Historical perspective: Human Thermal Physiology in Canada
Canada is considered a cold nation that lends itself naturally to studies on human exposure to cold. However, certain environmental, recreational,and occupational conditions can impose significant heat stress. Hence, this very brief historical overview of human thermal physiology in Canada will highlight research involving both heatand cold stress.
World War II was a significant incubator for research on cold weather operations conducted by physiologists such as John A. Hildes (1918 – 84; Hildes 1956). Hildes also addressed the unique challenges faced by indigenous peoples and health care workers in the Arctic (Hildes 1960), which led to his founding of the Northern Medical Unit that continues to promote health care in northern communities. Another defence-inspired effort was Allan C. Burton’s (1904 – 1979) co-publication of “Man in a Cold Environment” (Burton and Edholm 1955) that provides details on clothing insulation, cold tolerance, and the pathology of cold injury.
In the wake of these efforts were various studies to mitigate the hazards of cold exposure. Jacques LeBlanc (1921-2010) took a particular interest in the adaptation of cold-tolerant populations such as the Gaspé fishermen and the Inuit (Leblanc et al. 1960; LeBlanc et al. 1975). John S.Hayward (1937 – 2012) initiated predictions of survival time in cold water (Hayward et al. 1975) and subsequently led the development of the UVic Thermofloat jacket (later transferred to Mustang International) that provided additional insulation to the body’s regions of high heat loss. James B. Morrison focused on rewarming strategies for casualties of cold exposure, discovering the efficacy of rewarming hypothermic individuals via the inspiration of hot saturated air (Morrison et al. 1979).
Jan W. Snellen (1925 –2000) constructed a unique whole body air calorimeter (Figure 1) at Memorial University (Newfoundland and Labrador) with wind and moisture level adjustments to study body heat storage (Snellen et al. 1983). The calorimeterwas eventually re-located to the University of Ottawa under the auspices of Glen P. Kenny where it was used to quantify human calorimetry during rest and exercise (Reardon et al. 2006), and to further the understanding of non-thermal factors (e.g., aging, gender, diabetes, etc.) that govern thermal homeostasis (Kenny et al. 2013).
The Defence and Civil Institute of Environmental Medicine, established in Toronto in 1971 and led by Manny W. Radomski from1984 to 2001, was a key centre for thermal physiology research in Canada. Some of the many contributions from this institution include:
Sid D. Livingstone and Lorne A. Kuehn who confirmed that alcohol consumption does not enhance body cooling (Livingstone et al. 1980).
Tiit T. Romet explained the “afterdrop” effect of continued core cooling even after rewarming has been initiated due to the convective cooling of blood flow (Romet 1988).
John Frim spearheaded the use of thermal measuring devices including the radio pill and heat flux transducers (Frim et al. 1990).
Douglas Bell quantified the role and distribution of muscle activity during shivering (Bell et al. 1992).
Ira Jacobs discovered that shivering is suppressed with no additional depletion of muscle glycogen when exercise intensity is increased (Jacobs et al. 1985).
Andrew L. Vallerand quantified the contributions of carbohydrate and fat metabolism in humans exposed to cold (Vallerand et al. 1989).
Randall Osczevski revised the wind chill index (Figure 2) based on human skin freezing (Osczevski et al. 2005).
Michel B. Ducharme performed studies on cold thermal response including optimal cold survival strategies (Ducharme et al. 2007).
Peter Tikuisis and Allan A. Keefe developed the Cold Exposure Survival Model used as a decision aid by various search and rescue agencies (Tikuisis 1995; Keefe et al. 2008).
Thomas M. McLellan and Glen A. Selkirk developed safe work duration and water requirement guidelines for heat-related conditions (Selkirk et al. 2004).
Currently, Canada is home to many innovative thermal physiology laboratories. Gordon G. Giesbrecht, who heads the Laboratory for Exercise and Environmental Medicine at the University of Manitoba, demonstrated unabated shivering as the body cools to at least 32°C (Bristow et al. 1988) and initiated important outreach programs to improve cold water survival. Stephen S. Cheung, who heads the Environmental Ergonomics Lab at Brock University, found that the core temperature at the point of voluntary fatigue in the heat was remarkably consistent irrespective of hydration or heat acclimation status (Cheung et al. 2004). Francois Haman at the University of Ottawa has furthered research on substrate metabolism during cold exposure, most notably on the role of brown adipose tissue (Haman 2006). Matthew D. White of the Laboratory for Exercise and Environmental Physiology at Simon Fraser University has investigated the effects of hyperthermia on respiratory control (White 2006).This work was partially prompted by the controversial hypothesis of selective brain cooling during hyperthermia put forward by Michel Cabanac of Laval University (Cabanac 1993).
In addition to its leadership role in the field of thermal physiology, Canada has also served as an important training ground and early career stage for international leaders, many of whom have been highlighted by this brief history. Another leader of note is Igor B. Mekjavić who developed a diverse research program in environmental physiology at Simon Fraser University (Mekjavic et al. 1991) and co-founded the International Conference on Environmental Ergonomics, one of the leading scholarly meetings focused on thermal physiology.
