Lung compression effects on gas exchange in human breath-hold diving

[trux]

There is a new study by JR Fitz-Clarke speaking about gas exchange during deep freediving:

Lung compression effects on gas exchange in human ...[Respir Physiol Neurobiol. 2008] - PubMed Result

Well, I did not read the full document, but really like the conclusion in the abstract. I think I'll have to be little bit more careful with new PBs:

Hypoxemia with loss of consciousness prior to alveolar re-opening on ascent is predicted to occur on dives beyond 300m, depending on initial lung volume.

 

[Mullins]

An equation is derived for estimating collapse depth due to direct alveolar compression and time-dependent absorption atelectasis

Sounds like a 1m/s FRC dive to 100m should have the same effect as a 3m/s sled dive to 300m. I wonder if JR (He? She?) considered e-diving.

 

[Mullins]

I think I'll have to be little bit more careful with new PBs:

Trux, AIDA have now banned static at depth. Sorry.

 

[trux]

You ruined my day (together with the study), Dave. No more statics at 300m!

Well, the 300m is certainly based on some conditions (descend speed, lung capacity, etc), and knowing that Herbert went to 214 m practically on empty lungs (air exhaled into the coke bottle at some 20-30m), I'd tell Dr. Fitz-Clarke's estimate was not based on the 3m/s sled descend speed but something much slower. It might be interesting to read the entire document for that reason.

BTW, JR stands for John Robert. Dr. Fitz-Clarke is one of the most known physiologists in the freediving community, and I bet you'll meet him sooner or later too. He is also DB member and peeks in up and then with some comments - you can check his posts in his profile at DeeperBlue Forums - View Profile: Fitz-Clarke It would be nice if he saw this thread and commented on it.

 

[hteas]

it sounds from the abstract that it is a modeling study. if so, it is not likely to take into account where the air is in the lungs, but assumes uniformity. During the descent the alveoli will have more air than the thorax, amd on the ascent the alveoli are likely to totally collapse as the air rises in the chest. If so, the start of the ascent will be the killer (just when you thought you were safe).

Anyone have access to the entire article?

Howard

 

[efattah]

Even if the alveoli totally collapsed and gas exchange completely stopped, the blood would be almost fully oxygenated when that happens, giving the diver at least 3 minutes to 'go down and get back up' to a point where the alveoli are exchanging gas again.

I would imagine that total collapse and cessation of gas exchange might happen around 200m for a packing dive, which would give you 3 minutes to get to 300m and back again (=90 seconds to get down 100m, or 1.1m/s).

The 3 minute guideline is based on the full exhale static times of high level divers (which can reach almost 4 minutes), and at great depth the heart beats so slowly that O2 consumption is probably slowed down anyway.

 

[Fitz-Clarke]

Thanks for your interest in my paper. This is indeed a theoretical model. There is presently no other way to study what happens at great depth. It is part of my concept of the “Digital Freediver”, a comprehensive computer simulation of the cardiopulmonary physiology of breath-hold diving. This is one of a series of published paper on this topic. Previous papers pertained to analysis of circulatory changes and blood shifts, and the detailed mechanics of airway and lung collapse.

This particular paper has three main points: (1) lung collapse and reopening depths can be estimated as a function of initial lung volume based on known pulmonary mechanics, (2) gas exchange limitation between alveoli and blood depends on the ratio D/BQ of diffusing capacity to solubility and blood flow for each gas according to derived theory, (3) lung collapse necessitates reliance on dissolved oxygen stored in blood and tissues, which imposes a major limitation on ultimate depth. Fortunately the depth of critical hypoxia due to collapsed lungs is predicted to be at least 300 metres, depending on travel rate and initial lung volume presented in a graph.

I have indeed accounted for the effects of exhale diving and lung packing in the analysis. The model has matured to the point where it can begin to address many interesting questions.

John R. Fitz-Clarke, MD, PhD
Dalhousie University
Halifax, N.S., Canada

 

[trux]

Thanks, John, for taking your time to stop by and commenting! Are there any more details available about the "digital freediver" simulation software? Do you plan releasing it, or will you keep it stricly for the internal use in your laboratory?

 

[Fitz-Clarke]

At the present time it is strictly a research tool. As a scientist, my greatest interest is in deep diving, since that is where one sees the most extreme physiology. The problem is we don’t know much about what actually happens below 100 metres because those measurements have not been made. Let’s find some volunteers who can dive deep and do some serious measurements.

