Sharan M, Gupta S, Popel A S
Centre for Atmospheric Sciences, Indian Institute of Technology, Delhi, 110016, India.
J Theor Biol. 1998 Dec 21;195(4):439-49. doi: 10.1006/jtbi.1998.0805.
An increase of the partial pressure of oxygen in venules towards larger vessels has been observed experimentally, but the mechanism of this phenomenon has not been established. The present study considers a simple mathematical model of oxygen transport from a capillary to the surrounding tissue cylinder and analyses the conditions under which the end-capillary partial pressure of oxygen is lower than the mean tissue pressure. Under these conditions oxygen would diffuse into the venules since they are surrounded by the tissue with a higher partial pressure of oxygen. Cerebral circulation is chosen for these calculations and conditions of normoxia, hypoxic hypoxia, carbon monoxide hypoxia, anemia, and polycythemia are simulated. The tissue metabolic rate is also varied. It is found that under most conditions the relationship between the end-capillary and mean tissue partial pressures of oxygen can be reversed when one of the parameters is varied within its physiological range, i.e. the difference between these variables could be either positive or negative depending on the value of the parameters. Therefore, under many realistic conditions this mechanism would contribute to an increase of the partial pressure of oxygen in the venules. This conclusion should hold for a more realistic geometrical model of capillary network, but the relationships between the end-capillary and mean tissue partial pressures of oxygen, in addition to their dependence on the parameters considered in this study, would likely be dependent on the spatial location within the network.
实验观察到小静脉中氧分压朝着较大血管方向升高，但这一现象的机制尚未明确。本研究考虑了一个从毛细血管到周围组织圆柱体的氧传输简单数学模型，并分析了毛细血管末端氧分压低于平均组织压力的条件。在这些条件下，由于小静脉被氧分压较高的组织包围，氧会扩散到小静脉中。这些计算选取脑循环，并模拟了常氧、低氧性缺氧、一氧化碳中毒性缺氧、贫血和红细胞增多症的情况。组织代谢率也有所变化。研究发现，在大多数情况下，当其中一个参数在其生理范围内变化时，毛细血管末端和平均组织氧分压之间的关系可能会反转，即这些变量之间的差异可能为正或负，具体取决于参数值。因此，在许多实际情况下，这一机制会导致小静脉中氧分压升高。这一结论对于更实际的毛细血管网络几何模型也应成立，但毛细血管末端和平均组织氧分压之间的关系，除了依赖于本研究中考虑的参数外，可能还取决于网络内的空间位置。
