Original Research
29 September 2022
10.3389/fphys.2022.971757
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EDITED BY
José Eduardo Pereira Wilken Bicudo,
University of Wollongong, Australia
REVIEWED BY
Pasquale Longobardi,
Hyperbaric Center of Ravenna, Italy
Jacek Kot,
Medical University of Gdansk, Poland
*CORRESPONDENCE
Stian Lande Wekre,
stianlwe@stud.ntnu.no
†
These authors share first authorship
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This article was submitted to
Environmental, Aviation and
Space Physiology,
a section of the journal
Frontiers in Physiology
17 June 2022
ACCEPTED 12 September 2022
PUBLISHED 29 September 2022
RECEIVED
CITATION
Wekre SL, Landsverk HD, Lautridou J,
Hjelde A, Imbert JP, Balestra C and
Eftedal I (2022), Hydration status during
commercial saturation diving measured
by bioimpedance and urine
specific gravity.
Front. Physiol. 13:971757.
doi: 10.3389/fphys.2022.971757
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© 2022 Wekre, Landsverk, Lautridou,
Hjelde, Imbert, Balestra and Eftedal. This
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Hydration status during
commercial saturation diving
measured by bioimpedance and
urine specific gravity
Stian Lande Wekre 1*†, Halvor Dagssøn Landsverk 1†,
Jacky Lautridou 1, Astrid Hjelde 1, Jean Pierre Imbert 2,
Costantino Balestra 3,4 and Ingrid Eftedal 1
1
Department of Circulation and Medical Imaging, Faculty of Medicine and Health Sciences, NTNU
Norwegian University of Science and Technology, Trondheim, Norway, 2Divetech, Biot, France,
3
Environmental and Occupational Physiology Laboratory, Haute Ecole Bruxelles-Brabant HE2B,
Brussels, Belgium, 4DAN Europe Research, Brussels, Belgium
Excessive fluid loss triggered by hyperbaric pressure, water immersion and hot
water suits causes saturation divers to be at risk of dehydration. Dehydration is
associated with reductions in mental and physical performance, resulting in less
effective work and an increased risk of work-related accidents. In this study we
examined the hydration status of 11 male divers over 19 days of a commercial
saturation diving campaign to a working depth of 74 m, using two non-invasive
methods: Bioelectrical impedance analysis (BIA) and urine specific gravity (USG).
Measurements were made daily before and after bell runs, and the BIA data was
used to calculated total body water (TBW). We found that BIA and USG were
weakly negatively correlated, probably reflecting differences in what they
measure. TBW was significantly increased after bell runs for all divers, but
more so for bellmen than for in-water divers. There were no progressing
changes in TBW over the 19-day study period, indicating that the divers’
routines were sufficient for maintaining their hydration levels on short and
long term.
KEYWORDS
bioimpedance (BIA), hydration, hyperbaric saturation, saturation diving, total body
water, underwater work, decompression
Introduction
Commercial saturation divers must control their fluid intake to compensate for losses
triggered by their hyperbaric work environment. Failure to do so leads to dehydration
with negative effects on cognitive and physical performance. As the divers cannot drink
while they are in the water, attention is required during the time they spend in the dive bell
during underwater work excursions.
A water deficit of 2% or more of the body weight impairs mental performance in the
areas of short-term memory, arithmetic efficiency, and visuomotor tracking (Gopinathan
et al., 1988) as well as aerobic work performance (Erdman and Appel, 2005). Also,
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Materials and methods
dehydrated individuals report higher levels of perceived effort,
reduced alertness and increased levels of tiredness and fatigue
(Cian et al., 2000; Szinnai et al., 2005). It is known that
dehydrated workers are less effective and at increased risk of
accidents (Kenefick and Sawka, 2007). For this reason, the
United Kingdom Health and Safety Executive recommends
100–200 ml of water every 15 min, and 500 ml of water for
every hour of work to be drunk before working in areas
where provision of water is impossible (Powell and Bethea,
2005). However, these recommendations are aimed at high
heat working environments and do not take the complex
physiology in diving into account.
