Page 76 - JSOM Fall 2023

Altered Sympathoadrenal Activity
Following Cold-Water Diving

Karen R. Kelly, PhD *; Carina M. Pautz, MS ; Laura J. Palombo, MS ;
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Andrew E. Jensen, PhD ; Jorgen Melau ; Lorraine P. Turcotte, PhD ; Paul A. Solberg, PhD 7
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ABSTRACT
Introduction: Little data exist on the effect of extremely depth and pressure can result in a variable stress response. 1,2
cold-water diving on thermo-metabolic hormone secretion. The mammalian dive reflex is a phenomenon by which there
Moreover, the impact of repetitive dives on the stress response is an increase in parasympathetic tone resulting in a decrease
is unknown. The purpose of this study was to determine the in heart rate in order to conserve oxygen and reduce consump-
effects of two daily bouts of cold-water diving on the hor- tion at peripheral tissues. Stress, however, provokes the corti-
monal and metabolic profile of elite military personnel and sol (stress) response to maintain homeostasis and ensure host
to measure the stress response. Methods: Healthy, male, Nor- survival. Altered dive reflexes in humans during submersion
wegian Special Forces Operators (n = 5) volunteered for this are known. However, whether a corresponding biochemical
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study. Physiological and hormone data were analyzed prior to response is elicited is not well characterized.
and following twice-daily Arctic dives (3.3°C). Results: Core
temperature was maintained (p > .05), whereas skin tempera- The stress response to cold and cold-water immersion are well
ture was significantly reduced over the course of each dive defined. 5–11 Activation of the hypothalamic-pituitary-adrenal
(p < .01). Pairwise comparisons revealed adrenocorticotropic (HPA) axis and the (SAM/SNS) coordinate metabolism and
hormone (ACTH) and cortisol concentration significantly de- thermoregulation in an attempt to maintain homeostasis and
creased across both dives and days (p < .001). Adrenaline and host survival. Cold-induced response of these systems has been
noradrenaline significantly increased across both time and day characterized for terrestrial operations as well as cold-water
(p < .001). Leptin, testosterone, and IGF-1 significantly de- immersion. 12,13 However, to our knowledge there are limited
creased over time but recovered between days. Conclusion: The data on the acute stress response during submersion in Arc-
main findings of this effort are that there is a rapid sympathet- tic waters. There are a few studies that addressed cortisol and
ic-adreno-medullary (SAM/SNS) response to cold-water div- adrenaline response to short duration (15–20 minutes) dives,
ing and a suppression of the hypothalamic-pituitary- adrenal but the findings are ambiguous. 1,2,14 Moreover, data from
(HPA) axis and hormones related to repair and recovery. post-mortem blood samples of hypothermia-related deaths
While the sample size was too small to determine the role of and cold-exposed cell models suggest that cold-induced corti-
SAM/SNS, HPA, and thyroid hormone effect on thermoregu- sol secretion might occur via ACTH-dependent and indepen-
lation, it addresses a gap in our understanding of physiological dent pathways. However, beyond these few published efforts,
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adaptions that occurs in extreme environments. information on SAM/SNS and HPA response to cold-water
diving (submersion) is scarce.
Keywords: military diving; Arctic; acute stress response; tes-
tosterone; leptin Military personnel don protective equipment to prevent
against heat loss and hypothermia, and it is assumed that this
gear will mitigate the stress of cold exposure. Cold-water ex-
posure poses a risk for hypothermia and cold injury and of-
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Introduction
ten impacts physical and cognitive performance. 17–19 Military
Military divers are required to train and operate indepen- divers can experience waters as cold as <10°C and may require
dent of environmental temperature in order to achieve op- hours of exposure. 3,20 While these personnel routinely undergo
erational readiness. Equipped with thermoprotective gear to training in such conditions, little is known about the physio-
mitigate heat loss, reduction in core and skin temperature is logical impacts of intentional prolonged cold-water exposure.
inevitable when diving in the Arctic. Further, the undersea The majority of data that is available is during cold-water im-
environment creates a unique stressor in that the change in mersion aimed at hypothermia onset in an accidental exposure
*Correspondence to Karen.r.kelly8.civ@health.mil
1 Dr Karen R. Kelly is affiliated with the University of Southern California, Biological Sciences, Human and Evolutionary Biology, Dornsife Col-
lege of Letters, Arts and Sciences, Los Angeles, CA and the Naval Health Research Center, Warfighter Performance Department, San Diego, CA.
2 Carina M. Pautz, MS, is affiliated with the University of Southern California, Biological Sciences, Human and Evolutionary Biology, Dornsife
College of Letters, Arts and Sciences, Los Angeles, CA. Laura J. Palombo, MS, is affiliated with Leidos Inc., San Diego, CA and the Naval Health
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Research Center, Warfighter Performance Department, San Diego, CA. Dr Andrew E. Jensen is affiliated with the University of Southern Cali-
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fornia, Biological Sciences, Human and Evolutionary Biology, Dornsife College of Letters, Arts and Sciences, Los Angeles, CA, the Leidos Inc.,
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San Diego, CA, and the Naval Health Research Center, Warfighter Performance Department, San Diego, CA. Jorgen Melau is affiliated with the
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Norwegian Armed Forces, Joint Medical Service, Oslo, Norway. Dr Lorraine P. Turcotte is affiliated with the University of Southern California,
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Biological Sciences, Human and Evolutionary Biology, Dornsife College of Letters, Arts and Sciences, Los Angeles. Dr Paul A. Solberg is affiliated
with the Norwegian Naval Special Operations Command, Bergen, Norway.
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