Thermal Effects of Submersion on Humans in Cold Water

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Slide 1 :

Thermal Effects of Submersion on Humans in Cold Water - a Structural Equation Model By Thea Pretorius

Slide 2 :

Submersion – head submersed vs Immersion – Head out of water Submersion vs Immersion

Slide 3 :

Previous work:Dorsal Head Cooling in Cold Water Alexander – 1946: Unethical Studies in Dachau: 1-2°C water Emaciated POW Lockhart et. al. – 2005: Testing personal flotation devices 10°C water Both studies had shivering mechanism intact Giesbrecht et. al. - 2005 12°C water Shivering mechanism inhibited (meperidine) to isolate effect of surface heat loss Heat flux from the skin was measured

Slide 4 :

Results of Dorsal Head Studies Time Core Temperature Drop Insulated, Head out Insulated, Head in Exposed, Head out Exposed, Head in * 0 30 – 45 min Giesbrecht et. al. J Appl Physiol. 99: , 2005 0

Slide 5 :

Conclusion: Dorsal Head: Increases total heat loss with ~ 5% Only has an effect when body is exposed to the cold water and not when the body is insulated from the cold This is true for emaciated prisoners of war, and whether the shivering mechanism is in tact or not

Slide 6 :

Previous work:Whole Head Cooling in Cold Water . Pretorius T, Bristow G, Steinman A, Giesbrecht G. Thermal effects of whole head submersion in cold water on non-shivering humans. J Appl Physiol 2006; 101: 669-75. 2. Pretorius T, Cahill F, Kocay S, Giesbrecht GG. Shivering heat production and core cooling during head-in and head-out immersion in 17°c water. Aviat Space Environ Med 2008; 79

Slide 7 :

Results of Whole Head Studies in 17°C Water Time Core Temperature Drop Insulated, Head out Insulated, Head in Exposed, Head out Exposed, Head in 0 30 – 45 min * * 0

Slide 8 :

Conclusion: Whole Head: Increases total heat loss with 10%, but increases core cooling with 39% Has an effect whether body is exposed or insulated from the cold. The effect of the head is the same as when only the body is exposed to the cold water This is true whether the shivering mechanism is in tact or not

Slide 9 :

What is not known??? The integrated effect of variables affecting Core Cooling Rate

Slide 10 :

Variables Known to Affect Core Cooling Rate Water Temperature Tikuisis, 1995, Sagawa, 1988 Insulation Tikuisis, 1995, Lockhart, 2005, Giesbrecht, 2005, Pretorius, 2006 Body Fat, Weight, Height LeBlanc, 1954, Keatinge, 1960 White, 1992, Glickman-Weiss, 1998 Shivering Giesbrecht, 1997 Size of Thermal Core Vanggaard, 1999, Lockhart, 2005, Giesbrecht, 2005, Pretorius, 2006, Xu, 2007 Head Exposure Lockhart, 2005, Giesbrecht, 2005, Pretorius, 2006 Age Wagner, 1985, Glickman-Weiss, 1998 Nutritional State Jacobs, 1994 Watermovement Steinman, 1987 Heat Loss Basic Physics

Slide 11 :

Structural Equation Modeling was used to Determine: the integrated effect of these variables the magnitudes of these effects ON CORE COOLING RATE

Slide 12 :

Shivering Body Exposure Head Exposure Core CoolingRate E E Body Fat Core Cooling Rate is affected by: +0.77 -0.26 -0.71 -0.16 +0.23 +0.47

Slide 13 :

Conclusions: Body exposure, responsible for ~90% of heat loss, increases shivering and indirectly slows down core cooling rate Although increased body fat suppresses shivering, it is the biggest factor decreasing core cooling rate Head cooling (responsible for ~10% of heat loss) , despite decreasing shivering, has a net effect of increasing core cooling rate WHY????

Slide 14 :

Possible explanations: Increased core cooling rate with smaller thermal core (see explanation on next two slides) Less insulation from body fat on head

Slide 15 :

Perfused Body Mass/ Thermal Core Size of thermal core is affected by: Vasoconstriction due to cold and/or Diving Reflex as oxygen sparing mechanism when the face is cooled: Vasoconstriction Breath hold Bradycardia

Slide 16 :

Possible Mechanism: Perfused Body Mass (Thermal Core) Vasodilation -Body Insulated Vasoconstriction -Body Exposed Diving reflex?? O2 sparing: Bradycardia Breath hold Vasoconstriction as size of Perfused Body Mass Effect of head heat loss

Slide 17 :

Further Work is Warranted To Determine: The size and effect of the thermal core on core cooling during immersion and submersion How effectiveness of body fat as insulator during head submersion

Slide 18 :

Acknowledgements Dr Gordon Giesbrecht Dr Lisa Lix Farrell Cahill Dominique Gagnon Sheila Kocay

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