Bubble model vs. Gradient Factors redux

[Brett Hatch]

No you don't understand bubble detection, nothing to do with the EKG. For transthoracic echocardiography, a transducer is placed on the chest wall and can detect the bubbles, in the right side of the heart Transthoracic echocardiogram - Wikipedia. The bubbles in the right side of the heart come from the venous system. A connection between the right and left sides of the circulation, such as a PFO, can result in arterial side emboli.

Ah, when you wrote echocardiography, my eyes lied to me -- they said they saw electrocardiography, when clearly they did not!. Thank you for correcting this, I'll read up on the article you posted for TTE's (not to be confused with a thoracic EKG).

Maybe I need to back up here, and start with a dumber question: what is the "bubble grade", the vertical axis on the images rsingler posted on page 1? I was assuming it was a quantity of bubbles flowing through a particular region of the veinous blood, per unit of time... which might not be correct.

 

[dmaziuk]

Maybe I need to back up here, and start with a dumber question: what is the "bubble grade", the vertical axis on the images rsingler posted on page 1?

You'll have to read the paper and see exactly how they were grading their bubbles. See https://www.eubs.org/documents/DHM Vol44 No1.pdf for discussion.

 

[EFX]

@EFX So what would it take to test the bubble model vs. dissolved gas, one or more of the profiles as described in post 66, or something similar for a different proflile?

From your post #66 the profile for VPMB+2 vs. 75/75 looks good. Very similar run times.

 

[EFX]

"Tissue pressure" is neither a meaningful nor a measurable parameter. It's just a representation of the concentration of dissolved gas normalized against the Henry's constant. So if the "tissue pressure" of N2 is 0.79 ata, that just means that the amount of nitrogen dissolved in the tissue is equal to the amount of nitrogen dissolved in a liquid in equilibrium with air at 1 ata. It can not be measured, it's just a numerical representation of the modeled amount of nitrogen dissolved in a tissue represented by compartment number X.

Tissue pressure is just a mathematical construct to make the comparison between the modeled amount of dissolved gas and the partial pressure easier.

Whaaaat! Storker, come on. You wrote: "Tissue pressure is neither a meaningful nor a measurable parameter." Well, I'll agree with you that it's not a measurable parameter, certainly not to Haldane in his time, but it certainly is not just a mathematical construct. Geeesh! Storker, I got to break it to ya man. You can't get inert gas flow into and out of tissues without a pressure difference between the source and target tissues. That's just plain physics.

So, there won't be any studies to look at.

In regards to Haldanean models please direct me to a study that measures the pressures within tissues. Oh, we haven't measured those pressures. I guess the studies don't count.

 

[Storker]

Storker, I got to break it to ya man. You can't get inert gas flow into and out of tissues without a pressure difference between the source and target tissues. That's just plain physics.

You're trolling now, right?

Henry's law - Wikipedia
Perfusion - Wikipedia
Diffusion - Wikipedia

 

[KenGordon]

Ah, when you wrote echocardiography, my eyes lied to me -- they said they saw electrocardiography, when clearly they did not!. Thank you for correcting this, I'll read up on the article you posted for TTE's (not to be confused with a thoracic EKG).

Maybe I need to back up here, and start with a dumber question: what is the "bubble grade", the vertical axis on the images rsingler posted on page 1? I was assuming it was a quantity of bubbles flowing through a particular region of the veinous blood, per unit of time... which might not be correct.

You ought to go and read some of the extremely long and argumentative threads on bubble models vs dissolved gas models. They exist here, Rebreather World and on The Dive Forum. Some of it was about ascent rates, and a lot about the NEDU study, however there were significant diversions into the effects of temperature and other factors. Ross H, the (software bloke) author of VPlanner and Multi Deco takes a pro bubble model/dead stop view and attacks people quite a lot, various proper scientists took his position apart repeatedly. He is mostly banned from forums, however I learned a lot by reading what he had to say and the refuting arguments.

As a result of all that (literally years) arguing the current fashion is GF settings like 50/80 whereas in the past it was more like 30/85. The heat-maps you see quoted from Subsurface came about in those threads.