Saturation divers are exposed to multiple factors that
contribute to dehydration. The hyperbaric conditions
themselves cause a hyperbaric diuresis, also without water
immersion (Shiraki et al., 1985). Increased urinary neopterin
and creatinine during and immediately after saturation diving
have been reported, suggesting a reduction of renal function
(Mrakic-Sposta et al., 2020). Water immersion increases the
excretion of atrial natriuretic peptide and suppresses
vasopressin, thereby increasing the diuresis and excretion of
sodium (Miyamoto et al., 1991; Epstein, 1992; Norsk et al.,
1993). Saturation divers also use hot water suits to maintain
their body temperature in the cold water, and these suits
circulate hot seawater in direct contact with the diver’s skin.
The thermal stress from the hot water causes additional fluid
loss through sweat (Hope et al., 2005), possibly amplified by an
osmotic effect of salt water (Hope et al., 2001). Losses of up to
4–5kg, or 5–6% of total body weight, have been reported (Hope,
1995). This water must be replenished. In commercial
saturation diving, standards such as the Norwegian
NORSOK U-100 include routines for fluid intake (Norge
Standard, 2015).
Hydration status can be measured in several ways. Doing it
in the demanding environment of saturation diving poses
specific challenges, including high ambient pressure,
restricted use of electrical devices, and infection risk from
invasive procedures. Bioelectrical impedance analysis (BIA)
provides an easy to use, low cost, and non-invasive method
(O’brien et al., 2002). BIA measurements can be made by the
divers themselves inside the pressurized living chambers. Urine
specific gravity (USG) is also widely used as a measure of
hydration (Kavouras, 2002), and urine samples are easily
obtainable. USG can be measured by a refractometer outside
the pressurized living chambers.
In this study we examined divers’ hydration status during the
bottom phase of a commercial saturation dive to determine
whether they were successful at compensating for
dehydration. Two different methods, BIA and USG, were used
to before and after daily bell runs for underwater work
excursions, to determine whether there were acute and/or
progressing changes in total body water (TBW) during
18 days of saturation diving.
Frontiers in Physiology
Ethics
The study protocol was approved in advance by the
Norwegian Regional Committee for Medical and Health
Research Ethics (REK), approval reference ID 117404. All
eligible subjects were provided with information regarding the
aim and scope of the study, in addition to experimental
procedures and data handling. Written consent was given
before inclusion. The experimental procedures were conducted
according to the Declaration of Helsinki principles for ethical
human experimentation.
Study subjects
The study subjects consisted of 11 male saturation divers who
passed a pre-dive medical examination before they were
committed to saturation diving on board TechnipFMC’s dive
support vessel (DSV) Deep Arctic. Select anthropometric data for
the subjects are shown in Table 1.
Saturation diving
The study was done during a commercial saturation diving
campaign on the United Kingdom continental shelf in the
summer of 2021. The divers were grouped into four teams,
each team consisting of three divers. They were pressurized in
heliox to a living depth of 63 m of seawater (msw). The living
chambers were kept at 63 msw throughout the study period, with
an oxygen pressure of ≈ 40 kPa and temperature controlled
around 28–30°C. Humidity in the living chambers was set to
40%–50%. The teams were on 12-h shifts, with a new team
starting their shift every 6 hours. Each team worked the same
shift for the entire campaign, and thus had to adapt to different
circadian rhythms. During shifts, the divers would start with
personal morning routines (breakfast, hygiene etc.) before
continuing with a brief of the day’s planned work. They
would then proceed to prepare their equipment and move
into one of the vessel’s two diving bells. The bell was sealed
and lowered into a moon pool to deploy the divers to the ocean
floor. Once at bottom, two divers would go leave the bell for inwater work, while the third– the bellman - remained in the bell.