Bell, D.G., Tikuisis, P., and Jacobs, I. 1992. Relative intensity of muscular contraction during shivering. J. Appl. Physiol. 72: 2336-42.
Bristow, G.K. and Giesbrecht, G.G. 1988. Contribution of exercise and shivering to recovery from induced hypothermia (31.2 degrees C) in one subject. Aviat. Space Environ. Med. 59:549-52.
Burton,A.C. and Edholm, O.G. 1955. Man in a Cold Environment: Physiological and Pathological Effects of Exposure to Low Temperatures. Edward Arnold, London, UK. Cabanac, M. 1993. Selective brain cooling in humans: « fancy » or fact? FASEB J. 7:143-6; discussion 1146-7.
Cheung, S.S. and Sleivert, G.G. 2004. Multiple triggers for hyperthermic fatigue and exhaustion. Exerc. Sport Sci. Rev. 32: 100-6.
Ducharme, M.B. and Lounsbury, D.S. 2007. Self-rescue swimming in cold water: the latest advice. Appl. Physiol. Nutr. Metab. 32: 799-807.
Frim, J., Livingstone, S.D., Reed, L.D., Nolan, R.W., and Limmer, R.E. 1990. Body composition and skin temperature variation. J.Appl. Physiol. 68: 540-3.
Haman, F. 2006. Shivering in the cold: from mechanisms of fuel selection to survival. J. Appl. Physiol. 100: 1702-8.
Hayward, J.S., Eckerson, J.D., and Collis, M.L. 1975. Thermal balance and survival time prediction of man in cold water. Can.J. Physiol. Pharmacol. 53(1): 21-32.
Hildes, J.A. 1956. Some physiological aspects of arctic warfare. Can. Serv. Med. J. 12:776-86.
Hildes, J.A. 1960. Health problems in the Arctic. Can.Med. Assoc. J. 83: 1255-7.
Jacobs, I.,Romet, T.T.,andKerrigan-Brown, D. 1985. Muscle glycogen depletion during exercise at 9°C and 21°C. Eur. J. Appl. Physiol. Occupat. Physiol. 54(1): 35-9.
Keefe, A.A. and Tikuisis, P. 2008. A guide to making stochastic and single point predictions using the Cold Exposure Survival Model (CESM). Toronto: Defence R&D Canada.
Kenny, G.P. and Jay, O. 2013. Thermometry,calorimetry, and mean body temperature during heat stress. Compr. Physiol. 3: 1689-719.
LeBlanc, J., Dulac, S., Cote, J., and Girard, B. 1975. Autonomic nervous system and adaptation to cold in man. J. Appl. Physiol. 39: 181-6.
Leblanc, J., Hildes, J.A., and Heroux, O. 1960.Tolerance of Gaspe fishermen to cold water. J. Appl. Physiol. 15: 1031-4.
Livingstone, S.D., Kuehn, L.A., Limmer, R.E., and Weatherson, B. 1980. The effect of alcohol on body heat loss. Aviat. Space Environ. Med. 51: 961-4.
Mekjavic, I.B., Sundberg, C.J., and Linnarsson, D.1991. Core temperature « null zone ». J. Appl. Physiol. 71: 1289-95.
Morrison,J.B., Conn, M.L., and Hayward, J.S. 1979. Thermal increment provided by inhalation rewarming from hypothermia. J. Appl. Physiol.: Resp. Environ. Exer. Physiol. 46(6): 1061-5.
Osczevski, R. and Bluestein, M. 2005. The new wind chill equivalent temperature chart. Bull. Am. Meteor. Soc. 86: 1453-1458.
Reardon, F.D., Leppik, K.E., Wegmann, R., Webb, P.,Ducharme, M.B., and Kenny, G.P. 2006. The Snellen human calorimeter revisited,re-engineered and upgraded: design and performance characteristics. Med. Biol.
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Romet, T.T. 1988. Mechanism of afterdrop after cold water immersion. J. Appl. Physiol. 65:1535-8.
Selkirk, G.A. and McLellan, T.M. 2004. Physical work limits for Toronto firefighters in warm environments. J. Occup. Environ. Hyg. 1: 199-212.
Snellen, J.W., Chang, K.S., and Smith, W. 1983. Technical description and performance characteristics of a human whole-body calorimeter. Med. Biol. Eng. Comput. 21:9-20.
Tikuisis, P. 1995. Predicting survival time for cold exposure. Int. J. Biometeorol.39: 94-102.
Vallerand, A.L. and Jacobs, I. 1989. Rates of energy substrates utilization during human cold exposure. Eur. J. Appl. Physiol.58:873-878.
White, M.D. 2006. Components and mechanisms of thermal hyperpnea. J. Appl. Physiol. 101: 655-63.