The first phase of developing my computer model involved constructing the cardiovascular system including the pulmonary circulation and subjecting it to hydrostatic pressure. My interest was in quantifying the degree of blood shift into the heart and lungs during very deep dives, and to see if pulmonary capillary pressures could increase high enough to cause vascular injury. The second phase added more detail to the lung model, including mechanical properties of the branched airway tree and alveoli, and the contribution of surface tension. This was used to predict lung collapse depth and the statistical mechanics of alveolar reopening on ascent. The third phase added tissue compartments to look at transport of oxygen, carbon dioxide, and nitrogen and how these are affected by lung collapse. This paper also introduces a new theoretical mechanism of deep-water hypoxia due to lung collapse.

These papers have been published in the medical literature and are available.

 

[Fitz-Clarke]

Incidentally, one of the more interesting applications of this model has been conducting a forensic analysis of Audrey Mestre’s dive to 170 m based on the known timeline and depth profile. Physiological predictions from my model depend on her initial lung volume. If anyone knows of a doctor that might have conducted lung studies on her to measure RV and TLC, I would be grateful for any tips that might help access that data. I have tried to find this information without success.

 

[trux]

Well, you have already one freediver here in this thread who dives below 100m - Dave Mullins. And there are couple of others here on DB who reached the depth on CWT. As for Audrey's physician, if Eric does not know, then perhaps Carlos Serra could help you. Try pinging him by PM. And if you need any help with the programming, let me know, but I guess you have enough students for that task.

 

[Fitz-Clarke]

Thanks Trux. I sent a note to Carlos. If any other readers have leads, please let me know. I will let you know results of my analysis if I can obtain that lung volume data.

 

[efattah]

I recall reading about Audrey's lung volume on the IAFD website during her training for the fatal record. I believe it was around 5 or 6 litres, and she didn't pack her lungs. I have no idea what her residual volume was.

In terms of testing, I'm always available and I'm sure there are others here available too. I routinely go over 30m on full exhale dives and I can go way over 100m FRC with an assisted ascent (i.e. inflatable vest). I think I could make 200m+ on an inhale dive but safety is a grave concern and I don't think I've seen anything that satisfies me yet.

 

[Fitz-Clarke]

Thanks Eric. I had used an assumed lung volume of 7 litres for my initial calculations, since I have no other data. A dive to 170 m puts her very close to collapse depth for that volume. The additional time spent at depth awaiting rescue results in further alveolar gas absorption causing collapse of any remaining trapped air. She must then consume oxygen from the very limited blood and tissue stores only. While CO2 might have caused the breakpoint, it is very conceivable that she became critically hypoxic due to lung collapse during her unusually long bottom time, despite the high ambient pressure. If she did not pack, this scenario is even more likely. My model demonstrates how this could happen, given her dive profile.

As for future experiments, it would be great to discuss this with you. Can you personal mail me via DB with your email address, and I will forward some papers describing the model. I would like to see if we might be able to set something up to get some useful data.

 

[efattah]

The most interesting side-effect of cessation of gas exchange in the lungs is not so much the effect on the oxygen supply, but the absence of nitrogen absorption.

In the case of Carlos Coste, who packed fully before his near-fatal 183m no-limits dive, he may not have reached alveolar collapse (in my opinion).

His dive lasted for over 5 minutes and he spent most of it below 140m (as I understand it). Life threatening DCS upon the ascent would imply that he was absorbing nitrogen for most of the dive.

Also, given that FRC diving has not seemed to reduce my susceptibility to DCS at all, would imply that even on deep FRC dives I'm not in the alveolar collapse zone yet.

 

[Mullins]

I can go way over 100m FRC with an assisted ascent (i.e. inflatable vest).

You kept that pretty quiet Eric! Awesome...

 

[aquaholic21]

First of all...

This is an awesome topic and has answered a lot of the questions Ive had regarding deep dive freediving physiology! Im stoked to be able to see these questions answered by so many knowledgable people in the sport.

I did have a few things I was wondering if I could get cleared up though... for one, what happens during a lung collapse? Is all of the air in the lungs gone or is there just an extremely small amount left? Does this sort of event damage the alveoli in any way?

And also, what is FRC? I looked it up and one of the answers was Functional Residual Capacity. But what exactly does that mean?

Lastly, i saw that lung volume capacity plays a role in what depth your lungs would collapse. Is it the greater your lung capacity, the deeper your working lung depth?

Thanks again for taking the time to explain this stuff! Its really interesting how the body reacts to such stress!