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Pressure training

Thread Status: Hello , There was no answer in this thread for more than 60 days.
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New Member
May 17, 2002
I was wondering if there's another way to get used to the pressure at depth than actually going there. I can get in the water every day but not where it's deep enough.

I'm finding that i'm being held back by violent contractions starting at 22-24 meters...It's really hard to relax while ur whole body is spasming uncontrollably. I've been told it's because my body isn't used to the pressure...Does that mean I've done all these hundreds of scuba-dives for nothing? ;)

I've read some stuff about going down with empty (or almost empty) lungs. Isn't that dangerous for a lung squeeze? Does this help training for pressure or is there no substitute for getting down there?

any help would be greatly appreciated

Hi ender,

Yes Negative pressure(Empty lung) dives help heaps in getting your body used to pressure at depth. It's something you have to be careful with, and obviously requires a buddy.
I found it helped a lot once I started diving over 40m. I find my heart rate drops really low when I do it also.

The contractions you speak of may in fact just be normal running low on air ones, which isn't really good to get on your way down. You may actually be pushing it a bit too far.

Anyway with negative pressure dives you want to reverse pack, ie getting more air out of your lungs, before you go down. You want to build this up slowly, and eventually you should get to a point where you feel quite empty on the bottom. Where it feels like you have no air left to equalise your ears normally. I takes a while to get comfortable doing this.

Don't try to set any static records doing this either, remember your lungs are empty.

Negative dives.

Reading the above posts made me wonder.
When diving very deep the lungs compress to a point at which the small remaining volume fills with fluid.
Negative dives are touted to simulate the pressure on the lungs at great depth.

If one were to do a long, relatively shallow negative dive would the relatively high ambient pressure experienced by the lungs not do the same and cause fluid accumulation?
Then on surfacing, could some form of secondary drowning effect occur with the the ascent being so much quicker than usual from depth and the fluid not having much time to pass back into the lung tissue before trying to breathe ?

Has anyone ever coughed fluid after surfacing from a long negative dive ?
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Once or twice, I have to admit ....

After very long, deep(ish) neg dives, I've coughed up some stuff ... could be best described as bloody phleghm. I haven't done any lately, I've actually been out of training for about two months or so. Last time it happened was about 6 months ago. Not fun ...
I'm not sure about the validity of this 'lungs filling with fluid' stuff. I remember reading it years ago, and have attributed it to a misunderstanding of the blood shift effect. This lets the capilliaries in the lungs fill with blood - but that blood does not go into the actual air space of the lungs.

Theoretcially fluid can go into the lung air spaces, through the alveolar wall as blood plasma - known as pulmonary aedema. However this needs time, with significantly low pressure in the lung, compared to the blood. The only conditions that could elicit this whilst diving are when the lungs reach residual volume, and are forced to compress further against a strong elastic reaction. In other words pushing it to your max ear clearing depth. However, Eric Fattah's mouthfill technique could would increase the chances of this happening - because it allows the lungs to be compressed beyond the normal ear clearing limit.

I know of divers coughing up a bit of bloody spit on surfacing, and usually put this down to bursting of capilliaries in the airways whilst ear clearing. It would take a lot of blood plasma in the lungs to actually get it out by coughing - as there is a long way for that plasma to travel from alveoli to trachea.

Does that make sense?

Indeed it does

I've questioned the 'filled lungs' theory as well - not because of my medical background (????), but because I refuse to believe it. Stuff bursting in my lungs ? Now THAT I can believe :D
From what I've been taught I think this is a misconception: the chest volume normally occupied by the lungs is filled with the extra volume created when the organs are engorged with blood as a result of the "blood shunt" that is part of the mammalian diving reflex. The shunt reduces blood flow to the limbs, and keeps it in the head and torso. This helps keep the core heat and oxygen supply in close to the vitals, allowing the limbs to switch to anearobic functioning.

