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A deep stop during decompression from 82 fsw (25 m) significantly reduces bubbles and fast tissue gas tensions. (Article)

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In spite of many modifications to decompression algorithms, the incidence of decompression sickness (DCS) in scuba divers has changed very little. The success of stage, compared to linear ascents, is well described yet theoretical changes in decompression ratios have diminished the importance of fast tissue gas tensions as critical for bubble generation. The most serious signs and symptoms of DCS involve the spinal cord, with a tissue half time of only 12.5 minutes. It is proposed that present decompression schedules do not permit sufficient gas elimination from such fast tissues, resulting in bubble formation. Further, it is hypothesized that introduction of a deep stop will significantly reduce fast tissue bubble formation and neurological DCS risk. A total of 181 dives were made to 82 fsw (25 m) by 22 volunteers. Two dives of 25 min and 20 min were made, with a 3 hr 30 min surface interval and according to 8 different ascent protocols. Ascent rates of 10, 33 or 60 fsw/min (3, 10, 18 m/min) were combined with no stops or a shallow stop at 20 fsw (6 m) or a deep stop at 50 fsw (15 m) and a shallow at 20 fsw (6 m). The highest bubbles scores (8.78/9.97), using the Spencer Scale (SS) and Extended Spencer Scale (ESS) respectively, were with the slowest ascent rate. This also showed the highest 5 min and 10 min tissue loads of 48% and 75%. The lowest bubble scores (1.79/2.50) were with an ascent rate of 33 fsw (10 m/min) and stops for 5 min at 50 fsw (15 m) and 20 fsw (6 m). This also showed the lowest 5 and 10 min tissue loads at 25% and 52% respectively. Thus, introduction of a deep stop significantly reduced Doppler detected bubbles together with tissue gas tensions in the 5 and 10 min tissues, which has implications for reducing the incidence of neurological DCS in divers.
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UHM 2004, Vol. 31, No. 2 – Deep stop decompression
A deep stop during decompression from 82 fsw
(25 m) significantly reduces bubbles and fast
tissue gas tensions.
A. MARRONI
1,2
, P. B. BENNETT
4,5
, F. J.
CRONJE
5,7
, R. CALI-CORLEO
1,2
, P.
GERMONPRE
1,6
, M. PIERI
1
, C. BONUCCELLI
1
, C. BALESTRA
1,3
1
DAN Europe Foundation, Research Division.
2
Division of Baromedicine, University of Malta Medical School.
3
Haute Ecole
Paul Henri Spaak, Occupational and Environmental Physiology Dept., Bruxelles, Belgium.
4
Divers Alert Network (DAN) America.
5
Duke University Medical Center, Durham, NC, USA.
6
Center for Hyperbaric Oxygen Therapy, Military Hospital Bruxelles.
7
DAN
Southern Africa
Marroni A, Bennett PB, Cronje FJ, Cali-Corleo R, Germonpre P, Pieri M, Bonuccelli C, Balestra C. A deep
stop during decompression from 82 fsw (25 m) significantly reduces bubbles and fast tissue gas tensions.
Undersea Hyperb Med 2004; 31(2):233-243. In spite of many modifications to decompression algorithms,
the incidence of decompression sickness (DCS) in scuba divers has changed very little. The success of
stage, compared to linear ascents, is well described yet theoretical changes in decompression ratios have
diminished the importance of fast tissue gas tensions as critical for bubble generation. The most serious
signs and symptoms of DCS involve the spinal cord, with a tissue half time of only 12.5 minutes. It is
proposed that present decompression schedules do not permit sufficient gas elimination from such fast
tissues, resulting in bubble formation. Further, it is hypothesized that introduction of a deep stop will
significantly reduce fast tissue bubble formation and neurological DCS risk. A total of 181 dives were
made to 82 fsw (25 m) by 22 volunteers. Two dives of 25 min and 20 min were made, with a 3 hr 30 min
surface interval and according to 8 different ascent protocols. Ascent rates of 10, 33 or 60 fsw/min (3, 10,
18 m/min) were combined with no stops or a shallow stop at 20 fsw (6 m) or a deep stop at 50 fsw (15 m)
and a shallow at 20 fsw (6 m). The highest bubbles scores (8.78/9.97), using the Spencer Scale (SS) and
Extended Spencer Scale (ESS) respectively, were with the slowest ascent rate. This also showed the
highest 5 min and 10 min tissue loads of 48% and 75%. The lowest bubble scores (1.79/2.50) were with an
ascent rate of 33 fsw (10 m/min) and stops for 5 min at 50 fsw (15 m) and 20 fsw (6 m). This also showed
the lowest 5 and 10 min tissue loads at 25% and 52% respectively. Thus, introduction of a deep stop
significantly reduced Doppler detected bubbles together with tissue gas tensions in the 5 and 10 min
tissues, which has implications for reducing the incidence of neurological DCS in divers.
INTRODUCTION
Decompression procedures and tables have been modified many times over the last 40
years since scuba diving was initiated as a sport. However, in spite of the current prevalence of
dive computers to assist decompression, the incidence of decompression sickness (DCS) has
changed very little (1). This may be because critical factors, such as rate of ascent and shallow
stops, provide insufficient time to offload enough inert gas during critical phases of the
decompression, resulting in the generation of bubbles and occurrence of DCS.
Many attempts to prevent DCS in the past have relied on the Haldane hypothesis (2).
This based gas uptake or elimination from 5 so-called ‘tissue’ exponentials later increased to 6
by the U.S. Navy. These were the ‘fast’ half time exponentials of 5, 10 and 20 minutes and the
‘slow’ tissue exponentials of 40, 80 and 120 minutes. The premise was that excess gas retained
in any of these tissues or compartments during ascent could lead to bubble formation and DCS.
