How do I improve my air consumption?

[diverjed]

knobber once bubbled...
Ok, I'm beyond pi$$ed now. I work out cardio weekly like a freak--45 minutes of stairclimbing, usually burning around 1000-1100 calories. Two weeks before my trip, I started swimming in the pool with just my fins, back and forth along the bottom, holding my breath.
During the trip, I was averaging 80 feet, starting with 3000 lbs or 3100 in my tank. However, although I "appeared" to be the most fit in my group, I was only getting 24-27 minutes of total dive time out of my tank, surfacing with 500 lbs of air.
Everyone else, guys included, was getting 35-40 minutes of dive time. I wasn't even near the yellow of nitrogen saturation on my computer, while everyone else was at or near yellow.
What the hell? I'm 6'1", 205 lbs in great shape. I was not nervous, felt great, and tried as much as I can to breath slower and deeper. hell, I even tried different breathing methods all to no avail. What's going on?

You're a bigger diver, and newer.

that'll do it everytime. I've been diving 10 yrs, I dive as much as possible in a given season, and I stay in shape. But I'm also 6'4" and 245 ibs. And while I'm much better than I used to be, I still qualify as an air 'sucker'.

So I finally broke down and got bigger tanks (120's). Gotta live with it and adjust I guess.

 

[klausbh]

SCUBAMedicBill once bubbled...

The idea of the large lung is not a matter of how much oxygen you bring in, it has more to do with phsiology of gas exchange.

Agreed.

Though you bring in more air and oxygen, this doesnot mean that you utilize all of the oxygen that is inhaled. You breathing in 21% oxygen into you lungs, and exhale 16%. Your body only uses about 5 -7% of the oxygen you inhale. Even though volume increases, the body still only uses the small percentage.

I agree with the point you are trying to make, but your argument is unclear. Using 5-7% of a large volume of O2 would suggest that big lungs are, in fact, a benefit. The reason they are not is that the urge to breathe is triggered by CO2 buildup, not O2 depletion, so you cannot make use of the extra O2. This is especially important when diving because of high partial pressures. ( Side note: wouldn't it be great to last 4 times as long on each breath at 100 ft? sigh... )

But because your volumes are larger, you run through the contents of that tank faster than someone with a smaller lung size. Thats just our make up.

This is where you lose me. Air consumption depends not only on lung volume, but also on breathing rate. As I mentioned above this is a function of the % of CO2 in your lungs. Thus, twice the lung volume can vent twice as much CO2 per breath. The large amount of air used per breath should be canceled out by the slower breathing rate.

That said, my original idea is still that bigger people (which need more O2 and produce more CO2) tend to have bigger lungs. It's the size of the person that matters, not the size of the lung.

Once again, my understanding of this might be completely wrong. Please correct me.

-Klaus

 

[reubencahn]

For two reasons, I think you really might want to look at your total weight. You mentioned orally inflating your bc so you could make a slow descent. When properly weighted, you should have no difficulty descending slowly with no air in your bc--at least until you are at 30 ft or so. You also mention carrying 16lbs total. I'm a somewhat similar build--6', 195 lbs.--and with a 3 mil suit and an AL80, I carry 6 lbs. You're probably in better shape than me, hence more dense muscle, higher specific gravity, so 16lbs seems like a lot of weight.

Second, relaxation is everything. When I first started diving, I used a lot of air making certain that I didn't miss one single thing. Consequently, I was shooting back and forth across the reef and the current and covering much more ground than those who hung up a little bit shallower and let the current take them. I've seen the same thing in my son who makes a beeline for anything that interests him. He's small enough that he can get away with it, but he uses more air than he needs to.

Last, take some time to notice how you breathe on land. There are natural gaps in your breathing. You breathe in, pause, breathe out, pause. You're breathing underwater should be natural. Sometimes, with our emphasis on breathing continuously while underwater, we breathe in a very unnatural manner.

But do try dropping weight and see what happens.

 

[knobber]

reubencahn once bubbled...
You mentioned orally inflating your bc so you could make a slow descent.

No, I orally inflated my BC so I could float over to the down line. I let all the air out and my descent was verrrrrrry slow. I orally inflated it so I wouldn't waste tank air to inflate it on the surface when I jumped in. I don't think my weights are the problem, since I had an earlier trip where I had 12 lbs in, and couldn't get down unless I pulled myself the whole way down. once on the bottom, I BARELY stayed touching the bottom, even with a fully emptied BC. That was in salt water with a 3mm, as was this trip.

 

[reubencahn]

OK, I misunderstood, but I still thinks it's worth looking at your weighting. And you may find that as time passes, you are able to drop weight. I don't really remember how much weight I carried when I began diving but I know it was more than I use today. Yet I never believed I was overweighted. Somehow, it just seems to work that way for most divers.

