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Effect of varying deep stop times and shallow stop times on precordial bubbles after dives to 25 msw (82 fsw)

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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.
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Copyright © 2007 Undersea and Hyperbaric Medical Society, Inc 399
UHM 2007, Vol. 34, No. 6 – Decompression deep stop times
Effect of varying deep stop times and shallow
stop times on precordial bubbles after dives
to 25 msw (82 fsw).
Submitted 10/24/06; Accepted 5/15/07
P.B. BENNETT
1
, A. MARRONI
2,3
, F.J. CRONJE
4
, R. CALI-CORLEO
2,3
, P. GERMONPRE
2,5
, M.
PIERI
2
, C. BONUCCELLI
2
, M.G. LEONARDI
2
, C. BALESTRA
2,6
1
Duke University Medical Center,
2,3
DAN Europe Foundation Research Division, Division of Baromedicine, University of
Baromedicine, University of Malta Medical School,
4
DAN Southern Africa,
5
Center for Hyperbaric Oxygen Therapy, Military
Hospital, Bruxelles,
6
Haute Ecole, Paul Henri Spaak, Occupational and Environmental Physiology Department, Bruxelles,
Belgium
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; 34(6):399-406. 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 ½ 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 ½ 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.
INTRODUCTION
Recent research in divers indicates that a
deep stop, during decompression from a 25 msw
(82 fsw) dive, significantly reduces precordial
Doppler detectable bubbles (PDDB) and “fast”
tissue compartment (5 min, 10 min, 20 min) gas
tensions (1-3). This research showed that the
introduction of a deep stop at 15 msw (50 fsw),
in addition to the conventional 3-5 min shallow
stop at 3-5 msw (10-15 fsw), significantly
reduced or eliminated PDDB over a 90 minute
period after surfacing. The results suggest that
supersaturation of “fast tissue compartments”
(e.g. 5, 10 and 20 min compartments) may be
responsible for the predominantly neurological
forms of decompression illness (DCI) reported
in recreational scuba divers. This may be
perhaps due to inadequate gas elimination from
the spinal cord with its “fast” half time of 12.5
mins rather than the slower compartments used
in many decompression algorithms.
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Most decompression computer
algorithms and dive tables used by recreational
divers today have their foundations in the
original ideas of Haldane or Hill (4, 5).
Haldane modeled gas uptake and elimination
on 5 exponentials of “fast” to “slow” tissue
compartments, i.e. with 5, 10, 20, 40 and 75
min half times. Later this was increased
by Buehlmann to as many as 16 or 8 tissue
compartments (6, 7). The common premise
was that as long as none of these compartments
became supersaturated beyond a certain critical
threshold, decompression sickness (DCS)
could be avoided. Haldane also introduced the
concept that it was safe to come from 6 ATA
to 3ATA as it is from 4 ATA to 2 ATA etc. or
a 2:1 ratio of absolute depth. This ratio of ½
the absolute depth was gradually modified over
past decades, and now ranges from 4 to 1 for
fast tissue compartments to less than 2 to 1 for
slow tissue compartments.
An unforeseen consequence of these
modifications to prevent DCS is that an
important feature of Haldane’s 1906 proposal
- staged decompression at ½ the absolute depth
- has now become lost in the most common
forms of recreational diving. Instead a linear
ascent at 10 m (30 fsw)/min is common with a
“safety” stop at 3-5 msw (10-15 fsw). However,
a comparison between the Haldane proposal
for decompression (4) and linear ascent of Hill
(5) in the early last century was in favor of the
Haldane method rather than linear ascent.
In our recent research (3), the
introduction
of a deep stop at ½ the absolute
depth appears to significantly decrease PDDB.
Spencer 3 and 4 bubble grades are, in many
cases, reduced to zero. In this paper (3)
the optimal method for reducing post-dive
bubble production and tissue compartment
supersaturation during ascent is the combination
of an ascent rate of 10 msw (30 fsw/min) with
a 5 min deep stop at 15 msw (50 fsw) and a 5
minute shallow stop at 6 msw (20 fsw).
