Cokelet G R, Pries A R, Kiani M F
Department of Pharmacology & Physiology, University of Rochester, NY 14642, USA.
Microcirculation. 1998;5(1):61-70.
The accuracy of optical methods used to measure in vivo microvascular blood flow parameters is investigated using measurements made in all vessels of microvascular networks of the rat mesentery.
The principle of mass conservation was applied to in vivo blood flow rate and discharge hematocrit data, which were determined by photometric methods. One of the several implied assumptions of most interpretations of in vivo optical data is that the vessels are circular in cross-section: to see the impact of vessel lumen shape on one of these measurements, the average velocity of blood flowing through a D-shaped glass capillary tube was measured by the dual-slit method.
For in vivo data, significant imbalance exists in a large number of bifurcations, and the correlation between the blood flow imbalance and the red cell flux imbalance is very small (r2 = 0.39), indicating multiple sources of error. Furthermore, the measured discharge hematocrits were consistent with the observed flow directions at bifurcations in only 39% to 46% of the bifurcations in a network. The imbalance at these bifurcations is not simply caused by the inaccuracy of measurements in only a few microvessels that join such bifurcations, i.e., the inaccuracies are evenly distributed among the vessels. The results of the in vitro study of blood velocity measurement in D-shaped tubes indicates that the ratio of dual-slit velocity to the actual average blood velocity is sensitive to the shape of the vessel lumen, and is a function of blood flow rate, hematocrit, vessel lumen shape, and orientation.
Significant inaccuracies exist in the flow and hematocrit data obtained by current methods of interpretation of in vivo photometric measurements. These inaccuracies must be considered when making vessel to-vessel comparisons, or vessel-by-vessel comparisons between in vivo observations and model predictions, even though the inaccuracies are greatly reduced when comparing averaged data.
通过对大鼠肠系膜微血管网络中所有血管进行测量，研究用于测量体内微血管血流参数的光学方法的准确性。
将质量守恒原理应用于通过光度法测定的体内血流速率和排出血细胞比容数据。大多数对体内光学数据解释所隐含的假设之一是血管横截面为圆形：为了观察血管腔形状对其中一项测量的影响，采用双缝法测量了流经D形玻璃毛细管的血液平均流速。
对于体内数据，大量分叉处存在显著失衡，血流失衡与红细胞通量失衡之间的相关性非常小（r2 = 0.39），表明存在多种误差来源。此外，在一个网络中，仅39%至46%的分叉处测量的排出血细胞比容与观察到的血流方向一致。这些分叉处的失衡并非仅仅由连接此类分叉的少数微血管测量不准确所致，即不准确之处在血管中均匀分布。对D形管中血流速度测量的体外研究结果表明，双缝速度与实际平均血流速度之比对血管腔形状敏感，并且是血流速率、血细胞比容、血管腔形状和方向的函数。
当前体内光度测量解释方法所获得的血流和血细胞比容数据存在显著不准确之处。在进行血管间比较，或体内观察与模型预测之间的逐血管比较时，必须考虑这些不准确之处，尽管在比较平均数据时不准确程度会大大降低。
