Human vulnerability and variability in the cold: Establishing individual risks for cold weather injuries

Climate crisis risks to elderly health: strategies for effective promotion and response

The climate crisis significantly impacts the health and well-being of older adults, both directly and indirectly. This issue is of growing concern in Canada due to the country's rapidly accelerating warming trend and expanding elderly population. This article serves a threefold purpose: (i) outlining the impacts of the climate crisis on older adults, (ii) providing a descriptive review of existing policies with a specific focus on the Canadian context, and (iii) promoting actionable recommendations. Our review reveals the application of current strategies, including early warning systems, enhanced infrastructure, sustainable urban planning, healthcare access, social support systems, and community engagement, in enhancing resilience and reducing health consequences among older adults. Within the Canadian context, we then emphasize the importance of establishing robust risk metrics and evaluation methods to prepare for and manage the impacts of the climate crisis efficiently. We underscore the value of vulnerability mapping, utilizing geographic information to identify regions where older adults are most at risk. This allows for targeted interventions and resource allocation. We recommend employing a root cause analysis approach to tailor risk response strategies, along with a focus on promoting awareness, readiness, physician training, and fostering collaboration and benchmarking. These suggestions aim to enhance disaster risk management for the well-being and resilience of older adults in the face of the climate crisis.

Cold-induced vasodilation during sequential immersions of the hand

A common practice for those operating in cold environments includes repetitive glove doffing and donning to perform specific tasks, which creates a repetitive cycle of hand cooling and rewarming. This study aimed to determine the influence of intraday repeated hand cooling on cold-induced vasodilation (CIVD), sympathetic activation, and finger/hand temperature recovery. Eight males and two females (mean ± SD age: 28 ± 5 year; height: 181 ± 9 cm; weight: 79.9 ± 10.4 kg) performed two 30-min hand immersions in cold (4.3 ± 0.92 °C) water in an indoor environment (18 °C). Both immersions (Imm1; Imm2) were performed on the same day and both allowed for a 10-min recovery. CIVD components were calculated for each finger (index, middle, ring) during each immersion. CIVD onset time (index, p = 0.546; middle, p = 0.727; ring, p = 0.873), minimum finger temperature (index, p = 0.634; middle, p = 0.493; ring, p = 0.575), and mean finger temperature (index, p = 0.986; middle, p = 0.953; ring, p = 0.637) were all similar between immersions. Recovery rates generally demonstrated similar responses as well. Findings suggest that two sequential CIVD tests analyzing the effect of prior cold exposure of the hand does not impair the CIVD response or recovery. Such findings appear promising for those venturing into cold environments where hands are likely to be repeatedly exposed to cold temperatures.

Extremity cooling during an arctic diving training exercise

A field study was conducted to examine the vulnerability of military divers to non-freezing cold injury (NFCI) during Arctic ice-diving operations. Participants were instrumented with temperature sensors on the back of their hands and on the bottom of their big toe for each dive to measure cooling of their extremities. While NFCI was not diagnosed in any of the participants during this field study, the data indicate that the feet were particularly vulnerable during the dives given that they were mostly in a temperature zone that could cause pain and performance decrements. The data also show that for short term dives, the dry and wet suits with wet gloves in both configurations were thermally more comfortable for the hands than the dry suit with dry glove configuration; however, the latter would be more protective against potential NFCI during longer dives. Features such as hydrostatic pressure and repetitive diving that are unique to diving but not previously considered as risk factors for NFCI are examined herein and warrant deeper investigation given that symptoms of NFCI might be mistaken as decompression sickness.

Nonoptimum Temperatures Are More Closely Associated With Fatal Myocardial Infarction Than With Nonfatal Events

BACKGROUND

Ambient temperatures trigger hospitalisation, mortality, and emergency department visits for myocardial infarction (MI). However, nonoptimum temperature-related risks of fatal and nonfatal MI have not yet been compared.

METHODS

From 2007 to 2019, 416,894 MI events (233,071 fatal and 183,823 nonfatal) were identified in Beijing, China. A time-series analysis with a distributed-lag nonlinear model was used to compare the relative and population-attributable risks of fatal and nonfatal MI associated with nonoptimum temperatures.

RESULTS

The reference was the optimum temperature of 24.3°C. For single-lag effects, cold (-5.2°C) and heat (29.6°C) effects had associations that persisted for more days for fatal MI than for nonfatal MI. For cumulative-lag effects over 0 to 21 days, cold effects were higher for fatal MI (relative risk [RR] 1.99, 95% confidence interval [CI] 1.68-2.35) than for nonfatal MI (RR 1.60, 95% CI 1.32-1.94) with a P value for difference in effect sizes of 0.048. In addition, heat effects were higher for fatal MI (RR 1.33, 95% CI 1.24-1.44) than for nonfatal MI (RR 0.99, 95% CI 0.91-1.08) with a P value for difference in effect sizes of 0.002. The attributable fraction of nonoptimum temperatures was higher for fatal MI (25.6%, 95% CI 19.7%-30.6%) than for nonfatal MI (19.1%, 95% CI 12.1%-25.0%).