Given the finding that the deep stop
prevents the formation of gas bubbles during the
initial part of the ascent, the subsequent shallow
stop could possibly be shorter. Presumably,
a shorter deep stop also may be sufficient to
eliminate PDDB. It was therefore proposed that
both stops may be shortened and still reduce
PDDB. Several recreational diving agencies
have empirically recommended stopping for as
little as 1 min deep and 2 mins at 6 msw (20
fsw). This is considerably shorter than the 5
mins stops in the recent research protocol (3)
and may not be sufficient. The objective of the
present research is to vary the times for deep
and shallow stops to determine the optimal stop
times as evidenced by the least occurrence of
PDDB.
METHODS
209 Open Water dives were made to 25
msw (82 fsw) for 25 min by 14 volunteer Italian
recreational scuba divers (Sub Novara Laghi)
in the same manner as previously reported
(3). A total of 15 different dive protocols
were followed with varying times at the deep
and shallow stops. Some of the dives were to
25 msw (82 fsw) for 20 min following a first
dive to 25 msw (82 fsw) for a 3.5 hr surface
interval (indicated by asterisks in the tables).
The divers wore their own computers to record
the depth and times of each dive. They also
wore “blacked out” UWATEC dive computers
(sampling time 20 seconds) so recorded data
could not be seen by them. These were used
to permit analysis of the predicted gas tissue
compartment saturations for the various profiles
and to confirm accurate depth and time profiles
for the dives.
An Oxford Instruments 3.5 MHz
Doppler probe with a digital recorder was used
to make precordial Doppler bubble recordings.
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Measurements were made by specially trained
members of the diver teams. Recordings,
as previously (3), were made with the diver
standing, at rest for thirty seconds and again
for thirty seconds after performing two knee
bends. At 15 min intervals a total of six 1- min
recordings were made over a total period of 90
mins post dive. Later the recordings were all
analyzed for the presence of bubble signals by
a single experienced and blinded researcher.
The presence of PDDB was graded
according to three scales as previously
described (3): a simplified Doppler Bubble
Grading System (DBGS); the Spencer scale
(SS); and our modification of the Spencer Scale
(the Expanded Spencer Scale or ESS):
LBG – Low Bubble Grade: occasional
bubble signals, Doppler bubble Grades
(DBG) lower than 2 in the Spencer
Scale
HBG High Bubble Grade: frequent to
continuous bubble signals, DBG 2 and
higher in the Spencer Scale
HBG + - Very High Bubble Grade:
bubble signals reaching grade 3 in the
SS and 2.5 in the Expanded Spencer
Scale (see below)
Expanded Spencer Scale
The original Spencer Scale was adapted
by introducing “half grades” to allow a
more incremental grading:
Grade 0 = No bubble signals
Grade 0.5 = 1 to 2 sporadic bubble
signals over the 1 min recording
Grade
1 = up to 5 bubble signals
over the 1 min recording
Grade
1.5 = up to 15 bubble signals
over the 1 min recording, with
bubble showers
Grade
2 = up to 30 bubble signals
over the 1 min recording
Grade
2.5 = more than 30 bubble
signals over the 1 min recording,
with bubble showers
Grade
3 = virtually continuous
bubble signals over the 1 min
recording
Grade
3.5 = continuous bubble
signals over the 1 min recording,
with numerous bubble showers
Grade
4 = continuous bubble
signals over the 1 min recording,
with continuous bubble showers
To determine a relative index of
decompression stress, a “Bubble Score Index
– BSI” was calculated for each “Dive plus
Repetitive Dive” experimental profile
.
Doppler readings from the participants were
classified and recorded according to both
SS and ESS systems. The six recordings for
each diver were then added and divided by the
number of participating volunteer divers for
each profile to generate a mean score. Only 6
out of the 1,254 Doppler recordings could not
be interpreted adequately and these were not
included in the analysis.
While some authors have reported
concerns with a score based on medians (8, 9),
we concur with several others, who support this
method (10, 11). The Fishers exact test was
then applied to the HBG and LBG occurrences
to test the difference between proportions and
the method of small p-values has been applied
to calculate the two-sided p-value in analyzing
the data (12).
* The BSI is a unique Doppler bubble scoring system
that has been used extensively in research previously published
by the authors. It is a surrogate for continuous monitoring,
which is impractical for field studies and offers the equivalent
of ‘area under the Doppler bubble-time curve’. As such, it
cannot be compared with peak Doppler grades using any other
scoring system. The authors have found utility and consistency
when using this method to reflect collective decompression
stress.
