Pete,
The apnea conference...?
No disrespect intended but its my opinion that, for a variety of reasons, the Italians, and French for that matter, are a little behind the times in terms of their apnea diving research. Like others who've brought up this issue, much of the information that's been published is a re-hash of some old literature. I think they should really make the effort to get with the times.
The world UHMS (Undersea and Hyperbaric Medical Society) conference in Orlando, Florida (2006) will have a session (2 days long?) on breath-hold diving. I believe the session is being organized by Dr. Peter Lindholm & Prof. Claes Lundgren.
Will made an interesting point about bleeds. The pulmonary circulation is quite fragile, especially when under elevated exertional stresses, coupled with a considerable blood shifts. Conventioanal diving involves exercise +/then dive response, as opposed to dive response then exertcise response. What many divers fail to understand is that an exercise response that is conflict with a dive response will result in more elevated cardiac outputs which is not conducive to intelligent diving. The name of the game is minimal effort in the descent phase, allowing the dive response to promptly and strongly develop. One it is well established, any exercise that is initiated then will not result in excessive pulmonary pressures. The converse will maintain the circulation to working muscles open and thus result in tachcardia (reduced bradycardia) and more elevated cardiac outputs. There are other problems with excessive lung volumes also (see Fu et al. below). Of course excessive -ve intrathoracic pressures can result in bleeds, e.g., lung squeezes but through appropriate adaptations such as thickening of the pulmonary capillary membranes there is increased tolerance to pressure. One may have to, however, compromise enhanced gas-exchange during terrestrial exercise. A more elevated Hct can, howver, reduce this negative effect during diving so that O2 is easily absorbed even at low cardiac outputs .
For those interested the following article may shed some light on research in this area that was done some time ago.
Fu et al. High lung volume increases stress failure in pulmonary capillaries. J. Appl.Physiol. 1992; 73:123-135.
West et al. Stress failure of pulmonary capillaries as a mechanism for exercise-induced pulmonary hemorrhage. Equine Vet. J. 1994:; 26:441-7.
West et al. Stress failure in pulmonary capillaries in racehorses with exercise-induced pulmonary hemorrage. J. Appl. Phsiol. 1993; 75: 1097-1109.
West et al. Pulmonary Circulation. In Saltin, B. et al. (Ed.) (2000). Exercise and Circulation and Health and Disease. pp. 79-91
Sebastien
Aust.
