Apnea diving question

[chinadan]

Hi!

I have a question regarding apnea diving. The diver takes a deep breath and descend to rather extreme depth. So, his lungs are filled with 1 bar of air. With increasing depth, shouldn't the water pressure collapse his lungs? I could imagine that muscles can counteract the pressure somewhat, but at 100m? Or is the rib cage strong enough?

Answers appreciated!

 

[wetnorm]

Sorry to be confused, but do you mean free diving (holding breath, w/o SCUBA)? Diving for pearls may be done this way, but I thought at shallower depths (although with training to a remarkable depth and time period relative to most of the rest of us). If so, I am then also confused about depth of 100m. Wow!

Using SCUBA one should never hold breath. Further, using SCUBA, breathing feels pretty normal because the inpsired air pressure is at ambient pressure, meaning intra-thoracic pressure and ambient water pressure are equal, and no compression of thorax/ribs/etc occurs.

Skin divers must, and indeed do hold breath safely (intentional apnea). Since our bodies are mostly made of water, its density is very close to that of water. No substantial (ie., unsafe) compression of body elements (including the thorax) occurs. Yes, the volume of gas/air in lungs does get reduced (? amount), but the thorax is not easily elastic. Upon ascension, the lung volumes are restored and DCI/pneumothorax does not occur.

A dangerous skin diving practice is to hyperventilate to prolong bottom time by preventing build-up of pCO2. However, pO2 may decline especially with exertion causng hypoxia and loss of consciousness, then drowning, a deadly form of apnea. This occurs before the urge to breathe returns (pCO2 lower than 40 mm Hg).

Does this help?

 

[roakey]

To answer this in general, the gas in the lungs is always at ambient, so in fact the lungs do "collapse" as the external pressure increases with depth. But similar to a baloon taken to that depth, they collapse, then "reinflate" to their original volume upon ascent. This happens without any negative consequences.

Roak

 

[chinadan]

Hi wetnorm and roakey!

Thanks for your in-depth (no pun intended) answers.

In fact, I was referring to the apnea depth diving or freediving where the diver holds his breath and descends. I checked on the current world record which stands at 162 m depth in the "no limit" discipline. So at this depth, the water pressure is immense.

Since we have established that the air inside the lung is at surface ambient pressure of 1 bar and the ambient pressure at depth is roughly 17 bar and I would like to know how this works.

Per Boyle's law: at steady temperature, the volume of a gas of a given mass is inversely proportional to the absolute pressure.

Since I know that it works, I am assuming that the rib cage and the muscles surrounding the lungs are capable of bearing the load. I am no doctor but as the rib cage, well, has ribs, there are soft tisue areas in between the ribs which would be directly exposed to the water pressure...

Roakey, are you saying that the lung can collapse and then inflate w/o damage to the lung tissue? I know the bronchioles and alveoli are coated with something called surfactant on the inside. This surfactant prevents these structures from sticking together as they collapse, e.g. during exhalation. I am wondering if that is enough, given the brute pressure at such great depth.

At least, apnea divers seem to experience similar physiological symptoms as us scuba-folks...SWB, spasms...I think they call it the "Samba"...

Any additional ideas would be welcome....cheers.

 

[miguel sanz]

IN FACT MANY ALVEOLI GET FILLED WITH PLASMA AT THAT DEPTH. THERE IS SOME LITTERATURE ON IT BUT i CAN´T GIVE YOU THE REFERENCES RIGHT NOW.
THE FORMER WORLD LADY CHAMPION WHO DIED A FEW YEARS AGO WHILE ATTEMPIMG A NEW RECORD (170 METERS, SHE GOT THERE BUT PASSED OUT WHILE ASCENDING), WAS A BIOLOGIST THAT STARTED FREEDIVING AFTER FALLING IN LOVE WITH PIPIN (MALE CHAMPION) WHILE STUDING HIS LUNGS.
I´M NOT SURE YOU CARE ABOUT ALL THIS, BUT I THOUGHT IT WAS A NICE STORY.

 

[chinadan]

Thanks, Miguel, for the info...now I can sleep.

Sad story about the diver...I think it is quite incredible what these people can accomplish, holding your breath for 8 minutes, diving to depths which most equipment would fail...impressive.

Cheers, D.

 

[roakey]

Since we have established that the air inside the lung is at surface ambient pressure of 1 bar and the ambient pressure at depth is roughly 17 bar and I would like to know how this works.

Disconnect. I said ambient, not surface ambient. So if they're at 17 ATA, the gas in the lungs is 17 ATA as well, so its volume is 1/17th of the volume it had at the surface.

Roakey, are you saying that the lung can collapse and then inflate w/o damage to the lung tissue? I know the bronchioles and alveoli are coated with something called surfactant on the inside. This surfactant prevents these structures from sticking together as they collapse, e.g. during exhalation. I am wondering if that is enough, given the brute pressure at such great depth.

At least, apnea divers seem to experience similar physiological symptoms as us scuba-folks...SWB, spasms...I think they call it the "Samba"...

Well, we know empirically that it works, since breath hold divers are able to dive to great depths and live. If you want to go beyond the physics and into physiology, I can move this to the medical note and some of the doctors can answer there.

I certainly hope SCUBA divers aren’t suffering from SWB, that's a breath holding problem...

Roak

 

[holdingmybreath]

The lungs, when at great depth during a free dive, fill with a viscous fluid that prevents them from collapsing. That fluid is re-absorbed by the tissues on ascent. The body has amazing ways of adapting to the conditions eh?

 

[IndigoBlue]

To answer this in general, the gas in the lungs is always at ambient, so in fact the lungs do "collapse" as the external pressure increases with depth. But similar to a baloon taken to that depth, they collapse, then "reinflate" to their original volume upon ascent. This happens without any negative consequences.

Roak

In addition to Roak's excellent explanation of the physics, there is also evidence that blood pools in the chest area during an extreme freedive, so that the chest does not collapse even though the ambient pressure has shrunken the lungs to the size of grapefruits.

NAUI publishes a great booklet on this topic, called Breathhold Diving.

www.naui.org

 

[wetnorm]

Wow! I am shocked at what humans can do -- and presume its all done for LOVE like the biologists Don Juan (con permiso, Miquel) speaks of. Now I know the depths of love. I will go away and pity myself for being such a superficial kind a guy....