Jørgen Melau

Cold water immersion (CWI) is a significant cause of open-water drowning mortality. Epidemiological data challenge the prevailing assumption that hypothermia is the primary mechanism of death, pointing instead to acute responses that precede core cooling. The four-stage model (cold shock response, swimming failure, hypothermia, and circum-rescue collapse) provides a framework for understanding the sequential threats faced by an immersion victim. The cold shock response, triggered within seconds of immersion, can cause death through aspiration, hypocapnia-induced cerebral hypoperfusion, and cardiac arrhythmia before core temperature begins to fall; autonomic conflict and underlying channelopathies are candidate mechanisms for sudden arrhythmic death in susceptible individuals. Swimming failure follows as peripheral neuromuscular cooling impairs motor function at near-normal core temperatures. Hypothermia develops only after sustained exposure, and in most cold water drowning deaths it occurs after aspiration-induced hypoxic arrest rather than as the primary cause of death. Circum-rescue collapse, driven primarily by the abrupt loss of hydrostatic pressure on extraction, also carries significant mortality risk. Although fewer than 10% of drowning victims present in a shockable rhythm, when such a rhythm is encountered it should prompt investigation for a primary arrhythmic cause that may have precipitated submersion. This narrative review examines the four-stage model of CWI in light of these developments and addresses the modifying effects of alcohol and psychoactive substances, self-rescue strategies, and implications for prehospital management.

Objective: Cardiac troponins (cTns) are frequently measured in patients when suspecting coronary artery disease (CAD). However, recent studies suggest that elevated cTns following exercise may predict CAD and increased mortality. Although the mechanisms underlying postexercise cTn increase remain unclear, the cardiac troponin I (cTnI)/cardiac troponin T (cTnT) ratio shows promise for distinguishing cardiac pathologies. This study assesses the dynamics of cTnI and cTnT concentrations and the cTnI/cTnT ratio in serum samples collected 1–2 days before, within 1 hour after and 11–24 hour after completing Norseman Xtreme Triathlon. Methods: Using Abbott’s STAT High Sensitive Troponin-I assay and Roche’s Elecsys Troponin T hs assay, we measured cTnI and cTnT in venous serum of 93 adult triathletes. Results: Concentrations of cTnI, cTnT and cTnI/cTnT ratio increased from baseline to immediately after the race (cTnI median (25–75 percentile) from (3 (2–6) ng/L) to 69 (37–156) ng/L, cTnT from (6 (5–8) ng/L) to 40 (24–55) ng/L and cTnI/cTnT from (0.5 (0.3–0.8)) to 2.1 (1.5–2.9), all p<0.001). Serum cTnI and cTnT concentrations remained elevated the day after the race, whereas the cTnI/cTnT ratio declined the day after the race compared with baseline levels. Three participants displayed higher cTnI levels, and 14 participants showed higher cTnI/cTnT ratios the day after the race compared with immediately after. Conclusion: Serum concentrations of cTnI, cTnT and the cTnI/cTnT ratio increase immediately after a long-distance triathlon, and concentrations trend towards normalisation the next day. The clinical implications are unknown and warrant further investigation.

Swimming in cold water is intrinsically unsafe. One of the threats is a fall in deep-body temperature, which adversely affects all body systems and increases the risk of death. Wetsuits mitigate, but do not negate this threat. Environmental conditions may confound findings from laboratory studies or mathematical models. The study aimed to elucidate associations and patterns of deep-body temperature change in open water wetsuited swimmers, thus facilitating risk assessment and improving swimmer safety. In this exploratory cohort study, following collection of anthropomorphic data including a Dual-energy X-ray Absorptiometry scan, deep-body temperature was continuously measured in 76 open water swims by 31 wetsuited swimmers in water temperatures ranging from 8.4°C to 24.5°C. The temperature trajectories were analyzed by piece-wise and linear mixed model regression. Registered with clinicaltrials.gov NCT06685627. Following immersion, there was a tri-phasic deep-body temperature trajectory, although not all phases were present in all swims: an initial rise, then a plateau phase and then thermal decompensation. Water temperature was correlated with the duration of these phases, as was body habitus for the initial rise. Minimum deep-body temperature was correlated with pre-swim temperature. Despite environmental and individual variations, this paper identified a tri-phasic deep-body temperature trajectory for wetsuited swimmers and proposed physiological mechanisms that may account for them. The tri-phasic pattern of an initial rise, a plateau phase and then thermal decompensation, may be useful in assessing the risks of open water swimming and may facilitate development and validation of deep-body temperature models for wetsuited swimmers.

