Lindbom L, Mirhashemi S, Intaglietta M, Arfors K E
Department of AMES-Bioengineering, University of California, San Diego, La Jolla 92093.
Acta Physiol Scand. 1988 Dec;134(4):503-12. doi: 10.1111/j.1748-1716.1998.tb08524.x.
The effect of acute normovolaemic haemodilution on microvascular red blood cell flow was studied by intravital microscopy in the tenuissimus muscle of the rabbit. Blood was substituted isovolaemically with equal volumes of a 6% solution of dextran 70 (MW 70,000). The systemic haematocrit (Hsys) decreased from 36 +/- 4% (mean +/- SD) to 17 +/- 2%. Following haemodilution capillary haematocrit (Hcap), as measured by video densitometric methods, decreased by 20 +/- 9%. The reduction of Hcap was significantly smaller than that of Hsys, and Hcap normalized with respect to Hsys increased from 0.39 +/- 0.07 in the control situation to 0.62 +/- 0.18 after haemodilution. Red blood cell velocity (vrbc) increased by 45 +/- 20% and compensated for the decrease in Hcap in such a way that the red blood cell flux, calculated from vrbc and Hcap, remained unchanged. Measurements of volume flow in the feeding arterioles in the muscle revealed a fractional redistribution of blood flow in favour of the muscle capillaries following haemodilution at the expense of vessels in adjacent connective tissue supplied by the same arterioles. This fractional flow redistribution was likely the basis for the relative increase in capillary haematocrit seen after haemodilution. The present data demonstrate that an acute reduction of the systemic haematocrit is compensated for in an active regulating vascular bed by a proportionally smaller decrease in capillary haematocrit and by an increased capillary red cell velocity. Microvascular haematocrit was found not to be a constant fraction of the systemic value, which supports the view of capillary haematocrit as a 'controlled' physiological variable.
通过活体显微镜观察研究了急性等容性血液稀释对兔薄肌微血管中红细胞流动的影响。用等体积的6%右旋糖酐70（分子量70,000）溶液等容替代血液。全身血细胞比容（Hsys）从36±4%（平均值±标准差）降至17±2%。血液稀释后，通过视频密度测定法测得的毛细血管血细胞比容（Hcap）下降了20±9%。Hcap的降低明显小于Hsys的降低，相对于Hsys而言，Hcap从对照状态下的0.39±0.07增加到血液稀释后的0.62±0.18。红细胞速度（vrbc）增加了45±20%，并以这样一种方式补偿了Hcap的降低，即由vrbc和Hcap计算得出的红细胞通量保持不变。对肌肉中供血小动脉的体积流量测量显示，血液稀释后血流出现部分重新分布，有利于肌肉毛细血管，而以同一小动脉供应的相邻结缔组织中的血管为代价。这种部分血流重新分布可能是血液稀释后毛细血管血细胞比容相对增加的基础。目前的数据表明，在一个具有主动调节功能的血管床中，全身血细胞比容的急性降低通过毛细血管血细胞比容成比例较小的降低和毛细血管红细胞速度的增加得到补偿。发现微血管血细胞比容并非全身血细胞比容值的固定比例，这支持了将毛细血管血细胞比容视为一个“受控”生理变量的观点。
