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Re: Passive flooding of paranasal sinuses: an added risk to apnoea diving?

Dear Editor

Germonpré et al. have presented the possible mechanisms of a new technique to equalize middle ear and sinus cavities during extreme-depth apnoea diving by passive flooding of these cavities with surrounding water. Even though their measures were not made in water, they demonstrate that it is possible to flood the middle ear in order to better compensate during very deep apnoea diving. In addition to the risks of degeneration and/or infections, the supplementary risk of decompression sickness (DCS) must be underlined. There are two main limiting factors in very deep apnoea dives: cranial cavity compensation and apnoea duration. PM, by drowning his cranial cavities, succeeded in liberating himself from the first factor while playing on the second and thus limiting the risk of hypoxia. But he also considerably raised the ascent and descent speed (2 m.s-1), thus potentially increasing the risk of DCS. Although the exact mechanisms of DCS in breath-hold divers (BHDs) are not well known (Schipke 2005), DCS has already been observed after only one shallower apnoea dive (120 m) made using the same type of material (Magno et al., 1999). The concerned BHD had nausea, dizziness, fatigue, visual disturbance and hemiplegic symptoms that were resolved after a hyperbaric chamber session of some hours. PM experienced mainly extreme fatigue after his dive to 209 m; he also was transported to the hospital and treated in a hyperbaric chamber. This extremely fast ascent could disturb the evacuation of blood present around the lung, which would encourage the passage of bubbles into the arterial circulation and lead to DCS. For these reasons, I don't think that one can affirm with certainty that this technique increases the security of BHDs. It certainly permits them to reach greater depths, but the corresponding immersion dangers remain unknown.

References

Magno L, Lundgren CEG, Ferrigno M. Neurological problems after breath -hold diving. Undersea Hyper Med 1999;26:28-29.