new theory about risk in freediving (dcs/airtrapping)

[jome]

I usually don't have any contraction for depth disciplines. But, on this dive I had one single weird contraction at ~35-37m (I was sinking and relaxed). It was not a contraction from apnea or CO2. I remember that it broke my concentration, I focused my mind on my chest and stomach and the contraction disappeared. No contraction for the rest of the dive. It was a strange feeling.

I've had a similar thing happen a couple of times (but no squeeze so far). I think it has to do with the negative pressure pushing on your tratchea/epiglottis/whatever. Actually, I get similar "pressure contractions" with just negative packing dry apneas (contractions starting very early, way before the Co2 or o2 limits)

It's a moment when, if doing the mouthfill, the air usually escapes from my mouth and I suddenly feel the pressure on the throat-area and get a sort of panicy feeling. For me this is a definite sign to abort the dive, but I know people sometimes try to go past that (it's sort of hard to identify) and it's my gut feeling that in a lot of squeeze cases I've seen, it's been the case. I find that doing negative packing apneas up to really uncomfortable really helps getting used to this and maintaining control when the point approaches. Just speculation, but I believe this is the point when one, with the mouthfill, override the RV and "normal equalization" would start to fail. Ie you go deeper than you maybe should be going relative to your experience (with the mouthfill it's very easy to make huge leaps in depth, but it's not always just about equalization and hypoxia...).

For me, "normal contractions" at any depth I've been to seem to cause no problems, I've done some pretty long hangs (taking dozens of contractions) at depths close to or past my RV, and I'm pretty convinced that it's the kind of contractions described above that are the dangerous ones. Then again, never suffered a squeeze, so maybe I'm just one of the lucky ones and not that prone to it.

 

[DeepThought]

These kind of contractions also came up into my mind when I read that. But I wasn't sure if that was the case. Jome's post made the connection clearer.
The only obvious lung squeeze I had (spitting red blood, whizzy breath, reduced O2 uptake) was when I was doing a negative pressure dive. I lost my mouthfill (which accidently had some water/spit inside) and at that point got a small amount of water in the back of my throat. I got those rapid uncontrollable 2 per second contractions that had nothing to do with C/O2. Took me 2-3 seconds to react and ascend where it immediately stopped.
I guess it might be some kind of a defense reflex due to irritations in the throat, as it is known that similar irritations can trigger laryngospasm.

 

[naiad]

Actually, I get similar "pressure contractions" with just negative packing dry apneas (contractions starting very early, way before the Co2 or o2 limits)

That happens to me with negative statics. It must be the negative pressure, because it happens almost immediately, before it could be anything to do with CO2 or O2. It is a 'pulling' contraction instead of a 'pushing' one. Normal CO2 or O2 contractions are trying to force air out, but this kind is trying to breathe in. It is much worse.

I get the same contractions when I get into cold water, or if I dive without a mask.

It does get easier with training, and it doesn't happen as much now as it used to. I don't do many negative statics anyway, I must give it another try.

Lucia

 

[OceanMan]

I am not sure it was really a negative pressure contraction since I had this contraction at 35-38m when I was still above RV.
Nevertheless it's interesting. It might have been some sort of laryngospasm triggered by something.
But did the contraction produce the bleeding? Or did the bleeding trigger the contraction? And why and how could I have been in over-pressure back to surface ??

I also want to point out that if I hadn't spit by making mucus come up on purpose from deep in my throat, I would probably be thinking that the squeeze wasn't so bad. I think a lot of small/medium squeeze probably go undetected...

 

[bubestube]

These ... laryngospasm.

your xenu link ROCKs!!!!roflroflrofl

 

[DeepThought]

your xenu link ROCKs!!!!roflroflrofl

No one can resist clicking!
Hail XENU!!

​

 

[cdavis]

More like nice buns.

Well, back to the ah, subject. I get a very strange and very powerful diaphram/chest heave (contraction?) down around RV. The first time it happend was the first time I tried to dive deeper than 75 ft. I've learned to control it, and it usually doesn't show up now except on extreme (for me) negative preasure dives. If it gets out of control, its time to abort the dive. I'd never heard anyone describe it before. Is this the same thing that is being reported in this thread?

Connor

 

[naiad]

I think it is the same thing. It is quite different from a normal contraction. I thought I was the only one until I saw this thread.

