Fear the Squeeze

One hundred and seventy-six freedivers from around the world are training for the 2003 Freediver Open Classic in Cyprus. Many of them, hoping to follow in the footsteps of world champions like Coste, Cruickshank, and Stepanek—with the knowledge that the minimum depth to be competitive is at least sixty metres—will push themselves and risk suffering from barotrauma of descent a.k.a "lung squeeze," an injury largely ignored in the freediving world.

When Enzo Maiorca descended beyond –50m and then Jacques Mayol surpassed –100m, the phrase "barotrauma of descent" was forgotten in the collective consciousness of freedivers. In the early days, doctors warned Maiorca that his lung would collapse under the pressure of the abyss. In simple terms, their model for the lung at depth was that of a container filled with gas compressed with each atmosphere of pressure until the residual volume (RV), or the minimum volume of lung gas needed to maintain oxygen and carbon dioxide exchange, was reached. Beyond that, they thought, the lung would stick together like a popped bubblegum balloon and suffocate the diver. What the scientists didn’t understand was that blood pooling in the body’s core allowed freedivers to go much deeper than the theoretical depth calculated by Boyle’s Law.

We are all happy to imagine ourselves as dolphins or seals, one step ahead of science. We’ve got the blood shunt, we’ve got bradycardia, and peripheral vasoconstriction, and splenic contraction—we don’t need the doom and gloom of physicians that have been wrong in the past. Even I remember a feeling of defiance when I put the -50m mark behind me back in 2001. However, the lack of scientific certainty does not mean that diving below your residual volume is risk free. I did not reach Maiorca’s science-busting depth unscathed.

My Personal Experience with Barotrauma of Descent

In 2001, training for the Canadian Nationals, I wanted a spot on Team Canada. The weekend before the competition, I increased my personal best by eleven metres in one day, from -37m to -48m. At the time, I was not aware of the stress this sudden plunge downward had had on my lungs. Five days later, I announced –46m and made it, like a beginner, nervously sprinting the whole way. For about an hour following the dive, I spat blood and was wracked with body buckling coughs, wheezing and rales.

I made Team Canada, but I suffered lung squeeze at least three more times. I was going too deep too fast. I decided to start all over again at –35m with a longer warm-up, negative pressure dives of increasing intensity, and even repeated neutral-breath dives up to -25m. I increased the depth only after reaching a "safe" depth several times without any symptoms at all, gradually inching my way downward. Before Ibiza, I made several dives to over -50m without any symptoms. I was pretty happy that my precautions worked.

In the fall of 2002, after a year off from competing, I decided I wanted to train in no-fins constant ballast. Initial training went really well. And then it happened again, despite all of my precautions, and this time I experienced the worst lung squeeze ever.

I had set a new unassisted Canadian record of –35m with on September 14, 2002, after recovering from a two-week long chest cold. The following weekend, I tried for –42m, a depth well shy of my personal best with a monofin, and, I assumed, nowhere near a depth that could squeeze my lungs. When I surfaced from the dive, I told my buddy, Eric Fattah, that it was the hardest dive I had ever done. True, because I was gasping desperately for air. The coughing and wheezing was so bad, it took a good ten minutes for my arms and legs to recover their oxygen debt. I clutched the float, trying to ride the wave of spasms each cough ripped through my diaphragm. Stephanie Ortlepp dragged me back to shore because I couldn’t breathe well enough to swim on my own. I had the distinct feeling that my lungs were coated from the inside with blood, preventing the alveoli from absorbing oxygen. Not surprising, given the quantities of blood I was hacking up into the ocean. It took nearly two hours before I could take a full breath without coughing up bloody sputum; plenty of time to reflect on what had gone wrong. I took the whole week before the pain in my chest went away, and another week after that until I could breathe freely.

Respecting the Weight of the Ocean

What had happened? Was it because my chest congestion had not completely cleared, or was it the extra stress of using my arms for propulsion on the chest wall?

