Calculation estimation of Residual Volume

[baiyoke]

Hi.

I just fooled around with some graphs doing some exhale depth estimation.

Then it hit me: If I know at what depth I hit my Residual Volume approximately, and I know my Vital Capacity, and how much I pack, then I can do an estimate of my Residual Volume...

VC is 5 L, pack 1 L, app. depth hitting RV 38 m after pack.

I made a depth volume graph function like this: 1/(1+(0,1*X)

Then I took (5+1) * 1/(1+(0,1*X) wich shows my lungvolume at different depths, minus the residual volume. I then added numbers between 1 and 2 (litres) to estimate my total lung capacity (5+1+RV between 1 and 2) * 1/(1+(0,1*X), and when I entered 1,6, the function-graph hits app 1,6 L at 38 m. So that would be my estimated RV.

The graph looks like this (I added the green line afterwards):

What do you think about this way of estimating RV? Do you think it is accurate?

What could be the flaws in this estimate?

 

[cdavis]

Without getting into the details of the math, the concept is completely logical, should work for estimation at the moment the estimate is made.

One problem, flexibility of the chest and ability of the lung to handle negative pressure changes, sometimes hour to hour. Do a lot of exhale diving and you quickly discover that depth capacity at the same level of exhale increases (a lot) the more frequent is your diving. Slack off diving and the reverse occurs. Depth ability also increases through a day of diving.

 

[Bill]

I had fun crunching these numbers a few years back. Your simplified calculation is beautiful and probably quite accurate. If you take the averages numbers, you end up with.... Vc=5 then Vr=1.25 and add .25 for dead space and 0.1 for mask to end up with 1.6. The only variable not accounted for in this method is blood shift which can be over 0.5. That will extend your graph past 60 meters. I'm not sure that I fully understand the next step after that.

 

[harrychamas]

if all you want is your RV surly it would be more accurate if you dont pack and dive untill your RV, that way there are less variables. then divide 100 by the bar which you reached your VC at giving you your RV percentage. Now say your RV % is 20, you divide your VC by 80 (your VC %) and times it by 100 giving you your TLC, then devide your TLC by 100 and times it by 20 (RV) giving you your RV amount in liters

so if your VC is 6L and you hit your RV at 40m:-

100/5 = 20% (your RV in percentage)
6/80x100 = 7.5 L (your TLC)
7.5/100x20 = 1.5 L (your RV)

Bill is right, to be totaly acurate you would have to factor in your mask, but since you will be diving with a mask anyway you would be fine not doing that also.

am i right or should i go practice my maths?

 

[Mullins]

How do you know what depth you hit RV?? If I tried to estimate mine based on a real dive I wouldn't have got within 20m of it.

 

[baiyoke]

Cdavis: Yes, I startet to think about that also. For some odd reason I have always thought about RV as a constant size, when it is in fact what we as freedivers are trying to change...

Bill: Interesting. So in fact my RV is not 1,6 but more likely around 1,25 L. 1,6 could better be described as Total Dead Space or similiar...

Harry - at first I couldn't make heads or tail in that calculation.... But it does add up, and it actually does make sense that it is possible to just calculate it from those two known variables: VC and "RV-depth". (I thought it to be a function with two unknown variables). RV will show itself in how deep you meet it... So if RV=VC it will be met at 10 m, if RV was ½VC it would show up at 20 m... So actually you could make a really simpel graph of that, and just have the RV-percentage of VC, and then multiply the percentage with VC. Wow!!! (sort of a graphical presentation of your calculation):

Or calculate:
10/38 = 0,26 (as on the graph)
0,26 * 6 (my VC) = 1,58 RV (or actually more like "Total Dead Space")

So the function is: 10/depth*VC

Simple as that... wow!

About the packing as an unwanted variable: I added the packing to actually get more precise. I have unlimited packing power, but can only pack a very limited amount. On land it has proven very steady at around 1 L. I guess this is where my flexibility stops. I can reach this point easely in whater. However if I didn't pack, the water pressure would make me inhale less than full, because my inhale power is not as strong (but I don't know how big or small the difference would be). So that's why I added the packing - to get a better measure.

Mullins - well I can't say that I know for sure, but 2 months ago I did many repeatet dives to around 30-45 m. And before getting used to the "vacuum" feeling, I often tepeatedly swallowed my mouthfill and spit it up again in the 30-40m freefall. And around 37-39 m I couldn't get anything up again. So I just reckon that is the depth where I reach RV.