The role of bellman and in-water diver rotated so that each diver
took his turn as bellman every third day. The bell oxygen was
controlled at around 40–50 kPa. The diving mix provided a
ppO2 ranging from 60 to 80 kPa. One bell run lasted up to
8 h, with a maximum of 6 h of in-water work. A new team would
be heading down while the previous team was going up, ensuring
continuous underwater activity. The saturation diving profile is
illustrated in Figure 1.
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TABLE 1 Anthropometric data for the 11 study subjects.
Min
Age (years)
Height (cm)
Weight (kg)
BMI (kg/m2)
33
169
72
20.8
Max
67
196
115
31.2
Mean (±SD)
46.2 ± 11.6
184.6 ± 8.6
93.6 ± 17.0
27.2 ± 3.2
Mean given as arithmetic means ± standard deviation.
FIGURE 1
Heliox saturation dive profile. Vertical bars indicate bell runs. The storage depth was kept at 63 msw, and the maximum working depth was
74 msw. Partial pressure of oxygen was kept close to 40 kPa during storage, and raised during bell runs to 60–80 kPa for the in-water divers and
40–50 kPa for the bellmen.
Hydration routines
received training in use of the BIA device, Biody Xpert ZM from
Aminogram (La Ciotat, France), as per the manufacturer’s
instructions. Conduction between the skin and the electrodes
was standardized by wetting with a small amount of electrode gel
(Spectra 360 electrode gel, Parker Laboratories, Fairfield, NJ,
United States). The device is a multifrequency impedance meter,
accredited to the ISO 13485:2016 standard and CE marked,
measuring impedance at 200KHz, 100KHz, 50Khz, 20 KHz
and 5 KHz in addition to the phase angle at 50 KHz. It is
handheld and operated by a single 9V PP3 battery, and
suitable to operate within the pressurized living chambers.
Data was transferred over Bluetooth to a smartphone outside
the chambers, using the proprietary Aminogram Biodymanagerapp for android. The data is directly transferred from the device,
without interaction from the divers, ensuring truthful data. Urine
was collected into 50 ml containers as close to the bioimpedance
measurements as feasible, decompressed via the medical lock,
and analyzed in the DSV hospital using a digital refractometer
(ORF-P, KERN & SOHN GmbH, Balingen, Germany).
BIA and USG were first taken after the pre-dive medical
examinations before the divers entered the pressure chambers to
be compressed (baseline), and then daily before and after bell
runs. The divers were instructed to collect urine and measure
During bell runs, the divers had free access to bottled drinking
water, coffee, tea, and fruit. They had sport tablets (GO Hydro
electrolyte tablets, Science in sport, London, United Kingdom) to
add to the water if they preferred isotonic drink. The divers where
not monitored for daily intake of sport tablets during this study;
however, a survey conducted pre- and post-saturation showed that
over half of the divers on this vessel used them. They took 14 tablets a day when they were in-water divers and none on the
days they were bellman. Hydration routines during bell runs were
per the NORSOK U-100 standards (Norge Standard, 2015), which
requires in-water divers to return to the bell and take their helmet
off for at least 30 min for rehydration and lunch during the third or
fourth working hour. In-water divers were also at liberty to return
to the bell to drink at any time at their own request. The bellman
always had access to bottled drinking water and fruit.
Data and urine collection
Bioimpedance (BIA) data and urine were collected by the
study subjects themselves. After enrollment into the study, they
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bioimpedance before breakfast but after drinking fluids, and
again as soon as possible after the bell runs, before their next
meal. The procedure was repeated daily during 19 days of diving
and ended before the decompression back to the surface. Bell
runs were conducted continuously during the bottom phase,
except for 2 days where the ship moved to shore for crew shifts.
This resulted in data and samples from 18 bell runs for one team,
and 19 for the three others.
Total body water calculation
Total body water (TBW) was calculated from the
bioimpedance data using the equation by Kushner and
Schoeller (1986), as recommended by Aminogram.
FIGURE 2
The relationship between pre- and post-bell run values of
USG and BIA at 50 kHz analyzed by Spearman correlation
coefficients. All coefficients were statistically significant (p < 0,02),
implying that there was a negative correlation between USG
and BIA.
