New study on lung squeeze

[trux]

There is a new study released last month, trying to collect some data on pulmonary damage done during breath-hold diving:

Time course of carbon monoxide transfer factor aft...[Undersea Hyperb Med. 2009 Mar-Apr] - PubMed Result

Breath-hold divers may experience haemoptysis during diving. Central pooling of blood as well as compression of pulmonary gas content can damage the integrity of the blood-gas barrier, resulting in alveolar hemorrhage. The single-breath carbon monoxide test (DL,CO) was used to investigate the blood-gas barrier following diving. The study population consisted of 30 divers recruited from a training course. DL,CO levels were measured before diving and at 2, 10 and 25 min after the last of a series of four dives to depths of 10, 15, 20 and 30 m. When compared to pre-diving values, DL,CO values increased significantly at 2 min following diving in all subjects except one. Thereafter values progressively decreased toward baseline at 10 and 25 min in all subjects but one, while in four divers DL,CO values decreased below baseline. The early but transient increase in DL,CO levels shortly after diving supports the persistence of capillary pooling of red blood cells following emersion. Persistence at 25 min of high DL,CO values in one subject could be attributed by lung CT to extravasation of blood into the alveoli. Early or late DL,CO values >10% below baseline values suggest the presence of pulmonary edema. The relatively high prevalence of DL,CO alterations found suggests caution on the safety of breath-hold diving activities.

 

[trux]

There is another new interesting study about lung squeeze, better told about pulmonary edema (both terms are often used for the same symptoms, but a lung squeeze is actually a common barotraumatic cause of a pulmonary edema).

This study does not describe depth induced edema (barotrauma), but it investigates cases of pulmonary edema at triathlon athletes during surface swimming. It can be interesting for those suffering from lung squeeze at shallow depths, just like described in the recent thread http://forums.deeperblue.com/freediving-science/88389-spitting-blood-after-free-dives-help.html (though that one is more likely a sinus or trachea squeeze than pulmonary edema), or in greater details in the older thread of Ol Dirty Diver: http://forums.deeperblue.com/safety...dema-lung-squeeze-help.html?highlight=squeeze

What I find very interesting and possibly an important information to many freedivers and spearfishers is the identification of fish oil as risk factor. Since particularly spearfishers usually eat a lot of fish, and I know many freedivers consuming fish oil too, this information may be interesting for them.

The study: Elsevier

Background

Pulmonary edema related to water immersion has been reported in military trainees and scuba and breath-hold divers, but rarely in the community. To date, no risk factors for this phenomenon have been identified by epidemiological methods. Recently, sporadic reports of swimming-induced pulmonary edema (SIPE) have emerged in the triathlon community. We surveyed the population of a national North American triathlon organization (USA Triathlon) to determine prevalence of and risk factors for symptoms compatible with SIPE.

Methods

We surveyed the population of USA Triathlon through the organization's monthly newsletter distribution channel. We evaluated prevalence of symptoms compatible with pulmonary edema, and then followed up with a case-control study that included additional cases we had identified previously, to identify risk factors for this condition among triathletes.

Results

Symptom history compatible with SIPE was identified in 1.4% of the population. Associated factors identified in multivariable analysis included history of hypertension, course length of half-Ironman distance or greater, female gender and use of fish oil supplements. Of the 31 cases reported, only 4 occurred in the absence of any associated factors.

Conclusions

The identification of hypertension and fish oil in particular as risk factors raise questions about the role of cardiac diastolic function in the setting of water-immersion cardiac preload, as well as the hematologic effects of fish oil. Mechanistic studies of these risk factors in a directly observed prospective cohort are indicated.

 

[efattah]

Fish oil is known to thin your blood and reduce your heart rate as a result of the heart needing to do less work, and pumping more blood more easily on each stroke.

Presumably, thinner blood can enter the lungs easier than thick blood -- but the edema they are talking about sounds like pure plasma entering the lungs, and not red cells.

 

[Anders]

Even if it's pure plasma it may be affected by fish oil. As far as I know, the fish oil (more precisely EPA) makes your blood coagulate slower. This is due to the eicosanoids, which I think are in the plasma, not the erythrocytes. Therefore, the edema is more likely to occur in fish eating divers, no matter if its whole blood or just plasma.