I decided to rest for at least six weeks before diving again at all. I also decided that in addition to reevaluating the precautions I had taken in 2001, I would try to find out what diving medicine had discovered about barotrauma of descent since the 1960s, in order to avoid future injury altogether.

In my mind, I had a working definition of lung squeeze. It was a combination of pulmonary edema (the swelling of blood capillaries and accumulation of fluid in the lungs), intra-thoracic hemorrhaging (caused by negative pressure at the alveolar level that ruptures the alveoli and surrounding capillaries), and the resulting blood in the lungs and hemoptysis (the coughing up of blood in the sputum, as the body tries to eliminate the blood that is impeding alveolar gas exchange). The symptoms of lung squeeze, as I had experienced them and according to definitions of the conditions I just listed, include: cyanosis, an intense coughing reflex, coughing up blood, wheezing, rales, shortness of breath, dizziness, feeling of suffocation, weakness, extreme fatigue later in the day, tightness in the lungs, and pain in the chest area. The greatest danger of severe lung squeeze is that it can cause secondary drowning, meaning that instead of drowning under water, you drown in your own blood, as your blood-coated alveoli can no longer exchange carbon dioxide for oxygen. Not a nice way to go.

Some important questions remained. Did lung squeeze episodes cause permanent injury? Was I in some way predisposed to it? Was there one factor in particular that could predict an injury?

Looking for Answers

After my experience, I posted the details on the Canadian freediving forums and discovered that several new freedivers were flirting with lung squeeze. The freedivers most at risk were the ones trying to qualify for the AIDA World Cup in Kona, Hawaii.

Perry Gladstone, a contributor for Deeperblue, and a Team Canada hopeful in 2002, also ran into the same problem, with severe symptoms. And yet, when he sought advice as a patient and asked how he could avoid injury in the future, the experts in the field were unable to provide any definitive answers.

After my own searches turned up empty, I composed a letter to Dr. Claes Lundgren, Professor of Physiology at the State University of New York in Buffalo’s Center for Research and Education in Special Environments, and to other experts in diving physiology, including Dr. Ernest Campbell at www.scuba-doc.com, Dr. David Sawatsky, (the "Diving Doctor"), Dr. Guido Ferretti, and many others. I outlined my assumptions about the lung at depth during a breath-hold dive and asked for a list of risk factors. Those who responded all pointed me to Dr. Lundgren, who has published a large number of scientific papers on breath-hold diving and edited and contributed to two hefty and expensive books on diving, The Lung at Depth and Physiology and Medicine of Diving. Too busy to engage in a discussion, Dr. Lundgren kindly sent me a copy of a chapter on breath-hold diving from the second book. In his email, he said that my ideas were interesting, but that many questions remain unanswered.

It would be great if we could use the miniaturized submersible from the 1966 science-fiction film The Fantastic Voyage to penetrate the alveoli and see first hand what happens during a deep dive. Unfortunately, we would still need test subjects willing to suffer lung squeeze for science (and a scientific research ethics board to allow it). For now, we are limited to anecdotal evidence, simulated laboratory experiments in a hyperbaric chamber, and unproven theories.

So here I lay out my theory of lung squeeze and its contributing factors, based on personal experience in my own dives and the hints provided by scientific research. I hope that someone with the expertise and opportunity will take up this important line of research and help prevent future injuries.

A Theory of How to Minimize the Risk of Barotrauma of Descent

Since a freediver’s residual volume may depend on a number of variables (some divers have experienced lung squeeze as shallow as -20m), the following factors should be considered for any depth, even above the theoretical depth that residual volume is reached.

1) To prevent a negative pressure in the lung, the rib cage, thoracic tissues, and muscles must be allowed to collapse under ambient pressure as much as possible

2) Avoid extreme diaphragmatic contractions at depth, either from elevated levels of carbon dioxide, from equalizing effort, or shivering, that can exert a sudden negative pressure on the lungs. (One study found that freedivers making voluntary contractions at depths less than -25m coughed up blood at the surface, another cites the forced effort from valsalva equalizing creating sudden negative pressures in the lung as a possible cause of hemoptysis.)

