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avpro4
08-29-2007, 03:17
Hey gang, :CI06R376:

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. :smiley23: Remember my test was conducted on dry land as you consider the veracity of the idea.

ScubaGir1
08-29-2007, 03:36
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 :smiley36:

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... :smilie39:

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
08-29-2007, 07:44
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
08-29-2007, 08:00
Man, all I ever do is read the magazines at the doctor's office...

No Misses
08-29-2007, 08:39
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
09-13-2007, 14:16
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
09-18-2007, 08:41
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
09-18-2007, 16:31
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
10-03-2007, 20:11
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
10-03-2007, 21:01
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...

fire diver
10-03-2007, 21:50
The onyl way to tell what your respitory minute volume (also called surface air consumption rate) is to dive and take real world measurements. And you have to do it almost every dive becuase the number is never static. After a season you will see a steady range of numbers you fall under with occasional highs and lows outside the norm.
My normal diving usually is somewhere around .35 cubic feet SAC. Diving with doubles raises this. My highest and lowest rates recorded were within hours of each other. My highest was on a crappy, zero vis night dive (.49) my lowest was the next morning with a .23

So go dive, record your numbers, and start computing your SAC to where your range is.

FD

ohiofireman
10-04-2007, 16:54
I just finished my open water course and I have been told I am an air hog. I start my advanced course tomorrow and hope I can learn to slow the air consumption down a bit. My instructor told me that as I dive more it will go down. Any thoughts?

CompuDude
10-04-2007, 17:42
I just finished my open water course and I have been told I am an air hog. I start my advanced course tomorrow and hope I can learn to slow the air consumption down a bit. My instructor told me that as I dive more it will go down. Any thoughts?

There are some little things you can do, but in all honesty, what your instructor said is correct. As diving becomes less thrilling and new, you'll be more relaxed and comfortable in the water. That will cause your breathing rate to go down all on it's own. :)

The list was far from perfect, but IIRC a couple of months ago, Scuba Diving magazine had an article on things you can do to get better air consumption that had a few good ideas. If I have time I'll try to ferret out which month's issue it was in.

Edit: Found it: http://www.scubadiving.com/training/basicskills/18_ways_to_use_less_air

ohiofireman
10-08-2007, 18:33
I just finished my open water course and I have been told I am an air hog. I start my advanced course tomorrow and hope I can learn to slow the air consumption down a bit. My instructor told me that as I dive more it will go down. Any thoughts?

There are some little things you can do, but in all honesty, what your instructor said is correct. As diving becomes less thrilling and new, you'll be more relaxed and comfortable in the water. That will cause your breathing rate to go down all on it's own. :)

The list was far from perfect, but IIRC a couple of months ago, Scuba Diving magazine had an article on things you can do to get better air consumption that had a few good ideas. If I have time I'll try to ferret out which month's issue it was in.

Edit: Found it: http://www.scubadiving.com/training/basicskills/18_ways_to_use_less_air

Hey thanks for the tip. I have 3 dives tomorrow and hope to at least make it down to the wreck before I run out of gas on the first dive.

papawhisky
10-09-2007, 20:29
Air consumption is interesting. Especially if I could learn to use less of the stuff. I am 6 ft. I do 30 minutes of aerobic work 3x per week, and play tennis 3x per week. My resting heart rate is 55 bpm. I just measured my breathing--13 breaths per minute. I am very calm and relaxed when I dive, but often find that I use air faster than my girlfriend, who is far less active. I want to come up with the air consumption equivalent to 7 Minute Abs :-)

bperrybap
10-10-2007, 00:47
I think the concept of the calculations in the OP is correct.
It is the very same calculation as using a SAC rate. It just
comes up with the same numbers under different test
conditions. (Breaths/min * breath size at surface is
a SAC rate)
The main problem is that the numbers used
(lung volume and breath rate) are for sitting in a quiet
room being very still.
The breath rate and air usage will tend to be lower in
these conditions than on a real dive. This would cause
the air time remaining calculation to over estimate the
time because a diver will breath harder while diving
than while sitting in a quiet room.

As far as estimating the lung volume, I don't think
this works at all when the person is 10 or 11 inches into
the foot. For example for a 5 ft 6 inch person the
volume would be 560cc and for a 5 ft 10 inch person
the volume would be 5110cc or about 5 liters!
Obviously not correct.

For me personally, I had these measurements taken
at Cooper Clinic here in Dallas.
I'm 5ft 11 and fairly thin at around 155 lbs.
My Full lung capacity was just under 2 liters.
During the breathing/metabolic test,
my normal breath size was 944cc or just under 1 liter.
And my breath rate was 6.0 breaths/min.
(Yes, I was very relaxed during the test)

So from the metabolic test I consume 944 cc six times
per minute or 6 * 944cc or 5664cc or 5.664 liters/min.