 

[OceanMan]

I think I may have had an inhibited blood shift scenario this week end. I have healthy lungs and my heart was hopefully beating during the ascent.

It was a 45m dive with medium packing and at the end of the dive, at approximately 5m to the surface, I definitely felt over-pressure in my lungs. Just like if my lungs volume had decreased during the dive (maybe because of bloodshift). The volume of air was increasing back to the volume I had at the start of the dive (minus the amount of 02 consumed etc...) but my lungs seemed not to be able to contain all this air anymore. I started breathing out after a reaction time of 1-2 seconds.

One hour after the dive, I felt like mucus was coming up from my lungs/throat (like it happens when you are ill from lungs or nose), I cleared my throat hard to make it come into my mouth, and I spit blood. I don't know if the over-pressure was the cause or the consequence of bleeding (other things went wrong during this dive).

http://mattcl.free.fr/commun/squeeze_small.jpg

I just had a very interesting conversation with my doctor who is a CMAS doctor (though more specialised in scuba than in freediving).
We developed a new theory about the overpressure I had on a 45m dive (see the quote).
Let's try to explain it :
For this dive, I tightened my weightbelt quite hard on my hips so that it does not move during the dive. Then I did 10 packs and started the dive. At 25m my weightbelt fell off on my ribcage :duh It did not worry about it and forgot it to focus on my relaxation. On the way back up my weightbelt was probably somewhere on my belly. It's impossible for it to come back on the hips. But, with 10 packs, my belly has a greater diameter than my hips. Hence, when I reached 5m, the weightbelt was restricting my lung volume, probably producing the overpressure.

Anyway, the overpressure has probably nothing to do with the squeeze I had on this dive and the blood spitting. According to my doctor, the blood can only come from the alveolis and not the throat, trachea etc... which is quiet scary. He didn't seem too worried about the blood spitting though if it does not happen on every dive.

 

[tylerz]

I have long suspected that I was having blood spitting due to bleeding somewhere amongst or between the pharynx and the trachea. I believed this because I would often get blood spitting after many successive shallow dives (above 18m) coinciding with fatigue and stress especially relating to equalizing. Also, I never felt sore in or around my chest even after a couple deep dive blood spitting incidents. I would often feel that the back of my throat was somewhat tender, similar to when you get a sickness developing in your throat.

Recently I had another incident that brings me to feel confident that it is a correct conclusion that the blood spitting for my particular case is not involving alveoli. I had very intense contractions on a recent dive to a depth that I have regularly been to, yet is a depth that brings my lung volume below residual. The most severe contraction induced strain such that I noticeably felt the stress in my throat and noted it in my mind. Upon surfacing I felt fine in all ways. A half hour or so later, I had the familiar taste of minute amounts of blood when I would squeeze saliva up from my throat, like when you have phlegm in your throat and you try to extract it to spit out. I did not cough at first even though I could taste the blood. I had previously been very forcefully exhaling to test whether there was blood in my lungs, listening for the raspy bubbly sound, yet there was none.

Eventually, I did hear it and then began coughing a little. It subsided quickly, but later I noticed if I continued to squeeze my throat to bring up saliva that blood would appear each time, even though I had not been coughing any further. My throat also had the tender infected feeling. I could tell it was wounded in some way.

The following day I dove to deeper depths with much milder contractions and again found myself able to squeeze minute traces of blood up with the saliva, yet had no coughing or wheezing on ventilations. My throat stayed tender for the following days.

I now suspect that the fact that I could squeeze the blood up in saliva suggests the trachea is not what is bleeding but the epiglottis itself or the larynx. For the most part I suspect it is the epiglottis which is raised up behind the tongue slightly and therefore leaking blood seems possible to be forced up the throat.

Whichever it is, I am confident that there are many of us who spit blood which has sourced from above the lungs without damage to the alveoli. Hopefully some tests could be done by doctors to confirm this. Maybe I should guinea pig myself for one of them soon.

 

[Bill]

"the blood can only come from the alveolis and not the throat, sinusis etc.."
Can someone explain to me why this blood could not be from sinuses. Thanks for bringing the thread up again as I missed it in Aug.

My spear fishing buddy used to spit up small flecks of blood after long days in the water. Never mentioned a sore throat nor other symptoms. The fact that he hyperventilated for about an hour might support your suspicion Tyler.