Purpose: Laboratory studies have demonstrated that manual dexterity decreases with increasing cold, which may adversely affect performance. Dexterity may be impaired by cooling of the hand, cooling of the lower motor neurons, and cognitive impairment. Wetsuits are commonly used in open-water swimming and are mandated in some situations. This study investigates the effects of cold-water wetsuited swimming on dexterity. Methods: Five male and 4 female trained swimmers were recruited for this cohort crossover study. Following dual-energy X-ray absorptiometry scans to determine body composition, they swam in a freshwater lake on 7 occasions with water temperatures between 24.5 °C and 8.4 °C. Dexterity was measured preswim and postswim with a “nut–washer–bolt assembly time test” and cognition with a Stroop test. Core and peripheral body temperatures were continuously monitored. Effects were analyzed by linear mixed-model regression. Results: Pre–post swim difference in time to complete the nut–bolt assembly increased as water temperatures decreased (1.0 s, 95% CI, 0.5–1.5 per 1 °C, P < .0001; R² = .456), to a maximum of 14.7 seconds (95% CI, 3.3–26.0). This represented a 47.5% increase in assembly time from 24.5 °C to 8.4 °C, which we consider to be of practical significance. Decreased dexterity was associated with decreased forearm and scapular temperature and decreased cognitive function. Body composition did not affect dexterity, cognitive function, or body temperature during swims. Water temperature did not affect swim speed. Conclusions: Despite the use of wetsuits, manual dexterity decreased with cold-water swimming. Swimmers, triathletes, and event organizers should consider the implications for safety, performance, and equipment utilization.

Background: The aim of this study was to train and assess firefighters’ skill attainment in the use of tourniquets, and to assess their skill retention after 3 mo. The purpose is to show if firefighters can successfully apply a tourniquet after a short course based on the Norwegian national recommendation for civil prehospital tourniquet use. Methods: This is a prospective experimental study. The study population were firefighters, and the inclusion criterion was any on-duty firefighter. The first phase consisted of baseline precourse testing (T1), a 45-min course, followed by immediate retesting (T2). The second phase consisted of retesting of skill retention after 3 mo (T3). Results: A total of 109 participants at T1, 105 at T2, and 62 participants at T3. The firefighters achieved a higher proportion of successful tourniquet applications at T2 (91.4%; 96 of 105) as well as T3 (87.1%; 54 of 62) compared with 50.5% at T1 (55 of 109) (P = 0.009). Mean application time was 59.6 s (55.1-64.2) in T1, 34.9 s (33.3-36.6) in T2 and 37.7 s (33.9-41.4) in T3. Conclusion: A sample of firefighters can successfully apply a tourniquet after a 45-min course based on the 2019 Norwegian recommendation for civil prehospital tourniquet use. Skill retention after 3 mo was satisfactory for both successful application and application time.

A common effort for both military and civil healthcare is to achieve knowledge-based health care in cold weather injuries and fatal accidents in harsh arctic environment. The Cold Weather Operations Conference in November 2021, having more than 300 participants from 20 countries, was addressing the prevention and treatment of injuries and trauma care in cold weather conditions and the challenges for military prehospital casualty care. The intention of the programme was to stimulate further research and systematic knowledge-based clinical work. The abstracts from the conference present cold weather research and clinical experience relevant for readers of the International Journal of Circumpolar Health.

Endothelial vasodilatory function is dependent on the NO synthesis from L-arginine by endothelial NO-synthetase (eNOS). eNOS can be inhibited by asymmetric dimethylarginine (ADMA) by competitive inhibition on the binding site, and symmetric dimethylarginine (SDMA) can reduce the L-arginine availability intracellularly through competing for transport over the cellular membrane. To study the NO synthesis after prolonged exercise, we assessed circulatory L-arginine, the L-arginine/ADMA ratio, and SDMA before, after, and on the day after the Norseman Xtreme triathlon, an Ironman distance triathlon. We found significantly reduced levels of L-arginine and the L-arginine/ADMA ratio and increased levels of SDMA after the race (all p < 0.05). L-arginine rose toward baseline levels the day after the race, but ADMA increased beyond baseline levels, and SDMA remained above baseline the day after the race. The reduced levels of L-arginine and the L-arginine/ADMA ratio, and increased SDMA, after the race indicate a state of reduced capability of NO production. Increased levels of ADMA and SDMA, and reduced L-arginine/ADMA ratio, as seen the day after the race, are known risk markers of atherosclerosis and warrant further studies.

Triathlon and other endurance races have grown in popularity. Although participants are generally fit and presumably healthy, there is measurable morbidity and mortality associated with participation. In triathlon, most deaths occur during the swim leg, and more insight into risk factors, such as hypothermia, is warranted. In this study, we measured the core temperature of 51 participants who ingested temperature sensor capsules before the swim leg of a full-distance triathlon. The water temperature was 14.4–16.4 °C, and the subjects wore wetsuits. One subject with a low body mass index and a long swim time experienced hypothermia (<35 °C). Among the remaining subjects, we found no association between core temperature and swim time, body mass index, or sex. To conclude, the present study indicates that during the swim leg of a full-distance triathlon in water temperatures ≈ 15–16 °C, subjects with a low body mass index and long swim times may be at risk of hypothermia even when wearing wetsuits.