Lung Squeeze clarified

Lung squeeze is a shy topic among freedivers. There is very little information available either in books or on the internet and little scientific research seems to have been undertaken, as if it is a rare and uncommon problem. However, when asking around it seems most freedivers have suffered from it at some point in their diving careers, coughing up varying amounts of blood. Some continue diving and seem to get over it. For others it never goes away and they eventually retire from deep freediving with great frustration. Not coming from a scientific background, I struggled to find good explanations describing what happens and why and still am failing miserably to solve the problem despite giving myself time to try many different things that have worked for other people. I am also slowly learning from my mistakes. Here is some information that will hopefully help others to avoid what I have been experiencing.

You do not have to be a particularly deep diver to experience lung squeeze. I have heard of divers experiencing squeezes after dives as shallow as 4m (in a swimming pool), especially if they are diving on FRC, negatives or passive inhales. You do not actually have to cough up blood to be suffering from a lung squeeze. You may just be able to feel a little bit of fluid in your lungs after a dive and take a while to recover while breathing heavily. If you continue to dive after this then you will most likely make it worse and end up coughing up blood, requiring a longer time to recover.

There are two things that can happen. The first is that as you reach residual volume (the volume of air remaining in your lungs once you have fully exhaled) the negative pressure in the lungs will cause the lung walls to stick together and cause damage as they peel apart (essentially grazing the inside of your lungs) and the blood vessels can swell up and burst, causing bleeding inside the lungs (pulmonary edema). This creates a cough reaction to remove the fluid (blood) from the lungs. The likelihood of this happening is increased by diving deeper than your residual volume, the occurrence of contractions at depth or the use of the valsalva method of equalisation (pushing air directly from your lungs to equalise your ears), all of which create a huge negative pressure within the lungs and tension on the chest. Once a squeeze has occurred there will be scarring on the lung tissue and the chance of it happening again is greatly increased over the next few days and possibly weeks.

Other factors that could contribute to a squeeze are fatigue, discomfort and fear, tension or lack of flexibility through the chest/ribcage, or lack of elasticity in the lungs, which seems to be the case with a lot of pool divers who have stretched out their lung with a lot of packing. Over hydration can be a factor in blood spitting as there is already more fluid around the lungs which may not be retracted into the body after blood shift, however dehydration can make equalisation more difficult and cause the diver to tense up the chest area. Jet lag can make “easy” dives very uncomfortable and tiring. Careful adaption dives are fine while the body is jet-lagged however deeper dives should be delayed until the body has recovered. A general rule is that jet lag, whether you consciously feel it or not, lasts about one day for every hour difference.

There may be more blood if the squeeze occurs near a capillary where there is more blood available, so the quanity of blood is not a good indication of the severity of the squeeze. There may be a lot of pain or no pain at all depending on where the squeeze occurs, as there are no nerve endings in the lungs.

Trachea squeeze should also be noted. Sometimes divers come up with a sore throat and spit a little blood, usually just a small amount and only once. This is often after looking down at down at depth and creating a negative pressure in the incompressible and delicate trachea, which can also result in burst capillaries. It is possible to increase the flexibility of the trachea to avoid this.

The second issue is the potential for over pressurisation of the lungs (pulmonary barotrauma) on the ascent once bloodshift has occurred, which would suggest that full packing for deep diving is problematic. A freediver who packs on the surface will use a little air in equalisation and metabolism during the dive, however the overall quantity of air in the lungs does not decrease a great deal for the ascent. If there is blood remaining in the lung capillaries from the blood shift then there is again the potential for the already swollen blood vessels in the lungs to rupture near the surface and the diver experiences overpressure. Barotrauma is normally identified by foamy blood.

Lung squeeze can be serious. If your lungs are full of fluid, the alveoli are not able to pick up the oxygen from your lungs to transport it through your body to where it is needed for metabolism. Your oxygen saturation levels are low and can remain that way for a long time. In an extreme case this can cause secondary drowning. If it occurs at sea you may not be physically capable of swimming back to shore or the boat. You may not have the energy to remove your wetsuit or walk to the car. Fatigue and wheezing from serious squeezes have been reported to last up to a month in extreme cases.

Remember to always dive “one up, one down” with your buddy and ensure that they understand the potential dangers of squeeze. I often black out when I suffer a lung squeeze, even if the dive is much shallower than what I am usually capable of. My body is unable to absorb the remaining oxygen in my lungs to complete the dive and it is slow to recover when I begin breathing on the surface.

To try to avoid lung squeeze you should consider the following:

• Avoid stretching out at depth with arms or neck. This includes looking downwards, taking large strokes/pulls at depth and swimming or freefalling with arms stretched above your head.
• Try warming up if this reduces your contractions at depth
• Work on your ribcage flexibility and stretch this area before diving deep
• Turn before you experience contractions at depth
• Progress slowly each time you start diving to depth
• Avoid deep dives after travelling, especially if you have changed time zone or feel tired. Allow time to recover from jet lag prior to competing.
• Only dive as deep as you are comfortable with to avoid panic at depth
• Learn to relax at depth and release any tension from around the chest area prior to going to great depths. This can include tension from equalisation and learning to just keep the eustation tubes open during mouthfill equalisation may help or finding a very relaxed and streamlined body position that suits you.
• Learn the frenzel/mouthfill technique of equalisation
• If you are warming up and can feel the previous squeeze, do not continue with your deep dive
• If you have a history of squeezes, in competition nominate depths much less than the sucessful (no squeeze) dives you have completed in training and do not try for a personal best in the 3-4 days before
• If you have a history of squeezes, rest the day after a deep dive (even if you do not squeeze) as the potential for squeezing the second day seems to increase even if the second dive is much shallower.
• Maintain regular depth training sessions, even in the off season
• Start exhaling just before the surface (however this should be practised in a controlled environment)

If lung squeeze occurs you should:

• Stop diving and exit the water
• Stop any physical activity. Ask your buddy to tow you to shore and carry your equipment
• Breathe pure medical oxygen, if available
• Seek medical advice promptly, preferably from a designated dive doctor. They will quite likely give you some antibiotics to ensure you do not get a lung infection or pneumonia
• Drink plenty of fluids
• Take iron and vitamin C to help repair and reduce risk of colds
• Rest at least for several days before diving or putting any pressure on the lungs