Effect of varying deep stop times and shallow stop times on precordial bubbles after dives to 25 msw (82 fsw).
In our previous research, a deep 5-min stop at 15 msw (50 fsw), in addition to the typical 3-5 min shallow stop, significantly reduced precordial Doppler detectable bubbles (PDDB) and "fast" tissue compartment gas tensions during decompression from a 25 msw (82 fsw) dive; the optimal ascent rate was 10 msw (30 fsw/min). Since publication of these results, several recreational diving agencies have recommended empirical stop times shorter than the 5 min stops that we used, stops of as little as 1 min (deep) and 2 min (shallow). In our present study, we clarified the optimal time for stops by measuring PDDB with several combinations of deep and shallow stop times following single and repetitive open-water dives to 25 msw (82 fsw) for 25 mins and 20 minutes respectively; ascent rate was 10 msw/min (33 fsw). Among 15 profiles, stop time ranged from 1 to 10 min for both the deep stops (15 msw/50 fsw) and the shallow stops (6 msw/20 fsw). Dives with 2 1/2 min deep stops yielded the lowest PDDB scores--shorter or longer deep stops were less effective in reducing PDDB. The results confirm that a deep stop of 1 min is too short--it produced the highest PDDB scores of all the dives. We also evaluated shallow stop times of 5, 4, 3, 2 and 1 min while keeping a fixed time of 2.5 min for the deep stop; increased times up to 10 min at the shallow stop did not further reduce PDDB. While our findings cannot be extrapolated beyond these dive profiles without further study, we recommend a deep stop of at least 2 1/2 mins at 15 msw (50 fsw) in addition to the customary 6 msw (20 fsw) for 3-5 mins for 25 meter dives of 20 to 25 minutes to reduce PDDB.
Bennett
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PB
Duke University Medical Center, USA.
Marroni
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A
Cronje
F J
FJ
Cali-Corleo
R
R
Germonpre
P
P
Pieri
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M
Bonuccelli
C
C
Leonardi
M G
MG
Balestra
C
C
D003665:Decompression Sickness / Q000000981:diagnostic imaging / Q000517:prevention & control*; D004242:Diving / Q000592:standards*; D006801:Humans; D012016:Reference Values; D013118:Spinal Cord Diseases / Q000000981:diagnostic imaging / Q000517:prevention & control*; D013997:Time Factors; D014463:Ultrasonography