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Bubble Formation After a 20-m Dive: Deep-Stop vs. Shallow-Stop Decompression Profiles

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Bubble Formation After a 20-m Dive: Deep-Stop vs. Shallow-Stop Decompression Profiles

Abstract

It is claimed that performing a "deep stop," a stop at about half of maximal diving depth (MDD), can reduce the amount of detectable precordial bubbles after the dive and may thus diminish the risk of decompression sickness. In order to ascertain whether this reduction is caused by the deep stop or by a prolonged decompression time, we wanted to test the "deep stop" theory without increasing the total decompression time. From a modeling point of view, Haldanian theory states that this situation would increase the probability of observable bubbles, because of a longer stay at depth. Under these conditions, we examined whether a "deep-stop dive" (DSD) produces more bubbles or less than a "shallow-stop dive" (SSD). Recreational divers performed either a DSD or a SSD. Both groups were matched biometrically. MDD was 20 msw, bottom time 40 min and total diving time 47 min. In DSD, the "deep" stop (10 msw) replaced 3 min of the 7 min stop at 4 msw of SSD. DSD produced significantly more precordial bubbles than SSD after knee bends (P-values ranging from 0.00007 to 0.038). Our results indicate that at least for the tested dive profile, the higher supersaturations after surfacing overruled any possible beneficial effects of the deep stop on bubble formation. The usefulness of substituting a shallow stop with a deep stop in dives up to 20 msw can be questioned; at the least, more research is needed.
from: http://www.ingentaconnect.com/content/asma/asem/2008/00000079/00000005/art00004
Bubble Formation After a 20-m Dive: Deep-
Stop vs. Shallow-Stop Decompression Profiles
Authors: Schellart, Nico A.M.
1
; Brandt Corstius, Jan-Jaap
1
; Germonpré, Peter
1
; Sterk, Wouter
1
Source: Aviation, Space, and Environmental Medicine, Volume 79, Number 5, May , 2008 , pp.
488-494(7)
Publisher: Aerospace Medical Association
Schellart NAM, Brandt Corstius J-J, Germonpré P, Sterk W. Bubble formation after a 20-m
dive: deep-stop vs. shallow-stop decompression profiles. Aviat Space Environ Med 2008; 79:488-
94.
Objectives: It is claimed that performing a “deep stop,” a stop at about half of maximal diving depth
(MDD), can reduce the amount of detectable precordial bubbles after the dive and may thus diminish
the risk of decompression sickness. In order to ascertain whether this reduction is caused by the deep
stop or by a prolonged decompression time, we wanted to test the “deep stop” theory without increas-
ing the total decompression time. From a modeling point of view, Haldanian theory states that this
situation would increase the probability of observable bubbles, because of a longer stay at depth. Un-
der these conditions, we examined whether a “deep-stop dive” (DSD) produces more bubbles or less
than a “shallow-stop dive” (SSD).
Methods: Recreational divers performed either a DSD or a SSD. Both groups were matched biometri-
cally. MDD was 20 msw, bottom time 40 min and total diving time 47 min. In DSD, the “deep” stop
(10 msw) replaced 3 min of the 7 min stop at 4 msw of SSD.
Results : DSD produced significantly more precordial bubbles than SSD after knee bends (P-
values ranging from 0.00007 to 0.038).
Discussion: Our results indicate that at least for the tested dive profile, the higher supersaturations af-
ter surfacing overruled any possible beneficial effects of the deep stop on bubble formation. The use-
fulness of substituting a shallow stop with a deep stop in dives up to 20 msw can be questioned; at the
least, more research is needed.
References: 12 references open in new window
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Keywords: diving; shallow stop; deep stop; VGE; bubble grade; decompression theory
Document Type: Research article
DOI: 10.3357/ASEM.2164.2008
Affiliations: 1: From the Department of Medical Physics, Academic Medical Centre, University of
Amsterdam, The Netherlands (N. A. M. Schellart); Foundation of Diving Research, Amsterdam, The
Netherlands (N. A. M. Schellart); Scott Haldane Foundation, Loosdrecht, The Netherlands (J-J.
Brandt Corstius); Centre for Hyperbaric Oxygen Therapy, Military Hospital Brussels, Belgium (P.
Germonpré); and Dadcodat, Zuidwolde, The Netherlands (W. Sterk).
... 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. ...
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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.
... To allow parametric statistics, the ordinal KM scores were transformed to a numerical scale: the number of bubbles per centimeter squared (according to (13,18,34,36). However, the direct use of bubble counts can be inappropriate, since they show considerable deviation between subjects, which results in domination of high counts in the statistical analysis (the outlier problem). ...
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... (The rationale for applying logB is discussed in Ref. 35.) For KM ϭ 0 logB ϭ Ϫ3 is adopted (e.g., Ref. 34). ...
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... There were two dive profiles with a minor difference: One group made a dive with a single stop at 4 msw for seven minutes (1Sdive); the other group performed the 40-minute 20-msw dive with two stops (2Sdive), a fourminute stop at 10 msw and a three-minute stop at 4 msw. The reason for having two identical dive profiles with a slightly different decompression profile (but the same decompression time) was to perform another study with the same BG data comparing both profiles, see [8]. ...
... Since BGs could be measured only at two time points after surfacing, the maximum BG value is unknown. to approximate this maximum as well as possible, the largest of the 40-and 100-minute scores were used, a method applied previously [7,8]. ...
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