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Tissue Compartment Gas
Saturations
As previously (3) the 5 tissue-
compartment gas saturation was downloaded
from the blacked out depth-time recorders
worn by the divers and analyzed using a
modified Buehlmann algorithm (9) to predict
the saturation peaks for each of the 8 tissue
compartments during the ascent. The changes
in supersaturation were computed as fractions
of their respective M values from commencing
the ascent until reaching the surface.
RESUL
TS
Dive Profiles
The dive profiles were downloaded and
compared mathematically to the experimental
profile for consistency for time, depth and
ascent rate. The results confirmed that the
divers observed the prescribed dive profiles
with an accuracy of no less than 99.7% for all
parameters (SD = 0.0058; p = 0.12 Wilcoxon
Signed Rank Test). This shows no significant
difference from the experimental profile.
Doppler Bubbles Scores
Table 1 shows the BSI scores for the
15 profiles with varying deep and shallow stop
times ranging from 0 to 10 mins. There are three
groups of profiles: Profiles 1 to 5 had deep stop
times from 0 to 2 minutes. Profiles 6 to 10 are
all 2.5 min with shallow stop times gradually
decreasing from 5 to 1 minute. Profiles 11 to 15
have deep stops ranging from 3 to 10 minutes.
The greatest reduction in BSI was associated
with dive profiles with deep stops at 15 msw
(50 fsw) greater than 2.5 mins (Profiles 6 to
15). Shorter times, as in protocols 1 through
5 had higher bubble scores. Longer times, as
in profiles 11 to 15, gave no further advantage.
After the 2.5 min deep stop, the shallow stop at 6
msw (20 fsw) showed no significant difference
as the time was shortened between 5 min down
to only 1 min (see Profiles 6 to 10).
Without a deep stop at 15 msw (50
fsw) shallow stops as long as 10 minutes did
not reduce the BSI as effectively as any profile
for which a deep stop of more than 2 minutes
was performed. Without a deep stop, a 10 min
shallow stop was slightly better than only a
Profile
No.
Dives Depth
(m)
15 m Deep
Stop (mins)
6 m Shallow
Stop (mins)
T
Time
BSI
1 24 25 0 0 2.5 7.98
2 26 25 0 5 7.5 6.23
3 21 25 0 10 12.5 5.48
4 16 25 1 3 6.5 8.04
5 18 25 2 3 7.5 3.98
6 24 25 2.5 5 10 2.23
7 7 25 2.5 4 9 2.71
8 6 25 2.5 3 8 3.58
9 6 25 2.5 2 7 2.58
10 7 25 2.5 1 6 3.36
11 8 25 3 2 7.5 4.94
12 8 25 3 1 6.5 5.63
13 25 25 5 5 12.5 2.14
14 4 25 5 2.5 10 5.5
15 9 25 10 0 12.5 2.89
Table 1. Bubble Score Index for various deep (15 msw/50 fsw) and
shallow (6 msw/20 fsw) stops on ascent from 25 msw (82 fsw) at 10
msw/min (33 fsw/min).
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5 min shallow stop. However, the deep stop
appears essential to ensure the lowest bubble
production (See Figure 1).
In Figure 2 the BSI for Doppler bubbles
is compared at various times. The highest BSI
is with the 1 min deep and 3 min shallow stops
(1/3 in the Figure). With no deep stop but a 10
min shallow stop the BSI is less (0/10 in the
Figure).
On the other hand, if the deep stop is 10
min with no shallow stop (10/0 in the Figure)
the BSI is, as discussed above, much the same
as for only a 2.5 min deep stop. Again, with a
2.5 min deep stop, decreasing the shallow stop
had no significant effect.
Figure 3 shows the statistical significance
comparing a deep stop longer than 2 minutes
versus no deep stop (p < 0.0001). However, if
the comparison is done for deep stops overall
(even less than 2 minutes) the difference is
still at p < 0.004 Figure 3. The difference
between the proportions of occurrences for the
higher bubbles grades (HBG and VHBG) is
very significant for the deep stop longer than 2
minutes vs. no deep stop (p<0.0001), yet if the
comparison is done for the deep stops overall
(even less than 2 minutes) the difference is still
present (p<0.004) by the Fisher exact test (12).
the Fisher exact test (12).