Coughing up blood is not a result of the shunt, although it could be a result of high negative pressures that the body hasn't had time to learn how to deal with. Nose and ear bleeds (or worse) can also result if equalizing isn't done properly or is inhibited by swollen tissues. Intense use of the tissues in the head for equalizing can actually cause some swelling over the course of a few dives, which may result in developing equalization problems. I have first hand experience with this. :(

From what I'm told, the blood shunt is a fairly subtle effect that can be hard to notice. Tired, cold or slightly numb limbs, less negative pressure stress on the chest cavity at depth, a greater level of relaxation underwater. I distinctly noticed one time last week when I think I felt it happen rather suddenly at about 20m, and it was a definite improvement in my physical and mental state while underwater. Made a personal best of 24.1m at that point even though I was a bit concerned about my sinus problem (mentioned above).

Of course I'm just a newbie and I'm sure Eric Fattah could give you a much better answer...
My opinion

I think that all of these theories are correct; engorgement of organs near the lungs, as well as the plasma entering the lungs. In order for the plasma to actually enter the lungs, the negative pressure must be EXTREME, and there is an element of TIME required as well; the extreme negative pressure must be present for at least 10-15 seconds. As Ben mentioned, using the mouthfill technique and then descending with empty lungs allows negative pressure dives up to -25m. However, the negative pressure that is required to cause plasma to enter the lungs depends on the person; for me I need to dive to about 22m on empty lungs for it to happen (shallower if I reverse pack); if I do, I have this strange feeling in my lower lungs, and if I surface and inhale rapidly I will cough every time; the solution is to take a tiny breath (almost like a pack), wait, take a tiny bit of more air, wait, and keep doing this, slowly re-filling the lungs; this prevents coughing. My training partner Stephanie starts coughing after negative dives as shallow as -8m, but it seems her chest is less flexible than mine. I would also mention that once the plasma enters the lungs, it takes HOURS for it to go away, and during that time the gas exchange in the lungs is inefficient, and your diving ability is decreased dramatically. If you think your lungs 'filled with fluid' after a dive, but your diving ability has not dropped, you're probably mistaken about the fluid. Keep in mind that plasma is almost colorless; if you were to cough plasma the 'phlegm' would be colorless. If you cough blood after a dive, something is SERIOUSLY wrong, and something is being damaged, and you should stop whatever it was that caused the blood.

So, keeping all that in mind, extreme negative dives are certainly bad for dive 'prep' before a deep dive. Gentle negatives are better in that sense. However, extreme negative dives may be useful as a training tool for extremely deep diving, but only if no blood is coughed up.

My experience is that most people who do negative pressure dives 'exhale' then descend and continue equalizing. If you can equalize after exhaling, then you didn't exhale fully. If you exhale fully at the surface, the only way to equalize upon descending is by using a strange / non-standard technique of equalizing such as the watersuck, sinus flood, mouthfill etc...

As always, this is just my opinion; I could be wrong about everything.

Eric Fattah
BC, Canada
Yes Eric, you are wrong about everything! Just kidding :D

I just wanted to say that if you are coughing up "Stuff" after a NP dive there is something definately wrong...When I do a negative pressure dive it's usually to 15 - 18m with a little less than residual volume and at the bottom it does get hard to equalize...kinda goes along with Eric's thory about a "gentle negative"...you should be able to relax and experience bradycardia while holding at the bottom for a moment...Although gentle, it's not something that feels good by any means...I do negatives before all my deep dives and I still don't feel "comfortable." The whole idea of the negative (as it was explained to me) is to get the body under the same pressure that you would be feeling on the deep dive but at a shallower depth, thus not having to expend as much energy to go deep just to get the body in the pressure zone...Kinda like when you go out for fun freediving and ever consecutive dive gets easier and easier...I guess that's the whole theory of the NP Dive thingy...


David Lee
Jamaica W.I.

