Hudetz A G
Department of Anesthesiology, Medical College of Wisconsin, Milwaukee 53226, USA.
Adv Exp Med Biol. 1997;428:513-20. doi: 10.1007/978-1-4615-5399-1_73.
The dynamics and regulation of red blood cell flow in the cerebral microcirculation was studied by intravital fluorescence video-microscopy in a closed cranial window preparation in the rat. The studies revealed that capillary perfusion in the brain is essentially continuous but a stationary difference from capillary to capillary within the same microvascular network exists. The main mechanism of an increase in flow in cerebral capillaries is an increase in linear velocity with no or minor role for classical capillary recruitment. While cyclic opening and closing of capillaries is not evident, low frequency oscillations in capillary flow velocity are present when perfusion or oxygen supply to tissue is challenged. In hypoxic hypoxia and moderate hypercapnia, RBC velocity increases in all capillaries while in severe hypercapnia, redistribution of RBC velocity in the capillary network occurs. Both systemic hypotension and severe hypercapnia are accompanied by an increase in the homogeneity of capillary flow; this change involves the redistribution of RBC flow between thoroughfare channels and exchange capillaries. Thoroughfare channels may thus provide a recruitable flow reserve in the cerebral microcirculation. The capillary flow response to hypoxic and anemic hypoxia depends on the activity neuronal nitric oxide synthase. These findings suggest the presence of a physiological regulatory mechanism of cerebral capillary red blood cell flow and oxygen supply which may involve neuronal nitric oxide as a mediator.
采用大鼠颅骨开窗封闭制备法，通过活体荧光视频显微镜研究了脑微循环中红细胞流动的动力学及调节机制。研究发现，脑内毛细血管灌注基本持续，但同一微血管网络内不同毛细血管之间存在固定差异。脑毛细血管血流增加的主要机制是线性速度增加，经典的毛细血管募集作用不明显或作用较小。虽然毛细血管的周期性开闭不明显，但当组织灌注或氧气供应受到挑战时，毛细血管血流速度会出现低频振荡。在低氧性缺氧和中度高碳酸血症时，所有毛细血管内的红细胞速度均增加，而在重度高碳酸血症时，毛细血管网络内红细胞速度会重新分布。系统性低血压和重度高碳酸血症均伴有毛细血管血流均匀性增加；这种变化涉及红细胞血流在直捷通路和交换毛细血管之间的重新分布。因此，直捷通路可能为脑微循环提供可募集的血流储备。毛细血管对低氧性和贫血性缺氧的血流反应取决于神经元型一氧化氮合酶的活性。这些发现提示存在一种脑毛细血管红细胞流动和氧气供应的生理调节机制，其中神经元型一氧化氮可能作为介质参与其中。