Copyright © 2004 Undersea and Hyperbaric Medical Society, Inc. 233
UHM 2004, Vol. 31, No. 2 – Deep stop decompression
234
As military diving experience suggested that slow tissues were responsible for decompression
symptoms, the emphasis moved from preventing supersaturation in fast tissues to protecting the
slow ones by adding longer tissue half times. Thus for example, the Bühlmann tables and
computers were expanded to include 16 tissue half times (3) with the longest at 635 minutes.
Experience in recreational divers has shown that 65% of treated DCS cases are
neurological. They usually involve the spinal cord which has a “tissue” half time of only 12.5
minutes (4). During a 30 m (100 fsw) dive of 25 minutes, the 5 and 10 minute tissues will attain
a high degree of saturation. Even though current computer models de-emphasize the importance
of these tissues, these may, in fact, be controlling factors. Significantly more ascent time may
therefore be required to off-gas these critical fast tissues and avoid neurological DCS. Indeed, the
original Haldane table (2) for a 30 m (100 fsw)/25 minute dive required decompression stops at
9, 6 and 3 m (30, 20 and 10 fsw) for a total decompression time of 19 minutes. Yet today, with
an ascent of 9 m (30 fsw)/minute and a ‘safety stop’ at 5 m (15 fsw) for 3 minutes, the
recreational scuba diver is on the surface in only 6 minutes. This may be far too short for
adequate desaturation of a 5 minute tissue that has attained a high degree of saturation.
Haldane’s original research in 1906 maintained that for a dive to an absolute pressure of
P
1,
the absolute pressure reduction during decompression to a P
2
should not be less than half the
pressure of P
1
. This 2:1 ratio concept of Haldane is widely quoted but was not actually used in
his later decompression tables. Sir Leonard Hill (5), by contrast, believed in a slow linear ascent
model. In testing with goats, Haldane found that the Hill method of a slow linear ascent was
ineffective and resulted in significant DCS. Yet for many decades an empirical linear
decompression ascent rate of 18 m/min (60 fsw/min) was recommended by the US Navy. More
recently, the rate was reduced to a linear 9 m/min (30 ft/min), but when even this strategy did not
eliminate DCS, a single brief safety stop at 5 m (15 fsw) was introduced for 3-5 minutes. From 5
m (15 fsw) the diver would then surface – usually rapidly. The modifications to the Haldane
model by the US Navy thus eliminated the need for more decompression stops during the ascent
and the so-called ‘deep stop’ was lost. However, experience in pearl divers, and more recently in
technical divers, has led to empirical reintroduction of the deep stop with apparent success (6).
The research described in this paper tested the hypothesis that a deep stop is efficacious in
preventing neurological DCS in recreational scuba divers.
Marroni et al. (7) applied the above hypothesis to 1,418 normal recreational scuba dives
monitored using so-called ‘black box’ depth-time recorders to predict tissue gas tensions while
blinding the diver to the data collection. Precordial Doppler bubbles were measured at 15 minute
intervals up to 90 minutes and again 48 hrs after the last dive or with an altitude change.
Interestingly, as with other such Doppler studies, precordial bubbles did not appear until 30 or 40
minutes after surfacing. After repetitive diving, 85% of the dives produced bubbles, and though
18% were low grade (i.e., Spencer Scale of 1-2), 67% had high bubble grades (i.e., Spencer
Scale of 3-4). By retrospectively applying the Bühlmann algorithm (3) to the data from the black
box depth-time recorders, peak nitrogen tensions were determined in various tissue
compartments during the ascent (i.e., the leading tissue nitrogen pressure (PltN2) or critical
supersaturation). Consistent with the hypothesis, it was found that the presence of bubbles was
directly related to critical supersaturation in faster (5 to 20 minute) rather than in slower tissues.
Also consistent with the hypothesis was that the fast tissues controlled the ascent, the faster the
leading tissue (i.e., 5 vs. 10 minute; 10 vs. 20 minute), the worse the bubbling became.
As a result of this research and recent theoretical discussions (1) of the effects of linear
ascent rates (Hill) versus deep stops (Haldane), a matrix was developed for experimental dives to
UHM 2004, Vol. 31, No. 2 – Deep stop decompression
235
25 m (82 fsw) by volunteer divers using ascent rates of 3, 10 or 18 m/minute (10, 33, or 60
fsw/minute) and stops at 6 m (20 fsw) or both 6 m and 15 m (20 fsw and 50 fsw). Blacked-out
Uwatec depth-time recorders were again used to track predicted gas tensions for 5, 10, 20, 40
and 80 minute half time ‘tissues’. The hypothesis was that by combining a deep and a shallow
stop – to avoid critical supersaturation levels in the fast, leading tissues – decompression stress
would be reduced as observed by Doppler-detectable bubbles and lower predicted gas tensions
when compared to either a direct ascent, or direct ascent with only a shallow stop.
METHODS
The dives were carried out by 22 volunteer recreational divers. After reading and signing
the informed consent form, which excluded pregnancy from the study, the divers were instructed
to complete each of 8 possible combinations of ascent rate with or without decompression stops.
