Fear the Squeeze
Posted By Peter Scott on 7 April 2003
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.
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