Klementavicius R, Nemoto E M, Yonas H
Department of Anesthesiology and Critical Care Medicine, University of Pittsburgh Medical Center, Pennsylvania, USA.
J Neurosurg. 1996 Sep;85(3):482-7. doi: 10.3171/jns.1996.85.3.0482.
Previously the authors showed that hypothermia exerts a greater effect on the cerebral metabolic rate for oxygen (CMRO2) that is associated with the maintenance of cellular viability, or "basal" CMRO2, than on electroencephalogram (EEG)-associated CMRO2 or "functional" CMRO2. On the basis of their findings, the authors hypothesized that the ratio of CMRO2 over a 10 degrees C temperature range (Q10) for basal CMRO2 was greater than that for functional and total CMRO2. They tested their hypothesis by determining the Q10 for basal CMRO2 from 38 degrees C to 28 degrees C. They measured whole-brain cerebral blood flow (CBF) and CMRO2 in six rats during progressive hypothermia at a brain temperature of 38 degrees C and, after induction of an isoelectric EEG signal (50 microV/cm) with thiopental sodium, they repeated the measurements at 38 degrees C, 34 degrees C, 30 degrees C, and 28 degrees C. In a control group (five rats), six sequential measurements of CBF and CMRO2 were made while the animals were anesthetized by 0.5% isoflurane/70% N2O/30% O2 at a brain temperature of 38 degrees C over a time span equivalent to the hypothermic group, that is, approximately 3 hours. The Q10 for basal CMRO2 calculated over 38 degrees C to 28 degrees C was 5.2 +/- 0.92. However, the decrease in basal CMRO2 between 38 degrees C and 28 degrees C was nonlinear on a log plot, revealing a two-component response: a high temperature sensitivity component between 38 degrees C and 30 degrees C with a Q10 of 12.1, and a lower temperature sensitivity component between 30 degrees C and 28 degrees C with a Q10 of 2.8. The combined overall Q10 for basal CMRO2 between 38 degrees and 28 degrees C was 5.2. The energy-requiring processes associated with these high and low temperature sensitivity components of basal CMRO2 have yet to be identified.
此前，作者们发现，低温对与维持细胞活力相关的脑氧代谢率（CMRO2），即“基础”CMRO2的影响，比对与脑电图（EEG）相关的CMRO2或“功能”CMRO2的影响更大。基于他们的研究结果，作者们推测，基础CMRO2在10摄氏度温度范围内的CMRO2比率（Q10）大于功能CMRO2和总CMRO2的比率。他们通过测定基础CMRO2在38摄氏度至28摄氏度之间的Q10来验证这一假设。他们在6只大鼠脑温为38摄氏度进行渐进性低温时测量全脑脑血流量（CBF）和CMRO2，在用硫喷妥钠诱导出等电位EEG信号（50微伏/厘米）后，他们在38摄氏度、34摄氏度、30摄氏度和28摄氏度重复测量。在一个对照组（5只大鼠）中，在动物于脑温38摄氏度被0.5%异氟烷/70%N2O/30%O2麻醉期间，进行6次连续的CBF和CMRO2测量，时间跨度与低温组相当，即约3小时。在38摄氏度至28摄氏度之间计算出的基础CMRO2的Q10为5.2±0.92。然而，基础CMRO2在38摄氏度至28摄氏度之间的下降在对数图上是非线性的，显示出双组分反应：38摄氏度至30摄氏度之间的高温敏感性组分，Q10为12.1，以及30摄氏度至28摄氏度之间的低温敏感性组分，Q10为2.8。基础CMRO2在38摄氏度至28摄氏度之间的综合总体Q10为5.2。与基础CMRO2的这些高温和低温敏感性组分相关的能量需求过程尚未确定。
