How is water pressure communicated to the lungs?

[Jake]

Recently I've been reading/listening to books on diving pioneering, including free diving. One aspect of physiology that came up, particularly with respect to free diving, is lung squeeze ("thoracic squeeze"). The free diver can go so deep that eventually their lungs can become injured from being over compressed from the pressure.

Maybe this is a stupid question, but how do the lungs get into that over compressed state? I understand Boyle's Law and such with respect to gases under pressure, but I'm confused as to how the external water pressure is communicated to the lungs so dramatically. I'm not sure if it's a 1:1 relationship, but suppose a free diver descends 10 atmospheres; their lungs will have compressed by the same or similar factor as water pressure.

Our bodies don't compress in size by a factor of 10 in this scenario. We're not incompressible, but neither are we particularly compressible. So why do the lungs compress so much and so equally to water pressure?

If this has already been answered here maybe someone can point me in the direction of the earlier threads. Thanks!

 

[RobPNW]

Isn't the body like 85% liquid? And if so, pressure is distributed evenly throughout a liquid, including all the tissue surrounding the lungs. And because the fluid is not in the lungs, there is no counter acting fluid pressure.

 

[inquis]

If you look at pictures of freedivers when deep, their belly/diaphragm region will be visibly compressed inward. That thoracic cavity is not a rigid container, nor is it completely filled with incompressible fluid.

 

[BlueTrin]

Most of your body does not compress because your body is mostly made of materials that does not compress (much). For example, does not compress much at low pressure.

Your lungs have a huge cavity full of air. This will compress.

From this page Compressibility - an overview | ScienceDirect Topics

The compressibility of water is a function of pressure and temperature. The low compressibility of water means that even in the deep oceans at 2 miles depth, where pressures are on the order of 6000 psi, there is only a 1.8% decrease in volume. It is this low compressibility of water that leads to an incorrect assumption that water is incompressible.

 

[Jake]

If you look at pictures of freedivers when deep, their belly/diaphragm region will be visibly compressed inward. That thoracic cavity is not a rigid container, nor is it completely filled with incompressible fluid.

They don't even need to be that deep though. If you dive to 100 feet your lungs will have reduced to about 1/4 their size at the surface. That's a dramatic reduction at a relatively shallow depth.

 

[GJC]

Liquids and solids compress very little under pressure, so your bones, muscles, blood and other body tissues and organs don't compress noticeably.

Air and gases in your lungs and GI tract compress because your soft body tissues transmit the pressure from outside your body to the gasses inside. The chest compresses as much as the rib cage allows then your abdomen is pushed up against your diaphragm until the pressure in your lungs is equal to the pressure outside.

At 10 atmospheres, the air in your lungs is 1/10 the the size it would be at the surface. So yeah, a lot of the space inside your ribs is now occupied by abdominal stuff.

 

[GiraffeMarineSalvage]

Also, one note to add about the air in a feeediver's lungs compressing is that this is not felt by the diver. This is very important to realize since most people will feel an issue with their ears or sinuses not equalizing and hopefully therefore avoid those problems (unless stubbornly going deeper against good judgement...) BUT the same cannot be said about avoiding a lung squeeze...
In addition, just like someone that has been entirely sedentary shouldn't expect to start off exercise by doing a triathlon, it is important to let the body adapt to freediving gradually over time. Taking a proper freediving course will give the fundamentals to begin progressing (likely 2.5+ minute static breath hold and 50+ feet simply learning fundamentals) but freediving fitness which includes flexibility of the lungs to handle being compressed, like any kind of fitness, takes time to develop...

 

[John C. Ratliff]

Liquids and solids compress very little under pressure, so your bones, muscles, blood and other body tissues and organs don't compress noticeably.

Air and gases in your lungs and GI tract compress because your soft body tissues transmit the pressure from outside your body to the gasses inside. The chest compresses as much as the rib cage allows then your abdomen is pushed up against your diaphragm until the pressure in your lungs is equal to the pressure outside.

At 10 atmospheres, the air in your lungs is 1/10 the the size it would be at the surface. So yeah, a lot of the space inside your ribs is now occupied by abdominal stuff.

What you are referring to, which I know you already know, is 10 atmospheres absolute pressure. That includes the one atmosphere on the surface. I'm saying this so that those who may be new to diving physics can understand the relationship between pressure and volume:

P1V2/T1 = P2V2/T2 (using absolute pressure and degrees K or R for the temperature).

SeaRat

 

[John C. Ratliff]

Also, one note to add about the air in a feeediver's lungs compressing is that this is not felt by the diver. This is very important to realize since most people will feel an issue with their ears or sinuses not equalizing and hopefully therefore avoid those problems (unless stubbornly going deeper against good judgement...) BUT the same cannot be said about avoiding a lung squeeze...
In addition, just like someone that has been entirely sedentary shouldn't expect to start off exercise by doing a triathlon, it is important to let the body adapt to freediving gradually over time. Taking a proper freediving course will give the fundamentals to begin progressing (likely 2.5+ minute static breath hold and 50+ feet simply learning fundamentals) but freediving fitness which includes flexibility of the lungs to handle being compressed, like any kind of fitness, takes time to develop...

A couple of things here. From my understanding of diving physiology, there are no nerve endings to sense the pressure change in the lungs; therefore, no pain for a lung squeeze. Second, there is some research which shows that for extremely deep free diving, there is some liquid shift in the lungs to keep the lungs from completely collapsing in trained free divers.

While these studies elucidated thoracic blood shift during (deep) breath-hold diving as an important physiologic mechanism to prevent lung squeeze, athletes continued to compete for ever increasing record depths (Sharp, 2003). Umberto Pelizzari reached 150 m depth in 1999 and Loic Leferme set a record depth at 162 m in 20021. These depths could only be achieved using technical assistance such as weight sleds upon descent and balloons to assist ascent from depth, in order to keep breath-hold time to a tolerable minimum. However, consideration of RV/TLC ratio and thoracic blood shift alone would not allow subjects to survive exposures to these depths. An increased awareness by the scientific community of the record depths achieved by some elite breath-hold divers prompted early case studies of elite athletes who used a unique breathing technique to further increase their TLC (Örnhagen et al., 1998; Muth et al., 2003; Simpson et al., 2003; Lemaitre et al., 2010.

Kay Tetzlaff1*, Frederic Lemaitre2, Christof Burgstahler1, Julian A. Luetkens3 and Lars Eichhorn4, frontiers in Physiology,
published: 09 July 2021 doi: 10.3389/fphys.2021.710429

[PDF] frontiersin.org

[PDF] Going to extremes of lung physiology-deep breath-hold diving​

So there are other mechanisms involved in extremely deep free diving, and those are discussed in this paper.

SeaRat

 

[John C. Ratliff]

Here is another very interesting paper that discusses this phenomina:

Breath-Hold Diving – The Physiology of Diving Deep and Returning

Breath-hold diving involves highly integrative physiology and extreme responses to both exercise and asphyxia during progressive elevations in hydrostatic pressure. With astonishing depth records exceeding 100 m, and up to 214 m on a single breath, the human capacity for deep breath-hold diving...

www.frontiersin.org

SeaRat