:waterwork flooded sinuses?
Hi David,

you said you still don't feel "comfortable" doing a NP. For me this is the Mental aspect of NP training, to get used to the feeling, and to get comfortable. This then gives you added confidence of being comfortable when you actually are at depth.

In the pool, my first NP, doesn't last long, feels OK. On the second or third, I get really relaxed, and yes even comfortable, can easily do 1:45 no contractions.

Actually not sure if you still get contractions or maybe don't feel them because the lungs are so compressed ?
My heart also rate drops heaps doing them, down to low 20s.

I don't do a lot of NP, usually at least 3 or 4 every time I go to the pool, but I find it's helped me heaps.

I did my best depth dive a month ago, got down to 48m, when I got there I lied down on the bottom for at least 5 seconds and felt very relaxed being there. Almost wanted to stay down there but common sense says, dude you got to go up and breathe !

Wow, you guys are aggressive on your NP dives! My deepest was ~12m and I could go no farther due to a complete inability to equalize further. I was wearing my Cressi Minima at the time and didn't even have the mask's reserve airspace to equalize with (it is very low volume, not to mention that it tends to leak at the drop of a hat). About a month ago, during one negative pressure to 10m w/ full exhale, a crunch, several reverse packs, and the Minima I felt something go >>pop<< in my right facial sinus, and then I had a painful reverse squeeze on the way back up. I stopped doing negative pressures after that, but it limited my depth for the rest of the day to 5m and recurred the next two weeks after a few dives. Doctor checked it out as okay, and now (a month later) the problem seems to have healed. I don't recommend it though, and I haven't yet tried anything more than a 4m NP. :)

PS: I did try to keep a mouthful of air, but lost it due to the Minima's leaky nature.
Originally posted by A Brownsword

PS: I did try to keep a mouthful of air, but lost it due to the Minima's leaky nature.

I just have to put in the fact that the Minima is the best mask I've ever owned for freediving: much better seal than the Bandit, which is not double-skirted.
Erik Y.
Originally posted by Erik
I just have to put in the fact that the Minima is the best mask I've ever owned for freediving: much better seal than the Bandit, which is not double-skirted.
Erik Y.

Yes, sorry -- I didn't mean to slag it like that. Carlos loves it too. Its a fine mask, but the soft plastic seems to give both Brent and I problems with leaks along the laugh lines. We're just having too much fun underwater, I guess. I find that the Sphera seals much better, but if there is any movement to the water the distortion can be truly nauseating. The Sphera with the Minima's lenses would be perfect for me, I think.
bloody hell...


U guys are really something... :) I'm damn happy I found this place...I think the exchange of info going on here is saving lives and making a lot of difference in the diving for a lot of people...


So going down with empty lungs simulates pressure...cool.

So am i right in assuming that going down to 10meters with lungs 1/4 filled equals a dive to 40m (pressurewise)? And doing this a couple of times in a trainingsession is a good way of training your body to avoid these contractions?

Originally posted by Walrus
The contractions you speak of may in fact just be normal running low on air ones, which isn't really good to get on your way down. You may actually be pushing it a bit too far.

Maybe but I seriously doubt it. I reach 24meters in 30-35sec kicking very relaxed. And i do 2min shallow dives no problem.

Ender Wiggin: you can simulate 50 metre dive pressures in a 5 metre pool, with full exhale plus reverse packing.
The main benefits are.....practicing deep equalising, stretching the lungs (inwards), but the main benefit, I believe, is when an exhale dive is used at the beginning of a diving session. Dive to a depth that squeezes your lungs enough to drop your heart rate (typically to 20-30bpm) a few times before your max depth attempt, or even just for rec diving, and you will initiate the bloodshift and activate the spleen, saving you a half hour of "full lung" dives before getting that 3rd lung feeling. This may not be that important to some, but it is to those in cold environments. If we are diving in 6C water, then we need to activate the mammalian dive reflex as fast as possible, before we start getting cold and shivering, which kills bottom time and depth.
A side note: I don't believe that empty lung training at depth should include going into contractions...the chances of BO are very high, as you are at depth with the increased PPO2, which will drop as soon as you ascend. Doing static hangs with full lungs is ok at depth, but you must really know your limitations if you are going to start pushing contractions down there.
Erik Y.
ps...."Ender's Game" movie coming out next year :)
efattah wrote:
for me I need to dive to about 22m on empty lungs for it to happen

And I though that 15m was deep ;) How did you made that, just with mouthfull of air, or did you use some water-techs?