 

[Rik]

It is a nice article, but it isn’t comparable with free diving at all.

We assume that lung squeeze is caused by the stress of the negative pressure in the lungs during freediving. This stress can cause the rupture of blood vessels, causing bleeding. Use of antiplatelet compounds, like asperin, can aggravate bleeding, as described by Boussuges (1999).

Pulmonary edema is a whole different phenomenon. The left hart chamber is unable to regain its usual size during its resting point (diastolic dysfunction) which causes a build-up of pressure in the pulmonary arteries, pushing the plasma out of the lung arteries and veins.

While both problems can occur at the same time, they are caused by two different mechanisms and should not be confused.

The article has used an questionnaire to evaluate pulmonary edema, and this limits the quality of the article. It might also be prone to confounding factors. An athlete with complaints from pulmonary edema might choose to use fish oil because they believe it might improve their health compared to those who don’t have any health complaints. A different factor is selection bias, because only few members of the targeted audience responded on the inquiry (1,4%). While the represented age is similar, it is not known if the responders are equally active swimmers compared with those who didn’t respond to the questionnaire.

Conclusion. It is an well written article, but it only has a limited value for freediving, until a study is performed that differentiate between pulmonary edema and lung squeeze in freediving. The study itself has several limitations which are acknowledged by the authors.

 

[Rik]

Fish oil is known to thin your blood and reduce your heart rate as a result of the heart needing to do less work, and pumping more blood more easily on each stroke.

Presumably, thinner blood can enter the lungs easier than thick blood -- but the edema they are talking about sounds like pure plasma entering the lungs, and not red cells.

Any substance that has an anti-platelet effect doesn’t make the blood thinner.
This is a common misconception. Anti-platelet compounds, like aspirin and fish oil, only increase bleeding time. Fish oil might have a cardiovascular advantage on the fat levels in the blood. To my knowledge, it doesn't influence the hematocrit levels, which determines the "thickness" of the blood.

 

[Mr. X]

Pulmonary & cerebral edema/oedema are also concerns for mountaineers, as they are two common and potentially lethal symptoms of altitude sickness. I've not heard of any fish oil related incidents but I have heard of mountaineers taking olive oil on climbs for energy (although I also heard of a vegetarian Sheffield climbing leaving on a climbing trip with just a very large bag of carrots to eat - it certainly wouldn't suit everyone).

 

[trux]

It is a nice article, but it isn’t comparable with free diving at all.

I believe just the contrary. The cases of "squeeze" or pulmonary edema at freedivers who only dive relatively shallow are surprisingly common. They often suffer edema at dives above the negative depth (between 10 and 30m). There are possibly multiple factors playing a role in such cases: suspected triggers are packing, strong vasoconstriction, strong diaphragmatic contractions, insufficient thoracic and diaphragmatic flexibility due to muscle tension (stress or cold induced), and others. However, I see no reason why we should exclude the same triggers that lead to pulmonary edema at surface, also at freediving. If 1.4% of the population were identified with the symptoms, there is no way some of them are not freediving too. In that case they will be likely more susceptible to pulmonary edema both at shallow as well as at deep dives.

This additional factor may contribute to explaining some of the cases of squeezes that some freedivers are often fruitlessly fighting with. The following thread describes some of such cases, but I know about several others both from DB, as well as from other forums, and from real-life too:

http://forums.deeperblue.com/safety/69802-immersion-pulmonary-edema-lung-squeeze-help.html

So if someone suffers frequent lung squeezes while freediving, knowing about this risk factor is certainly important. Hence I would not tell that there is little value for freediving in this report.

 

[trux]

And another new study about pulmonary edema at breath-hold diving was published a few days ago:

Pulmonary edema during breath-hold diving immersio... [J Appl Physiol. 2010] - PubMed result

Unfortunately there is no abstract (yet), hence I do not know what exactly the conclusions are. Hopefully, some of our academic members will have access to the document and will be able to report back.