H2
TBW (0.382 + (0.014pSex))p
+ (0.105 + 0.038)pW
Z50kHz
+ 0.084pSex.
(1)
TBW = Total body water in liters, Z50kHz = impedance at
50 kHz, Sex = 1 for males and 0 for females, H = height in cm,
W = weight in kg.
time we applied a repeated measures analysis of variance
(ANOVA). Post hoc comparisons using Tukey’s test were
performed where a significant difference was indicated by
the ANOVA. Mauchly’s test of sphericity was used to
validate the ANOVA, and the Greenhouse & Geisser
correction was applied where the assumption of sphericity
was not met.
Statistics
The following questions were asked in the statistical analysis:
1) Were USG and BIA correlated? 2) Was there a difference in
hydration between in-water divers and bellmen after a single bell
run? And 3) Was there a progressing change in hydration over
time spent in saturation? For this final question, the data were
pooled into three batches for comparison: days 1–6, days
7–12 and days 13–19. Statistical significance was set a priori
to p < 0.05 for all tests.
Statistical analysis was done in GraphPad Prism version
9.3.1 for Mac (GraphPad Software, San Diego, CA,
United States) or IBM SPSS Statistics for Windows (Version
27.0. Armonk, NY: IBM Corp). Prior to the analysis, the data
were checked for normality by Shapiro-Wilk’s test and visual
inspection of Q-Q plots. Normally distributed data were analyzed
by parametric tests, whereas data that were not normally
distributed were analyzed using non-parametric tests.
BIA and USG data were compared using the Spearman rank
correlation coefficient. Days with missing data points were
excluded, resulting in an equal sample size for all
calculations in the correlation matrix (n = 174). Absolute
values BIA at 50 kHz and USG were used for the
comparison. Differences between in-water diver and bellman
data were analyzed using a paired t-test for normally distributed
data, and a Wilcoxon matched pairs test for data that were not
normally distributed. To analyze changes in hydration over
Frontiers in Physiology
Results
Correlation between bioelectrical
impedance analysis and urine specific
gravity
BIA and USG showed a weak but significant negative
correlation. As BIA measurements are inversely proportional
to TBW, this was the opposite of what was expected and implies
that the divers’ body water was higher at time points when their
urine was denser. The results of the correlation analysis are
shown in Figure 2.
Comparison of in-water divers and
bellmen after single bell runs
BIA was significantly lower after a single bell run for the
bellmen, whereas no change was seen for the in-water divers. By
inference, TBW increased after bell runs for the bellmen.
However, the TBW calculation exposed a statistically
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FIGURE 3
Boxplot showing the % change in hydration markers during bell runs, for bellmen and in-water divers. Box edges represent 25th and 75th
percentiles. Whiskers are minimum and maximum values. Calculation of differences were done using a paired t-test for urine specific gravity and
Wilcoxon matched pairs test for bioimpedance and total body water. *median different from zero (p ≤ 0,05). *** significant difference between
bellmen and in-water divers (p ≤ 0,001). “ns” no significant difference between bellmen and in-water divers.
FIGURE 4
TBW calculated from BIA data collected pre- and post-bell runs from 11 saturation divers Diamonds and whiskers are means ± SD. The mean
pre-saturation TBW baseline is shown as a horizontal stapled line. Panel shading indicates the three periods for which data were pooled to analyze
progressing changes in TBW. “*” indicates that the mean of pre-bell run TBW for the period was significantly below the pre-saturation baseline. There
were no differences in post-bell run TBW compared to baseline (p < 0.05).
Total body water during time spent in
hyperbaric saturation
significant increase also for the in-water divers: the Wilcoxon
matched pairs test showed that the bellmen had a median change
in total body water of 4.8 percent, whereas the in-water divers
had a median change of 0.7 percent, giving a median of
differences of 4.1 (p = 0.001). There were no changes in USG
after bell runs. Results of single bell run comparisons are shown
in Figure 3.