That means that during that test I had a SAC
rate of 5.664 liters/min or converting that to Imperial
0.199314 CuFt/min

However, I know from real world measurements that
my current SAC rate from diving tends to be
around 0.43 CuFt/min (12.1762 L/min) for a relaxing non
stressful dives.
My lowest SAC ever has been 0.35 CuFt/min or 9.911 Liters/min

So what this indicates at least for me is that when I'm
sitting in a quiet room with my eyes closed, relaxed and
in a zen-like state, breathing into a metabolic machine,
I use less than half the air per minute that I use on a typical relaxing dive.

--- bill

Aussie
10-10-2007, 04:55
I think more people should just go diving and not really bother in worrying about air consumption. Especially those that are only recently certified. Everyone is different and there is always exceptions to to rule.

I have seen recently certified divers that use little air and I have seen experienced divers with years of diving experience suck a tank dry. Seen ultra fit people last 20 minutes or less and huge over weight people last over 100minutes.

Sort out your proper weight and streamline yourself as much as you can. Wear proper thermal protection for the diving you do and most important, Relax and enjoy yourself.

You will soon be adding the minutes to your bottom time.

Aussie

mm2002
10-13-2007, 09:49
This is something I've been very curious about. What about lung efficiency? I quit smoking a year ago, but prior to that I was a two+ pack a dayer for 28 years. I often get the feeling that I'm not getting enough oxygen while diving, and in turn I breath more rapidly. I go through air almost twice as fast as my wife, who has never smoked. I haven't talked with a doctor about it, but my theory is that I must have at least some partial damage of the aveole (sp?), which makes my lungs less efficient at absorbing oxygen. I've been working very hard at getting my air consumption down, and it's a bit better, but still nowhere near what I think it should be. Or could this all be in my head??

Aussie
10-13-2007, 10:06
Most of my Instructor friends in Thailand are heavy smokers and they use little air.

mm2002, your profile says you only done 0-24 dives........most newbys use alot of air. Compare your air consumption now and then when you do say 100 dives. I believe that there would be a great difference.

Aussie

mm2002
10-13-2007, 11:03
Most of my Instructor friends in Thailand are heavy smokers and they use little air.

mm2002, your profile says you only done 0-24 dives........most newbys use alot of air. Compare your air consumption now and then when you do say 100 dives. I believe that there would be a great difference.

Aussie

Yeah, I'm sure you're right, and I will work on it as I get to dive more. I was just wondering about the lung "efficiency" thing. I've heard that lungs don't heal. Interesting about the Thai divers, that gives me new hope!!!

Aussie
10-13-2007, 11:22
Most of my Instructor friends in Thailand are heavy smokers and they use little air.

mm2002, your profile says you only done 0-24 dives........most newbys use alot of air. Compare your air consumption now and then when you do say 100 dives. I believe that there would be a great difference.

Aussie

Yeah, I'm sure you're right, and I will work on it as I get to dive more. I was just wondering about the lung "efficiency" thing. I've heard that lungs don't heal. Interesting about the Thai divers, that gives me new hope!!!

bperrybap
10-13-2007, 12:15
This is something I've been very curious about. What about lung efficiency? I quit smoking a year ago, but prior to that I was a two+ pack a dayer for 28 years. I often get the feeling that I'm not getting enough oxygen while diving, and in turn I breath more rapidly. I go through air almost twice as fast as my wife, who has never smoked. I haven't talked with a doctor about it, but my theory is that I must have at least some partial damage of the aveole (sp?), which makes my lungs less efficient at absorbing oxygen. I've been working very hard at getting my air consumption down, and it's a bit better, but still nowhere near what I think it should be. Or could this all be in my head??

Women just tend to use less air. They tend to be smaller
with smaller lungs and tend to have much less muscle
mass which means they just need less air.
My wife is also an ex-smoker. She smoked for about
as long as you as well. She quit 7 years ago.
When we started diving about 2 years ago, I used
just about twice the air as her. On a few dives she
came up with me after 40-45 minutes on an AL80
and still had over 1500 PSI left!

After about 80 dives or so we were much closer.
Now She still normally uses less air than me on most dives
but not by much and on some dives (like night dives)
I use less.

I found the biggest thing that helps reduce my air
usage is comfort. That and getting my weighting and trim set. If my weighting and trim is off, my air usage goes
up. It amazing how much having proper trim helps.

--- bill

mm2002
10-13-2007, 18:30
Thanks so much for the input folks!

fyrediver
10-24-2007, 22:51
Uh, explain his one. I'm robust, smoke moderatly, and excersise 3-5 time a week, on an eleptical machine. Skinny, young non-smokers in my group, hit the half tank mark, and I usually walk out of the water with about 1000psi. Left. I think I relax, and they are in an amusement park. I also am sure if I DIDN'T smoke, I'd do better. I will quit, after this next pack:)

Krakenn
10-24-2007, 23:35
Im old (Not quite verc vintage though) smoke, dont exercise and have the same problem, I even ended up selling one of my 125s to a mate and getting a 100 to allow my buddy to have a chance and give me some more time under.

I think it comes from baby breathing, that is that a baby breathes deep and uses all the lung capacity compared to adults who reflex learn to take shorter breathes more often. Try it.

Kraks