 

[Tim Ingersoll]

reubencahn once bubbled...
OK, I misunderstood, but I still thinks it's worth looking at your weighting. And you may find that as time passes, you are able to drop weight. I don't really remember how much weight I carried when I began diving but I know it was more than I use today. Yet I never believed I was overweighted. Somehow, it just seems to work that way for most divers.

Very good advice. I started with ten more pounds than I carry now and am diving with guys who sometimes dive without any weight at all (no wetsuit, warm water). I generally try at least one pound less a year. I truly appreciate dive ops that take an interest in weighting and encourage divers to shed excess pounds. Others seem to overlook obvious overweighting in order to get divers in and out of the water quicker.

The comment made earlier in the thread about watching your breathing on your descent is also very inciteful. That one took me about three years to figure out for myself.

 

[knobber]

thanks guys. when I can get back to salt water, i'll check out the weighting factor

 

[SCUBAMedicBill]

I'm sorry, my point may not have been clear. Basically the oxygen content of the air is less important than the lung capacity. My point is that no matter what the oxygen content is (don't confuse this point with the reasons for using nitrox), the body is only going to use a small amount of the inspired oxygen. But, the combination of the lung total capacity (the amount of air that fills the lungs) and rate of respiration per minute is the major determining factor in how much air we consume, regardless of the amount of oxygen our body actually utilizes. A person with a ltotal capacity of 6 liters who's rate is 12/min has a minute volume of 72 liters/min. A person who has a 5 liter total capacity who is breathing at 12/min has a minute volume of 60 liters/min. By looking at this, we can see that the 6 liter person is going to use their air at a faster rate then the 5 liter person. (This is why using nitrox will not necessarily lengthen our down time, just our nitrogen absorption.) These are physical and physiological triats we can't change, but we can alter how we breath, how we swim, our weght, etc., that might help in our air consumption.

What I was referring to you was that large lungs are not bad, nor are small lungs, because the oxygen transfer will be the same, you'll use about 5% of the inhaled oxygen. We are designed to take in a full lung of air and utilize it as needed. The problem we have a depth, not including the extra complicating factor of Boyle's Law, is that we have a limited amount of air, along with a set amount of lung total volume. The bigger the total volume, the faster we use the limited air, the shorter our stay. By taking shallow breaths, we don't really solve anything because chances are that we will not satisfy the needs of the body because we decrease that amount of good air that we bring in. Example: if your normal total volume is 5 liters, and you can effectively exhale all of the good air out of you lungs (which isn't easy), and completely replace it with fresh air, you will only actually be bringing in 4.85 liters or good air into the lungs. This is because about 150 cc of that bad air was stuck in whats called the dead air space (Bronchials, brochi, trachea phaynx, mouth). That a 3% reduction in good air. If we shallow breath only 3 liters, which you couldn't do consistantly, minus the dead air, you bring in 2.85 liters. That 150 cc is now 5% reduction of inspired air and over a 50% reduction in what the body is used to. This will undoubtable result in either a forced increase in respiration, or a very uncomfortable dive which probably gives the person pangs of air starvation.

I hope I'm explaining it in a clearer fashion and have ended any confusion.

Bill

 

[CBulla]

knobber once bubbled...
Ok, I'm beyond pi$$ed now. I work out cardio weekly like a freak--45 minutes of stairclimbing, usually burning around 1000-1100 calories. Two weeks before my trip, I started swimming in the pool with just my fins, back and forth along the bottom, holding my breath.
During the trip, I was averaging 80 feet, starting with 3000 lbs or 3100 in my tank. However, although I "appeared" to be the most fit in my group, I was only getting 24-27 minutes of total dive time out of my tank, surfacing with 500 lbs of air.
Everyone else, guys included, was getting 35-40 minutes of dive time. I wasn't even near the yellow of nitrogen saturation on my computer, while everyone else was at or near yellow.
What the hell? I'm 6'1", 205 lbs in great shape. I was not nervous, felt great, and tried as much as I can to breath slower and deeper. hell, I even tried different breathing methods all to no avail. What's going on?

Come to SWFL.. we can dive together maybe figure this out. I've helped my wife in getting her SAC lowered to .54, mine is even lower at .42 on my last dive. Some things I noticed with her were how she kicked, where her arms were positioned, and gear drag. Once we got those little details beaned out, her SAC rate went down by about 40%. I took notes and did the same evaluation on myself.

One side note, I notice my SAC rate will go up or down depending on which fins I use due to the amount of exertion needed to create the desired result.

 

[fgray1]

.81 Not real bad but not real good. I'm 5'9" and weigh 200 lbs and started with a SAC rate of .67 now I'm down to .40 depending on the dive.
Mine goes up alot when I cave dive because of the stress. Mainly due to my heart racing 90 miles an hour in the begining of the dive. but it improves on the second dive after I've calmed down.
It's good to keep track of your SAC on each dive that way you will know if your breathing is improved. I have a dive program that includes the SAC calculator. If you want it I will send it to you. It's a small file I can e-mail it.
Fred