Frontiers in Physiology
The divers’ TBW was higher at baseline than during their
time in hyperbaric saturation, with differences reaching
significance for the two last periods of pooled data: between
baseline and days 7–12 (p < 0.03, decrease of 3.4%) and days
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from the suits. The increase in TBW that we saw among the
bellmen may very well be because of maintenance of good
hydration routines based on their days of in-water diving.
Opposite to what we expected, the BIA and USG data were
negatively correlated (Figure 2). This may be explained by
differences in what the two methods measure. Both methods
are widely used as indices of hydration status, as they are noninvasive, inexpensive, and can be done with minimal equipment.
While USG is considered a good measure of hydration status as
the concentration of solutes in urine increases with water deficit
(Oppliger et al., 2005) and USG is strongly correlated with urine
osmolality (Armstrong et al., 1994; Popowski et al., 2001), its
correlation decreases in pathological urine (Imran et al., 2010).
BIA on the other hand, measures the body’s conducting
properties (Kyle et al., 2004). By combining the impedance
with the subject’s height and weight it is possible to calculate
TBW (Kushner and Schoeller, 1986). However, the BIA method
also has its own set of constraints that may influence the results
(González-Correa and Caicedo-Eraso, 2012), where consistent
limb positioning is the most important (Kushner et al., 1996).
The study subjects were given training in BIA, but we cannot
eliminate the possibility of variations in body positioning, contact
with conducting material, skin-electrode contact etc. When
interpreting the BIA data. Also, most equations to calculate
TBW are based on euhydrated people, and it has been found
that the concomitant fluid and electrolyte changes that occur
with dehydration may confound BIA measurements (O’brien
et al., 2002). The negative correlation observed between the two
methods in our study may also be related to hyperbaric diuresis
during exposure to high pressure (Shiraki et al., 1985). This is
characterized by an increase in urine flow and decrease in
osmolality, associated with a decrease in antidiuretic hormone
(ADH) and increase in atrial natriuretic peptide (ANP)
(Miyamoto et al., 1991; Goldinger et al., 1992). Taken
together, a decrease in USG may occur even when TBW is
low – and vice versa.
13–19 (p < 0.02, decrease 3.5%). The TBW data are shown in
Figure 4.
Discussion
Dehydration increases the risk of accidents at work.
Saturation divers are especially prone to dehydration and
must amend their fluid intake to compensate for this. In this
study we monitored divers’ hydration status daily during the
bottom phase of a commercial saturation diving camping, using
two non-invasive methods: BIA and USG. Our main findings
were that the divers were not dehydrated after single bell runs,
nor did they become progressively dehydrated as the diving
campaign proceeded.
Water immersion and elevated environmental pressure both
trigger diuresis, and excess fluid loss is common in diving (Hong
et al., 1977; Shiraki et al., 1985; Shiraki et al., 1987; Sagawa et al.,
1990). A recent study suggests that increased pressure may cause
a reduction in renal function (Mrakic-Sposta et al., 2020). In
addition, saturation divers suffer increased loss of water through
sweating in their hot water suits (Hope et al., 2005), reported to
be up to 4–5 kg during a single dive (Hope, 1995). Failure to
replenish the lost body water will lead to a state of hypohydration,
which is associated with multiple adverse effects on both
cognitive (Grandjean and Grandjean, 2007) and physical
performance (Barr, 1999). For divers specifically, dehydration
has been shown to increase the risk of severe decompression
sickness in an animal model of simulated diving (Fahlman and
Dromsky, 2006) and pre-dive hydration lowers the risk for
decompression sickness (Gempp et al., 2009). The task at
hand for saturation divers, such as welding, construction or
inspection requires physical fitness and mental alertness. This
is further complicated by the diving- and life-support systems for
which the requirements are “much stricter than those for lifesupport systems used in outer space operations” (Brubakk et al.,
2014). It is safe to say that dehydration may have negative effects
on both the efficiency and safety of a diving operation, and that
good hydration routines are essential. We found no progressing
dehydration among the divers in our study. Although TBW was
higher at baseline than during hyperbaric saturation, no further
changes were observed over their time in saturation (Figure 4).
