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

这个长期的研究项目主要关注人体在热/环境应激下的体温调节、神经肌肉和代谢反应，使用基础和应用方法。1)众所周知，冷引起的物理性能下降更多地与局部冷却有关，而不是与核心冷却有关。我们打算使用经颅磁刺激和电刺激来提供“中枢疲劳”的详细分析，并测试低温会导致中枢疲劳的假设，包括运动皮质兴奋性下降和皮质内抑制增加。2)虽然我们对肌肉运动中底物的利用了解很多，但在相同代谢强度下，冷致寒战代谢与自主运动之间的比较分析缺乏。我们将比较在低强度和高强度代谢率的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)我们还打算确定冷水中部分和全部水头浸没对堆芯冷却效果的夸大机制。一系列的研究将确定短期（屏住呼吸）和长期（呼吸）将后脑勺、脸或两者浸泡在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周围血液流动和核心冷却产生更大的影响。一项验证研究将确定全肢热含量的测量是否可以用作外周血流量的指标。然后进行背部、面部或整个头部浸泡的长期身体浸泡，同时测量整个肢体的热量含量。这将有助于确认头部不同部位浸没后的血流效果。4)最后，一项研究将通过比较躯干上的背心和头部上的兜帽的温水灌注效果，来测试实际防止寒冷压力下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.