Page 77 - JSOM Fall 2023

(e.g., falling through ice on a frozen lake, falling off a boat, car standard military issue wool under layers that consisted of
accident into a body of water in winter). We recently measured long pants, a top, and wool socks. Over the wool under layer,
a 53% increase in metabolic rate over a 6-hour cold-water a wool sweater was worn on top and nylon/polyester softshell
dive in 5°C coupled to significant decreases in core, skin, and pants over the bottom. Divers wore rubber soled shoes with
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extremity temperature with divers passively sitting. Divers in swim fins for the duration of the dive.
that effort maintained core temperature above hypothermia
(35°C); however, the physiological impact and hormonal stress Thermoregulation
cascade is unknown. Dives were completed over 2 days with a rest day in between.
On days 1 and 3, two dives were completed—one in the morn-
Another aspect to military diving is the repetitive nature of ing, after breakfast (0800) and one in the afternoon (1500).
training; military divers are often required to dive in harsh During the open sea dives (average time 48.3 ± 8.2 minutes),
conditions daily, whereas recreational divers can choose when the participants engaged in an underwater navigation exer-
and how often to expose themselves. As such, exercise prior cise that required finning 1000 meters at a low- to moderate-
to and during cold exposure may compromise the ability of intensity as verified via heart rate measurements. Activity
military divers to successfully complete a mission due to al- outside of the dives was controlled for meaning on dive day; no
tered thermoregulatory capacity 11,22,23 and the impact of the other activity was allowed. On non-dive days, the participants
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dive reflex from changes in parasympathetic activity. Rapid conducted a 60-minute weight lifting workout in the gym.
cold habituation has been suggested with repeat serial immer-
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sions, but whether this extends to submersion is unknown. Each diver was provided a core pill (VitalSense, Bend, OR),
which was ingested 4 hours prior to splash time, one time per
Thus, the purpose of this study was to determine the effects day to ensure its transit to the lower gastrointestinal tract.
of two daily bouts of cold-water diving operations on the Thermistor-based capsules have a sensing range of 25°C to
hormonal and metabolic profile of elite military personnel 50°C with reported accuracy ±0.1°C. Immediately prior to
and to determine whether 3 consecutive days of cold-water the dive, skin temperature patches (VitalSense, Bend, OR)
immersion reduces the stress response. We hypothesized that were affixed to the right side of the participant at the follow-
two daily bouts of cold-water diving would be associated with ing sites: dorsal hand, dorsal foot, mid pectoralis (chest), arm
an activation of the SAMS/SNS and the HPA axis as well as (lateral deltoid [arm]), mid-thigh (thigh), and mid-calf (leg).
changes in metabolic hormones. We also hypothesized that the Reported accuracy of the skin patches is ±0.25°C (–20°C to
hormonal changes induced by cold-water diving would be at- 32°C). Mean skin temperature was calculated using Ramana-
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tenuated on day 3 versus day 1 due to acclimatization. than equation. Temperature data were captured immediately
pre- and post-dive via telemetry.
Methods
Physiological Measurements
Participants Upon waking, divers reported to the locker room at 0600 and
Healthy, active-duty, male, Norwegian Special Forces divers laid down on a bench for fasted metabolic measurements via
volunteered for the study (age: 32.8 ± 3.4; height: 181.0cm ± indirect calorimetry (Oxycon Mobile CareFusion, CA). Fast-
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6.8; weight: 83.3kg ± 10.5; VO max: 60.0 ± 5.6). The research ing metabolic measurements were recorded for 15 minutes
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protocol, instructions, and consent process were provided to each morning. Immediately upon surfacing from the dive, div-
all potential participants in English and Norwegian, and all ers removed their mouthpiece, and a fitted mask was placed
participants provided written and verbal consent to take part over the nose and mouth to collect respiratory gases. Respira-
in the research study. This study was approved by the Institu- tory gases were collected for 5 minutes. Metabolic data from
tional Review Board of the Naval Health Research Center and indirect calorimetry pre-dive and post-dive were summarized
adhered to the Department of the Navy human research pro- into a digital data file and exported to Microsoft Excel as pre-
tection policies (Protocol NHRC.2017.0019), as well as the viously described. Heart rate was measured throughout the
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European Ethics Committee. dive using a Polar Team Pro monitor (Polar Electro, Inc., Lake
Success, NY).
Demographic and Anthropometric Assessment
Height and weight (ProMed 6129 Detecto, MO, USA) and Blood glucose and ketone concentrations were measured
body composition for each subject were recorded using a prior to and following both dives. Capillary whole blood was
digital scale with height rod and via InBody (InBody, CA, collected via finger stick and was used immediately to assess
USA). A modified Balke treadmill test was completed to as- blood glucose and ketone concentrations via handheld glu-
sess each subject’s VO peak. During the graded exercise stress cometer (Freestyle Lite, Abbott Laboratories, Chicago, IL) and
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test (GXT), respiratory gases were continuously collected ketone meter (Precision Xtra, Abbott Laboratories, Chicago,
and analyzed using the Parvo Medics TrueOne 2400 (Parvo IL). Urine specific gravity via refractometer was used to assess
Medics, Inc., UT, USA) metabolic cart system, and heart rate hydration (Model UG-α, ATAGO ; WA, USA). Urine samples
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was measured using a Polar monitor (Polar Electro, Inc., were obtained prior to and immediately following each dive.
NY, USA).
Hormone Analysis
Cold-Water Dives Fasting whole blood (10mL) was collected in tubes coated
All dives occurred in the high Arctic Circle (ambient air tem- with Ethylenediaminetetraacetic acid (EDTA) following meta-
perature of –5.1°C and a water temperature of 3.3°C) during bolic measurements in the morning (~0630) and prior to con-
scheduled underwater navigation training. This training was sumption of breakfast. This morning blood sample served as
the first winter dive of the year for all divers. All divers wore “pre-dive” value. Upon surfacing, the post-dive blood sample
standard military issue dry suits. Underneath the dry suit, was acquired immediately after the metabolic measurement.

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