Our impression during the study was that both the divers and
supporting personnel paid a great deal of attention to the divers’
fluid intake, and the BIA and USG data indicate that their
routines were adequate to maintain daily as well as long-term
hydration levels.
The significant difference between the bellman and in-water
divers must be seen in context of their different exposures. The
in-water divers are exposed to effects of immersion and hot water
suits and are not at liberty to drink at their own leisure without
returning to the bell. The bellman, on the other hand, always has
drink available is not affected by neither immersion nor the heat
Frontiers in Physiology
Strengths and limitations
The data for this study was collected during a commercial
diving campaign with a minimum of changes to the divers’
routine. However, minimal interference complicates the
execution of research. The divers were asked to do their BIA
measurements and urine collections at set times before and after
bell runs. But as other task relevant for the work, e.g., bell checks,
maintenance, testing of equipment, briefs or similar had to be
prioritized, there was inevitable variation in the timing of data
and urine collections.
Food and drink consumption were not recorded, and neither
were changes in body weight or net fluid loss. This was not
central to the aim of this study but could be included in future
studies to examine in detail how the divers compensate for fluid
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Author contributions
loss. A useful comparison could be made to a study by Deb et al.
(2021), who did a comprehensive analysis of the energy intake
and expenditure during a similar dive. This dive was done under
similar conditions, and on the same DSV. Tracking the types,
volumes and times of fluid intake would also be useful when
interpreting the USG and BIA data to eliminate bias from intake
shortly before measurements (Dixon et al., 2006; Logan-Sprenger
and Spriet, 2013).
The impact of sea-water immersion on the conducting
properties of human skin is not fully mapped out. BIA is
heavily influenced by the conduction properties of the skin and
electrodes (González-Correa and Caicedo-Eraso, 2012) and for
this reason the electrode gel was used to standardize the contact
surface. This does not, however, affect the properties of skin itself.
Long term exposure of sea water makes the skin absorb moisture,
which has been shown to increase the conductivity and thus
decrease the impedance (Björklund et al., 2013). Also, the
temperature of the skin effects the impedance inversely
(Gudivaka et al., 1996). This was not controlled for in the study.
SW, JL, JI, CB, and IE conceptualized and designed the study.
SW and IE collected the material, and HL and AH performed the
analyses. All authors collaborated on the interpretation of results
and writing and approval of the final manuscript.
Funding
This study was funded by the NTNU Medical Student
Research Programme, and the Norwegian Research Council
and Equinor on behalf of PRSI Pool through the Large-scale
Programme for Petroleum Research (PETROMAKS2), project
no. 280425, via an integral part dedicated to research on Health,
Safety, and Environment (HSE) in the petroleum sector.
Acknowledgments
Conclusion
The divers, TechnipFMC, Repsol and crew of the Deep Arctic
DSV are gratefully acknowledged for their contribution to this
study during the 2021 Repsol Blane diving campaign.
In conclusion, the divers successfully maintained their
hydration levels during the bottom phase a commercial
saturation campaign with daily bell runs for underwater work.
A negative correlation between BIA and USG measurements may
reflect differences in what the two methods measure.
Conflict of interest
Author JI was employed by the company Divetech.
The remaining authors declare that the research was
conducted in the absence of any commercial or financial
relationships that could be construed as a potential conflict of
interest.
Data availability statement
The raw data supporting the conclusions of this article will be
made available by the authors, without undue reservation.
Publisher’s note
Ethics statement
All claims expressed in this article are solely those of the
authors and do not necessarily represent those of their affiliated
organizations, or those of the publisher, the editors and the
reviewers. Any product that may be evaluated in this article, or
claim that may be made by its manufacturer, is not guaranteed or
endorsed by the publisher.
The studies involving human participants were reviewed and
approved by Norwegian Regional Committee for Medical and
Health Research Ethics. The patients/participants provided their
written informed consent to participate in this study.
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