steve75
Barracuda
Incompetents invariably make trouble for people other than themselves
Posts: 89
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Post by steve75 on Nov 11, 2004 9:38:50 GMT -5
Maybe somebody can help me here?We just have a discussion last evening.I think,that you have less nitrogen intake when you use less air.If I´m right,that must say then that I can stay longer on my dive then my friend, who uses more air.This is theori only.I´m right there or no?
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Post by tekmac on Nov 11, 2004 9:55:50 GMT -5
Good question!Theoretically i think you are right there,but how you want to calculate it?I have to read up on that a little bit more.
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Post by scubadave on Nov 11, 2004 11:16:45 GMT -5
Theoretically, yes. If all things between you are the same, your physiology, your personal Nitrogen absorption rate, and so on, if you breathe less than him, then you take in less Nitrogen, and so would have more time before possible DCS. The less Nitogen you take in, the less Nitrogen you'd absorb. But in reality you follow the tables or your computer, cuz there isn't anything yet that measures your personal nitrogen load. Leading a lot of beginner divers, some out of shape, overweight divers that really breathed down their air quickly, I would have them do extra long safety stops just to give them more time to offgas.
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Post by LSDeep on Nov 11, 2004 11:36:18 GMT -5
some gas - integrated computers may take that aspect in consideration. got to find about that a little more in detail. otherwise i have to agree with the others, yes you absorb less nitrogen.
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Gregs
Puffer
Have Gear , Will Travel.
Posts: 47
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Post by Gregs on Nov 17, 2004 18:22:59 GMT -5
Yes, that's correct. However the difference is relatively small, generally. It all comes down to partial pressures, less volume is naturally going to give less nitrogene to be absorbed because at the same partial pressure the volume will be less. As for the Maths behind it, I'm tired and sick so I will figure it out later!! Sorry.
Gregs.
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knotical
Puffer
To err is inevitable.
Posts: 36
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Post by knotical on Nov 21, 2004 15:16:11 GMT -5
Shame on me, the brand new member, for seeming to (partly) disagree, but I’m confused. I don’t see how using less air would reduce the absorption of N2. Here’s my reasoning: I agree that absorption will be based on the partial pressure of nitrogen. But whether you breathe slowly (using less air), or not, the partial pressure of nitrogen in your lungs should be related solely to the percentage of nitrogen in the gas you are breathing, and the ambient pressure. The only way I see that partial pressure might change is if the percent of gas in your lungs changes. How could this happen? Perhaps as you metabolize O2 and replace it with CO2 there might be a very small nitrogen percentage change, but only related to the relative difference in the size of the O2 or CO2 molecules. Even if this were so, I think the difference would be so tiny that I’d be surprised if it could be measured. The only other way I see a possible change in N2 absorption is if the user of less air keeps his lungs less inflated than other divers, thus exposing less alveoli surface area for the transfer of gases. However, I think the pressure gradient across the cell membrane would at least partly overcome this difference, if there is any. I’d sure like to see if anyone can find anything in the literature on this one.
This leads me to two other thoughts that might be more appropriate for a different string, but here goes anyway:
1. Some time back, I theorized that when those of us who live at altitude (Colorado), and adapt our metabolism to reduced O2, travel to sea level and dive, we would use less air because our bodies are more efficient. I was shot down by someone more versed in physiology than I who pointed out that our breathing reflex is triggered by CO2, which would not be affected.
2. The reduced lung volume possibility ties in with a technique I mention to students to make their air last longer. Since breathing is triggered by CO2, if we do a better job of flushing our lungs of CO2, our breathing reflex will be less active. Exhaling more fully will accomplish just that. When they voice concern about a regulator failing just as they’ve exhaled, I have them practice exhaling in the classroom without inhaling. They’re often surprised how long they can go without inhaling.
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Post by scubadave on Nov 21, 2004 21:51:27 GMT -5
In reply to Knotical, we aren't saying that breathing less is going to somehow change the absorption rate of nitrogen in a person's body. The theory is that the longer you stay at depth, the more air you breathe, and the more saturated your body becomes with nitrogen. If a person breathes less than another person, then they are taking in less nitrogen, and so slowing the body's rate of nitrogen saturation. In a single breath of air, both divers will have basically the same N2 absorption rate, but the diver that breathes faster will have more of those breaths and so will increase the speed in which his body becomes saturated with N2. The way nitrox extends your bottom time is by reducing the partial pressure of N2, effectively reducing the amount of N2, and so slowing the body's saturation, but thoretically, you could also reduce your saturation by reducing the amount of N2 intake through slowing your breathing.
