Simon Eckhart
Max-Planck-Institute for Heart and Lung Research, W G Kerckhoff-Institute, Parkstrasse 1, 61231, Bad Nauheim, Germany.
Eur J Appl Physiol. 2007 Sep;101(1):19-30. doi: 10.1007/s00421-007-0449-0. Epub 2007 May 30.
Selective brain cooling in humans, with venous blood returning from the head surface as the relevant heat sink, was proposed more than two decades ago as a mechanism protecting the brain against damage in hyperthermic conditions. Brain cooling was inferred from decreases of tympanic temperature under the premise that it reflected brain temperature closely, even in conditions of external head cooling. In mammals with a well-developed carotid rete selective brain cooling and its quantitative relevance are experimentally well established by directly monitoring brain temperature. For humans, however, the dispute about the existence and physiological relevance of selective brain cooling has remained unsettled, especially, as far as arguments have been exchanged on the basis of thermophysiological data and model calculations considering brain metabolism, brain hemodynamics and the anatomical preconditions for arterio-venous heat exchange. In this essay two seminal studies in support of the existence of human selective brain cooling in the condition of exercise hyperthermia, with and without dehydration, are re-examined from two points of view: first the stringency of the working hypotheses underlying data evaluation and their subsequent fate. Second the minimum theoretical requirements for data interpretation. The working hypotheses supporting data interpretation in favor of selective brain cooling in humans were heuristic and/or had become questionable at the dates of their application; today, they may be considered as outdated. Data interpretation becomes most conclusive, if tympanic temperature simply is not taken into account.
二十多年前就有人提出，在人类中，以从头部表面回流的静脉血作为相关热沉进行选择性脑冷却，是一种在高温条件下保护大脑免受损伤的机制。在外部头部冷却的情况下，即使在鼓膜温度下降的前提下推断脑冷却，前提是它能密切反映脑温。在具有发达颈动脉网的哺乳动物中，通过直接监测脑温，选择性脑冷却及其定量相关性在实验上已得到充分证实。然而，对于人类而言，关于选择性脑冷却的存在及其生理相关性的争论仍未解决，特别是，就基于热生理数据以及考虑脑代谢、脑血流动力学和动静脉热交换解剖学前提的模型计算所进行的争论而言。在本文中，从两个角度重新审视了两项具有开创性的研究，这两项研究支持在运动性高热（有或无脱水）情况下人类存在选择性脑冷却：首先是数据评估所依据的工作假设的严格性及其后续命运。其次是数据解释的最低理论要求。支持有利于人类选择性脑冷却数据解释的工作假设具有启发性，并且/或者在其应用时就已受到质疑；如今，它们可能被视为过时。如果根本不考虑鼓膜温度，数据解释将变得最具决定性。
