Lung collapse estimate including bloodshift.

[baiyoke]

Can you help me find the flaw in this logic calculation:

My TLC including pack is 7,6 L.
My RV is 1,58 L.

At 100 m depth the lungs have collapsed to 1/11 size = 0,09.

0,09 x 7,6 L = 0,69 L well below my RV, and lungs could be squeezed.

BUT if bloodshift i strong and working I might add app.1 L of blood to my lung volume below 30 m.

0,69 L + 1 L = 1,69 L well ABOVE my RV.

So.... No squeeze for me on a 100m dive! Except that is hardly the case in reality, and I'm not in the mood for testing that :blackeye

But where's the flaw?

 

[Mullins]

But where's the flaw?

Making up numbers at random is probably not very reliable. Assuming the 1l of blood shift is a made up number, of course.

Even if you did have an accurate number for bloodshift, I doubt RV would be much of an indication you'd get squeeze. It's just your max exhale and doesn't say much about your flexibility below that volume.

Then you've got contractions, shivering and other odd upper body movements.

 

[baiyoke]

Making up numbers at random is probably not very reliable. Assuming the 1l of blood shift is a made up number, of course.

Well, I wouldn't say at random, just doing some math and using a qualified guess I'd say. But of course I don't really know, could be anything between a drop and a few litres.. I was just crunching numbers to estimate simulated depth in a 4 meter pool exhale dive, and it hit me, that the bloodshift is unaccounted for in my calculations, and that 1 L would make a HUGE difference in estimations of real deep dives...

Even if you did have an accurate number for bloodshift, I doubt RV would be much of an indication you'd get squeeze. It's just your max exhale and doesn't say much about your flexibility below that volume.

I can see how RV does not say how you handle pressure below that. BUT it does say something, I would think, about the likelyhood of getting squeezed if your lungs are still ABOVE RV. Then you can still equalize all air spaces, and shouldn't then squeeze be very unlikely (if we keep it simpel, and just look at air spaces and pressure).

Then you've got contractions, shivering and other odd upper body movements.

Point taken - but this again really won't aply above RV, will it??? Do you think people can get squeezed when diving above RV? (both with or without bloodshift)

Btw when writting this answer, searching on google for stuff, I just feel over an interesting text by Sebastian: freediving - squeeze Might be interesting to others as well.

Does anyone know if bloodshift has to be "trained", does it increase with training?

 

[trux]

Have a look in the forum archive, there are a few very interesting threads about squeeze. There are people who get squeezed at 8m, or even on surface (exercise enduced edema). Packing freedivers are better candidates for a lung squeeze than non-packing ones. There may be several mechanisms behind it - tissue damage compromising the resistances of the blood vessel walls caused already by the packing self, is then the entry point of the squeeze in dept; positive squeeze (overpressure) due to the abdomen compression at the duck-dive; possible barotrauma at packing freedivers near to the surface. The, of course, as Dave wrote contractions can get you far above the negative depth (given by your TLC/RV).

And bloodshift is not only positive, but also negative - the blood vessels in lungs are full of blood, stretching the walls of the capillaries, hence when there is already some damage done by packing, or when the walls are not strong enough, the blood enters the lungs easily.

 

[Bill]

The calculation is a little more complicated than that. I just spent half-a-day with a lung specialist and all his machines. Your 1,69 number ignores the non compressible air spaces. The sinus cavities will require about 0,2 at that depth and the 'non functional' part of your lungs, throat and trachea I think, are only partly compressible. Guess 10% of Vc. Now the estimate at 100 meters is under 1,2.

 

[baiyoke]

Ok, thanks everybody. I have now cancelled my scheduled 100m attempt :blackeye No, just kidding...

I can't help wonder if those contractions perhaps can simulate a lot of negative pressure periodically. in "spikes", or if it's the forcefull muscle contraction itself that rips something apart. I can not find this info about contractions: Are the sucking or pushing air. I've read once they actually are pushing air out, allthough it feels like sucking movement. Wich one is it?

 

[Mullins]

Both. It's an involuntary attempt to breathe, so there's typically an expiration then an inspiration immediately afterwards. Or there would be, if you didn't have your mouth closed.

 

[Fitz-Clarke]

Your flaw is assuming that RV is related to squeeze. It’s not lung volume that causes squeeze. It’s negative pressure. That makes it more complicated. For trachea squeeze causing spitting of blood, it is ambient minus airway pressure Pamb – Paw. For smaller airways and alveoli inside the chest getting pulmonary edema, it is intrathoracic (pleural) minus airway pressure Pp – Paw. You need to know your lung and chest compliance curves to quantify. Blood shift helps relieve the pressure difference. This depends on stiffness of the chest vasculature including heart chambers, vena cava, aorta, and lung vessels. There are many variables.

Residual volume is meaningless on a dive. It’s a dry land definition based on ability of your expiratory muscles to expel air against increasing chest stiffness. It has no real meaning underwater because you don’t use your expiratory muscles. However it does roughly indicate stiffness of the chest/diaphragm at low volumes, but it’s not a hard limit, and it’s too simplistic. Lungs don’t have a residual volume. That’s a chest wall property.

You need to look at pressure changes. Here are some calculations assuming your packed TLC of 7.6 litres plugged into a model that includes all of the above properties. VL = lung volume, Paw = airway pressure in cm H2O relative to ambient, BS = blood shift in litres relative to that at dry land FRC:

...... VL Paw BS
Dry 2.73 0 0.00
Imm 1.88 0 0.54
Pack 7.60 69 0.07
10 m 4.08 16 0.12
20 m 2.74 6 0.21
30 m 2.03 0 0.33
40 m 1.64 -4 0.44
60 m 1.16 -8 0.60
100 m 0.75 -12 0.78

Simple water immersion already causes 0.54 litres blood shift into the chest, but packing almost reverses this due to high Paw. Airway pressure drops to zero at 30 m, roughly at the depth where lung volume drops to immersed surface FRC, but with a small blood shift. You reach RV at 40 m where airway pressure is –4. This is not very negative, but you will feel it. Airway pressure obviously becomes more negative deeper, and this depends on stiffness of the chest/diaphragm. Because the compliance curve is fairly flat here, there can be considerable pressure drop for a small volume change, then compliance of the blood vessels becomes important. Negative airway pressure will exceed these values if you are stiff or tense.

The pressure limit resulting in squeeze injury is anyone’s guess because negative pressure tolerance is not generally known. That is a property of tissue stress and vascular permeability. There are probably other factors like muscle tension, contractions, neck movement, body twisting, etc. that pull more negative airway pressures.

 

[baiyoke]

Hey Fitz-Clarke. Thanks for the answer, forgot to reply. But this looks some heavy stuff... I'll have re-read your answer some time again, some of it is beyond the level of detail I can currently take in... I know the RV is kind of a "concept" and not a lung property as such... again it about the level of detail..