Breathing physiology... whats best for off-gassing

[100days-a-year]

NetDoc,I know you're lookin'Will you agree to play if the boys stay on thier best behavior.My motives are impure ,of course.The one that isn't is that this is the ONLY place I've found on the net with intelligient discourse without to much chest-beating or derisive and offensive content.I know the physics and physiology involved,but I'd like to see eveyone get to the point that we can say either attitude has an effect on off-gassing and here's why or it does not and here's why. cheeriodles(as he slinks off to eat more Holyday sweets)

 

[large_diver]

Man, I take a couple of days "off" from Scubaboard for the holidays and I miss all of the fun ;-)

:flame:

I always thought it was logical that our lungs and our ability to breathe are impacted by changes in external pressure. My thinking was based on the simple experience of doing laps in a pool.

We've all had the sensation of being out of breath after or during strenuous exercise, but I have to admit, this sensation is heightened for me when I'm doing an intense swimming workout. When resting at the end of the pool after a VERY hard set of laps with my body immersed from the neck down, I aways find it harder to catch my breath than on dry land after similar exercise. I always assumed this was because of the added pressure of the water on my chest cavity. I have to assume that a few feet of depth would result in similar differences in lung breathing effort (and offgassing efficiency).

Then again perhaps this is all psychological......
:stupid:

 

[Blargh]

Disclaimer - I havent bothered to go though every single word of every post. it entirely possible that I've missed a point or two.

That said, *do* allow me to mention something that might make this a bit clearer :boxing: - assuming that a) I got the facts correct and b) I got the vocabulary correct.

One interesting side-effect of true weightlessness (as experienced by astronaus) is the confusion that is experienced by the cardio-vascular system due to the lack of that very pressure differential that is being discussed of late around here.

As far as I remember, the heart, arteries, and rest of the whole shebang is tuned by m.Nature to operate at a slight pressure differential between top and bottom of our bodies. Furthermore, being a bipedal upright (ok, maybe not at Xmas) species, our cardiovascular system has a more pronounced bias towards pushing against said differential than the one of any quadruped one might think of.

The *lack* of this differential in orbit, combined by the above mentioned tuning leads to the system pushing more strongly towards the head/brain than towards the legs/feet, causing in *some* individuals a sensation of being turned upside down. Individual tolerance/adaptation varies as well as the discomfort experienced, although (again, afair) in some individuals this discomfort exceeds *some* limit and makes them unsuitable for orbital (weightless) missions.

I'd really appreciate it if someone could "peer review" , as it were, my post, since I'm writing off the top of my head about stuff that I was deeply interested in in my schoolyear - quite some time ago, iow.

Now, assuming that I haven't completely lost the plot here, this weghtlessness effect would seem to indicate that there *is*, as a matter of fact, a pressure differential across our bodies. Incidentally, this also would indicate that our bodies are tuned to deal with the minimal delta-pee in air, thus any underwater calculations should deduct this number.


Backing up a bit here now. Our bodies, by and large, are NOT a rigid system. However, one must take extreme care applying analogies (of any kind), since our bodies aren't homogeneous either. The lungs, while certainly not a rigid system, are not a exactly a sponge either. Try to think of them as a one-way-ish sponge... glued to the inside of a flexible (but not jelly-like) container. Lung over-expansion will press the tissues against the container, and damage then. Lung.. erm.. under-expansion will not cause any significant damange until 1) the rib cage collapses and 2) the lower intestines get sucked into the rib cage enough. Incidentally, rib cage collapse can become an issue when freediving - iirc, around the 60 meter (6 bar delta-pee) mark, but I digress.

Anyway, to summarise ... roakey is correct, although his presentation isn't rigid enough.


ttfn

 

[The Chairman]

Gosh guys,

Interesting theories, some obvious glitches, and I have no idea where to begin. I have E-Mailed some of the doctor types personally to come in and straighten all of us out. At this point, I would really like to know, but I have reason to distrust each and every theorem, including my own. I have already expounded (ad nausea) my theories on the subject, and I have nothing to add to them. However, up until large_diver, we have been given little (if any) substantive or empirical evidence to support various claims. In my mind (as simple as it may be), the issues are; 1) IS there is a reduced (or increased) efficiency in our respiration dependent on our attitude (vertical or horizontal) in the water, 2) the actual mechanics of that change (if any), and 3) the degree of change (if any), which is probably the most important issue.