 

[mystiach]

Hi trux,

It's not an article per se, but one of a whole lot of short academic texts debating this (let me know if the link doesn't work).

JAP is free for public after a year... I doubt they will put abstracts up, as it's not really the correct format. I'll try and summarise later today, don't have time now! At a glance there's plenty for both the for and against, though, as she says in the main article, slightly easier to prove the affirmative.

So... good news for us the jury is still out :blackeye

Cheers from down under

 

[Rik]

While both problems can occur at the same time, they are caused by two different mechanisms and should not be confused.

I don’t claim that pulmonary edema can not occur among freedivers. Nor do I claim that pulmonary edema is an irrelevant topic. I do claim that pulmonary barotrauma and pulmonary edema are two different afflictions that should not be confused. This is also confirmed in the original article (Swimming-induced pulmonary edema in triathletes).

There is another new interesting study about lung squeeze, better told about pulmonary edema (both terms are often used for the same symptoms, but a lung squeeze is actually a common barotraumatic cause of a pulmonary edema).

The above quote is not correct because: a. the terms are not used for the same symptoms among (most) physicians, b. pulmonary barotrauma doesn’t cause the described pulmonary edema in the referred article.

The “Swimming-induced pulmonary edema in triathletes” study isn’t comparable with free diving because:
1. The described study population isn’t comparable with breath-hold divers, thus any conclusion might not apply to breath-hold divers.
2. There is a different hypothesis for the cause of complaints (cardiac induced pulmonary edema versus the mechanical or pressure related rupture of tissue), thus the design of the test might miss anything relevant for breath-hold divers and the results might not apply to breath-hold divers at all.

Even if some of the 1,4% of the divers are breath-hold divers, it is still unknown if the described risk factors do apply to them. There is no sense in warning people for a dubious risk factor for a phenomenon that might or might not apply to them.

The cause and effects of pulmonary edema in athlete’s are under debate. The mentioned article of R. Prediletto is part of a discussion titled: Comments on Point:Counterpointulmonary edema does/does not occur in human athletes performing heavy sea-level exercise.

The conclusions in this discussion are varied. Suggested causes are cardiac and possible altered pulmonary microvascular permeability and individual predisposition. R. Prediletto does suggest a link between the symptoms of pulmonary barotraumas and pulmonary edema, but doesn’t explain how the mechanical cause in breath-hold diving could be similar compared to the described cases within athletes doing exercise.

The symptoms of lung squeeze can mimic pulmonary edema, and several other ailments. Without a detailed history, physical examination and perhaps even field tests, it is difficult to make a diagnosis of the affliction. This problem was also mentioned by the authors of “Swimming-induced pulmonary edema in triathletes”.

Divers should see a diving or sport physician if they suffer from repetitive lung squeeze like symptoms. The physician could help to establish the diagnosis.

Currently there is no established treatment for exercise induced pulmonary edema. And there is no evidence that lowering the blood pressure or avoiding fish oil might prevent pulmonary edema. Thus talking about this risk factor isn’t a solution at all, and is only cause for confusion and possible delay of treatment of a more serious cause.

 

[trux]

Rik, I agree with you in many points, but you are unjust in some of your judgments.

So for example I stand behind my original claim that the terms pulmonary edema and squeeze are often used for the same thing, and that they are often mixed up (and often incorrectly). If you look up the literature about pulmonary edema at breath-hold diving, you can easily see that it speaks about the barotraumatically induced edema, and not about edema caused by modified cardiac output. See for example documents like Pulmonary edema and hemoptysis after breath-hold diving at residual volume, Pulmonary edema after competitive breath-hold diving, or just the previously mentioned Pulmonary edema during breath-hold diving immersio... [J Appl Physiol. 2010] - PubMed result, and many others. In contrary, a layman ordinary freediver will rarely use the term pulmonary edema, but will always speak about "squeeze", although it is often not at all any barotraumatically induced edema, but it may come from other reasons (or it is a complicated mixed case) - the cases of freedivers suffering frequent "squeezes" at shallow diving mentioned in my previous message are the best example. And for example most French freedivers do not use the term "squeeze" at all - they only use the term edema.