Regarding coughing up blood or blood in the phlegm.

Can surfactant (like lung lube which keep the alveolar walls from sticking together) be squeezed out with significant prolonged negative pressure?

In which case I would imagine that rapid ascent from a deep depth or rapid inhalation after a negative may cause some microtears in the alveolar calls and therefore the capillaries which make up the walls.

If this is true...what Eric described by taking slow small volume inhales upon surfacing from a negative might be the best way of preventing these (imagined) tears. (could an exhale from 10 meters up...especially if packing performed...be the other preventative measure, or does that increase a SWB risk?).

my 2 cents

allright....I'll try some of them negative thingies when I get back in the water (stepped on a piece o' glass...have to stay dry for a few days :( )

Originally posted by Erik
ps...."Ender's Game" movie coming out next year :)

yeah i heard...I also heard that that brat from the 6th sense is playing ender...can't say i'm thrilled by that. we'll see :)
Exhale dives


About the 22m negative dive; it was with one mouthfill of air (no water used), for me 25m is the max with one huge mouthfill and fluid goggles; with a mask the max for me is about 20m on one mouthfill. It's a great way to check the efficiency of your mouthfill technique. I also managed 15m on one mouthfill using a large-volume cressi big-eye mask.

Eric Fattah
BC, Canada

In response to Ender's original question about getting used to being deep, I still don't know if negatives REALLY help for that. Negatives to 8-15m (and semi-exhales to deeper depths) help train equalizing technique, help you get used to sinking deeper and deeper, and help with rib cage flexibility. I know that some people who can only train in the pool can do extreme negatives but then have problems equalizing and with lung squeeze when they exceed 40m in the ocean.

But somehow doing negatives in a pool (5m depth maximum) is no substitute for doing them in the ocean, which is no substitute for diving past residual volume (to around 40m). You cannot simulate negative pressures on the rest of your body during a negative dive (as far as I know).

I think negatives can help technique, and semi-breath dives (with a spotter) to 20m+ are good too, but the best thing is to return often to the depth where you were having problems . If you feel like you're having contractions or whatever, learn to relax more, examine your breathe-up, body tension at depth (is your chest tight as you fight the increase in pressure?), etc....

Techniques like the mouth-fill do indeed make it easier to get pulmonary edema (which I had last year). It definitely can happen and I had to take several weeks off diving to let my lungs heal. The mouth fill allowed me to jump ten metres in one day of training, which is a bad idea. I spit up blood for a long time, wheezed, felt weak and dizzy, lethargic for more than a day. I asked experienced freedivers like Kirk Krack and diving doctors for their opinion and to them it sounded like edema. This condition can lead to secondary drowning (aveoli coated in blood, which reduces oxygen absorption into the blood) So my advice is to proceed gradually to those depths below 30m.

My typical diving warm-up for getting back into depths deeper than 40m is to do a negative to 8-10m, a neutral breath dive to 20m (to practice mouth fill), a dive to 35m, then another to 43m-45m (no packing). For someone who hasn't been to 40m before, I'd add another negative, and maybe a dive to 30m and 40m.

Nice to see you on the site, David! I tried no-fins constant weight yesterday in the ocean and did 30m (8 lbs of weight, 5mm suit--I sank like a rock!)..... It was fun! Perhaps someday I can afford to set a FREE record.... :D


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