The dives were undertaken over 8 separate weekends, with no dives in between, and involved a
25 m (82 ft) dive for 25 min followed by a repetitive dive to 25 m (82 fsw) for 20 minutes after a
3h30 minute surface interval. The prescribed ascent rates were 3, 10 and 18 m/minutes
respectively, with or without 5 minute stops at 15 and 6 m. An 18 m/minute ascent profile
without stops was excluded intentionally for safety reasons. Most subjects completed all 8
profiles. Two divers were excluded before completing the fifth profile, due to pregnancy. A few
divers omitted the repetitive dive profile due to feeling too cold or due to adverse sea conditions.
The following data were collected: 24 dives for profile 1-1R; 25 dives for profile 2-2R; 27 dives
for profile 3-3R; 26 dives for profile 4-4R; 26 dives for profile 5-5R; 25 dives for profile 6-6R;
14 dives for profile 7-7R; and 14 dives for profile 8-8R. All in all, 181 dives were completed
with 1086 Doppler readings.
Table 1 - Matrix of Experimental Dive Profiles
Profile
(code no. for dives)
Depth (m) Time (min) Ascent Speed m/min Stop @ 15 m Stop @ 6 m Total Ascent Time (min)
1 (13) 25 25 10 0 0 2,5
1R (11) 25 20 10 0 0 2,5
2 (13) 25 25 3 0 0 8
2R (12) 25 20 3 0 0 8
3 (15) 25 25 18 0 5 6,5
3R (12) 25 20 18 0 5 6,5
4 (16) 25 25 10 0 5 7,5
4R (10) 25 20 10 0 5 7,5
5 (13) 25 25 3 0 5 13
5R (13) 25 20 3 0 5 13
6 (13) 25 25 10 5 5 12,5
6R (12) 25 20 10 5 5 12,5
7 (7) 25 25 18 5 5 11,5
7R (7) 25 20 18 5 5 11,5
8 (7) 25 25 3 5 5 18
8R (7) 25 20 3 5 5 18
UHM 2004, Vol. 31, No. 2 – Deep stop decompression
236
All dives were recorded for each time-depth profile as described previously (8, 9).
Blacked out Uwatec computers were worn by the divers to assure objective dive profile
recording and to allow subsequent mathematical calculation and analysis of the predicted tissue
saturations. Doppler recordings were performed by specially trained members of the volunteer
divers’ group, using an Oxford Instruments 3.5 MHz probe with a digital recorder (8, 9).
Recordings over the precordial area were made with the divers standing, at rest for thirty
seconds, and again for thirty seconds after performing two deep knee bends. The highest bubble
grade attained was used. A total of six one-min recordings were made at 15 minute intervals for a
total of 90 minutes after the dives. The recordings were later analyzed by a blinded, experienced
researcher. The Doppler bubble signals were scored according to three scales: The Spencer Scale
(SS), our simplified Doppler Bubble Grading System (DBGS), and our modification of the
Spencer Scale (called the Expanded Spencer Scale or ESS) defined as follows (10, 11, 12).
Simplified Doppler Bubble Grading System:
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 = 1-2 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
Table 2 provides a comparison between these scales.
To determine the relative index of
decompression stress, a “Bubble Score Index - BSI” was calculated for each “Dive plus
Repetitive Dive” experimental profile. Peak Doppler readings from the participants were
classified and recorded according to both SS and ESS systems. These were then added and
divided by the number of participating volunteer divers for each profile to generate an average
score. The individual incidence of BSI and various grades of Doppler detected bubbles were
compared using a generalized estimating equation (GEE) (13, 14) to account for repeated
observations from the same subject.
UHM 2004, Vol. 31, No. 2 – Deep stop decompression
Table 2
In order to correlate BSI to tissue saturations, all dive
profile data were downloaded from the depth-time recorders and
analyzed using the Bühlmann algorithm (3) to predict the
supersaturation peaks for each of the 8 tissue compartments
during the ascent. The changes in supersaturation were expressed
as fractions of the respective M Values, and calculated from
commencing the ascent until reaching the surface.
237
Fig. 1b: Doppler Grade Variations (SS) after each dive profile. The comparison of means has been done computing
the peak Doppler scores for each individual after each dive profile according to the Expanded Spencer Scale (ESS)
and Spencer Scale (SS). The means have been compared using parametric tests when possible after KS normality
testing (ANOVA with Neuman-Keuls post tests) and Kruskal-Wallis and Dunn’s post test when the normality
testing does not allow parametric evaluation. By accepting a ESS score of 1.5 and an SS score of 2 as “safe”, it can
be seen that the deep stop appears “safer” using both ESS and SS scales, while repetitive profiles 1,2,3 and 5 are
“unsafe”.
RESULTS
Figure 1 (a, b) summarizes the effect of the different
profiles on ESS and SS Doppler bubble scores respectively. It
shows the range of Doppler grade variation after each profile as
expressed by the mean of the individual Doppler grade peak for
each dive profile. Profile 2/2R (i.e., slow linear ascent) achieves the highest mean BSI, whereas
profile 6/6R (i.e., deep and shallow stop with a 10 m/min ascent rate) is the lowest.
SS SDBG ESS
0 LBG 0
1 LBG 0.5
1 LBG 1
2 LBG 1.5
2 HBG 2
3 HBG+ 2.5
3 HBG+ 3
4 HBG+ 3.5
4 HBG+ 4
Fig. 1a: Doppler Grade Variation (ESS) after each dive profile
P1
P1r
P2
P2r
P3
P3r
P4
P4r
P5
P5r
P6
P6r
P7
P7r
P8
P8r
O
verall
0.0
0.5
1.0
1.5
2.0
2.5
*** ***
**
*
*
**
Peak of doppler grade
0
1
2
3
Peak of Spencer doppler
grade
**
**
P1
P1r
P2
P2r
P3
P3r
P4
P4r
P5
P5r
P6
P6r
P7
P7r
P8
P8r
O
verall
UHM 2004, Vol. 31, No. 2 – Deep stop decompression
238
Figure 2 (a-d) shows the various regression analyses for BSI vs. saturation of the 5, 10,
20 and the 10 and 20-minute tissues combined as predicted by the Bühlmann algorithm. It can be
seen that the correlation between the predicted saturation of the 10 minute tissue, and the 10 and
20-minute tissues combined, vs. BSI achieve statistical significance but not for the 5 or 20-
minute tissues.
