It seems to me that someone who uses more air, has more nitrogen in their bodies given the same dive time. I would think this is a rather significant variable but I havent found anything on the topic. I started thinking about this as I have been trying to decide which computer to get with the reasoning that if I suck a lot of air, maybe I should go with a Suunto as it is conservative and may offset the fact that I am taking in a lot of nitrogen. It appears to be such a large potential variable I'm surprised computers (or tables for that matter) dont have a user changeable parameter categorizing how efficient one is with their air. Or does this not make much of a difference some how? I guess along the same lines bigger people would be able to handle more nitrogen. As I try to get my arms around this I guess I am wondering why there arent considerations for body weight and air consumption in the calculations of how long one might need to de-gas whether it be at 15 feet or on the boat. Thanks in advance for your thoughts.
Does an air hog have more of a chance of getting the bends?
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JeffG
Contributor
Thanks for the quick response. I still dont quite understand. The air contains nitrogen and if you breathe more in and it takes longer to leave your body, how could you not have more? The nitrogen comes into your body along with the oxygen, you utilize the oxygen but the nitrogen is not easily expelled. You are not expelling the nitrogen with your exhale, not much anyway. If one person sucks in 1/2 their tank and another uses it all, given the fact that the nitrogen takes a relatively long time to leave your body, how could the person that used all the air in their tank not have more nitrogen?
unless you are saying that just breathing it in doesnt necessarily mean it's absorbed into the body. Or the amount the body absorbs for some reason is not dependent on how much you breathe in but just on how deep you are (pressure) and time. I get the pressure and time I guess I just would think that the amount of nitrogen (air) breathed in should have some effect as well.
I'm thinking that someone who breathes in a lot of air is also breathing out a lot of air.
I don't understand the physiology myself, but I imagine if you have a big plastic bag with a pinhole in it, water drips out at roughly the same rate whether you pour water in and out using a bucket or a teacup?
I don't understand the physiology myself, but I imagine if you have a big plastic bag with a pinhole in it, water drips out at roughly the same rate whether you pour water in and out using a bucket or a teacup?
JeffG
Contributor
Yes.
Nope. Your lungs just try to balance the "concentration" of gasses between your bloodstream and the gas you just inhaled.
Increased pressure (ie increased depth) increases the concentration of the gases of the inhaled gas.
This creates a higher concentration in the lungs with a lower concentration in the blood.
Therefore your body absorbs some gas into the bloodstream which is then transported to the other areas of the body.
You are almost there with understanding how it works. The air you exhale is very close in composition to the air you inhale. The most dramatic change is between the percentage of CO2 in (.04%) versus (5%)out. JeffG is right in that the amount of gas that transfers into tissue is related to the partial pressure but it is more accurate to state that it is the difference between the partial pressure of the gas breathed and the partial pressure in the tissue that determines which way the gas transfer moves. ie. if the partial pressure of N2 in the lungs is 1 atmosphere and in the blood it happens to be say .90 atmospheres the gas will transfer to the blood until it is saturated. When that happens depends on time and pressure. That is where the term "saturation diving" comes from. These divers spend enough time at depth that their blood and tissues are saturated with nitrogen. In that case they exhale the same amount of nitrogen as they breathe in. But there is always a difference in the partial pressures in the amount of O2 in the inhaled air and the partial pressure of the O2 in the blood because the venous blood has less O2 due to the absorbtion in the tissue where it came from (same partial pressure difference process there too). The same idea goes for the CO2. Partial pressure in the tissue is higher than the blood, therefore the tranfer is to the blood. In the lungs that holds true again, the CO2 transfers to the exhaled air.
So you can breathe to your hearts content since it really depends on time, depth and partial pressures. The air you breathe out is not that different from the air that went in.
Ahh,,,I see JeffG was typing at the same time as I was. He said the same thing as I did but more succinctly. Cheers,
Actually, being an air hog will probably result in a lesser chance of being bent, at least compared to someone who breathes like a girl, since you can't stay down as long. It's nature's way of helping to keep you safe until you get a few dives under your belt.
HBO MD
Contributor
The guys are right : diffusion of gas follows gradients, whether it be from tissue to blood or blood to alveoli.
The issue of being an "air hog" and DCS risk, may however be linked to overall cardio-respiratory fitness. That is to say, a less fit person will consume air relatively faster as they reach their anerobic threshold sooner for the same level of exertion. In that case, the risk of DCS may be relatively increased compared to someone with greater "physiological reserve", fitness, under the same level of workload.
Of the computers available, the Uwatec Galileo Sol takes into account heart rate and respiratory rate to compute dive times.
The issue of being an "air hog" and DCS risk, may however be linked to overall cardio-respiratory fitness. That is to say, a less fit person will consume air relatively faster as they reach their anerobic threshold sooner for the same level of exertion. In that case, the risk of DCS may be relatively increased compared to someone with greater "physiological reserve", fitness, under the same level of workload.
Of the computers available, the Uwatec Galileo Sol takes into account heart rate and respiratory rate to compute dive times.
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