CONCLUSIONS

Fatal MI was more closely associated with nonoptimum temperatures than nonfatal MI, as evidenced by single-lag effects that have associations which persisted for more days, higher cumulative-lag effects, and higher attributable risks for fatal MI. Strategies are needed to mitigate the adverse effects of nonoptimum temperatures.

We are all exposed, but some are more exposed than others

This paper defines functional cold exposure zones that illustrate whether a person is at risk of developing physical performance loss or cold weather injuries. Individual variation in body characteristics, activity level, clothing and protective equipment all contribute to variation in the effective exposure. Nevertheless, with the right education, training, and cold-adapted behaviours the exposure differences might not necessarily lead to increased risk for cold injury. To support the preparation process for cold weather operations, this paper presents a biophysical analysis explaining how much cold exposure risk can vary between individuals in the same environment. The results suggest that smaller persons are prone to be underdressed for moderate activity levels and larger persons are prone to be overdressed. The consequences of these discrepancies place people at different risks for performance loss or cold weather injuries. Nonetheless, even if all are well-dressed at the whole-body level, variation in hand morphology is also expected to influence hand skin temperatures that can be maintained; with smaller hands being more prone to reach skin temperatures associated with dexterity loss or cold weather injuries. In conclusion, this work focusses on bringing cold science to the Arctic warrior, establishing that combating cold stress is not a one size fits all approach.

To the extreme! How biological anthropology can inform exercise physiology in extreme environments

The fields of biological anthropology and exercise physiology are closely related and can provide mutually beneficial insights into human performance. These fields often use similar methods and are both interested in how humans function, perform, and respond in extreme environments. However, these two fields have different perspectives, ask different questions, and work within different theoretical frameworks and timescales. Biological anthropologists and exercise physiologists can greatly benefit from working together when examining human adaptation, acclimatization, and athletic performance in the extremes of heat, cold, and high-altitude. Here we review the adaptations and acclimatizations in these three different extreme environments. We then examine how this work has informed and built upon exercise physiology research on human performance. Finally, we present an agenda for moving forward, hopefully, with these two fields working more closely together to produce innovative research that improves our holistic understanding of human performance capacities informed by evolutionary theory, modern human acclimatization, and the desire to produce immediate and direct benefits.

Efficacy of closed cell wet-suit at various depths and gas mixtures for thermoprotection during military training dives

Purpose: To evaluate a closed-cell wet-suit for thermal protective capability during extreme cold water exposure at various depths. Methods: Thirteen (n = 13) elite military divers who were tasked with cold-water training, participated in this study. To mimic various depths, the Ocean Simulation Facility (OSF) at the Navy Experimental Diving Unit (NEDU) was pressurized to simulate dive depths of 30, 50, and 75fsw. Water temperature remained at 1.8-2.0°C for all dives. Four divers dove each day and used the MK16 underwater breathing apparatus with gas mixes of either N202 (79:21) or HeO2 (88:12). Mean skin temperature (T_SK) (Ramanathan, 1964), core temperature (Tc), hand and foot readings were obtained every 30 min for 30 and 50fsw and every 15 min during the 75fsw dive. Results: T_C was significantly reduced across all dives (p = 0.004); however, was preserved above the threshold for hypothermia (post dive Tc = 36.5 ± 0.4). There was no effect of gas mix on T_C. T_SK significantly decreased (p < 0.001) across all dives independent of depth and gas. Hand and foot temperatures resulted in the termination of three of the dives. There were no significant main effects for depth or gas, but there were significant main effects for time on hand temperature (p < 0.001) and foot temperature (p < 0.001). Conclusion: Core temperature is maintained above threshold for hypothermia. Variatioins in T_C and T_SK are a function of dive duration independent of depth or gas for a closed-cell wet-suit in cold water at various depths. However, both hand and foot temperatures reached values at which dexterity is compromised.

The peripheral vascular responses in non-freezing cold injury and matched controls

NEW FINDINGS

What is the central question of this study? Does non-freezing cold injury (NFCI) alter normal peripheral vascular function? What is the main finding and its importance? Individuals with NFCI were more cold sensitive (rewarmed more slowly and felt more discomfort) than controls. Vascular tests indicated that extremity endothelial function was preserved with NFCI and that sympathetic vasoconstrictor response might be reduced. The pathophysiology underpinning the cold sensitivity associated with NFCI thus remains to be identified.