Fig 3. The difference between the proportions of
occurrences for the higher bubbles grades (HBG and
VHBG) is very significant for the deep stop longer
than 2 minutes vs. no deep stop (p<0.0001), yet if the
comparison is done for the deep stops overall (even less
than 2 minutes) the difference is still present (p<0.004)
by the Fisher exact test (12).
Tissue Compartment Gas
Saturations
The calculated tissue compartment gas
saturations for the various stop times are shown
in Table 2 (See page 404) from data recorded
by the UWATEC computers worn by the divers
during the dives.
Fig. 1. ZBG : Zero bubble grade; LBG : Low bubble
grade; HBG : High bubble Grade VHBG : Very high
bubble grade
Fig. 2. BSI and total decompression time at various deep
and shallow stop times.
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The origin at 5 min deep 5 min shallow
stops (Profile 13) showed the lowest tissue
saturation of 29 for the 5 min tissue compartment
(14) with a BSI of 2.14. The 2.5 min deep and
5 min shallow (6) also showed a low gradient
of 35 with a BSI of 2.23. Interestingly the very
long shallow stop of 10 mins with no deep stop
had a gradient of only 30 but a BSI of 4.93. So
lengthening the shallow stop was ineffective at
reducing bubbles.
DISCUSSION
These results give further support to
the findings reported in the previous paper (3)
that a deep stop significantly reduces PDDB.
However, the correlation with lower
fast tissue compartments is not as strong due to
the aberration of Profile 3 with a low gradient
but high BSI. According to the present results,
the optimal time for a deep stop at 15 msw (50
fsw) is 2.5 mins for a 25 msw (82 fsw) profile.
Shorter times increase the BSI. Further it
would seem that after the 2.5 min deep stop,
the shallow stop time at 6 msw (20 fsw) makes
little difference to the BSI but could be less
than the 3 to 5 min currently recommended.
Results of our earlier deep stop research
and technical diving data were discussed at
the U.S. National Association of Underwater
Instructors meeting in 2003 in Florida. NAUI
has since recommended that instead of the 3
min safety stop at 20 fsw (6 msw), divers should
take a 1 min stop at half the bottom depth and a
2 min stop at 20 fsw (13). The present data do
not support this recommendation as shown by
Profile 4 whose high BSI is virtually the same
as Profile 1 with no stops. A time of 2.5 mins
appears necessary for the deep stop at 15 msw
(50 fsw) after a 25 msw (82 fsw) dive. The
data indicates that the shallow stop is not as
important as a deep stop for this profile, but for
practical purposes, the original 3-5 min shallow
stop could be retained as it also attenuates the
risk for pulmonary barotrauma.
Table 2. Tissue compartment gradients for 5, 10, 20 and 40 min tissue compartments calculated from
UWATEC computers worn by the divers as compared to decreasing BSI. The values are given as percent
saturation with 100% fully saturated.
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Our research seeks to control bubble
growth by the intervention of a deep stop to
prevent supersaturation at depth and bubbles
forming at that time but growing in size with
ascent in accordance with Boyle’s Law. If
the deep stop is effective in stopping this
bubble formation, the shallow stop, as the
present research indicates, becomes much less
important. This method of decompression may
be designated as “beating the bubble” rather
than “treating the bubble”.
Deep stops also have been commonly
used by recreational technical divers who have
empirically devised their own methods for
decompression. This has led to other methods for
determining ascent profiles based on reduction
of bubbles rather than supersaturation, such as
the Wienke ‘Reduced Gradient Bubble Model
(RGBM)’ (14). The RGBM is now utilized
in a number of dive computers. There have
been no extensive formal field trials validating
the RGBM, but a data bank has been created
to record some dives: By 2004, some 2,300
dives had been recorded with 20 cases of DCI,
mainly after repetitive dives with nitrox and
using reverse profiles (15).
A recent French paper (16) investigated
the use of deep stops in three protocols tested
in the wet compartment of a decompression
chamber. In Profile I eight subjects dived to 60
msw (192 fsw) and in Protocol I used a deep
stop beginning at 27 msw (86 fsw) followed
by many other stops to the surface. Protocol
II was a repetitive dive to 50 msw (160 fsw),
a 3 hr surface interval followed by the second
dive with the deep stop at 18 msw (58 fsw).
Protocol III went to 60 msw (192 fsw) but
used a single shorter stop at 25 msw (80 fsw).
