Empty Lung Dives

[mattharvey]

I've been doing a lot of shallow diving lately just hanging out and watching the fish etc. On one of these occasions I didn't bother
bringing a weight belt, So to get to the bottom I had to nearly
completely empty my lungs, the first few dives were a bit weird
(sank like a stone) but after a while I got used to it and found I
needed less of a breath up and felt very relaxed on the dive due to lungs not being stretched. I’ve read somewhere that marine mammals use this Tec' and freedivers practicing for deep dives,
but wondered if anyone else had any ideas on it? wondered if it makes SW blackout more or less likely?(my guess would be less likely).

Matt Harvey
Hong Kong.

 

[mattharvey]

What depths have people achieved using this tec?
what about the flooded sinuses equalising?
I understand why its used in training more intrested in
the swb issue and the marine mammal isssue

Thanks Matt

 

[Walrus]

Hi Matt,

yes these are called empty lung dives, or 'negatives', they are very good for training. But you shouldn't be doing them without a spotter, much too dangerous !
You are much more likely to blackout with these then any other training technique. Really need close supervision. For myself, and most people I know that do them, the urge to breathe and contractions come very late, if at all.

The main thing you have to remember is you start with much less air, your blood oxygen level start dropping very quickly. So your bottom time is much less. For example in a pool I have done a static about 2.30 on empty lungs, versus a 6 minute static on full lungs. So don't try and get anywhere near your normal bottom time.

You felt relaxed because your dive reflex does kick in faster, ie your heart rate drops quite quickly. Also even though you become very hypoxic, you don't build up so much CO2. This is why it feels like you don't need as long a recovery between dives.

Please dive safe

Wal.

 

[Shadowkiller]

Originally posted by mattharvey
what about the flooded sinuses equalising?

Have you ever flooded your sinuses? Not a particularly enjoyable feeling...

oh and marine mamals can do those neg dives because of the way they store oxygen in their tissue. We have to rely more on our lungs to store our supply...

 

[SpearSlinger1]

what about the flooded sinuses equalising?

I never tried it for equalizing purposes and doubt if it would work very well. I do, however, go to the beach and flood my sinuses repeatedly to wash them out when I have a cold or sinus infection. Clears me out pretty well, now for the disclaimer part, but I don't recommend anybody else do it. For one thing near a populated area you really don't know what kind of microbial nasties are in the water. The other reason is, you know that saltwater-in-the-eyes burning feeling? Imagine the whole inside of your head feeling like that. Sure, it goes away pretty soon, but that's what it feels like when you deliberately flood your sinuses.

 

[Shadowkiller]

Originally posted by mattharvey
if it makes SW blackout more or less likely?

Matt, what does the term Shallow Water Blackout mean to you exactly?

 

[mattharvey]

Passing out on or near the surface

I'm not planning on carrying out any exsperiments with this
just wondering if others mammals use this Tec to combat swb.

 

[Erik]

Actually Matt, they dive empty to stop narcosis, 02 toxicity, DCS and embolism!
Cheers,
Erik Y.

 

[Shadowkiller]

And avoiding Ascent Blackout (SWB) has nothing to do with it? :hmm

You have to wonder what other benefits a negative dive may have for a marine mammal (apart from those mentioned by Erik). I'm sure they didn't attend PADI courses to learn about DCS, so what would have made a land animal (back in the days when land mammals re-discovered the oceans) exhale before diving? Or is this a natural reflex?

hmm might be time to go swimming with my dog, he likes to dive for rocks..

 

[mattharvey]

ok any kind of blackout

Anyone know where I can find any info on research carried out
on this subject??

 

[BREATHLESS]

A few years ago I watched a close friend Bill Kroll,do a empty lung dive
on a school of White Sea Bass.Bill was a fine freediver and president of our club, Long Beach Neptunes. A week later he drown spearfishing in less than 30' of water at Catalina Island Ca.
I wish I could have convinced him that this can be a very deadly
Tool.
All The Best, Don Paul Gaboury

 

[samdive]

marine mammals - surely they would exhale before diving so they could sink more easily? as well as all the technical physiological stuff they learnt in school ; )

another risk from empty lung dives - ear probs - I messed up an ear drum big time on an empty lung dive to 5m. Don't do em any more...

sam x

 

[Shadowkiller]

Originally posted by mattharvey
ok any kind of blackout

Anyone know where I can find any info on research carried out
on this subject??

