Autonomic defense responses to extremely strong heat stress

我们研究了人类受试者对极端热应激的体温调节防御反应。1. 热致皮肤血管收缩（HIVC）。当手部局部加热到高于身体核心温度时，手指血管收缩，手指体积减小。当受试者处于高温状态时，这种血管收缩是一致的，而在没有动静脉吻合术（AVA）的前臂皮肤中没有观察到。当受试者报告局部热感觉急剧上升时，HIVC被标记。在此期间，手部的皮肤交感神经活动增加。通过浅表毛细血管和位于深部的AVA的血流分区测量证实，负责HIVC的血管室主要是AVA。根据这些结果，我们提出，HIVC是一种反应，以延缓热接触物体的热量传递到已经过热的身体。2. 通过使者静脉向内流动的选择性脑冷却增强。我们证实，通过角眼静脉（AOV）等传递静脉的选择性脑冷却是使高温受试者的脑温度（由耳膜温度（T_<ty>）表示）低于体温的重要过程。通过AOV的机械阻塞导致全身升温时T_<ty>的升高。面静脉的机械阻塞增加了aov向内流动，抑制了T_<ty>的上升速率。这些结果有力地支持了这样一种观点，即输送静脉将静脉血输送到海绵状窦中，海绵状窦在人类体温过高时起到冷却大脑的散热作用。

We studied thermoregulatory defense responses to extreme heat stress in human subjects. 1. Heat-induced skin vasoconstriction (HIVC). Finger vessels constricted and finger volume decreased when the hand was heated locally to temperature above body core temperature. This vasoconstriction was consistent when the subject was hyperthermic, and was not observed in the forearm skin where arteriovenous anastomoses (AVA) do not exist. HIVC was marked when the subject reported a sharp rise of local thermal sensation. During this period, skin sympathetic nerve activity to the hand increased. Partitional measurements of blood flow through superficial capillaries and deeply located AVA's confirmed that the vascular compartments responsible for HIVC were mainly AVA'S. From these results, we propose that HIVC is a response to retard heat transfer from hot contact objects to the body in already hyperthermic subjects. 2. Selective brain cooling enhanced by inward venous flowing through emissary veins. We confirmed that selective brain cooling via emissary veins such as angular oculi veins (AOV) was an important process enabling brain temperature (indicated by tympanic membrane temperature (T_<ty>)), to become lower than body core temperature in hyperthermic subjects. Mechanical obstruction of flow through AOV resulted an increase in the rise of T_<ty> during whole body warming. Mechanical obstruction of facial veins increased inward flowing of AOV-flow and suppressed the rate of rise in T_<ty>. These results strongly support the idea that emissary veins supply venous blood into the cavernous sinuses which act as a heat sink to cool the brain during hyperthermia in humans.