As LD pointed out, I have reduced our little 'er' discussion' in my own mind to looking at it with your mouth at water level with just your chest immersed. Any pressure differential would be substantively less at any other depth (this is the worst case scenario). At rest, I noticed little if any difference than sitting on the bank (can you tell, I have been actively trying to work this out???). This is not empirical, but qualitative in nature, mind you (subjective, rather than objective, if you will). In fact, I noticed that the breathing effort (once initiated) seemed to be easier ON my regulator than off. So already, I have introduced a variable that mitigates any findings, qualitative or quantitative.

As LD pointed out, it is indeed harder to catch your breath after you swim than after you run (or so it seems). The initial question that comes to mind is whether this is due to lung constriction from the pressure of the water, a reaction to inhaling some water (congestion), OR does the timing of our breathing (1-2-3-breathe or 1-breathe) during exercise really depress our oxygen saturation. Obviously, it might possibly be explained by a combination of all three! Still, it was the first observation that seemed to make any sense.

As for models/analogies, the vessel that is comprised of our chest cavity (lungs, muscle, and rib cage) is not statically determinate (NOT statistically, but statically). That is, it is not entirely rigid, neither is it entirely amorphic, so it is not possible to determine HOW it will react under various environments without actually measuring it’s deformation. I can think of several ways to measure it, but only two seem to make sense. These would be blood gas analysis, and volumetric efficiency with the former being the most accurate to ascertain respiratory efficiency. Unfortunately, this will not determine the mechanism of any change; it would only document a change and then quantify it. As a diver, this alone would suffice for me.

As for the contention that the horizontal position is better than the vertical/head up position, I would say if that were true, then please take it to it's logical conclusion. We could then deduce that a vertical/head down position would be even better yet for the same reasons given by Roakey and Uncle Pug. We should all then be doing our safety/deco stops on our heads... It is my personal belief however, that this whole theory evolved from someone (who knows who or where) trying to produce more reasons for a cave diver to practice "perfect trim", as if silt outs weren't reason enough! Prima fascia, it sounded reasonable, so it stuck in certain circles as undisputed fact. Still, we have not been given any objective measurements to prove it so.

Finally, I do not believe that the amount of difference would be enough to put anyone in danger. I believe the number given was 5%, and that for only the lower alveoli. If the average depth of all alveoli (between 6 and 18 inches) equated to a 1 foot increase of depth, this would only be an actual 3 % change of pressure at water level(1/33=0.0303). This would be reduced to a mere 2% change at a 15 foot safety stop(1/48=0.0208) (for simplicity’s sake, I just used 33 ft for the first atmosphere of pressure- just multiply by 100 to get the actual percentage. BTW, there -is- a more accurate way to calculate this, however there will be no difference in the final numbers). I contend that being right or wrong on this one issue would not pre-dispose anyone to DCI. There are far greater issues that will induce that, IF you dive within your tables. Of course, that does not take into account any effect the chest cavity would have on reducing these external pressures on the lungs (which was the crux of this debate in the first place). Somehow, I just identify with that smug DM…

 

[watergal]

Gosh, I just stepped away to open a few presents and sip a little eggnog and look what happened! And cool new smileys too!

Ok, I don't have time to sort through the whole thread and get to the office for 8am patients, so just a few points:

1) There is a pressure difference in various body compartments, not so much due to the water column in which we are diving, but dur to the closed circuit pressure columns in the body. The blood water column creates more pressure in the veins in the legs than in the scalp. Hence varicose veins, swollen feet at the end of the day hemorroids etc.

2)There is a pressure difference from top to bottom in the lungs when diving--again not due to the surrounding body of water, but due to the pressure of the gas in the lungs & trachea. Yes, this is a very small difference, but if the issue is it there, the answer is yes, when one is not actively moving the diaphragm.

3) It is harder to breathe when swimming laps with one's chest in the deep end due to the pressure of water on the chest wall. This is not an issue with Scuba as the regulator delivers air at the same pressure the chest wall is pushing against. While swimming you are breathing surface air at lesser pressure so more work for your chest. So, a true observation, but unrelated to the thread starters point.