 

[harrychamas]

Hay Mullins, the easyest way to figure out your RV is to do a dive without packing or doing a mouthfill and turn when you can bring up any air to equilise any more. then divide 100 by the Bar you reach giving you your RV percentage. to get your VC you have to use a special computer thingy doctors have.
Baiyoke i'm loving the graphs! did you try taking your last breath in a horizontal position, you shouldnt feel any pressure from the water that way.

 

[Simos]

For reference there is another method of measuring RV here:

http://forums.deeperblue.com/genera...-simulation-calculation-empty.html#post888349

If you feel like it and you have the right equipment, maybe you could compare the two methods and see what you get

 

[Mullins]

Hay Mullins, the easyest way to figure out your RV is to do a dive without packing or doing a mouthfill and turn when you can bring up any air to equilise any more. then divide 100 by the Bar you reach giving you your RV percentage. to get your VC you have to use a special computer thingy doctors have.

When I sat in the special thingy that the nice man in the white coat directed me to, it told me my RV was 1.5 and my theoretical failure depth was therefore 90m. I would have estimated RV to be somewhere around 70m based on where I felt I could "bring air up".

 

[Bill]

I still like the old method. Down to ten meters, turn up, exhale as much as possible through the snorkel then pull back to the surface. Just before you get there, invert a two liter container full of water over the snorkel and exhale as much as you can again. Caution, Kiwis may need to use a gallon container.

 

[Mullins]

^ I've always thought that'd be the best method, though I've never tried it. You'd want to limit mouth volume at depth as much as possible though.

 

[baiyoke]

Well it's only a rough estimate I guess. It needs adjustment for different factors clearly, like Bill mentioned.

Mullins is the deadspace and the (perhaps early) mouthfill (and perhaps mask) accounted for in the RV-depth estimation of 90m? I.e.is 70m when you can not keep filling your mouthfill, or is it where you can not get it up if swallowed.
Did you remember to relax and not look up... he he, no just kidding on that one, but your'e right that it's probably not identical, the theoretical RV and the actual air-failure RV. Maybe because of factors like deadspace, mouthfill, changes in relaxation etc.

to get your VC you have to use a special computer thingy doctors have.

Well, actually I measured mine with my snorkel, a 1 L jug, and a kitchen sink. Repeatedly blowing air out 1 L at a time, after filling the jug with water. Simple

did you try taking your last breath in a horizontal position, you shouldnt feel any pressure from the water that way.

I might try that actually, good idea.

Bill and Simos I'll try the other way on sunday, I need to test my exhale-measurement thingy at the same time (for exhale-diving). But I might not be able to hit RV full-lung as the lake is just about the same depth... I'll give it a go...

I still can't believe how simpel the final calculation is... beautiful (even if it needs adjustment for many different factors):

RV= 10*VC /depth

it's the freediving version of E=M*C2:t

 

[Simos]

Maybe I misunderstood what you wrote but you don't need to hit RV to measure it using the 'other' method right?

 

[baiyoke]

I know, it was just that you said I could compare the two methods, and since my diaphragma flexibility might have changed a bit, it would be more acurate to do both within a relatively small period of time. So I'll try do both in one day.

 

[harrychamas]

When I sat in the special thingy that the nice man in the white coat directed me to, it told me my RV was 1.5 and my theoretical failure depth was therefore 90m. I would have estimated RV to be somewhere around 70m based on where I felt I could "bring air up".

So the man in the white coat told you that you have a 15l TLC?

 

[Mullins]

No. The machine the man in the white coat was operating told me that.

 

[apneaboy]

What is your estimated (or recorded) maximum inhale included packing Dave?

 

[Mullins]

Largest recorded FVC was 13.6l with packing. It varies a lot though depending on the measuring equipment - it's generally less with a hand-held spirometer.

 

[harrychamas]

Thats impressive Dave

 

[baiyoke]

Just for the record, I tried the measure thingy today 3 times, but it was not ideel conditions... The measures went all over the place due to different factors.

First of all I have to say that to get a good measure, it's probably important to stay really calm, because exhaling complety at 10m was less funny and more physically stimulating than I somehow expected... lol

Anyway, the only "good" measure (no errors) was the last one, and it said 0,9 L. The two others were 0,4 and 1,4, so I guess it's:

Measure-thingy vs. Reality 0-1 for now...


Mullins: Impressive set of lungs you got there... :-0

I wanna know who the man in the white coat is... Are you the white man in the coat Mullins?...