Fig. 2a. 5-min tissue saturation versus BSI Fig. 2b. 10-min tissue saturation versus BSI
0
10
20
30
0.0
2.5
5.0
7.5
10.0
r² = 0.46; r = 0.67;
p
=0.6
Saturation in 5
BSI
60.0 62.5 65.0 67.5 70.0
72.5
75.0
0.0
2.5
5.0
7.5
10.0
= 0.17; r = 0.41; p =0.17; y=0.35 x - 18
Saturation in 20 min HT tissue (%)
BSI
40
50
60
70
6;
y
=0.1312 x + 0.76
min HT tissue (%)
40 50 60 70
0.0
2.5
5.0
7.5
10
.
0
BSI
Fig. 2c. 20-min tissue saturation versus BSI Fig. 2d. 10 and 20-min tissue saturation versus BSI
10
min
and
20
min
HT
tissues
saturation
Vs
40 50 60 70 80
90
0.0
2.5
5.0
7.5
10.0
r² = 0.29; r = 0.54; p =0.03; y=0.16 x - 4.8
Saturation in 10/20 min. HT tissues (%)
BSI
80 90
r²=0.5173; r=0.72;
=0.044;
=0.1646x -4.581
Saturation in 10 min HT tissue (%)
Figure 3 shows a regression analysis of BSI vs. total ascent time. This shows the absence
of a significant correlation between total ascent time and BSI.
Fig. 3. BSI vs. total ascent time
0
2
4
6
8
10
12
14
16
18
0
1
2
3
4
5
6
7
8
9
10
Total ascent time (min.)
BSI
r²=0.2935; r= 0.54;
p
=0.165;
y
=0.2945x+8.5885
UHM 2004, Vol. 31, No. 2 – Deep stop decompression
This together with the significant correlation found between the 10 minute tissue
saturation and the BSI supports our hypothesis that the level or supersaturation of the fast tissues
determines the BSI, rather than the time it takes to reach the surface. The Highest Doppler scores
were observed after linear ascents with no stops. Here predicted tissue saturations of the 5 and
10 minute tissue compartments exceeded 50 to 80% of the Bühlmann M Values (see Figure. 4a).
The BSI for these dives reached values of 8.78 / 9.97 (ESS / SS) at an ascent rate of 3 m/min and
7.51 / 8.46 (ESS / SS) at an ascent rate of 10 m/minutes. For safety reasons the linear ascents at
18 m/minutes were not performed.
Fig. 4 a. Tracing of predicted tissue saturations for 5, 10 and 20-minute tissues according to the Bühlmann
algorithm, vs. fraction of M-value achieved, during decompression from profile 2 (slow linear ascent of 3 m/min)
0
0.2
0.4
0.6
0.8
1
1
Fraction of M-value
1.522.533.54
ambient pressure (ATA)
5 min 10 min 20 min
Fig. 4 b. Tracing of predicted tissue saturations for 5, 10 and 20-minute tissues according to the Bühlmann
algorithm, vs. fraction of M-value achieved, during decompression from profile 6 (10 m/min ascent rate with deep
and shallow stop
)
0
0.2
0.4
0.6
0.8
1
1
Fraction of M-value
1.522.533.54
ambient pressure (ATA)
5 min 10 min 20 min
239
UHM 2004, Vol. 31, No. 2 – Deep stop decompression
240
High Bubble Grades (HBG) also were observed after dives with a stop only at 6 m for 5
minutes, with the predicted 5 and 10 minute tissues saturation exceeding 30% and 65%
respectively. The BSI was 8.10 / 10.4 (ESS /SS) for the 3m/minute ascent rate; 7.41 / 8.78 (ESS /
SS) for the 18 m/minute speed of ascent; and 5.39 / 7.07 (ESS / SS) for the 10 m/minute speed of
ascent (Table 3). Finally, when a deep stop was also added, the predicted 5 and 10 minutes
tissue tensions dropped to between 22 and 28%, and 49 to 55% respectively (see Figure 4b). The
observed Doppler BSI reached minimum values of 3.25 / 4.64 (ESS / SS) for the 18m/minute
speed of ascent, only 1.79 / 2.50 (ESS / SS) for the 10-m/minute speed of ascent, and 3.50 / 4.53
(ESS / SS) for the 3-m / minute speed of ascent.