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knotical
Puffer
To err is inevitable.
Posts: 36
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Post by knotical on Nov 22, 2004 12:28:19 GMT -5
Thanks, scubadave. But I guess I’m still from Missouri. I just found a discussion at: www.scuba-doc.com/faqphys.htmlmislabeled (I think) as “SAC (Surface Air Consumption) Nitrogen consumed, nitrogen absorbed“. It responds to the question: ”If two divers had exactly the same dive profile (same depth and length of time underwater) but one consumed more air than the other then shouldn't the one with more air consumed have also more nitrogen in his body?”<br>The response says, among other things “As the diver descends, blood is saturated rapidly with nitrogen (independent of the breathing rate)”<br>It also refers to books by Bove and by Edmonds, neither of which I own. After reading your response, and scuba-doc’s article, I still suspect the amount or rate of air I breathe won’t affect my nitrogen absorption because it doesn’t affect the (high) percent of nitrogen in my lungs. Nitrogen going out of the cylinder does not equate to nitrogen going into my body tissues (it equates to nitrogen going into my lungs temporarily until I exhale all that nitrogen into the water). For now, I’ll remain skeptical that using more (or less) air will affect nitrogen absorption, at least until I understand some mechanism that explains otherwise. At the very most, I think any difference would be extremely insignificant. - But then I've been wrong before.
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Post by scubadaddy on Nov 23, 2004 5:40:35 GMT -5
not shure if i am smart enough to answer this question, but if i try to reduce it to be simple. 2 divers going scuba. Lets say sitting on the ground on 20 m. The one is breating fast, the other taking a deep breath and slowly exhaling for more than a minute. after about 25 minutes, he lets say only took 20 breaths, the other one hundreds. Both go quik to the survace. I guess both have the same risk of deco, and the same amount of nitrogen, asumed they are the same shape. Isn´t absorbtion of nitrogen the matter of time and pressure? I think it doesn´t matter how much you breathe, it might effect the use of oxigen, but not nitrogen. .... hmmm
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Post by scubadave on Nov 24, 2004 2:38:49 GMT -5
Thanks Knotical, I read the link you provided and was surprised as it seemed to say that breathing rate doesn't make a difference, but I am now more confused. I agree with scubadaddy, that both divers, if they were to shoot up to the surface, have just as good a chance of getting DCS. The article says that the blood and tissues are saturated with nitrogen independent of the breathing rate. What I'm confused about is where this nitrogen comes from, if not from the breathing. If a person is breathing faster aren't they taking in more nitrogen, and so increasing the rate at which their body become saturated? Absorption is dependent on depth and time, we all know that, but what does time have to do with it if it isn't that with more time you're taking in more breaths and so more nitrogen. I thought that was the whole thing behind nitrox, less nitrogen you breathe in means more time before you are saturated, so in the same sense, if you breathe less, aren't you getting less nitrogen? I guess I'm looking at it too simply if I am wrong, which maybe I am, but lets say we compare it to something else: alcohol. Two guys each have 5 beers to drink, guy 1 drinks them all in 20 minutes, and so is obviously drunk, guy 2 drinks one beer an hour for 5 hours and so never becomes drunk. Here time seems to be the determining factor, but it is also the amount, as were guy 2 to drink 5 beers in 20 minutes repeatedly for 5 hours, he would be very drunk, and constantly at the urinal (or he'd be dead from alcohol poisoning). Basically, if the amount of nitrogen you inhale in one breath at depth is enough to completely saturate you, then I can see I'm totally wrong, but if it takes more than one breath to saturate you, then I think I'm kind of right, though I think the difference between the divers would be so little for it to really matter.
