Surface time 1 hour because of Microbubbles
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scjoe
Contributor
The deep stops referenced by Shark_Tamer have come under question in a 2008 study by DAN which found that deep stops without a switch in breathing gas actually increased the risk of DCS in its study.
scjoe
Contributor
It is the 2008 Tech Diving Conference that is under the Medical Research bar on the homepage. The information is in a Power Point Presentation. I believe it is in the materials for the afternoon of the first day of the conference.
The 2007 DAN - Europe study talked about amount of VGE, not DCS risk.
Bennett, PB; Marroni, A; Cronje, FJ; Cali-Corleo, R; Germonpre, P; Pieri, M; Bonuccelli, C; Leonardi, MG; Balestra, C. Effect of varying deep stop times and shallow stop times on precordial bubbles after dives to 25 msw (82 fsw). Undersea Hyperb Med. 2007 Nov-Dec;34(6):399-406. RRR ID: 7901
Nice to see I did not waste my time on those drawings or the re-write of that article to include references.
Please check this thread!
scjoe
Contributor
The DAN presentation January 18-19, 2008 was by Gerth, Doolette and Gault and was entitled “Deep Stops and Their Efficiency in Decompression. The test was conducted by a Navy Experimental Diving Unit.
The authors state that their efforts to empirically confirm the theoretical benefits of deep stops were unsuccessful. If I am reading the charts in the Power Point presentation correctly, there were 11 DCS incidents using deep stops versus 3 using traditional ascents. In each case it looks like almost 200 dives were done.
In their conclusions, the authors state that both DCS and VGE were higher after a deep stop schedule than after a traditional ascent schedule. They also state that a deep stop without a switch in breathing gas may be beneficial in certain circumstances, but only to correct a defective algorithm and that the deep stop will require a lengthening of the subsequent decompression. Finally, they state that a switch to a higher PO2 breathing gas is usually beneficial, but the benefit is not a property of the deepness of the stop.
The authors state that their efforts to empirically confirm the theoretical benefits of deep stops were unsuccessful. If I am reading the charts in the Power Point presentation correctly, there were 11 DCS incidents using deep stops versus 3 using traditional ascents. In each case it looks like almost 200 dives were done.
In their conclusions, the authors state that both DCS and VGE were higher after a deep stop schedule than after a traditional ascent schedule. They also state that a deep stop without a switch in breathing gas may be beneficial in certain circumstances, but only to correct a defective algorithm and that the deep stop will require a lengthening of the subsequent decompression. Finally, they state that a switch to a higher PO2 breathing gas is usually beneficial, but the benefit is not a property of the deepness of the stop.
Ahh... Wayne's abstract from the UHMS meeting is here:
Gerth, WA; Gault, KA; Doolette, DJ. EMPIRICAL EVALUATION OF THE EFFICACY OF DEEP STOPS IN AIR DECOMPRESSION DIVES. Abstract of the Undersea and Hyperbaric Medical Society, Inc. Annual Scientific Meeting held June 14-16, 2007. Ritz-Carlton Kapalua Maui, Hawaii. RRR ID: 5069
The technical report from that dive series is not available yet.
One thing about microbubbles is they are harmless except they are the nuclei that big bubbles can form on.
Have you ever noticed the bubbles in a beer glass seem to appear at a certain spot on the side, just not uniformly throughout the glass. That is because small imperfections in the glass act as a bubble nuclei and that is where the dissolved gas tends to form into bubbles. Diving with micobubbles just give the dissolved gas more places to form bigger bubbles.
Have you ever noticed the bubbles in a beer glass seem to appear at a certain spot on the side, just not uniformly throughout the glass. That is because small imperfections in the glass act as a bubble nuclei and that is where the dissolved gas tends to form into bubbles. Diving with micobubbles just give the dissolved gas more places to form bigger bubbles.
Although the study raises some interesting questions about deep stops - I don't think it applies very well to non-decompression stop diving- as the dives were quite extreme. 170fsw working dive on air with decompression on air- this is a pretty extreme profile, I think this is born out by the high incidents of DCS on both schedules.
Some more recent studies have shown the benefits of deep stops for recreational dives - by extending the 50% of max depth stop to 2.5 minutes a reduction in doppler micro bubble scores was significant. Increases in the 15ft safety stop showed no such reductions even with increases up to 20 minutes.
Some more recent studies have shown the benefits of deep stops for recreational dives - by extending the 50% of max depth stop to 2.5 minutes a reduction in doppler micro bubble scores was significant. Increases in the 15ft safety stop showed no such reductions even with increases up to 20 minutes.
scjoe
Contributor
Actually, I think the origins of the deep stop theory is deep technical diving. My understanding is that the deeper the dive, the more important the deep stop is supposed to be.
One of the reasons deep stops at shallower depths might not create problems could be that you are much closer to a depth where no additional gas loading is occurring so the additional loading is slower. The Bennett study used a maximum depth of 85 feet which would mean the deep stop was in the 40 foot range. According to Gerth study, the problem with deep stops is the continued gas loading that is going on during the stop.
In the end, you have theories and conflicting empirical studies.
One of the reasons deep stops at shallower depths might not create problems could be that you are much closer to a depth where no additional gas loading is occurring so the additional loading is slower. The Bennett study used a maximum depth of 85 feet which would mean the deep stop was in the 40 foot range. According to Gerth study, the problem with deep stops is the continued gas loading that is going on during the stop.
In the end, you have theories and conflicting empirical studies.
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