Using PDDB scoring, it was concluded that
these experimental deep stop profiles provided
no benefit compared with the standard MN 90
French Navy decompression table. Though no
times are given for the stops, from the graphs
they appear to be only about 1 min. If so, these
could have been ineffective, as was the case
with a similar too short deep stop from our
25 msw (82 fsw) dives. The depth of 60 msw
(192 fsw) is also much deeper than our present
work and may require different stop times and
stop depths to significantly reduce the PDDB
scores.
As a result of our deep stop research
(3), the Italian Recreational Diver Federations
have recommended the use of a 2.5 min deep
stop at 15 msw (50 fsw) from a 25 msw (82
fsw) dive and similar dives during ascent so it
will soon be possible to compare diving with
and without the deep stop and the incidence
of DCS resulting from its use for correlation
with PDDB. However, reduction of PDDB
may nevertheless help to make recreational
diving safer. This would be consistent with
the comments by Nishi et al. (8) who state “the
incidence of DCS is higher when many bubbles
are detected and that the incidence of DCS is
low when few or no bubbles are detected. Thus,
when evaluating decompression profiles, dives
which produce many bubbles in a majority of the
divers can be considered stressful with a higher
risk of DCS and should be avoided. Conversely
dives which produce few or no bubbles in the
majority of divers can be considered safe.”
CONCLUSIONS
We conclude that 2.5 min at 15 msw (50
fsw) is the optimal deep stop time following
25 msw (82 fsw) dives for 20 to 25 min for
preventing PDDB. Shorter or longer times are
not as effective. The shallow stop at 6 msw (20
fsw) for 3-5 mins normally recommended does
not seem as important. However, longer times
do not afford additional benefit in reducing
PDDB.
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ACKNOWLEDGMENTS
We would like to thank the enthusiasm and
professional recreational divers of the Italian Dive Club
“Sub Novara Laghi” led by Daniele Pes and Carlo
Bussi for carrying out the many open water profiles and
Doppler recordings with great accuracy and without
whom this research would not have been possible.
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... dcS is influenced by multiple factors such as dive profile and physical characteristics of the diver [5]. Previous studies have shown an association of dcS with age [6,7], adiposity [7,8], a history of dcS [8], pre-existing conditions such as hypothermia and viral meningitis [4], patent foramen ovale [9], fatigue [10], gender [11], menstruation [12], smoking [13], strenuous diving activity [6], dehydration [14], cold exposure after diving [15], deep-sea diving [5], technical diving (different from recreational diving in terms of factors such as depth and duration of bottom time) [5], deep and shallow stops [16][17][18][19], use of nitrox gas [5,9], ascending and descending repetitive diving [5], and flying after diving [20]. The presence of each or combinations of these risk factors may increase the risk of dcS. ...
... The questionnaire included 30 items grouped into four categories: personal profile, condition before diving, condition during diving, and condition after diving. Each of the items in the categories and the exact wording used were based on previously reported studies [6][7][8]10,11,[14][15][16][17][18][19], and this questionnaire is considered a valid method for evaluating risk and preventive factors for dcS in different populations. ...
... Our previous study revealed that a dive depth of >30 msw was a high-risk factor; increased water depth causes an increase in the accumulation of inert gas [21], which is probably related to the onset of dcS [5,21]. in the present study, a dive depth of >30 msw was not a significant risk factor; however, the maximum depth of the dcS group (26.39 ± 0.06 msw) was significantly greater than that of the control group (24.33 ± 0.04 msw). This result indicates that the dive depth (approximately 30 msw) is related to the possibility of accumulation of inert gas in the diver's tissues. in addition, Marroni, et al. [17] and Bennett, et al. [18] recommended a 2.5-minute deep stop at a depth of 15 meters and a three-to five-minute stop at 6 m during ___________________________________________________________________________________________________________________________________________________________ ___ [19] and any type of safety stop helps prevent the accumulation of inert gas. Our findings revealed deep stops and safety stops as preventive factors and, in concurrence with the recommendations of Marroni, et al. [17] and Bennett, et al. [18], that the implementation of deep stops and safety stops was crucial in the prevention of dcS. ...