Table 3 – Fast tissue saturation and bubble scores after the different dive profiles
Ascent Rate Stops Average
surfacing
saturation (%):
5 min Tissue
Average surfacing
saturation (%):
10 min Tissue
BSI
(ESS/SS)
Total Time to
Surface
minutes
3 m/min (Profile 2) No Stop 48 75 8.78 / 9.97 8
3 m/min (Profile 5) 6 m / 5 min 30 60 8.10 / 10.04 13
3 m/min (Profile 8) 15 + 6 m / 5 min 22 49 3.50 / 4.53 18
10 m/min (Profile 1) No Stop 61 82 7.51 / 8.46 2.5
10 m/min (Profile 4) 6 m / 5 min 43 65 5.39 / 7.07 7.5
10m/min (Profile 6) 15 + 6 m / 5 min 25 52 1.79 / 2.50 12.5
18 m/min (Profile 3) 6 m / 5 min 42 60 7.41 / 8.78 6.5
18 m/min (Profile 7) 15 + 6 m / 5 min 28 55 3.25 / 4.64 11.5
Although variations in the rate of ascent and the inclusion of a safety stop all affected the
BSI and individual diver ESS scores (see Table 4) the lowest scores (1.79/2.50) were obtained by
the addition of a 5 minute deep stop at 15 m (profile 6). Conversely, the highest BSI and ESS
scores were associated with a linear, direct ascent to the surface at an ascent rate of 3 m/minutes
with no stops (profile 2). Such high grade scores have, in previous studies by others, been
associated with a higher risk of DCS (10, 16, 18).
DISCUSSION
In spite of gradual reductions in bottom time over the past decades, ascent rate and the addition
of an arbitrary shallow safety stop at 5 m (15 ft) for 3-5 minutes, neurological decompression
sickness remains a significant problem in recreational diving. A primary target for DCS appears
to be the spinal cord with its 12.5 min half-time (4). This research with human divers produced
two primary findings: (1) Slow ascents (3m/min) produced greater bubble grades than faster
ascents (see Figure 5); and (2) the inclusion of a deep stop together with a shallow stop yielded
the lowest bubble grades (see Figure 6). Therefore, contrary to popular belief, this study has
indicated that a slow, linear ascent may produce significantly more bubbles than a more rapid
ascent rate with a deep and shallow stop. Further, the optimal method for reducing post-dive
bubble production is the combination of an ascent rate of 10 m/min (30 fsw/min) with a deep
stop at about half the depth of the dive and a stop at 15 fsw (5 m) for 3-5 minutes.
UHM 2004, Vol. 31, No. 2 – Deep stop decompression
241
Table 4 – Incidence of Doppler detected bubbles after the different dive profiles
Dive Profile BSI
(ESS / SS)
Grade 0
%
Low Grade
%
High Grade
%
Ver
y
Hi
g
h Grade
%
1 – 1R 7.51 / 8.46 9.7 63.9 17.4 9.0
2 – 2R (worst) 8.78 / 9.97 10.0 50.6 19.4 20.0
3 – 3R 7.41 / 8.78 16.0 56.2 19.8 8.0
4 – 4R 5.39 / 7.07 18.6 62.8 10.9 5.7
5 – 5R 8.10 / 10.04 5.1 65.4 19.2 10.9
6 – 6R (best) 1.79 / 2.50 64.7 33.3 2.0 0.0
7–7R (2
nd
best)
3.25 / 4.64
34.5 64.3 1.2 0.0
8 – 8R (3
rd
best) 3.50 / 4.53
33.3 63.1 3.6 0.0
These observations suggest that it is necessary to re-examine strategies for gradual
decompression of the fast tissue compartment to improve diving safety. By using the known dive
data collection methodologies employed in Divers Alert Network Project Dive Safety; Project
Safe Dive; and recently Project Dive Exploration and the Diving Safety Laboratory in America
and Europe respectively, the effect of varying ascent rate and decompression may be evaluated.
The present research with recreational divers was able to show, in accordance with our
hypothesis, that the introduction of a ‘deep stop’ greatly reduced decompression stress as
observed by Doppler-detectable bubbles. The regression analyses indicate that the 10 min tissue
is most closely related to BSI scores for this type of diving. Therefore decompression profiles
may need to focus more closely on the this ‘tissue’ as not only being a critical factor in the
production of bubbles, but also possibly reflecting supersaturation within the spinal cord.
These observations also confirm a prior hypothesis of the authors (15) that the Delta-P
imposed on the leading tissue (i.e., the depth of the first stop) may be a critical factor
for the
production of precordially detectable bubbles, and, possibly, for the development of neurological
DCI in recreational dives.
While this study did not use DCS as an endpoint, there is previous research to support
that high grades of bubbles do correlate with an increased incidence of DCS (10, 16-18). This
study also indicates an improved gas elimination due to the inclusion of a deep stop which is the
probable reason for the significant bubble reduction.
CONCLUSIONS
The introduction of a deep stop during decompression ascent appears to significantly
decrease Doppler recorded bubbles and predicted gas tensions in the fast ‘tissues’ which may
relate to actual gas exchange within the spinal cord. The authors conclude that such a deep stop
may therefore significantly reduce the incidence of spinal cord related decompression sickness.
Further studies are planned to prove the direct correlation between this reduction in
precordial bubbles and tissue gas tensions in the so-called fast tissues and the appearance of
DCS. These observations and conclusions are relevant only to the types of recreational dives
UHM 2004, Vol. 31, No. 2 – Deep stop decompression
studied. They should not be extrapolated to deeper and longer decompression dives without
additional research and analysis.
Fig. 5. Ascent Rate vs. % high & very high bubble grades for all profiles
Fig 6. Percentage high and very high bubble grades versus stops (all ascent rates)
ACKNOWLEDGEMENT
This work would not have been possible without the enthusiasm and professional
dedication of the divers of the Italian Dive Clubs – “Ravenna Sub” and “Sub Novara Laghi” led
respectively by Riccardo Pepoli and Daniele Pes. The data they provided – which include the
dive profiles and Doppler recordings of excellent quality – have made an invaluable contribution
to the advancement of recreational dive safety.
