Hi everyone,
I'm on vacation in Ontario--beautiful Georgian Bay (windy!

). Thanks for the invite to go diving Aaron, doesn't look like I'll have any time. But hopefully we can talk on the phone before I leave.
Couple of points:
1. Yasemin's thoracic filling: I think what she is referring to is the non-traumatic seeping of plasma into the lungs to protect them on very deep dives. I don't remember if this has been proven or if it is theory. I know that some deep freedivers "feel" plasma filling their lungs on dives over 60m+. Apparently, it usually retreats into surrounding tissues as the diver ascends. Sometimes it won't completely clear up and a diver will cough once or twice, but I believe in general it is clear fluid and not bloody. Yasemin's equalization with seawater has nothing to do with "plasma filling" of the lungs.
2. My theory about the cause of squeeze could be tested and I'm working on finding a physiologist and doctor to try to do some follow up experiments to test my theory. Basically, the more pressure on your lungs and heart from lung volume, the higher the risk of squeeze. What I would like to measure is the effects of packing on blood supply near the lung and in the thorax and also measure the amount of time required for it to return (if the first part is proven) versus a given increase in ambient pressure. Or you could separate it into two parts: 1. speed of descent vs. blood pooling (constant lung volume) and 2. lung volume vs. blood pooling (constant descent speeds).
3. From my personal experience and by talking with other divers, I've narrowed down a list of most crucial factors contributing to squeeze:
-speed of descent (especially in first 30m)
-lung volume (higher lung volume increases risk of squeeze)
-flexibility and elasticity of thorax (rib cage, muscles, and connective tissues)
4. I believe that other contributing factors include:
-hydration levels
-tension and anxiety
-body position or movements (arms)
-body temperature
-sudden jumps in depth
-breathing efficiency
-cardiovascular fitness (if you pack to the max, what effect and pressure must the heart overcome to ensure proper blood flow to the lungs and thorax?)
5. I also can say from my own experience that having congested lungs is almost a guarantee for some sort of squeeze episode
6. There is a difference between squeeze of the esophagus or upper bronchii and a barotrauma of the lungs. In my opinion, the difference is in the symptoms of coughing, wheezing, volume of blood coughed up, and long term symptoms like pain, difficulty breathing, dizziness, weakness, etc... So far people with esophagus squeezes don't have persisting symptoms or much more than a little blood after surfacing.
7. Many, many freedivers flirt with squeeze and are in denial about how close they are to having a bad episode. Most of them are in the 25m-55m range.
8. I haven't met any instructors who really paid attention to squeeze and how to avoid it in their course curriculum. Probably because they haven't experienced it themselves.
My protocol for avoiding squeeze is as follows:
-good cardiovascular shape (which is sometimes at odds with training methods that I prefer)
-FRC warm-ups for exceptional chest flexibility (30m+)
-staying warm, hydrated, relaxed and confident
-slow descent speed in the first 30m (0.5-0.7 m/s)
-minimal packing
I feel that this routine gives my body the chance to adapt to the stresses imposed on it by deep dives. I've had to adopt it out of necessity, since my lungs seem more easy to squeeze than most other people's. But I know that a lot of other people are at risk.
If anyone else has theories or questions, I'm glad to hear them.
Cheers,
Pete Scott
Vancouver, BC