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Post by scubadaddy on Nov 24, 2004 5:21:55 GMT -5
i guess the slightly difference between alcohol and nitrogen is, that alcohol stays, nitrogen you exhale. of course as more you breath as more nitrogen you get, but you also exhale more - it doesn´t mean you absorb more nitrogen ... ...looks like a endless story ... isn´t there a real specialist here
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knotical
Puffer
To err is inevitable.
Posts: 36
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Post by knotical on Nov 24, 2004 7:22:30 GMT -5
I love your alcohol analogy scubadave. I chose to think of it in terms of a concept I was taught in a biology course more years ago than I care to admit. The idea was that things aren't really in our body until they get absorbed through cell walls. Thus the stuff in our mouth, stomach, and so on, isn't really in us; it's just in a sort of long, twisted donut hole that runs through. The alcohol doesn't affect us until it is absorbed through either the stomach or intestine walls (I forget which, maybe both). I guess that's why bulemics can keep the weight off after binge eating (they shove the food back out the way it came in). Sort of similarly, the gas in our lungs isn't in our bodies, it's in the pouch that holds air in our chests. We always have some in there, but most of it comes right back out. The gas that is in our lungs when breathing air is constantly about 79 percent nitrogen, but when breathing nitrox 32 is constantly about 68 percent Nitrogen. That is my understanding of how nitrox works. We simply have less nitrogen to absorb on the "outside" of the cell wall. Whether we are a fast or slow breather, we are almost constantly flushing our baggie of a lung with fresh gas from the cylinder on our back. Kind of like a constant breeze of slightly varying speed. Don't know if this helps anyone else, but I enjoyed it.
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knotical
Puffer
To err is inevitable.
Posts: 36
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Post by knotical on Dec 3, 2004 15:45:33 GMT -5
I found something more in the book “Dr. Sawatzky’s Diving Medicine Notes”, a collection of his articles from Diver Magazine (Canada). On page 44 Dr. Sawatzky agrees with scuba-doc that as the diver descends blood is saturated rapidly with nitrogen. He also says the amount of air used doesn’t affect nitrogen absorption. But he says that after depth and time, the next thing affecting nitrogen absorption is heart rate, because an increased heart rate pushes more blood through the lungs to get saturated. Since people who use more air usually also have a higher heart rate (out of shape, or nervous) they will absorb more nitrogen and therefore be at greater risk of DCS. That same diver is probably also less likely to get in serious DCS trouble because he will have to surface earlier than a more efficient diver would (me talking now, not Sawatzky). In another situation, two divers using the same amount of air might absorb different amounts of nitrogen if one has a higher heart rate, but a more efficient breathing pattern. I now see that I was wrong and Steve75, tekmac, scubadave, Isdeep and Gregs are right, for an indirect reason. The diver who sucks more air will usually absorb more nitrogen because his heart rate is usually higher! < - always learning >
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Post by diverjohn on Mar 15, 2005 21:40:41 GMT -5
Lots of good arguments here. The most important factor to consider is the pressure gradient between the nitrogen in your lungs and the nitrogen in your blood. The only thing that really makes a difference here is Nitrox, which reduces the partial pressure of N2 in the lungs, and therefore has less pressure to "push" it into the blood and tissues. I suppose heart rate or blood flow has some effect, but it is likely a minor one here.
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Post by diverjohn on Mar 16, 2005 11:51:09 GMT -5
Me again ... thought about the N2 absorption thing while running this morning and came up with a new insight. On one breath at depth, the N2 in the lung will start entering the blood and tissue. The rate decreases as the nitrogen leaves the lung airspace for the blood. Thus, a fresh volume of air will have a higher rate of diffusion than an aged volume. So, it seems that a fast-breathing diver will maintain a higher pp of N2 than a slow-breathing diver. Restated - A fresh breath of air has 78% nitrogen. As the body absorbs some of the N2, the percentage drops. As the %N2 in the lungs drops, the pressure gradient lessens so the rate of nitrogen absorbtion is less. So, if you desire to maintain a high rate of nitrogen absorbtion, then breath more deeply and quickly to keep the nitrogen % high in the lungs. Time is the enemy of the gradient! Now, whether or not this is a significant difference is another matter. If I have any more revelations I will certainly post it. ;D
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Post by BubbleGuy on Mar 25, 2005 22:34:09 GMT -5
I think that everyone here is talking about the same thing........ consuming less air will accumulte less nitrogen in their system but it's an extremely insignificant amount less....rember from your basic DM physiology that it takes approximately 12 hours for your body to fully re-saturate (is that a word?) with nitrogen at depth so the couple hundred psi from a scuba tank that we're all talking about is relatively small.