There is some other embedded opinion in organisations about what a good ascent looks like. Guru’s have arrived at or adopted ideas which have been pushed strongly and taught to people as gospel, when those ideas are challenged it takes a lot to change their minds. There is a lot of ‘agenda’ about.

 

[atdotde]

The heat-maps you see quoted from Subsurface came about in those threads.

To give credit where it is due: As far as I know, @UWSojourner came up with these heat-maps. At Subsurface, we saw those and liked them so we added them to the program.

 

[EFX]

You're trolling now, right?

Henry's law - Wikipedia
Perfusion - Wikipedia
Diffusion - Wikipedia

Nope. Not trolling. Partial pressures drives diffusion. Watch this video.
In the video they use the term partial pressures. There's no hint that pressure is a mathematical construct. If I'm misunderstanding something please elaborate and help me to understand.

 

[Storker]

If I'm misunderstanding something please elaborate and help me to understand.

At equilibrium, the amount of gas dissolved in a liquid is proportional to the partial pressure of the gas. Henry's law.

The concentration can be expressed as g/L, or, if recalculated using the Henry constant, the gas pressure required to give that concentration at equilibrium. That is your "tissue pressure".

In our lungs, gas is dissolved into the blood more or less according to Henry's law. The blood, having a certain concentration of dissolved N2, goes to the tissues. Some tissues have an ample delivery of blood, those are the "fast tissues'. Some tissues have a limited delivery of blood, that's the "slow tissues". In any case, the blood has a higher concentration of dissolved N2 than the tissues it delivers to (on descent, that is). This is the perfusion that Bühlmann wrote about. When the N2-saturated blood reaches the tissues, dissolved N2 diffuses into said tissues. Stay long enough, and the concentration of N2 in the tissue reaches the concentration which the tissue would have had if it were in equilibrium with the N2 partial pressure in your lungs. Which is expressed as a "tissue pressure" equal to the ambient partial pressure, recalculating the concentration as a "pressure" using Henry's constant.

But it isn't a real pressure. It's a concentration. And the driving force isn't pressure, it's a concentration difference. It's Fick's law.

On ascent, the concentration of N2 in a given tissue might exceed the concentration limit given by Henry's law. And you start to bubble. In Bühlmann-speak, your tissue pressure is above the ambient pressure. But it still isn't a physical pressure.

 

[EFX]

At equilibrium, the amount of gas dissolved in a liquid is proportional to the partial pressure of the gas. Henry's law.

The concentration can be expressed as g/L, or, if recalculated using the Henry constant, the gas pressure required to give that concentration at equilibrium. That is your "tissue pressure".

In our lungs, gas is dissolved into the blood more or less according to Henry's law. The blood, having a certain concentration of dissolved N2, goes to the tissues. Some tissues have an ample delivery of blood, those are the "fast tissues'. Some tissues have a limited delivery of blood, that's the "slow tissues". In any case, the blood has a higher concentration of dissolved N2 than the tissues it delivers to (on descent, that is). This is the perfusion that Bühlmann wrote about. When the N2-saturated blood reaches the tissues, dissolved N2 diffuses into said tissues. Stay long enough, and the concentration of N2 in the tissue reaches the concentration which the tissue would have had if it were in equilibrium with the N2 partial pressure in your lungs. Which is expressed as a "tissue pressure" equal to the ambient partial pressure, recalculating the concentration as a "pressure" using Henry's constant.

But it isn't a real pressure. It's a concentration. And the driving force isn't pressure, it's a concentration difference. It's Fick's law.

On ascent, the concentration of N2 in a given tissue might exceed the concentration limit given by Henry's law. And you start to bubble. In Bühlmann-speak, your tissue pressure is above the ambient pressure. But it still isn't a physical pressure.

I think we're both right. It takes a partial pressure to increase the concentration of molecules at a particular barrier. Then diffusion moves those molecules from the higher concentration to a lower concentration. Thanks for the articles. I read them and found them interesting. OK. Moving on.