4) It is not pressure itself which is a problem, but the pressure difference between that of the body and that of the environs. Aveoli would/do collapse with a large difference between the inspired air and the ambient pressure. Hence regulators that delever air at ambient pressure. For healthy people, the pressure of the water column per se does not impact the lungs BECAUSE we are breathing air at the same pressure, so there is no differential with proper scuba technique. So freedivers aveoli may collapse at greater depths, scuba divers do not any more than they would at the surface.

4) For someone interested in small pressure differences, I suppose one could argue that under the same theory it would be "harder" to expand the chest in an upright vertical position underwater than horizontal or upside down as the regulator would be shallower than one's chest. I have no idea if this is physiologically significant.

5) I have no idea if offgassing upside down and vertical, right side up and vertical or horizontal actually makes any difference.

6) I would THEORIZE --and this is only an educated guess, not a medical fact-- that horizontal would be somewhat more efficient than either vertical position due to the trachea and bronchi being horizontal and not creating a pressure column, but I do not actually know any more than any previous poster. I would actually surmise that there are so many other factors at work that whatever position is most comfortable for the diver would end up being best and that any position that compromises chest wall expansion (eg lying flat on the bottom with tanks on the back) would be more detrimental than any difference in gas exchange due to position. I have no idea if upsidedown vertical is better or worse than rightsideup vertical. And for the ideal diver with all other factors being ideal, I cannot shead any light on what position is best

I bet DoctorDeco knows!

HTH

watergal, MD

 

[Natasha]

I know what position is best for me

 

[The Chairman]

Like I have said before... You're my kinda gal!!! ROTFLX10

 

[roakey]

Pete,

To keep things short I'm not going to address all your points in one reply, but to hit on a few...

I've always noticed a greater work of breathing when at the surface in a vertical position, so I guess we'll just have to disagree on that point.

I don't understand the basing of a pressure percentage on 1 ATM, there's nothing that significant about 1ATM, if you took someone down to 33 feet (2 ATM) in a hyperbaric chamber they’ll notice no difference in WOB since there's no external pressure gradient (because they’re in a gas environment).

Earlier I alluded to a mechanical approach to the problem. Without going into it fully here, let's for the moment assume that a diver in a vertical position cannot breathe through a two-foot snorkel (if someone has the real number, please supply).

That puts the midpoint of the lungs at about 3 feet under the surface (assuming 1 foot from your mouth to the midpoint of your lungs), or only 1.5 PSI greater than the ambient pressure at the surface (that’s 9% according to your calculations based on 1 ATM).

Obviously that 1.5 PSI or 9% is pretty significant if you can’t breathe!

I know that 1.5 PSI isn’t much, but it’s enough to completely stop you from breathing. So the lungs and chest are pretty sensitive to very small pressure differentials.

That means that simply being in a vertical position in water, which is a .5 PSI difference between your mouth and your lungs, you’re a full 1/3 (33%) on your way to being completely unable to breathe. So, the question is, is this progression linear? At a .5 PSI delta is your WOB 33% greater? Is your lung’s tidal volume 33% less? I certainly feel that that’s the case. I do know that it’s not all or nothing. In other words you don’t breathe free and easy until you reach 1.5 PSI and suddenly you can’t breathe. The level of difficulty does increase progressively (as I found out when I was a kid and tried it with a piece of garden hose).

Roak

 

[watergal]

I ran part of this past a pulmonologist buddy today.

His thought is that upside down and vertical is worse than rightside up and vertical or worse than horizontal due to the limitations of diaphragmatic excursion when the abdominal contents (guts, stomach...) are sitting on top. Did I read that someone's son pointed out the importance of the diaphragm? An A+ to him!

Again, this has NOTHING to do with water column pressure gradient, but my final thought is that upside down and vertical is IN THEORY a less efficient gas exchange position for divers decompressing/saftey stopping on scuba. I still do not know of any data or studies to confirm it, and I do not know if any difference is significant enough to be worth worring about.

HTH

Watergal, MD

 

[The Chairman]

I will make sure my son gets his A+ when I take him diving this New Years Day...

Breathing comes mostly from the diaphragm, and I agree any difference in efficiency would be very minimal... 2% max (either way) at 15 ft!

A bouquet of :balloon: to you for your fact finding efforts...