Air consumption &/or lung volume

[avpro4]

Hey gang,

My wife finally convinced me I should see somebody about my snoring. Turns out I may have apnea. So in the process of getting tested, I went to a pulmonologist who stuck me in a little closet sized booth and with a fancy medical-grade clothespin on my nose had me breathe in and out both normally and as hard as possible thru a tube in my mouth to measure my resting and working lung volume. While waiting for the results, I mentioned my scuba habit to the technicians, and we discussed how knowing this might be useful in dive planning and gas management.

As it turned out one of the techs remembered a study from his college days that demonstrated a direct correlation between a patient's height and lung volume, and it's very easy to remember: Take the digits corresponding to your height in feet and inches, multiply times 10 and you will have your approximate lung volume in CC's.

Another tech questioned the simplicity of that concept and we decided to see how that formula worked in my case since the computer was just printing out the results of my test. I am 5'6" tall, and my measured average lung volume turned out to be 560 CC's! So according to this formula, a person who's 6'6" would have an average lung volume of 660 cc's.

So I would invite everyone to consider this idea in light of your own dive experience. (Any pulmonologists on the Forum?)

Since Scuba is a pretty relaxing activity (at least once you're under), wouldn't it make sense to time your breathing (say 20 breaths / minute) times your personal average lung volume, divided into the cubic volume of your full tank (converted to CC's), and divide that again by your max or current depth (in atmospheres) to determine in advance how many minutes of gas will be consumed during each phase of your dive?

According to metricconversions.com, 80 cu. ft. equals 2,265,347.736 cu.cm. (ml). So, I leave it to you all to do the arithmetic and offer your opinions as to whether you think this concept: A) Is true based on your personal height and experience beneath the waves, and B) Potentially useful for dive planning and gas management. Remember my test was conducted on dry land as you consider the veracity of the idea.

[ScubaGir1]

Well, lets see, I'm ~5'2" so my lung capacity would be about 520 CC's. And I breath about 9x a minute (on dry land), yes I know, I'm naturally a slow breather lol.

But, I think another thing that needs to be taken into account is if the person is really fit, or lazy. Someone who is really fit will have a more efficient breathing rate vs. a couch potato

Not sure if that was what you were getting at though LOL.

Strictly speaking on numbers though, the bigger the person, the less "efficient" they will be for breathing during scuba diving. With every breath, they take in more air, which means they require more air than a smaller person. Right? At least that's what makes sense in my mind...

My mom and sister are roughly the same height (I'm the shortest) and they have very different breathing rates. My sister will use up her air quite quickly compared to my mom and me.

[Charlotte Smith]

I understand everything you are talking about but when it comes down to it...I use a different amount everytime...it really depends on how excited I get about whats below and if I am just swimming around looking at things. I spearfish and a few big catfish and fighting them will wipe my air out pretty quick.

[mm_dm]

Man, all I ever do is read the magazines at the doctor's office...

[No Misses]

If there was no better way to judge your gas consumption, then maybe this would be useful. Keep in mind that you have to compensate for pressure at average depth. I use an Aeris Atmos AI Dive computer. It knows my starting pressure, average depth, and ending pressure. From there it is very easy to calculate SAC in cf per minute. This is much more helpful to know when dive planning. IMHO

[coralcrazed]

Originally Posted by No Misses

If there was no better way to judge your gas consumption, then maybe this would be useful. Keep in mind that you have to compensate for pressure at average depth. I use an Aeris Atmos AI Dive computer. It knows my starting pressure, average depth, and ending pressure. From there it is very easy to calculate SAC in cf per minute. This is much more helpful to know when dive planning. IMHO

great point... now are those snapers in your avatar?

[jo8243]

That just tells you your max lung volume. But it doesn't tell you how much air you consume per minute. That depends on lots of other factors. If this told you anything, all tall divers would be air hogs and all short divers would have gills.

[CompuDude]

It's probably true, but individual cardio-pulmonary efficiency has a lot more to do with your actual SAC than a mere measure of lung volume. Remember, you don't actually use all of the air you breathe in with each breath.

[scubajane]

I am 5 ft 5 and my husband is 6 ft 4 we dive together and we use almost identical amounts of air. when we first started diving i would have 1200 left when he had 500 then he learned how to breathe long and slow and improved his air consumption. we just dove for 90 min and took our tanks from 2800 to 500 psi. average depth was 30 ft

[Steve Scuba]

Interesting information. I still have the math to do, but I'll definitely have to put that to the test.

I wish I could remember what my lung volume was. Had to get tested for wildland fire-fighting, and that's one tough test. Blow as hard as you can as long as you can into this tube that seems to have no resistance. Talk about a quick path to fainting...