Article
Background: Decompression sickness (DCS) is a rare condition that is often difficult to diagnose in deep-sea divers. Because of this, prevention and early diagnosis are important. In this case-control study, we examined the risk and preventive factors associated with DCS. Methods: Our original questionnaire survey was conducted among 269 recreational divers in Okinawa. Divers who were diagnosed with DCS by a physician (n = 94) were compared with healthy recreational divers (n = 175). The questionnaire consisted of 30 items and included a dive profile. Odds ratios and multiple logistic regression analysis were used to estimate the relative risk of DCS. Results: Logistic regression analysis revealed the following risk factors for DCS: a past history of DCS, drinking alcohol the evening before diving, indicating decompression stops, cold exposure after the dive, and maximum depth. Preventive factors included hydration before the dive, deep stops, safety stops and using nitrox gas. The results were reliable according to the Hosmer-Lemeshow and omnibus tests. Conclusion: We identified certain risk factors, together with their relative risks, for DCS. These risk factors may facilitate prevention of DCS among Okinawa divers.
... Thus, the authors decided to use a combination of compressed air, as the main breathing gas, and Nitrox50 (a mixture of 50% oxygen and 50% nitrogen) as a decompression gas. Hence, authors also decided to incorporate deep decompression stops of two minutes into the method as such a procedure is recommended for decreasing bubbling (Bennett et al, 2007). ...
Article
Full-text available
Diver-based underwater visual census (UVC), particularly transect-based survey, is a widely used method for the study of tropical and temperate fish assemblages. However, due to logistical constraints associated with conventional SCUBA diving, deeper habitats, such as vertical rocky reefs, are rarely studied and poorly known. This paper describes the Deep Vertical Transect (DVT) method as a safe and effective method for assessing fish in waters up to 50 m of depth. It is based on sampling of vertical transects browsing within it (S-type transect) by divers using Full HD video cameras. The diving profile includes the use of deep decompression stops and Nitrox 50 as a decompression gas. Hence, the study yields information on fish assemblages associated with deeper vertical coralligenous reefs. The results of 51 recorded species, yielded 41 considered as reef-associated and 10 as occasional. This suggests that underwater steep coralligenous reefs are marine biodiversity hotspots. They may be considered to represent a distinctive marine subecosystem, possessing its own food chain, with the depth, in relation to temperature, as the most important factor responsible for the diversity of fish assemblages within this habitat.
... The impact at the time was notable and still is today across the full spectrum of diving. Recreational 1/2 Deep Stops and Reduced Doppler Scores: Analysis of more than 16,000 actual dives by Divers Alert Network (DAN) prompted suggestions that decompression injuries are likely due to ascending too quickly [23]. Bennett found that the introduction of deep stops, without changing the ascent rate, reduced high bubble grades to near zero from 30.5% without deep stops. ...
Article
Full-text available
The question of deep and shallow decompression stops is interesting and fraught with controversy in diving circles and operations, training, exploration and scientific endeavors. Plus fraught with some misunderstanding which is understandable as the issues are complex. We accordingly detail a short history of deep and shallow stops, physical aspects, staging differences, diving tests, models, data correlations, data banks, diver statistics and DCS outcomes for diving amplification. Pros and cons of deep stop and shallow stop staging are presented. Misinformation is corrected. Training Agency Standards regarding deep and shallow stops are included. A tabulation of well known and popular dive computers and software algorithms is given. From diving data, tests, DCS outcomes, data banks and field usage, we conclude that both deep stops and shallow stops are safely employed in recreational and technical diving today. For diver safety this is important.
... Recreational 1/2 Deep Stops And Reduced Doppler Scores: Analysis of more than 16,000 actual dives by Divers Alert Network (DAN) prompted suggestions that decompression injuries are likely due to ascending too quickly (Bennett and Marroni, 2007). Bennett found that the introduction of deep stops, without changing the ascent rate, reduced high bubble grades to near zero from 30.5% without deep stops. ...
Conference Paper
Full-text available
The question of deep and shallow decompression stops is interesting and fraught with controversy in diving circles and operations, training, exploration and scientific endeavors. Plus fraught with some misunderstanding which is understandable as the issues are complex. We accordingly detail a short history of deep and shallow stops, physical aspects, staging differences, diving tests, models, data correlations, data banks, diver statistics and DCS outcomes for diving amplification. Pros and cons of deep stop and shallow stop staging are presented. Misinformation is corrected. Training Agency Standards regarding deep and shallow stops are included. A tabulation of well known and popular dive computers and software algorithms is given. From diving data, tests, DCS outcomes, data banks and field usage, we conclude that both deep stops and shallow stops are safely employed in recreational and technical diving today. For diver safety that is important.