References
1. Bennett PB, Marroni A, Balestra C, Cali-Corleo R, Germonpre P, Pieri M, Bonuccelli C. What ascent profile for the
prevention of decompression sickness? I – Recent research on the Hill/Haldane ascent controversy. Proceedings of
the 28
th
Annual Scientific Meeting of the European Underwater and Biomedical Society, pp 35-38:2002. September
4-8. Brugge, Belgium.
2. Hempleman HV. History of decompression disorders. In The Physiology and Medicine of Diving, 4
th
edition. Eds
PB Bennett and DH Elliott, pp 342-375:1993. Saunders, London.
3. Bühlmann AA. Decompression theory: Swiss practice. In The Physiology and Medicine of Diving, 2
nd
edition.
Eds PB Bennett and DH Elliott, pp 348-365:1975. Williams and Wilkins, Baltimore.
242
UHM 2004, Vol. 31, No. 2 – Deep stop decompression
243
18.
4. Edmonds C, Lowry C and Pennefather J. Historical and physiological concepts of decompression. In Diving and
Subaquatic Medicine, pp 40-158:1992. Butterworth-Heinemann.
5. Valentine R. Physiologists, Fathometers and Menfish. Proceeding 10
th
Conference Historical Diving Society.
Plymouth UK Historical Diving Times, pp 26:10-14:2000.
6. Wong RM. Empirical diving techniques. In Bennett and Elliott’s Physiology and Medicine of Diving, 5
th
edition.
Eds AO Brubakk and TO Neuman, pp 64-76:2003. Saunders, London.
7. Marroni A, Bennett PB, Balestra C, Cali-Corleo R, Germonpre P, Pieri M, Bonuccelli C. What ascent profile for the
prevention of decompression sickness? II – A field model comparing Hill and Haldane ascent modalities, with an
eye to the development of a bubble-safe decompression algorithm. Proceedings of the 28
th
Annual Scientific
Meeting of the European Underwater and Biomedical Society, pp 44-48:2002. September 4-8. Brugge, Belgium.
8. Marroni A, Cali-Corleo R, Denoble P. Understanding the safety of recreational diving. DAN Europe’s Project
SAFE DIVE Phase I: Fine tuning of the field research engine and methods Proceedings of the International Joint
Meeting on Hyperbaric and Underwater Medicine, EUBS, ECHM, ICHM, DAN., p. 279-284:1996 September 4-8
Milano, Italy.
9. Marroni A, Cali Corleo R, Balestra C, Voellm E, Pieri M. Incidence of Asymptomatic Circulating Venous Gas
Emboli in Unrestricted, Uneventful Recreational Diving. DAN Europe’s Project SAFE DIVE first results. EUBS
2000 Proceedings. Diving and Hyperbaric Medicine, Proceedings of the XXVI Annual Scientific Meeting of the
European Underwater and Baromedical Society, R Cali Corleo ed., p 9-15:2000, September 14-17 Malta.
10. Spencer MP, Johanson DC. Investigation of new principles for human decompression schedules using the Doppler
ultrasonic blood bubble detector. Tech. Report to ONR on contract N00014-73-C-0094, Institute for Environmental
Medicine and Physiology, Seattle, Wash. USA. 1974.
11. Marroni A, Cali Corleo R, Balestra C, Longobardi P, Voellm E, Pieri M, Pepoli R. Effects of the Variation of
Ascent Speed and Profile on the Production of Circulating Venous Gas Emboli and the Incidence of DCI in
Compressed Air Diving. Phase 1. Introduction of extra deep stops in the ascent profile without changing the original
ascent rates. DSL Special Project 01/2000. EUBS 2000 Proceedings. Diving and Hyperbaric Medicine, Proceedings
of the XXVI Annual Scientific Meeting of the European Underwater and Baromedical Society, R. Cali Corleo ed.,
2000: p 1-8: 2000, September 14-17 Malta.
12. Marroni A, Cali Corleo R, Balestra C, Longobardi P, Voellm E, Pieri M, Pepoli R. The Use of a “Proportional M-
Value Reduction Concept” (PMRC) Changing the Ascent Profile with the Introduction of Extra Deep Stops Reduces
the Production of Circulating Venous Gas Emboli after Compressed Air Diving. DSL Special Project 01/2001.
EUBS 2001 Proceedings of the 27
th
Annual Meeting. U van Laak ed., p 69-73: 2001, September 12-16, Hamburg,
Germany
13. Diggle P, Liang KY, Zeger SL. 1995. Analysis of Longitudinal Data. Oxford Science Publications, Clarendon Press:
Oxford.
14. Zeger SL, Liang K-Y, Albert PS. Models for longitudinal data: a generalized estimating equation approach.
Biometrics 44, 1049-1060; 1988.
15. Marroni A, Cali Corleo R, Balestra C, Longobardi P, Voellm E, Pieri M, Pepoli R. The Use of a “Proportional M-
Value Reduction Concept” (PMRC) The Speed of Ascent Dilemma: “Instant Speed of Ascent” or “Time to Surface”
– which one really matters? Instant speed of ascent vs Delta-P in the leading tissue and post dive Doppler Bubble
production.. DSL Special Project 02/2001. EUBS 2001 Proceedings of the 27
th
Annual Meeting. U van Laak ed.: p
74-78: 2001, September 12-16, Hamburg, Germany
16. Nashimoto I, Gotoh Y. Relationship Between Precordial Doppler Ultrasound Records and Decompression Sickness.
In: CW Shilling, MW Beckett (eds) Underwater Physiology VI. Undersea Medical Society, Bethesda 1978:497-501.
17. Marroni A, Zannini D. Effetti della variazione della velocità di risalita sulla produzione di bolle gassose circolanti
dopo immersioni ad aria compressa. Min Med 1981(Dec):3567-3572.
