Very interesting question. Is pretty well established that a moderate exhale in the last few meters of CW, (5-10 ?) reduces the possibility of BO. Generally quoted reasons include gas exchange in reexpanding lungs and reduced chance of cranial blood preasure changes as expanding lungs put preasure on carotid blood vessels. The possibility that exhale helps maintain blood shift adds a reason I had not considered, maybe an important one. The question of how deep to start an exhale is also a good one. Some of the old descriptions of polynesian pearl divers diving 20-30 meters, mention slow exhales starting on the bottom. Starting an exhale very deep might bring in some of the characteristics of frc diving, with effects I can't quite imagine. Seems like the energy cost of fighting to get down then fighting more to get back up would be pretty prohibitive, but maybe not if blood shift was strong enough.
Anybody experimented with very deep exhales??
Connor
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