Ubbink D T, Reneman R S, Jacobs M J
Academic Medical Centre, Amsterdam, The Netherlands.
Eur J Clin Invest. 1999 Sep;29(9):737-43. doi: 10.1046/j.1365-2362.1999.00523.x.
Various vasoconstriction mechanisms after a change in posture are involved in controlling skin blood flow and capillary transmural pressure to maintain adequate transcapillary exchange. The role of venous orthostatic pressure in the regulation of capillary nutritive perfusion, however, is less clear.
We investigated capillary perfusion in 30 healthy subjects using intravital capillary microscopy of the big toenail-fold. Measurements were made in the supine and the sitting positions before and after incremental elevation of venous resistance, and thus the pre- to post-capillary pressure difference, by inflating a cuff around the ankle.
On dependency, median capillary density rose (P < 0.0001), whereas red blood cell perfusion decreased (P < 0.0001). Cuff inflation of 30-60 mmHg in the supine position induced similar phenomena. Repeatedly, the same capillaries were found to be recruited after an increase in transmural pressure.
We conclude that post-capillary pressure appears to be an important factor in the regulation of capillary perfusion, because an increase in venous resistance mimics the effects of dependency. The findings in this study support the theory of 'minimum perfusion pressure' for each capillary to be perfused with erythrocytes.
姿势改变后的各种血管收缩机制参与控制皮肤血流和毛细血管跨壁压力，以维持足够的毛细血管间交换。然而，静脉直立压力在毛细血管营养灌注调节中的作用尚不清楚。
我们使用大脚趾甲襞活体毛细血管显微镜检查，对30名健康受试者的毛细血管灌注进行了研究。通过在脚踝周围充气袖带增加静脉阻力，从而增加毛细血管前至后压力差，在仰卧位和坐位时，于静脉阻力递增前后进行测量。
站立时，毛细血管密度中位数升高（P < 0.0001），而红细胞灌注减少（P < 0.0001）。在仰卧位时，袖带充气至30 - 60 mmHg会引发类似现象。反复观察发现，跨壁压力增加后，相同的毛细血管会被重新灌注。
我们得出结论，毛细血管后压力似乎是调节毛细血管灌注的一个重要因素，因为静脉阻力增加模拟了站立的影响。本研究结果支持每个毛细血管被红细胞灌注所需的“最小灌注压力”理论。