Safe Diving!
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Post by Argo on Apr 21, 2005 8:29:07 GMT -5
OK then I guess guys it's time I put my two cents in............ Firstly, I think you are all forgetting one thing; Fat tissue absorbs and holds Nitrogen fast and longer. I'll explain: Two divers go diving same dive profile, But one of them is thin and stringy weighing in at 80kgs (160lbs) and the other is 150Kg (300lbs) the rest of the factors being exactly identical. The larger diver will absorb the Nitrogen a lot faster than the other diver. Also the off gassing times will be different. The larger diver will need longer. Even if you had two divers of equal weight and size there would still be differences. Theoreticaly the person using less air would have less Nitrogen in their tissues BUT this is only theory as various physiological factors can never be the same e.g. lung volume, fitness etc, etc, I will mention one thing to perhaps make you laugh; I once had a petite swiss girl instructor working for me, we used to dive a lot together, same profile and she would always come out of the water with a lot more Air in her tank than me. I was getting peeded off because of her ribbing me about using more air than her. So, trying to be smart I told her that it was only normal for a woman to use less air than a man as its a medicaly proven fact that a females brain is smaller than a males. Therefore she needed less oxygen........... Needless to say this didn't stop her jokes, in fact it made things worse..............But thats another story.....
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Post by tompouce on Apr 21, 2005 18:50:13 GMT -5
Hi All,
First Post here so be nice to me ;D
My feeling is that whether you breath more or less gas doesn't change the amount of Nitrogen you absorb. If you breath more, you are just going to waste more gas. The gas you reject will be richer in O2 and N2.
A diver that breath less gas "could" in my opinion actually absorb more, since he "might" be more efficient in on gassing. At the end of the day I would think that the tissue saturation in nitrogen only depends on depth and time at this depth.
My 2 cts.
Tompouce
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cooldiver
Goby
Do not ask the question if you are not ready for the answer
Posts: 12
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Post by cooldiver on May 3, 2005 1:37:05 GMT -5
Hi everyone. Just a quick note. The way Nitrogen get's absorbed through the membranes, is by Osmotic pressure, so according to the different concentrations of a substance between the two sides of the membrane, the system will try to equilize the levels by letting the substance flow from the Highest concentration to the lowest untill equilibrium is achieved.
Different Concentrations of substance lead to different Pressure, so the gradient might be higher or smaller according to the % of substance on each side of the membrane. Considering that we are breating air with a constant % of N2, regardless of the fact that this air might be fresh or "used" , we should not be affecting the amount of N2 absorbed with our breathing rate.
Also the amount of gas exchanged is not related to the surface of gas exchange, because the whole blood vessels are working in a network, so the pressure fo the 2 substances is the same at any given time in any point of the system ( in the arteries the PPN2 is the same regardless of which part of the arteries you will consider ) Therefore deeper or shallower breath do not affect the gas exchange
So the only way to put more N2 in the system is to increase the difference in PPN2 between the lungs and the blood, as someone pointed out, you can do that by either increasing the % of N2 in the air you breath, or by letting the blood flow faster, allowing the % of N2 in the blood to be taken away faster requiring a bit more of N2 to go through in the unit of time. Considering that heart rates can differ just a mimimum without entering in the pathological, I think the diffenrece can be considered minimal.
I hope it makes sense.
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Post by andrewjubber on Jul 10, 2005 9:07:43 GMT -5
I have a question unrelated to the topic but still on nitrogen absorption. Why on the PADI tables does it recommend you add 4m when calculating dives in cold water? I am against the cold more then I'm against mugabe so haven't dived in anything less then 23oc. I cannot see how cold water can directly increase your absorption rate. Does it affect your breathing, or am i wrong and it affects your body tissues ability to absorb nitrogen? Does it have to do with strain? On the above topic. I think if all the variables are the same except breathing rate then yes you will absorb more nitrogen if you breath more, and vise versa.
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