Nutritional Needs in Cold and High-Altitude Environments Applications for Military Personnel in Field Operations (1996) / Chapter Skim
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15 Drug-Induced Delay of Hypothermia
15 Drug-Induced Delay of Hypothermia
Pages 257-270
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From page 257... ...
A pharmacological approach with thermogenic agents is certainly an attractive and promising avenue, particularly from a metabolic point of view. In view of the importance and number of animal studies in this field, they will be briefly reviewed first before focusing on human studies.
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From page 258... ...
Although these studies were very useful to the understanding of cold-induced thermogenesis also known as thermoregulatory thermogenesis it is now apparent that they have little direct application to humans. For instance, the catecholamineinduced improvement in heat production is usually directly related to brown adipose tissue, the long-term use of high doses of thyroxine is not recommended in euthyroid subjects, the long-term use of high cortisol doses increases protein breakdown and is associated with Cushing's syndrome, and finally the long-term use of growth hormone leads to insulin resistance and is associated with acromegaly (for a review, see LeBlanc, 1975; Sellers, 1972~.
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From page 259... ...
Energy Substrate Mobilization and Cold Tolerance Based on the theory above, which stated that energy substrate mobilization regulates thermoregulatory thermogenesis, a commercially available recreation and sports bar (Cold Busters has been recently developed. It is purported to delay markedly the onset of hypothermia in humans as a result of its energycontaining substrates and theobromine content.
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From page 260... ...
Furthermore, whole body carbohydrate oxidation was increased following the ingestion of either the pure carbohydrates or the sports bar (also high in carbohydrates) , exactly as expected.
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From page 261... ...
Identical results were obtained (Figure 15-21. The first question that arose from the conflicting results between these studies and those of Wang was related to laboratory procedures: Could methodological differences possibly explain the fact that the energy substrate mobilization theory of Wang et al.
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From page 262... ...
A second possible explanation for the conflicting results may have been that the dose of energy substrates was simply not optimal in the sports bar study to observe a positive influence of substrate mobilization on M in this laboratory. However, this explanation is unlikely for two precise reasons.
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From page 263... ...
This was achieved through a significantly greater whole body lipid oxidation and a slightly greater carbohydrate oxidation (Figure 15-5~. This enhanced thermoregulatory thermogenesis was directly related to a significantly lower heat debt, slightly warmer Tre, and significantly warmer T,*
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From page 265... ...
-en 1 ~ r ~ " 4~ .......
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From page 266... ...
Jacobs, Defence and Civil Institute of Environmental Medicine, North York, Ontario, Canada, 19961. Table 15-1 also highlights the advantages of a heat balance analysis and the necessity of performing it more often since the heat debt appears as a more robust index of cold resistance than Tre alone.
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From page 267... ...
Since ephedrine-xanthines do increase heat production without muscular contractions at comfortable ambient temperatures and since ephedrine-xanthines increase cold thermogenesis without any indication of greater shivering, it is thus possible that ephedrine-xanthines act via mechanisms unrelated to shivering, either at the level of the striated muscle or at the level of the smooth muscle in the vascular bed, as recently suggested (Colquhoun and Clark, 1991~. These exciting hypotheses require further study.
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From page 268... ...
Future work is required to determine their effectiveness at deeper levels of hypothermia as well as during much longer albeit less severe "survival-like" exposures. ACKNOWLEDGMENTS It is with great pleasure that the expert assistance of Ingrid Schmegner, the collaboration of Ira Jacobs, as well as the dedication of all subjects employed throughout the cold stress studies are acknowledged by the author.
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From page 269... ...
:S191-S193. 1992b 1993a Interaction of a food supplement, intermittent exercise and cold exposure on heat balance.
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From page 270... ...
Schmegner, and I Jacobs 1992 Influence of the Cold Buster™ sports bar on heat debt, mobilization and oxidation of energy substrates.
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