... The RGBM was also correlated with Bennett and Maronni [17] Doppler score reductions with 1/2 deep stops in recreational air diving. A very interesting study by Balestra [18][19][20] of DAN-DSL Europe centers on DCS incidences using dissolved gas (shallow stop ZHL16) computers versus bubble model (deep stop RGBM) computers. In 11,738 recreational dives, a total of 181 DCS cases were recorded and were almost equally divided between the ZHL16 and RGBM computers, that is, the ZHL16 incidence rate was 0.0135 and the RGBM incidence rate was 0.0175. ...
... Analysis of more than 16,000 actual dives by Divers Alert Network (DAN) prompted Bennett [27] to suggest that decompression injuries are likely due to ascending too quickly. He found that the introduction of deep stops, without changing the ascent rate, reduced high bubble grades to near zero from 30.5/stops. ...
... Analysis of more than 16,000 actual dives by Divers Alert Network (DAN) prompted Bennett [27] to suggest that decompression injuries are likely due to ascending too quickly. He found that the introduction of deep stops, without changing the ascent rate, reduced high bubble grades to near zero from 30.5/stops. ...
Book
Full-text available
A short treatise on modern dive computers for the computer scientist, mathematician, doctor, physiologist, engineer, commercial and technical diver, dive computer manufacturer, table designer, dive instructor, surface tender, military diver, statistician, physicist, recreational diver, biologist. lawyer and any interested individual in the many aspects of modern dive computers, operations, models, correlations, data banks, risk analyses, wet and dry tests, ad hoc protocols, training agency and computer vendor algorithm implementations and the related interplay for safe and sanel computer diving.
... The RGBM was also correlated with Bennett and Maronni [17] Doppler score reductions with 1/2 deep stops in recreational air diving. A very interesting study by Balestra [18][19][20] of DAN-DSL Europe centers on DCS incidences using dissolved gas (shallow stop ZHL16) computers versus bubble model (deep stop RGBM) computers. In 11,738 recreational dives, a total of 181 DCS cases were recorded and were almost equally divided between the ZHL16 and RGBM computers, that is, the ZHL16 incidence rate was 0.0135 and the RGBM incidence rate was 0.0175. ...
Article
Full-text available
This short article deals with useful and modern bubble models used to stage divers to the surface and correlations, if and when they exist, with actual data, usually decompression sickness (DCS) outcomes across a limited spectrum of exposures. Many of the early (wet) tests were carried out by world Navies, later by hyperbaric chamber testing and today also by statistical inference from downloaded computer profiles. All have contributed to correlation of models and data but in varying degrees as the scope of mixed gas, open circuit (OC) and rebreather (RB), nonstop to saturation and sea level to altitude diving is immense. No amount of wet or chamber testing will ever cover the ground here, but there is considerable hope and potential for downloaded computer profile data coupled to DCS outcomes to provide necessary correlations across the varied activities of modern diving.
Chapter
Synonyms of decompression illness (DCI) are dysbaric illness (DI), decompression sickness (DCS), decompression accident or caisson disease. As DCS and AGE quite often occur together, these are commonly summarised as DCI or DI which is used as the preferred term for decompression-related accidents. DCS alone is rather subject to inert gas bubbles related to decompression effects as aetiology by itself. Neurological symptoms of DCS might be quite similar to AGE caused by pulmonary barotrauma. However, spinal symptoms are only found in DCS. DCI is a spectrum, which may have no symptoms at all, minor unspecific symptoms like fatigue up to fatal complications.
