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Too many Negative Pressure dives a bad thing??

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bevan dewar

Well-Known Member
Sep 26, 2001
In talking to a Performance Freediving clinic graduate, he mentioned that they were advised against doing negitive dives lasting more than 15 second(or hanging at depth for more than 15s proberbly). The reason they were given as far as he can remember, and from what it says in the manual was to do with plasma entering the lung, effecting O2 uptake. This apparenty being a reason why very deep divers only do one deep dive/day as it takes hours to dissapear.(if I remember correcrtly)

I've always been of the opinion that more negitive dives the better. I do at least 5 in my warmups, to about 12m, lasting about one minute, before deep dives. My theory has been that the more blood shift the better. And I would also have thought that this would reverse within the hour. (I'm taking here about normal pulmonary erection, not edema where the blood/plasma actually enters the lungs airspace and hinders O2 gass transfere)

I was also of the beleif that the only reasons for not doing repeat deep dives was lactic acid buildup and possible DCS.

Could Kirk/Martin be talking only about lung squeeze edema i.e coughing blood rather than just normal negitive pressure induced blood shunt? Can anyone else support the idea that to many/long empty lung dives can be a bad thing. This would be the first I've heard of such a theory. Thanks in advance

just found the email in which I was told this theory, I'll include it because I didnt discribe 100%

quote: Plasma entering the lungs is
common for diving more than 120 feet, but can also happened by doing long
negatives at the bottom of a 15' pool._ It is not harmful, but takes some
hours to dissimulate out of the lungs and will negatively effect the volume
of air you can put in your lungs and the ability of the lungs to pull O2 out
of the air and into your blood until it dissimulates._ This is why real deep
divers only dive deep once a day.
Last edited:
My thoughts are that it depends on what type of negative dive you are doing and what response your body has to negative dives.

Most importantly would be your own body's response. If you find that you are coughing this could be a sign you are getting plasma entry into your lungs. If after doing a negative you do a forcefull exhale and you hear a weezing/bubbling at the tail end of the exhale, then the same possibility. If either of these are true then theoretically, your lungs will have space taken up by this plasma and the possibility of affected apnea.

So this goes hand in hand with how far past negative you go and probably more importantly at what acceleration are your lungs collapsing. It may be quite a while after negative that you would succumb to plasma entering the lungs. It may be immediately.

So it seems when you say "coughing blood" you are referring to the same thing in the quote which mentions the plasma entering the lungs. Blood shunt could be induced by doing negatives, without the consequence of plasma entering the lungs/"coughing blood".


Thanks Tyler. That along the lines of what I would have thought.

I'm shure 5m is enough depth for someone to suffer squeeze if they were new to empty lung/deep dives. But as you say, it's more likely to happen with a quick decent than with a slow decent, which makes me surprised that if, according to Martin, you can get to 5m without squeeze, you could then later still suffer sqeeze if you stayed down for more than 15 or so seconds.

It's a fine line between shift and sqeeze I find. Some days, doing my usual warmup, I've had a mild cough reflex and have noticed a few microscopic orange/brown coloured flecks in my saliva, a sign of overdoing it.

My dive buddy has on occasion coughed up fresh, bright red blood, definity not good, but surprisingly he has had very strong dives therafter?

One thing I've wondered, if you one did ever suffer sqeeze to any degree, does it make one more succeptible to suffering squeeze again?(as happens for example to people who suffer hernias)

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