Aloha
Bill

 

[Fitz-Clarke]

I see no reason why the blood would have to come from alveoli. Some cases might, but blood can come from anywhere in the respiratory tract when it is under a negative pressure, either from depth or from contractions. There are two circulations in the lungs: the pulmonary circulation under relatively low pressure passing through the alveolar capillaries, and the bronchial circulation off the aorta under higher systemic pressure supplying the walls and mucosal surfaces of the trachea, bronchi, and smaller airways. Throat and sinuses are other possible sources. The only way you could be sure of the source is to see evidence of blood in the alveoli on xray or CT, or by bronchoscopy in the airways.

 

[OceanMan]

According to my doctor, the blood can only come from the alveolis and not the throat, trachea etc...

This is the opinion of my doctor about my particular dive. Though he is not a squeeze specialist, he is still a doctor, hence I have some confidence in what he says.
I am not saying that, in other conditions, the blood cannot come from other areas. Yet, he seemed to see no reason why the blood would come from the throat or trachea.
I have still doubts myself. Indeed, since I never felt short of breath and since I had the feeling on the next days that my lower throat had a wound of some sort (was not like normal), I thought that the blood was not coming from the alveolis. But it's only feelings and thoughts.

No comments about the overpressure theory so far?

 

[diveoceanos]

Hello all. I am mostly involved and studying the physiology of SCUBA diving. Since this is a very interesting subject I thought to participate if you don't mind.

A resent reasearch I did in the medical bibliography revealed that DCS is a fact. There have been more than 90 cases reported in the medical journals internationally. I speculate that if one adds the cases that go untreated or un-diagnosed this number is expected to be higher. The condition after which DCS occur are not clear. If however one applies the decompression theory that is being used to calculate Nitrogen loading during a SCUBA dive, with certain assumptions, to free diving one can easily see that DCS is not far from real issue on very deep single dives or repetitive dives especially with short surface intervals (recover periods). I can present some results of a simulator that I developed if you find it usefull.

With regards to the other issue that is being discussed which is hemoptysis Iwould also like to draw you attention on the following thoughts. It is well established that alveolar rupture along with rupture of the surrounding capilaries may result in hemorrhage and penetration of gas in the circulation. This can result from a number of reasons including local blockage of the airways from tar or phlegms or blood. A mechanism of alveolar damage during breath-hold dives has been proposed in Chest magazine in 2001. According to the authors there is a combination of contributing factors that include:

A. Negative intrathoracic pressure due to the forced attempt to breathe (high CO2 effect)
B. Voluntary diaphragmatic contractions at the beggining of the ascent
C. Abnormally high stress in the walls of the pulmonary capillaries due to increased BP and higher volume of blood in the vessels. The pulmonary blood-gas barrier needs to be extremely thin for efficient gas exchange and thus it is vulnerable to extreme stress.

I hope this helps and doe not complicate the whole issue.

Please note that for the a lay person DCS and Lung Overexpansion Injuries need not to be differentiated as they share many common symtoms and signs and they are also treated similarly with the administration of Oxygen, Liquids and transfer to a recompression chamber. When the predominating symptoms are cough and hemoptysis, alveolar rupture might be the case. Arterial gas embolism to my perosnal opinion (just because it makes sense) in these cases should not be ruled out.

 

[DeepThought]

Hello all. I am mostly involved and studying the physiology of SCUBA diving. Since this is a very interesting subject I thought to participate if you don't mind.

Welcome aboard.

I can present some results of a simulator that I developed if you find it usefull.

That would be great!

 

[trux]

Yes, definitely DCS simulation or DCS models for freediving is something that was long missed. You should also consider contacting manufacturers of freediving computers (Liquivision, Suunto, Mares, ...) and propose them adding DCS handling based on your simulations. They usually contain DCS for scuba, but this feature is not active in the freediving modes, so freedivers can only rely on their experience, or on the surface intervals recommended by AIDA.

 

[diveoceanos]

Welcome aboard. That would be great!

I am skipping the details on the working principle of this program. Briefly it uses the Schreiner equation (Nitrogen Loading and offgasing at a constant rate of ascent descent, which is not the case in apnea diving. In apnea diving there is an acceleration downwards and upwards especially in no-limits or variable weights). Buhlmann M Values are being used. If anyone needs to have more information we can do this in a separate thread as this is not the purpose of this posting.