So do not tell me that the terms edema and squeeze are not often used for the same issue, because it is simply the case, whether you like it or not, and whether the use is correct or not.

Now back to your claim that there is no sense in warning people for a dubious risk factor for a phenomenon that might or might not apply to them. I simply do not agree. There is absolutely no reason why this risk should not concern freedivers too. Even if the relation to barotraumatic pulmonary edema was not studied, as I wrote there are numerous cases of freedivers suffering pulmonary edema even without diving to negative depths. So concerned people may be glad to know about this possible risk which may be very well the same as at triathlonists or swimmers.

And then, although not studied and confirmed, it would be rather expectable that a factor increasing exercise induced risk of pulmonary edema will have very similar effect at a barotraumatically induced edema too. Perhaps you are right, and perhaps it has no influence, but frankly told it would be very surprising that a person susceptible to an exercise induced edema would be resistant against barotraumatic edema.

However, nobody in this thread ever claimed that the conclusions from the study about triathlon athletes should be applied to freedivers. I merely posted it here, because I believed that it was of interest, and I know that there are at least some people who appreciate knowing about it.

As a conclusion, I agree with you that anyone suffering an edema or squeeze should consult a specialist. The only problem is that even good pulmonary specialists know rarely something about the specifics of freediving physiology, and that unfortunately not always they are very helpful. In better case they cure you adequately, in worse case they forbid you diving.

 

[Rik]

Dear Trux,

I understand you are trying to aid other freedivers by mentioning articles. The medical knowledge on freediving is quite scattered, and there it is sensible to post those articles on Deeperblue. And I have to admit that my previous post where perhaps too harsh.

However it is important to know that not all articles are equally helpful. Some article’s contain errors, other articles have used weak statics. Some articles are even difficult to interpreted for those with a degree in medical sciences.

My initial comment was a response to the article “Swimming-induced pulmonary edema in triathletes”. And I have explained why this article doesn’t give useful information for freedivers. You can agree, or disagree with that. This is just my review of this specific article.

I don’t ignore that freedivers might have exercise induced pulmonary edema in combination with pulmonary edema due a lung barotrauma (or any other alternative description of lungsqueeze).

Exercise induced pulmonary edema might be a cause of complaints after shallow dives. However, we shouldn’t forget that the medical community itself isn’t clear about this subject. Pulmonary edema itself might be a symptom of various causes, each asking for an unique approach.

I agree that physicans in pulmonology and cardiology might not know enough of freediving. But they should know enough to rule out most other common causes. Without their evaluation, it is just pure speculation on the cause of the complaints of this specific group within the freediver community. And speculation alone won’t give a reliable cure of those symptoms.

Perhaps a national medical advisor connected to a national freediver association could help those individuals with a unexplained medical history of shortness of breath after diving. Finding one physican for this particular task won’t be a big problem. The national advisor doesn’t have to treat the freediver, but could refer affected freedivers to physicians that can help them with their situation.

 

[Johan Andersson]

A new study about "lung squeeze".
Maintenance of vital capacity during repetitive ... [Respirology. 2011] - PubMed - NCBI

Background and objective:  Cough and a reduction in vital capacity have recently been reported following breath-hold dives to depths of 25-75m. We sought to investigate whether repetitive dives to depths of less than 30m would elicit similar effects. Methods:  Participants in a single-day spearfishing competition were recruited. Subjects performed spirometry before and after the five hour event. Demographics, medical and diving history, respiratory symptoms and competition diving statistics were collected. Results:  25 subjects (2 female), age 33 (11) [mean (SD)] years, were studied. During the competition each subject completed 76 (33) dives, to 10 (3) m depth, with each dive lasting 0.9 (0.3) min. Maximum depth was 17 (4) m. No respiratory symptoms were reported. There was no difference in spirometry before and after competition except for FEF(25-75%) which increased by 0.16(0.34) L (P < 0.05). Conclusions:  Pulmonary oedema or lung injury is not common after repetitive breath-hold diving to depths to 25m, or is too mild to be reflected in symptoms or spirometry.