Article
Full-text available
Editorials by Bennett (1-6) in the Divers Alert Network magazine Alert Diver noted that although decompression tables had been modified over the last twenty years and computers, many giving much shorter times at depth than the U.S. Navy tables, had virtually taken over recreational diving, the incidence of decompression sickness had changed very little. In fact, the incidence was very consistent with the distribution for sex, age and training among divers rather than use of different computers or tables. The problem, it was inferred, was the rate of ascent, which had changed very little over the last 40 years and was the real controller of incidence of decompression illness. In the 19 th century, for example, Paul Bert in 1878 quoted rates of 3 ft/min (.9 m/min) and Haldane in 1907, 5 ft/min (1.5 m/min) up to 30 ft/min (9.1 m/min). From 1920-57 rates of 25 ft/min (7.6 m/min) were recommended. Then in 1958, during the production of the U.S Navy Diving Manual, the rate of ascent to be proposed came under review (7). Cdr. Fane of the West Coast Underwater Demolition Team wanted rates for his frogmen of 100 ft/min (30.4 m/min) or faster. The hard hat divers on the other hand considered this not practical for the heavy suited divers used to coming up a line at 10 ft/min (3 m/min). Thus a compromise was reached of 60 ft/min (18.2 m/min), which was also a convenient 1 ft/sec (0.3 m/sec) (2). So from 1957-1993 the U.S. Navy tables advocated, on this purely empirical approach, 60 ft/min (18.2 m/min) and many early computers followed suit.
Article
The past decade has seen substantial research on exact inference for contingency tables, both in terms of developing new analyses and developing efficient algorithms for computations. Coupled with concomitant improvements in computer power, this research has resulted in a greater variety of exact procedures becoming feasible for practical use and a considerable increase in the size of data sets to which the procedures can be applied. For some basic analyses of contingency tables, it is unnecessary to use large-sample approximations to sampling distributions when their adequacy is in doubt. This article surveys the current theoretical and computational developments of exact methods for contingency tables. Primary attention is given to the exact conditional approach, which eliminates nuisance parameters by conditioning on their sufficient statistics. The presentation of various exact inferences is unified by expressing them in terms of parameters and their sufficient statistics in loglinear models. Exact approaches for many inferences are not yet addressed in the literature, particularly for multidimensional contingency tables, and this article also suggests additional research for the next decade that would make exact methods yet more widely applicable.
Article
An approach to decompression modeling, the reduced gradient bubble model (RGBM), is developed from the critical phase hypothesis. The phase limit is introduced, extended, and applied within bubble-nucleation theory proposed by Yount. Much is different in the RGBM algorithm, on both theoretical and applied sides, with a focus on permissible bubble excesses rather than just dissolved gas buildup, something of a departure from traditional models. Overall, the approach is conservative, with changes in parameter settings affording flexibility. Marginal profiles permitted by tables and meters are restricted by the bubble algorithm. Highlighted features of the conservative algorithm include: (1) reduced no-stop time limits from the varying-permeability model (VPM); (2) short safety stops (or shallow swimming ascents) in the 10-20 feet of sea water (fsw) zone; (3) ascent and descent rates of 60 fsw/min, or slower; (4) restricted repetitive exposures, particularly beyond 100 fsw, based on reduced permissible bubble excess; (5) restricted spike (shallow-to-deep) exposures based on excitation of additional micronuclei; (6) restricted multi-day activity based on regeneration of micronuclei; (7) consistent treatment of altitude diving within model framework; (8) algorithm linked to bubble-nucleation theory and experiment. Coupled to medical reports about the long term effects of breathing pressurized gases and shortcomings in dissolved gas models, conservative modeling seems prudent.
Article
This article discusses extensions of generalized linear models for the analysis of longitudinal data. Two approaches are considered: subject-specific (SS) models in which heterogeneity in regression parameters is explicitly modelled; and population-averaged (PA) models in which the aggregate response for the population is the focus. We use a generalized estimating equation approach to fit both classes of models for discrete and continuous outcomes. When the subject-specific parameters are assumed to follow a Gaussian distribution, simple relationships between the PA and SS parameters are available. The methods are illustrated with an analysis of data on mother's smoking and children's respiratory disease.
Article
Seventy-six men and 7 women performed a 2nd dive in a pressure chamber under dry conditions after intervals at the surface of 10, 30, 90, or 120 min. Of these, 35 persons performed a 3rd dive after an interval of 20 or 90 min (118 repeated dives). Air was the breathing gas during all phases of the tests. During exposure to overpressure the divers exercised on a bicycle-ergometer. The decompressions for dives 2 and 3 were the same as for the first dive. After the 2nd or 3rd dive, certain symptoms of decompression sickness of the skin occurred in 5 of the 118 exposures, and 1 diver complained of muscular aches. These results suggest that no general sensitization occurred after the 1st dive. We concluded that a slightly more conservative decompression with regard to ascent velocity and profile is feasible for repeated dives.