Heat transfer through the head, and cold-induced muscle failure

这个长期的研究计划侧重于人类温度调节，神经肌肉和代谢反应在热/环境压力，使用基础和应用的方法。1)众所周知，冷诱导的物理性能下降与局部冷却的相关性大于与堆芯冷却的相关性。 我们打算使用经颅磁刺激和电刺激来提供对“中枢疲劳”的详细分析，并检验低温会导致中枢疲劳的假设，中枢疲劳包括运动皮层兴奋性降低和皮层内抑制增加。2)虽然在肌肉锻炼过程中对底物利用有很多了解，但缺乏在相同代谢强度下冷诱导的颤抖代谢与自愿运动之间的比较分析。我们将比较低强度和高强度代谢率下等代谢颤抖和运动条件下的底物利用率。我们假设，与运动相比，颤抖将更多地依赖于脂质而不是碳水化合物作为燃料。3)我们还打算确定部分和全部水头浸没在冷水中的夸大堆芯冷却效应的机制。 一系列研究将确定短期（屏气）和长期（呼吸）将后脑勺、面部或两者浸入冷水中对心血管和外周血流量的影响。 我们预计面部浸泡会对外周血流量和核心冷却产生更大的影响。验证研究将确定是否可以将整个肢体热含量的测量值用作外周血流量的指标。然后进行背部、面部或整个头部的长期身体浸没，同时测量整个肢体的热含量。这将允许确认头部不同部分浸没的血流影响。 4)最后，一项研究将通过比较在躯干上穿一件背心或头上戴一个头巾的温水灌注效果，来测试实际防止冷应激身体核心冷却的能力。

This long-term research program focuses on human thermoregulatory, neuromuscular and metabolic responses during thermal/environmental stress, using both basic and applied approaches. 1) It is known that cold-induced decrement in physical performance correlates more with local than core cooling.  We intend to use Transcranial Magnetic Stimulation and electric stimulation to provide a detailed analysis of 'central fatigue' and test the hypothesis that hypothermia will cause central fatigue that includes decreased motor cortical excitability and increased intracortical inhibition. 2) Although much is known about substrate utilization during muscular exercise, comparative analysis between cold-induced shivering metabolism vs voluntary exercise at the same metabolic intensity is lacking. We will compare substrate utilization in iso-metabolic shivering and exercise conditions at low intensity and high intensity metabolic rates. We hypothesize that shivering will rely more on lipids vs carbohydrates for fuel compared to exercise. 3) We also intend to determine mechanisms for exaggerated core cooling effects of partial and total head submersion in cold water.  A series of studies will determine the cardiovascular and peripheral blood flow effects of short term (breath holding) and long-term (breathing) immersion of the back of the head, the face or both, in cold water.  We expect facial immersion to impose a greater effect on peripheral blood flow and core cooling. A validation study will determine if measurements of whole limb heat content can be used as an indicator of peripheral blood flow. Long term body submersions with dorsal, facial or whole head submersions will then be conducted while measuring whole limb heat content. This will allow confirmation of the blood flow effects of submersion of different parts of the head.   4) Finally, a study will test the ability to actually prevent core cooling of a cold-stressed body by comparing effects of warm water-perfusion of a vest on the torso, or of a hood on the head.