Nishi RY, Brubakk AO, Eftedal OS. Bubble detection. In: Bennett and Elliott’s Physiology and Medicine of Diving.
AA Brubakk, T Newman (eds) 5
th
edition. WB Saunders Company, London 2003:501-529.
... 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.
... The frequency of leading tissue involvement was also investigated. Aqueous tissues, with low gas solubility, were usually considered "fast tissues" (in terms of saturation time) as compared to "slow tissues" with high gas solubility (Bennett and Elliott, 1982;Marroni et al., 2004); starting from this the various "tissues" were grouped into three Leading Tissue Groups (LTG) in the DAN DB, to better manage the 16 investigated tissues, data recording and the related statistical analysis: ...
... Doppler recordings were evaluated according to a modified Spencer Scale (Spencer and Johanson, 1974) named Expanded Spencer Scale (ESS) (Marroni et al., 2004) However a simplified bubble grading system was used for our statistical evaluation, as follows: (Marroni et al., 2004) Zero ...
... Doppler recordings were evaluated according to a modified Spencer Scale (Spencer and Johanson, 1974) named Expanded Spencer Scale (ESS) (Marroni et al., 2004) However a simplified bubble grading system was used for our statistical evaluation, as follows: (Marroni et al., 2004) Zero ...
Article
Full-text available
Introduction: The popularity of SCUBA diving is steadily increasing together with the number of dives and correlated diseases per year. The rules that govern correct decompression procedures are considered well known even if the majority of Decompression Sickness (DCS) cases are considered unexpected confirming a bias in the “mathematical ability” to predict DCS by the current algorithms. Furthermore, little is still known about diving risk factors and any individual predisposition to DCS. This study provides an in-depth epidemiological analysis of the diving community, to include additional risk factors correlated with the development of circulating bubbles and DCS. Materials and Methods: An originally developed database (DAN DB) including specific questionnaires for data collection allowed the statistical analysis of 39,099 electronically recorded open circuit dives made by 2,629 European divers (2,189 males 83.3%, 440 females 16.7%) over 5 years. The same dive parameters and risk factors were investigated also in 970 out of the 39,099 collected dives investigated for bubble formation, by 1-min precordial Doppler, and in 320 sea-level dives followed by DCS symptoms. Results: Mean depth and GF high of all the recorded dives were 27.1 m, and 0.66, respectively; the average ascent speed was lower than the currently recommended “safe” one (9–10 m/min). We found statistically significant relationships between higher bubble grades and BMI, fat mass, age, and diving exposure. Regarding incidence of DCS, we identified additional non-bubble related risk factors, which appear significantly related to a higher DCS incidence, namely: gender, strong current, heavy exercise, and workload during diving. We found that the majority of the recorded DCS cases were not predicted by the adopted decompression algorithm and would have therefore been defined as “undeserved.” Conclusion: The DAN DB analysis shows that most dives were made in a “safe zone,” even if data show an evident “gray area” in the “mathematical” ability to predict DCS by the current algorithms. Some other risk factors seem to influence the possibility to develop DCS, irrespective of their effect on bubble formation, thus suggesting the existence of some factors influencing or enhancing the effects of bubbles.
... The echocardiographic VGE signals over the 1 min recording were evaluated by frame-based bubble counting as described by Germonpré et al [17], but also scored according to the Eftedal-Brubakk categorical score [18,19]. ...
... Very recent data show that the FMD reduction encountered after a single dive without presence of VGE, is comparable to the reduction encountered with the presence of VGE [19]. The divers that volunteered in our saturation experiment were taking some antioxidant "medication" (see table 3) as a protective measure, the trend of our data doesn't show a clear inflexion for some participants that could be explained by antioxidants intake, although 60% of the divers declared doing so. ...
Article
Full-text available
Background and Objectives: Saturation diving is a technique used in commercial diving. Decompression sickness (DCS) was the main concern of saturation safety, but procedures have evolved over the last 50 years and DCS has become a rare event. New needs have evolved to evaluate the diving and decompression stress to improve the flexibility of the operations (minimum interval between dives, optimal oxygen levels, etc.). We monitored this stress in saturation divers during actual operations. Materials and Methods: The monitoring included the detection of vascular gas emboli (VGE) and the changes in the vascular function measured by flow mediated dilatation (FMD) after final decompression to surface. Monitoring was performed onboard a diving support vessel operating in the North Sea at typical storage depths of 120 and 136 msw. A total of 49 divers signed an informed consent form and participated to the study. Data were collected on divers at surface, before the saturation and during the 9 h following the end of the final decompression. Results: VGE were detected in three divers at very low levels (insignificant), confirming the improvements achieved on saturation decompression procedures. As expected, the FMD showed an impairment of vascular function immediately at the end of the saturation in all divers but the divers fully recovered from these vascular changes in the next 9 following hours, regardless of the initial decompression starting depth. Conclusion: These changes suggest an oxidative/inflammatory dimension to the diving/decompression stress during saturation that will require further monitoring investigations even if the vascular impairement is found to recover fast.
... Aural detection was also performed by 8 expert observers on such signals. By comparing the results of the tests, we found that large values for S (S ≥ 10) cause a reduction both in the number of bubbles detected and in the related Spencer level [40,41]. Therefore, with the aim of finding a unique value for S, applicable to the entire data set, various experimental tests have been carried out with S between 1 and 9. From the analysis of the different outputs it emerged that the optimal value for S is equal to 5. ...