3) Use the right stimulus and allow enough time for optimal core blood pooling to maintain intra-thoracic pressure equilibrium.

4) Have sufficient plasma volume for the blood shift. Dehydration and poor cardiovascular fitness could likely contribute to insufficient blood pooling in the body’s core.

5) Avoid diving with any sort of lung congestion. (As I write this, I am recovering from a chest cold. I am taking a break from training to be safe.)

6) Use the Frenzel-Fattah mouth-fill equalizing technique carefully. Filling up your mouth at depth, between –25m and -35m, draws a significant volume of compressed air out of your lungs all at once. It could aggravate lung squeeze by suddenly pushing your lung volume below RV.

Since my injury in 2002, I’ve been following the following training routine to minimize the risk of lung squeeze:

-A daily thoracic stretching regimen, including yoga stretches, pack stretches, graduated negative pressure dives, and, of course, multiple dives to the same depth before going deeper. A flexible and elastic diaphragm, ribcage and thoracic muscles makes equalizing easier and helps to maintain the intra-thoracic pressure equilibrium.

-A slower depth training progression over weeks and months.

-A longer and more specific warm-up in the water. Despite the usefulness of negative pressure dives in preparing the body for deep dives, I find that dives of increasing depth are a more specific stimulus to prepare the body for increased ambient pressure. And the problem with negative pressure dives is that it is too easy to stress the lungs with extreme simulated depths.

-Slower descents to allow the body time to react to the relatively rapid change in ambient pressure.

In summary, my new approach to deep freediving is to "take it easy." For other competitors who want to get deeper fast, this is not how they want to train.

Preventing Lung Squeeze in New Freedivers

The Polynesian and Ama divers appear to have learned that diving below –40m, the average depth where residual volume is reached for many people, is a dangerous undertaking not to be taken lightly. Or else they find what they need at shallower depths. Just because modern freedivers can dive much deeper does not mean that we should take that ability for granted.

Other unknowns also complicate the risk evaluation of going "deep." The function of the cardiovascular and circulatory system is tied to the pulmonary system. Changes in blood pressure, stroke volume, heart rate, and other variables may also increase the risk of pulmonary edema and intra-alveolar hemorrhaging. However, without specific proof, it is unlikely that freedivers will take these additional factors into consideration.

More research is needed to develop a guide to reducing the risk of lung squeeze, just as attention has been focused on blackouts. We still don’t have a meaningful medical examination protocol for freediving. Most doctors have no clue how to examine freedivers on their way to a competition.

The freediving community also needs to gather statistics on barotrauma of descent. National freediving organizations (such as AIDA chapters) should keep track of athletes who surface with the symptoms of lung squeeze. I invite Philippe Afriat, the AIDA International physician at the Cyprus competition, to be on the lookout for such incidents and keep track of the depths inscribed, experience level of each diver, and severity of the injury.

Instructors who offer freediving courses should also consider making lung squeeze a part of teaching safety. To my knowledge, few address lung squeeze and how to minimize the risk.

In closing, I hope that freedivers will start to recognize barotrauma of descent as another important risk to actively minimize in the freedive training. I also hope that accomplished divers will recognize that the freedivers most at risk are their friends diving below –30m for the first time.

Peter Scott freedives in British Columbia, Canada. After competing in the World Championships for Canada in 2001, he has continued his exploration of the ocean through writing, art, photography, freediving, swimming, surfing, windsurfing, and travel. Visit his website at www.holdyourbreath.ca.


  1. Hi Peter, nice piece on squeezes. Could you please direct me to the studies that you reference above, “One study found that freedivers making voluntary contractions at depths less than -25m coughed up blood at the surface, another cites the forced effort from valsalva equalizing creating sudden negative pressures in the lung as a possible cause of hemoptysis.”? Thank you.


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