Here we go:

Single Dives.

Descent Rate = Ascent Rate = 75 m / min. Bottom time is 6 seconds. Total Dive time 3,65 minutes. Possible DCS for dives deeper than 133m

Descent Rate = Ascent Rate = 50 m / min. Bottom time is 6 seconds. Total Dive time 4,66 minutes. Possible DCS for dives deeper than 114m.

Multiple Dives.

Descent Rate = Ascent Rate = 35 m / min. Bottom time is 1':30". DEPTH = 30m. Total Dive time 3,2 minutes. Recovery time 1 minute. Possible DCS from repetition 16.

Descent Rate = Ascent Rate = 35 m / min. Bottom time is 1':30". DEPTH = 30m. Total Dive time 3,2 minutes. Recovery time 2 minutes. Possible DCS from repetition 22.

Descent Rate = Ascent Rate = 35 m / min. Bottom time is 1':30". DEPTH = 30m. Total Dive time 3,2 minutes. Recovery time 5 minutes. Possible DCS from repetition 97.

Descent Rate = 25 m / min, Ascent Rate = 40 m / min. Bottom time is 2':00". DEPTH = 40m. Total Dive time 4,6 minutes. Recovery time 3 minutes. Possible DCS from repetition 8.

Every combination is possible to be analysed with this simulator.

IMPORTANT NOTICE: Reader must understand the limits of this simulator programs. The program is based upon sound scientific knowledge but shall not be used to plan or predict the possibility of DCS in BHD. The same algorithm is being used to effectivelly plan and execute SCUBA Dives beyond the recreational dive limits, however there are great differences between a BHD and a SCUBA dive. Current knowledge, including the knowledge that being used in this program is not sufficient to establish guidelines or even advice.

 

[diveoceanos]

Two important issues on this simulator program.

There is no way of calculating the effects of high CO2 on the likelihood of DCS. We know that elevated CO2 increases the risk but there is no exact rule on CO2 - DCS risk relationship. As such in any simulation program there must be some conservative factors to be on the more "safe" side.

It is also clear that the great amount of research on DC theory and experiments performed at much lower ascent rates compare to the actual ascent rates of BHD. Fast Ascents are clearly a risk factor. Therefore an additional conservative factor shuld be incorporated.

So far there is no work on how to approach these two issues. The results in my previous post do not account for any effects of elevated CO2 or ascent rate on the DCS risk. DCS risk is therefore expected within the "no-risk" zone as well.

 

[trux]

Thanks for the info. It is excellent to finally see some data. Although it is clear that there are other important factors not included in the calculation, and that DCS can happen due to those factors sooner, it would be nice if the algorithm were used in freediving computers, warning so divers of emittent danger.

May I post a link to this part of discussion on Suunto's corporate forum? I already opened a thread about freediving DCS and the missing DCS calculation on freediving computers, so your information is definitely relevant, and hopefully someone in the corporation may be interested in it:

Suunto Discussions: Nitrogen calculations in freedivng mode

 

[diveoceanos]

Thanks for the info. It is excellent to finally see some data. Although it is clear that there are other important factors not included in the calculation, and that DCS can happen due to those factors sooner, it would be nice if the algorithm were used in freediving computers, warning so divers of emittent danger.

May I post a link to this part of discussion on Suunto's corporate forum? I already opened a thread about freediving DCS and the missing DCS calculation on freediving computers, so your information is definitely relevant, and hopefully someone in the corporation may be interested in it:

Suunto Discussions: Nitrogen calculations in freedivng mode

Feel free to post a link to Suunto's corporate forum. Suunto is known as a leading manufacturer of dive computers and employs some recent concepts on DCS theory (RGBM approach). It is also known as one of the most conservative manufacturers, as their algorithm is more restrictive compare to the one used by their American Based Competitors. I personally find it quite unlikely that Suunto will ever proceed with any free dive algorithm because the data on this area are currently very limited. Maybe in the future we will see something.

However Pelagic has allready introduced some computers with a real algorithm. They are using DSAT (PADI) algorithms (similar to those used in SCUBA diving) with some modifications. Their products are marketed by two major American companies, namely, Oceanic and Aeris.

I am a representative of one of these two companies in my country. I thought it would be fare for you to know.