Diving in the Arctic: Cold Water Immersion’s Effects on Heart Rate Variability in Navy Divers

Abstract

Introduction: Diving close to the Arctic circle means diving in cold water regardless of the time of year. The human body reacts to cold through autonomous nervous system (ANS)-mediated thermoregulatory mechanisms. Diving also induces ANS responses as a result of the diving reflex. Materials and Methods: In order to study ANS responses during diving in Arctic water temperatures, we retrospectively analyzed repeated 5-min heart rate variability (HRV) measures and the mean body temperature from dives at regular intervals using naval diving equipment measurement tests in 0 • C water. Three divers performed seven dives without physical activity (81-91 min), and two divers performed four dives with physical activity after 10 min of diving (0-10 min HRV recordings were included in the study). Results: Our study showed a significant increase in parasympathetic activity (PNS) at the beginning of the dives, after which PNS activity decreased significantly (measure 5-10 min). Subsequent measurements (15-20 min and onward) showed a significant increase in PNS activity over time. Conclusion: Our results suggest that the first PNS responses of the human diving reflex decrease quickly. Adverse effects of PNS activity should be considered on long and cold dives. To avoid concurrent sympathetic (SNS) and PNS activity at the beginning of dives, which in turn may increase the risk of arrhythmia in cold water, we suggest a short adaptation phase before physical activity. Moreover, we suggest it is prudent to give special attention to cardiovascular risk factors during pre-dive examinations for cold water divers.

Diving Responses in Experienced Rebreather Divers: Short-Term Heart Rate Variability in Cold Water Diving

“…This physical activity, although not strenuous, could have caused the SNS activation seen in the submersion measure. From this measure forward, SNS activity decreased over time, as in our earlier study ( Lundell et al, 2020 ).…”

“…These results give support to the hypothesis that was presented in our previous work: the trigeminocardiac part of the diving reflex causes the initial strong PNS stimulus, but its effect also diminishes quickly. The secondary PNS activation is most likely caused by cold, and pressure induces changes in blood distribution as discussed in our previous study ( Lundell et al, 2020 ). As seen in this study, temperature, estimated from Tskin, decreased during the dives significantly.…”

“…In an earlier study, we discussed the role of different parts of the diving reflex in contributing to PNS activation at the beginning of diving in very cold conditions ( Lundell et al, 2020 ). Because divers submerged directly when entering the water in that study, we could only speculate on the roles of the following parameters.…”

“…Diving predominantly causes an increase in PNS activity. Studies have been performed in hyperbaric chambers ( Lund et al, 2000 , 2003 ) and in pool-like conditions ( Schipke and Pelzer, 2001 ; Chouchou et al, 2009 ), with various dives in different depths ( Noh et al, 2018 ), but to the best of our knowledge, only one involved cold water conditions ( Lundell et al, 2020 ). In the aforementioned literature, prominent PNS activation occurred, whereas SNS activity decreased.…”

The Circulatory Effects of Increased Hydrostatic Pressure Due to Immersion and Submersion

“…There is an inverse relationship with water temperature: the effect is stronger in cold water. The effects are transient, dissolving after approximately 5–10 min ( Lundell et al, 2020 ).…”