Check this thread for some links to webpages dealing with the subject.

http://forums.deeperblue.net/showthread.php?s=&threadid=16379

 

[Alun]

i think the important thing with negative/FRC/empty lung dives - whatever you want to call them.... is to progress slowly. don't do full exhales when you start doing them, and maybe only do one or two during each session. over weeks and months you can increase the number of dives, depth and the amount of air you exhale. as with most physical things, your body needs time to adapt. this is the approach i've taken, and i've never had any problems.
when i started i only used to go down to 3m or so, just once or twice. these days nearly half of my dives are done after a passive exhalation. one thing i think i've noticed is that over time you end up with less air in your lungs after doing a passive exhalation - probably due to increased flexibility in your diaphragm and chest. when i now do a truly passive exhalation in water my lungs are virtually empty. i have only enough air to half fill my mouth.

 

[mattharvey]

Alun, How deep are you going?

Still wondering if mammals use this to help combat swb(only my personal thoughts nothing to back this up)
read some comments in Eric Fatahs posts that maybe
this will help atchieve greater depths in the future??

I have continued to use this tec over the last few weeks
and feel very relaxed while doing it(only very shallow 5mtrs max)
feels realy nice diving in a pair of shorts with just a mask and fins.
Back to the uk next week for a holiday will have to put the 7mm
back on

 

[mattharvey]

Alun, How deep are you going?

Still wondering if mammals use this to help combat swb(only my personal thoughts nothing to back this up)
read some comments in Eric Fatahs posts that maybe
this will help atchieve greater depths in the future??

I have continued to use this tec over the last few weeks
and feel very relaxed while doing it(only very shallow 5mtrs max)
feels realy nice diving in a pair of shorts with just a mask and fins.
Back to the uk next week for a holiday will have to put the 7mm
back on

 

[Alun]

deep enough, but not too deep

i'm certainly no marine biologist, but i don't think that certain marine mammals exhale to avoid swb. i think it has more to do with reducing narcosis and the risks of decompression. from what i know, most of these marine mammals store only a small proportion of O2 in the their lungs anyway. i would imagine that another reason is reduced buoyancy changes, which i think makes diving more efficient for them.

i'm sure it's true that diving on empty lungs reduces or even eliminates the chances of swb... but that doesn't make them any safer. all you do is exchange one BO mechanism for another. instead of blacking out due to SWB, you black out due to plain hypoxaemia. so the fact that it reduces the risk of a SWB is basically a red herring from what i can tell. (i hope that expression means something to non-British people, otherwise it would sound pretty bizzarre!)

 

[mattharvey]

good job i'm a Brit

 

[Shadowkiller]

Henry's Law and Lung Surface area

After much navel gazing and a trip down to the uni library for textbooks I've come up with the following, feel free to correct where applicable because I'm sure I've missed things.

Ascent Blackout (Shallow Water Blackout) is "caused" by the expanding air in the lungs. This release in pressure (as you ascend) "sucks" oxygen out of the lungs. See Terry Maas's books "Freedive" and "Bluewater Hunting".

Henry's Law states: The pressure of the gas above a solution is proportional to the concentration of the gas in the solution.

Now, if we change that pressure the following relationship applies: C1/P1 = C2/P2
That is, an increase in pressure will result in an increase in concentration and vice versa.

So as we descend our blood concentration of oxygen is boosted, as we ascend it is reduced.

Now, as this relationship is independent of volume it seems a negative dive has just as much inherent danger of an Ascent Blackout as a full lung dive.

But. A negative dive involves purging as much air as possible from the lungs. This reduction in lung volume should mean that there is less surface area within the lung for the diffusion of blood oxygen into the lung, during ascent, to occur. In other words, the diffusion should be slower.

And this is the point where I got stuck. Without any scientic references I can't back up that statement. Is the rate of gas exchange within the alveolar tissue is pressure dependent? I think so but can't say for sure. Does a reduced lung volume imply a reduced surface area for the alveolar diffusion? I don't know...
I suspect that if sections of lung tissue collapse completely during a dive then the answer is most likely yes. If the lung tissue partially collapses, evenly, then the answer should be no. But which is it?

As Alun stated: Even if a negative dive means that the ascent blackout (ie the one dependent on Henry's Law) mechanism is "impaired" or eliminated, you can still blackout via other mechanisms. So there is no reduction of risk to the diver.

Still its an interesting topic in my opinion.

Some handy references:
http://scidiv.bcc.ctc.edu/wv/09/0009-006-henry.html
http://www.scuba-doc.com/Brdprpgases.html
Tiplers Physics for Scientists and Engineers
Terry Maas: "Bluewater Hunting"

Disclaimer: Theoretical discussion only. Not to be taken as gospel.

 

[Alun]

"Now, as this relationship is independent of volume it seems a negative dive has just as much inherent danger of an Ascent Blackout as a full lung dive."....

i don't think that's true, because with a full lung, you'll have more O2 passing into the blood on descent, and hence more being drawn out on ascent. diving on empty lungs means there is much less O2 to transfer. as you said, there is less surface area with empty lungs, but furthermore, a greater proportion of that surface area is non-alveloar, which should mean that diffusion is even slower.

my brain hurts... i need to lie down...