostatic pressure along the length of the entire, erect, immersed, human body. Someone who is 1.5 M tall will have a pressure differential of 0.15 bar along the body when erect, and an erect stop at 3 metres head-height is a 3.5 M stop at the waist and a 4.5 M stop at the ankles. The off-gassing pressure gradient at the ankles is less than at chest height and so offgassing from these tissues will be less.

If you lie horizontally in the water for your stops all of your body is close to the stop, not above it nor below it.

So there are good theoretical reasons why an erect stop is less efficient overall at off gassing.

Many agencies teach horizontal stops and it would seem to be the most efficient way of off-gassing. As the entire mixed venous circulation passes through the pulmonary bed at least once a minute I suspect the gaseous exchange in the lungs is pretty efficient, whatever the posture. I am not at all sure that the lungs are the limiting factor here at all.

Please correct me if I am wrong and I am sure you will let me know many more reasons you can think of for using the horizontal position, or not, as the case may be.

kind regards,

Paul T

 

[100days-a-year]

Miles,.......our bodies are not incompressible.They are comprised of solids,(bone etc...)liquids with gasses in suspension and a few elastic materials which compress also(cartilage)If the body was incompressible,it would negate the possibility of DCS.Furtermore the bodies reponse to immersion(vasoconstriction,reduced respiration to name a few)are well documented.The contentions were whether the DeltaP gradients inherent in a vertical position were sufficient to impede off-gassing.Due to the dynamic nature of the respiratory system it couldn't really be defined as a closed system.O2,CO2and N are constantly being in and off-gassed between the blood,tissues,pulmonary system and the environment during exhale.I have a hard time sometimes with all the ways a body responds VS the way a in-animate pressure vessel would.That is the line that is coming out in this whole thread.Where do we differ from theory?

 

[Uncle Pug]

Pete.... are you still with us???
You can still hang vertically....
If not smugly....
Or efficiently....

 

[The Chairman]

And how could I leave??? Still waiting to see some hard data... none cited or given yet. The best theories in the world can be destroyed by one lousy piece of data. We (as a group) have presented so many theories and counter theories, that it makes the head spin. Without a comprehensive study of actual respiratory efficiency at depth in the upright, prone and inverted positions, we are all merely passing gas (pardon the pun).

Too many times, theories have been created to support erroneous or unsubstantiated opinions. While this conjecture might be the beginning of science and critical thought, we cannot accept it at face value. That would be presumptuous and counter productive scientifically speaking. The world once thought the earth to be flat. Egyptians thought the best treatment for a cut was to rub horse feces into it. The Titanic was certified "unsinkable" by the very engineers who designed her. Only through a methodical critical analyses can the real truth be revealed. Relying on "intuition" or "analogies" to prove your point can be catastrophic, if not embarrassing when the eventual truth comes out. Emphatically representing theories as fact is merely pseudo-science.

I would prefer to maintain an open mind until such time as someone offers up some actual data. Even then, I would want reproducible results to relieve all of my doubts. Those that create theories to promote their own agenda are suspect at the very least. It shows a blatant disregard for science and a willingness to stretch the truth just to prove they are "right". I am confident that no one on this board created this theory. I think I know who did, and I respect them less for it. Who is right is un-important; what is right IS important.

That you offered another reason to be horizontal was good. Some of Roakey's reasons, i.e. practice and that this is his normal position in the water are also completely acceptable (not that ANYONE needs my approval). To dismiss another way of doing essentially the same thing (hover at a safety stop) because one ascribes law status to a theory, is disturbing to me. The law of gravity has been proved... the theory of respiratory efficiency being dependant on your attitude in the water has not been. At least not to this "smug DM"...