Autonomic defense responses to extremely strong heat stress

我们研究了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)当手被局部加热到高于身体核心温度时，手指血管收缩，手指体积减少。当受试者体温过高时，这种血管收缩是一致的，在不存在动静脉吻合(AVA)的前臂皮肤中没有观察到这种收缩。当受试者报告局部热感急剧上升时，HIVC被标记。在此期间，皮肤对手的交感神经活动增加。通过浅毛细血管和深层AVA的血流分区测量，证实了引起HIVC的血管腔主要是AVA的。根据这些结果，我们认为HIVC是对已经高热的受试者从热接触物体到身体的热传递的延迟反应。2.通过使者静脉内流强化选择性脑降温。我们证实，在高热受试者中，通过眼角静脉(AOV)等发出静脉的选择性脑降温是使脑温度(以鼓膜温度(T&lt；ty&gt；)表示)变得低于体温的重要过程。机械阻塞AOV血流导致在全身取暖时T&t；ty和Gt；升高。机械闭塞面静脉使AOV-血流内流增加，并抑制T&T；这些结果有力地支持了这样的观点，即使状静脉向海绵窦供应静脉血液，海绵窦在人类体温过高时起到散热器的作用，为大脑降温。

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.