Zhu L, Lemons D E, Weinbaum S
Department of Mechanical Engineering, City College, City University of New York, NY 10031, USA.
Ann Biomed Eng. 1995 Jan-Feb;23(1):1-12. doi: 10.1007/BF02368295.
This study attempts to measure the hyperthermic response of individual microvessels in skeletal muscle tissue subject to local heating and then to predict the enhancement in thermal conductivity that results from the observed changes in vascular diameter and flow. In contrast to existing studies, which have tried to relate changes in tissue thermal conductivity to local blood perfusion using thermal clearance and self-heated thermistor techniques, we have developed a two-dimensional muscle tissue preparation in which the hyperemic response has been quantified by measuring the in vivo changes in diameter and blood flow of 1A to 4A generation vessels of rat cremaster muscle when the temperature was raised in 2 degrees increments from 34 to 42 degrees C. Only 3A and 4A vessels showed vasodilation when subject to hyperthermia, indicating that the measured increase in flow in the 1A and 2A vessels was the result of a decrease in downstream resistance. Our cremaster muscle preparations have also been used to obtain the first detailed anatomic measurements of the number density and length of countercurrent vessel pairs between 50-200 microns diameter. These combined measurements have been used to establish the limits of validity of the Weinbaum-Jiji theory. Our experimental data indicate that the Weinbaum-Jiji expression for keff is valid in cremaster muscle and cat mesentery tissue for both normal and hyperthermic conditions provided the largest vessels are < 200 microns in diameter. The theory predicts that significant enhancements in keff start to occur for vessels that are 70 microns in diameter or larger, that a 2.5-fold increase in keff can be achieved for a maximally dilated 200 microns diameter 1A vessel pair in cremaster muscle of larger rats, and a 6-fold increase is predicted for maximally dilated 200 microns diameter vessels in the cat mesentery. The experiments also show that maximally dilated 1A to 4A vessels in the microcirculation closely satisfy the condition Q(flow)/(2a)3 = constant, which is consistent with the hypothesis that there is an adaptive regulation of vessel diameter which keeps the wall shear stress nearly constant during temporal changes in flow.
本研究试图测量骨骼肌组织中单个微血管在局部加热时的热反应，然后预测由观察到的血管直径和血流量变化所导致的热导率增强。与现有研究不同，现有研究试图使用热清除和自热热敏电阻技术将组织热导率的变化与局部血液灌注联系起来，我们开发了一种二维肌肉组织制剂，通过测量大鼠提睾肌1A至4A代血管在温度从34℃以2℃增量升至42℃时的体内直径和血流量变化，对充血反应进行了量化。只有3A和4A血管在受热时表现出血管舒张，这表明在1A和2A血管中测得的血流量增加是下游阻力降低的结果。我们的提睾肌制剂还被用于获得直径在50 - 200微米之间的逆流血管对的数量密度和长度的首次详细解剖测量。这些综合测量被用于确定温鲍姆 - 吉吉理论的有效性范围。我们的实验数据表明，只要最大血管直径<200微米，温鲍姆 - 吉吉关于有效热导率（keff）的表达式在提睾肌和猫肠系膜组织中对于正常和受热条件均有效。该理论预测，对于直径为70微米或更大的血管，有效热导率开始出现显著增强；对于较大大鼠提睾肌中最大扩张的直径为200微米的1A血管对，有效热导率可增加2.5倍；对于猫肠系膜中最大扩张的直径为200微米的血管，预测有效热导率可增加6倍。实验还表明，微循环中最大扩张的1A至4A血管紧密满足条件Q（流量）/（2a）³ = 常数，这与以下假设一致：存在血管直径的适应性调节，在流量随时间变化期间使壁面剪应力几乎保持恒定。