ABSTRACT

The impact of non-freezing cold injury (NFCI) on peripheral vascular function was investigated. Individuals with NFCI (NFCI group) and closely matched controls with either similar (COLD group) or limited (CON group) previous cold exposure were compared (n = 16). Peripheral cutaneous vascular responses to deep inspiration (DI), occlusion (PORH), local cutaneous heating (LH) and iontophoresis of acetylcholine and sodium nitroprusside were investigated. The responses to a cold sensitivity test (CST) involving immersion of a foot in 15°C water for 2 min followed by spontaneous rewarming, and a foot cooling protocol (footplate cooled from 34°C to 15°C), were also examined. The vasoconstrictor response to DI was lower in NFCI compared to CON (toe: 73 (28)% vs. 91 (17)%; P = 0.003). The responses to PORH, LH and iontophoresis were not reduced compared to either COLD or CON. During the CST, toe skin temperature rewarmed more slowly in NFCI than COLD or CON (10 min: 27.4 (2.3)°C vs. 30.7 (3.7)°C and 31.7 (3.9)°C, P < 0.05, respectively); however, no differences were observed during the footplate cooling. NFCI were more cold-intolerant (P < 0.0001) and reported colder and more uncomfortable feet during the CST and footplate cooling than COLD and CON (P < 0.05). NFCI showed a decreased sensitivity to sympathetic vasoconstrictor activation than CON and greater cold sensitivity (CST) compared to COLD and CON. None of the other vascular function tests indicated endothelial dysfunction. However, NFCI perceived their extremities to be colder and more uncomfortable/painful than the controls.

Peripheral sensory function in non-freezing cold injury patients and matched controls

NEW FINDINGS

What is the central question of this study? Is peripheral sensory function impaired in the chronic phase of non-freezing cold injury (NFCI)? What is the main finding and its importance? Warm and mechanical detection thresholds are elevated and intraepidermal nerve fibre density is reduced in individuals with NFCI in their feet when compared to matched controls. This indicates impaired sensory function in individuals with NFCI. Interindividual variation was observed in all groups, and therefore a diagnostic cut-off for NFCI has yet to be established. Longitudinal studies are required to follow NFCI progression from formation to resolution ABSTRACT: The aim of this study was to compare peripheral sensory neural function of individuals with non-freezing cold injury (NFCI) with matched controls (without NFCI) with either similar (COLD) or minimal previous cold exposure (CON). Thirteen individuals with chronic NFCI in their feet were matched with the control groups for sex, age, race, fitness, body mass index and foot volume. All undertook quantitative sensory testing (QST) on the foot. Intraepidermal nerve fibre density (IENFD) was assessed 10 cm above the lateral malleolus in nine NFCI and 12 COLD participants. Warm detection threshold was higher at the great toe in NFCI than COLD (NFCI 45.93 (4.71)°C vs. COLD 43.44 (2.72)°C, P = 0.046), but was non-significantly different from CON (CON 43.92 (5.01)°C, P = 0.295). Mechanical detection threshold on the dorsum of the foot was higher in NFCI (23.61 (33.59) mN) than in CON (3.83 (3.69) mN, P = 0.003), but was non-significantly different from COLD (10.49 (5.76) mN, P > 0.999). Remaining QST measures did not differ significantly between groups. IENFD was lower in NFCI than COLD (NFCI 8.47 (2.36) fibre/mm2 vs. COLD 11.93 (4.04) fibre/mm2 , P = 0.020). Elevated warm and mechanical detection thresholds may indicate hyposensitivity to sensory stimuli in the injured foot for individuals with NFCI and may be due to reduced innervation given the reduction in IENFD. Longitudinal studies are required to identify the progression of sensory neuropathy from the formation of injury to its resolution, with appropriate control groups employed.

Finger anthropometrics may not be a primary influence on the thermal responses to cooling and rewarming

The fingers have a large surface area to volume ratio (SA:V), minimal muscle mass, and potent vasoconstrictor capacity. These qualities make the fingers prone to heat loss and freezing injuries during whole-body or local cold exposure. Anthropologists have proposed that the large inter-individual variability in human finger anthropometrics may be an ecogeographic evolutionary adaptation, where shorter and thicker digits (i.e. smaller SA:V ratio) provide a favorable adaptation for cold climate natives. We hypothesized that the SA:V ratio of a digit has an inverse relationship with finger blood flux and finger temperature (Tfinger) during cooling and rewarming from cold. Fifteen healthy adults with no or limited cold experiment experience performed 10 min of baseline immersion in warm water (35.0 ± 0.1°C), 30 min in cold water (8.4 ± 0.2°C), and a final 10 min of rewarming in ambient air (~22°C, ~40% relative humidity). Tfinger and finger blood flux were measured continuously across multiple digits per participant. Average Tfinger (p = 0.05; R2 = 0.06) and area under the curve for Tfinger (p = 0.05; R2 = 0.07) during hand cooling showed significant, negative correlations to digit SA:V ratio. There was no relationship between digit SA:V ratio and blood flux (i.e. average blood flux and AUC) during cooling as well as between SA:V ratio and digit temperature (i.e. average Tfinger and AUC) or blood flux (i.e. average blood flux and AUC) during rewarming. Overall, digit anthropometrics do not appear to play a dominant role in extremity cold response.