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

Abstract

Human tolerance to cold environments is extremely limited and responses between individuals is highly variable. Such physiological and morphological predispositions place them at high risk of developing cold weather injuries [CWI; including hypothermia and/or non-freezing (NFCI) and freezing cold injuries (FCI)]. The present manuscript highlights current knowledge on the vulnerability and variability of human cold responses and associated risks of developing CWI. This review 1) defines and categorizes cold stress and CWI, 2) presents cold defense mechanisms including biological adaptations, acute responses and acclimatization/acclimation and, 3) proposes mitigation strategies for CWI. This body of evidence clearly indicates that all humans are at risk of developing CWI without adequate knowledge and protective equipment. In addition, we show that while body mass plays a key role in mitigating risks of hypothermia between individuals and populations, NFCI and FCI depend mainly on changes in peripheral blood flow and associated decrease in skin temperature. Clearly, understanding the large interindividual variability in morphology, insulation, and metabolism is essential to reduce potential risks for CWI between and within populations.

Keywords: Cold survival; acclimation; adaptation; blood flow; energy metabolism.

Figure 1.

Conceptual illustration of thermoregulatory pathways involved in heat loss (Hloss, in blue) and heat production (Hprod, in red). Changes in temperature are detected by thermal receptor at the skin (Tskin) and in the preoptic area of the hypothalamus (Tcore). Neural integration of these afferent signals (in yellow) coordinates thermoeffector responses to reduce Hloss (peripheral vasoconstriction, CVC) and to increase Hprod (non-shivering thermogenesis, NST, and shivering thermogenesis, ST). Determinants of cold perception, Hprod and Hloss are also presented.

Figure 2.

Conceptual representation conditions leading to risks of hypothermia. Potential of conservation for heat storage by increased tissue insulation (e. g. lower skin temperature and increased metabolic response).

Figure 3.

Conceptual representation conditions leading to risks of cold weather injuries including nonfreezing cold weather injuries (NFCI) and frostbite. The symbol (?) denotes a lack of scientific support. Wind speed of 5 km/h at 10 meters was considered. The website used for the wind chill chart was: https://www.candac.ca/.

Figure 4.

Panel A) nude resting neutral temperature for full range of population spanning small body surface area (1. 4 m²) and very large body surface area (3 m²). Panel B) nude resting neutral temperature for specific population average body weights: AS: Asia, AF: Africa, W: World, LA: Latin America, EU: Europe, OC: Oceania, NA: North America.. Panel C: Clothed (2. 5clo), moderate activity (4 MET) neutral temperature for full range of population spanning small body surface area (1. 4 m2) and very large body surface area (3 m2).; Panel D) Clothed (2. 5clo) moderate activity (4 MET) neutral temperature for specific population average body weights. For all panels resting metabolic rate is calculated according to Roza & Shizgal for 35 year old persons; male and female metabolic rates are combined.

Figure 5.

Average changes in regional skin temperature at baseline and between 75–90 min of A. mild cold exposure and B. moderate cold exposure. – including metabolic response. Data modified from Haman et al (2002) and Haman et al (2004, 2005).

Figure 6.

Average changes in regional skin temperature at baseline and between 75–90 min in two non-cold acclimatized men of similar morphology. A) insulative responder with lower extremity skin temperature and B – metabolic responder with higher extremity skin temperature. Data modified from Haman et al (2002) and Haman et al (2004, 2005).

Figure 7.

Average changes in regional skin temperature at baseline and between 105–120 min of mild cold exposure in non-cold acclimatized men with A. low glycogen reserves and, B. high glycogen reserves during moderate cold exposure. Data modified from Haman et al (2004).