... In this work, each pair of embolic events occurred in distinct frames with maximum spacing in time of 20 ms were grouped to form a shower of bubbles. The last part of the proposed detection algorithm is about the determination of Spencer level and the corresponding individual embolism risk [18,40,41]. It is possible as the proposed algorithm has been designed to store the instant of occurrence as well as the duration of all bubble events and showers. ...
Article
Full-text available
Divers’ health state after underwater activity can be assessed after the immersion using precordial echo Doppler examination. An audio analysis of the acquired signals is performed by specialist doctors to detect circulating gas bubbles in the vascular system and to evaluate the decompression sickness risk. Since on-site medical assistance cannot always be guaranteed, we propose a system for automatic emboli detection using a custom portable device connected to the echo Doppler instrument. The empirical mode decomposition method is used to develop a real-time algorithm able to automatically detect embolic events and, consequently, assess the decompression sickness risk according to the Spencer’s scale. The proposed algorithm has been tested according to an experimental protocol approved by the Divers Alert Network. It involved 30 volunteer divers and produced 37 echo Doppler files useful for the algorithm’s performances evaluation. The results obtained by the proposed emboli detection algorithm (83% sensitivity and 76% specificity) make the system particularly suitable for real-time evaluation of the decompression sickness risk level. Furthermore, the system could also be used in continuous monitoring of hospitalized patients with embolic risks such as post surgery ones.
... The echocardiographic VGE signals over the 1 min recording were evaluated by frame-based bubble counting as described by Germonpré et al. (2014), but also scored according to the Eftedal-Brubakk categorical score (Eftedal and Brubakk 1997), while Doppler signals recording retrieved from the server were blindly reviewed to obtain a posteriori bubble grade according to the expanded Spencer scale. For the purpose of comparison and correlation testing both categorical score were converted within the simplified bubble grading system (BGS) (Marroni et al. 2004). ...
Article
Full-text available
PurposeData regarding decompression stress after deep closed-circuit rebreather (CCR) dives are scarce. This study aimed to monitor technical divers during a wreck diving expedition and provide an insight in venous gas emboli (VGE) dynamics.Methods Diving practices of ten technical divers were observed. They performed a series of three consecutive daily dives around 100 m. VGE counts were measured 30 and 60 min after surfacing by both cardiac echography and subclavian Doppler graded according to categorical scores (Eftedal–Brubakk and Spencer scale, respectively) that were converted to simplified bubble grading system (BGS) for the purpose of analysis. Total body weight and fluids shift using bioimpedancemetry were also collected pre- and post-dive.ResultsDepth-time profiles of the 30 recorded man-dives were 97.3 ± 26.4 msw [range: 54–136] with a runtime of 160 ± 65 min [range: 59–270]. No clinical decompression sickness (DCS) was detected. The echographic frame-based bubble count par cardiac cycle was 14 ± 13 at 30 min and 13 ± 13 at 60 min. There is no statistical difference neither between dives, nor between time of measurements (P = 0.07). However, regardless of the level of conservatism used, a high incidence of high-grade VGE was detected. Doppler recordings with the O’dive were highly correlated with echographic recordings (Spearman r of 0.81, P = 0.008).Conclusion Although preliminary, the present observation related to real CCR deep dives questions the precedence of decompression algorithm over individual risk factors and pleads for an individual approach of decompression.
... He concluded that a deep stop at half the dive depth should reduce the critical fast gas tensions and lower the DCS incidence rate. Earlier Marroni concluded studies with the DSL European sample with much the same thought [24]. Although he found that ascent speed itself did not reduce bubble formation, he suggested that a slowing down in the deeper phases of the dive (deep stops) should reduce bubble formation. ...
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.
... He concluded that a deep stop at half the dive depth should reduce the critical fast gas tensions and lower the DCS incidence rate. Earlier Marroni concluded studies with the DSL European sample with much the same thought (Marroni and Bennett, 2004). Although he found that ascent speed itself did not reduce bubble formation, he suggested that a slowing down in the deeper phases of the dive (deep stops) should reduce bubble formation. ...
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.
... Earlier Marroni [28] concluded studies with the DSL European sample with much the same thought. Although he found that ascent speed itself did not reduce bubble formation, he suggested that a slowing down in the deeper phases of the dive (deep stops) should reduce bubble formation. ...
... Earlier Marroni [28] concluded studies with the DSL European sample with much the same thought. Although he found that ascent speed itself did not reduce bubble formation, he suggested that a slowing down in the deeper phases of the dive (deep stops) should reduce bubble formation. ...
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.
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 development of doppler instrumentation for non-invasive detection of gas emboli moving through the arteries and veins is traced from its beginning in 1967 through 1974. The design and construction of the IEM and P precordial blood bubble detector is described in detail. The use of the doppler technique in the study and solution of decompression problems in divers is described. (Author)
Understanding the safety of recreational diving. DAN Europe’s Project SAFE DIVE Phase I: Fine tuning of the field research engine and methods
  • A Marroni
  • Cali
  • R Corleo
  • P Denoble
  • Echm
  • Dan Ichm
Marroni A, Cali-Corleo R, Denoble P. Understanding the safety of recreational diving. DAN Europe’s Project SAFE DIVE Phase I: Fine tuning of the field research engine and methods Proceedings of the International Joint Meeting on Hyperbaric and Underwater Medicine, EUBS, ECHM, ICHM, DAN., p. 279-284:1996 September 4-8 Milano, Italy
History of decompression disorders
  • Hv Hempleman
Hempleman HV. History of decompression disorders. In The Physiology and Medicine of Diving, 4th edition. Eds PB Bennett and DH Elliott, pp 342-375:1993. Saunders, London