RV/TLC - Depth calculations

[sxc]

I'm curious about whether one can estimate RV and TLC from the depth at which RV is reached. I reach my RV at 57-58M. This is the depth at which I can't hold air in my mouth without my glottis being consciously closed, and the depth at which reverse packing air up becomes extremely difficult.

So, I'm wondering whether its possible to determine a rough RV size based on just the depth at which RV is reached, and if so, what a formula for that would be? I know that the ratio of RV:TLC is mostly static (although, can be quite different for some people who have extremely flexibility), so the next step would be estimating TLC using that.

I will be using a spirometer at some point to get a more accurate TLC (and to see how this measures up with that), but for now, this is more fun .

Paging trux!

 

[esom]

hi, I think the process is exactly the other way around, in a double sense -after you learned through the standarised courses or by a thread on DB that there is a RV...

you find out that there no reflection of RV in diving, because there is no thing like a RV. You produce the RV while diving. Consquently, instead of your diving reflecting RV, your way of diving produces RV.
Further, the RV (whatever it -is-) is not determining the diving, but the diving is determining the significance of the idea* "RV" in freediving.

hope it helps... maybe also look at the posts of cdavis and efattah in "debunk the lungvolume myth" thread, discussed recently in "beginner freediving". They are putting things less extreme and maybe easier to chew for someone who just began to sort out variables for calculating


*for sure there are a few different ways to understand the concept "RV"

 

[Mullins]

It's very unlikely that your estimate is accurate, sxc. If I had tried to estimate my RV by diving, I'd have been wrong by at least 20m.

 

[baiyoke]

Here are some thoughts:

Apart from the problem Mullins mention, there are other aspects making it difficult in my opinion:

First of you are estimating from a small measure to a big measure (RV->TLC) so a small difference in measurment/estimate, will make a big difference on TLC, and the chance of getting that number wrong (theoretically it works better the other way around, I would say: From big numbers to small).

Second, hitting RV at 50-60m indicates your RV is very small compared to TLC compared to most people, so the above problem gets even bigger.. (other factors might be causing the deep "RV-depth").

Thirdly, your body seems to work quite differently than other peoples, for some reason. (I quickly read some other posts of yours), so I'm not sure an estimate of your RV is a good measure for anything, not even RV. (Being able to reverse pack a lot, and then go to 15m is very extreme, and by the way sounds very, very dangerous... I'd advice you to stop that immediatly).

Bloodshift is another factor, that will mess up your RV estimate: You don't know the volume of bloodshift (sounds to me, like you probably get big and strong bloodshift). Like Esom mentioned RV is a strange concept. Bloodshift is a factor that changes the airspace.

Besides I don't think your explanation of how you find your RV-depth is solid (allthough I use a similar one to describe it). However:

I reach my RV at 57-58M. This is the depth at which I can't hold air in my mouth without my glottis being consciously closed, and the depth at which reverse packing air up becomes extremely difficult.

!

About the air in mouth thing; There's negative pressure in lungs beneath passive exhale... even before RV.

About the reverse packing thing: This depends probably more on your ability and power in reverse packing, combined with your flexibility. So it's not really a good theoretical measure of RV (however usefull for planning mouthfill etc.).

Sooo... I don't think you will get much from the calculation...

But just for the fun of it, this is what I came up with:

RV = (10/depth) * VC (depth in m)

You can read more in this thread: http://forums.deeperblue.com/freediving-science/96129-calculation-estimation-residual-volume.html

 

[baiyoke]

And that would even just give you a ratio, and no actual volume, since you don't know your RV volume...

 

[Fitz-Clarke]

What you are measuring does not sound like RV. It would be your immersed FRCi if there is no pressure across the glottis. That is lung volume while relaxed at the surface with the glottis open. It’s equal to lung volume at the depth where airway pressure drops to zero, roughly around 30 metres for an average person. So if you are in water to your neck and relax, your airway pressure is zero and lung volume is FRCi, which is less than dry land FRC due to immersed hydrostatic pressure on the chest and blood shift.

In theory, using Boyle’s law you could calculate your immersed RVi, which is less than dry land RV for the same reasons as above. I will use subscript “i” to denote volumes during immersion as opposed to dry land.

TLCi * (10 + Paw) = FRCi (Dz + 10)

where Paw is airway pressure at TLCi breath-hold with the glottis closed, typically about 30 cm H2O or 0.03 msw without packing, so it can be ignored. Dz is the depth in metres where you would feel airway pressure drop to zero relative to ambient and no pressure gradient across the glottis. Therefore the above equation becomes:

(FRCi + ICi) * 10 = FRCi * (Dz + 10)

Then if you exhale from FRCi down to residual volume RVi while immersed at the surface, that exhaled volume is called expiratory reserve volume ERVi. Then inhale from FRCi up to TLCi which is inspiratory capacity ICi.

RVi = FRCi - ERVi

Therefore your calculated RVi works out to:

RVi = (10 * ICi / Dz) - ERVi

So you could rig up a home-made spirometer from bottles or bags. Immerse yourself to the neck. Measure ICi and ERVi (which sum to vital capacity). Then dive and note the depth Dz where airway pressure drops to zero. That would be the hardest part, and prone to error.

As an example assume you measure:
ICi = 5.4 L
ERVi = 0.6 L
Dz = 30 m

Works out to RVi = 10 * 5.4 / 30 - 0.6 = 1.2 L

Then if you want to correct this to obtain your dry land RV, you would have to take RVi and subtract the volume of blood shift due to immersion (0.5 to 0.7 litres), and add volume from the hydrostatic pressure head acting on the chest centroid multiplied by chest wall compliance at low volume (1.2 to 1.5 litres). That would be complicated and probably quite inaccurate. But in theory you would get what a pulmonary lab would simply measure as RV.

Sorry if that’s long and boring. Let me know if anyone actually tries this.