Inhaling in negative depth

[trux]

It was already discussed here on DB several times (for example here or here), whether it is possible to take a breath from a scuba diver in depth.

Well, it is obvious to everyone who ever took a scuba course, that there is a huge risk of barotrauma, because a freediver is used to hold his breath (closing the epiglottis) even on ascent, so when he forgets to exhale, panics, or gets unconscious, barotrauma may kill him.

Then there is serious risk of DCS - because freediver is quite high on CO2 (which amplifies DCS onset), and ascents relatively fast in comparison to a scuba diver, inhaling in depth would seriously increase the risk of DCS.

Then there was excellent answer of Eric Fattah in this thread, where he lists some other problems of inhaling in great depth - HPNS, narcosis, O2 toxicity, blackout, ...

So that's apparently not what I want to discuss. I know inhaling in positive depths (say above some 30 m), although not really an advisable practice, it is possible. We had to do it ourselves, when I did my scuba license decades ago - we had to dive to the tank in 15 m on apnea. It is no big deal.

The question is now whether inhaling from a tank at a great negative depth is physically possible at all. Please understand that this is purely theoretical question - I want to ignore the obvious risks, and possible fatal consequences mentioned above. I am just curious whether a freediver with lungs compressed below its residual volume, is capable of inhaling at all. Would he be able opening the epiglottis to let the air in? Or aren't the trachea or larynx collapsed so that they do not allow any air through even if it comes with sufficient pressure from a regulator? Anyone here on the forum ever attempted to inhale in a negative depth?

[Mullins]

Unfortunately I can't provide first-hand experience because I've never tried, but I can't see why it wouldn't be possible. I find it very hard NOT to inhale on deep CW dives because contractions are so strong. My epiglottis doesn't feel strong/reliable enough to prevent an inhale this so I need to clamp my tongue/soft palate closed in order to avoid breathing water. Fairly easy to test without too much risk I suppose - just do an FRC dive to 20-30m and see if you can inhale through a reg.

[Jon]

Can't you just push the purge button on the reg and make it positive pressure- to force air into your lungs??

I know it has risks (air embolism, pneumothorax, subcutaneuos emphysema, medistinal emphysema, etc.) but then all of this stuff that your talking about entials risk.

Jon

[trux]

Yes, I know I can try it relatively safely on an empty lungs dive, but I won't get the opportunity in the next days or even weeks. And since this topic was just discussed in another forum, I thought someone already tried it.

As for using the purge - if the epiglottis is closed in a way similar to laryngospasm, or perhaps even in case of collapsed trachea, it may not work, or as you tell there might be strong risk of injury. But first of all, I am not sure at all if there is any kind of block at all. Or perhaps it is individual and also depends on the diver's physiognomy.

David's experience seems to show though that there is no such block.

This question came up on a Czech forum, where someone heard (I believe) Martin Stepanek in some interview telling that a freediver is unable to inhale in depth from a scuba diver. So we discuss now whether he meant he was really unable to take the breath physically, or whether he rather meant that it could not be done because of all those risks.

[Jon]

A number of years ago PADI tried to work out a positive pressure scuba regulator for in water CPR- it was based on a Scubapro A.I.R. 1 second stage that was metered for proper lung inflation.

The idea was abandoned, but maybe it would work for deepwater rescues of freedivers. I prefer the idea of rapid lifiting, but then it's not my butt down there at 500' so my opinon doesn't count for much.

People use motuh-to-mouth to open up the epiglottis during black-outs so it might work at depth as well.

Jon

[trux]

Yes, opening the epiglottis in normal conditions is not a big problem. With laryngospasm it may be more difficult. So if the negative pressure creates any block similar to it, it maight be the similarly too. However, I never heard about such block, and just wanted to assure there is indeed none.

[bam bam]

it is possible, Pipin did this:

"In the spring of 1997, Pipin pulled off something called the Cayman Challenge, a "two-breath" dive off Grand Cayman Island. On one breath, Pipin rode his sled to 300 feet, where he then took a second breath from a scuba tank tied to the line and continued down to 500 feet."

from this article:
Is Time Running Out for the Mythic Man Fish? | Outside Online

[trux]

Thanks. That's what I wanted to hear. On the other hand I am surprised he survived it. Going to read the article to see what mix he used

[Jon]

He used air. Breathing helium for ascents that fast would bring on DCS for sure.

In Carlos's book he implied that Pipin did this trick on all of his deep dives.

Jon

[trux]

Yes, helium would cause not only DCS, but also HPNS on inhaling, and deep hypoxia on ascending (as Eric wrote in the other thread). However, inhaling more plain air seriously increases the risk of DCS and oxygen toxicity too, so it was indeed very hazardeous. I see now in the article, that Pipin had also a DCS incident after one of these stunts, and had to be heliported in convulsions to a hyperbaric chamber.

[apneaboy]

If the speed that a mouth fill is lost back to the lungs if you don't keep the glottis in the right position is anything to go by i think the lungs would fill pretty quick too

[Erik]

Positioning might affect this ie: head-down, head-up.

[efattah]

It is definitely possible to inhale down there. You can also just 'pack' the first few bits of air into your lungs and then once your lungs inflate a bit, inhale the rest.

[hteas]

I know that there was some question of whether taking a breath might have saved Audrey. I know a couple of the divers that were there. Nothing was tested or proven, but Matt Briseno thought that she wouldn't have been able to take a breath at 170 m. Too bad we don't have her here to tell us it was possible that deep.
Howard

[trux]

Although, as cleared here, it would be mechanically possible to take the breath, as Eric already explained in the other thread, inhaling both deep mix or shallow gas mix might have equally fatal consequence, so Matt was actually right.