Bosman J, Tangelder G J, oude Egbrink M G, Reneman R S, Slaaf D W
Department of Biophysics, Cardiovascular Research Institute Maastricht, University of Limburg, P.O. Box 616, 6200 MD Maastricht, The Netherlands.
Pflugers Arch. 1995 Sep;430(5):852-61. doi: 10.1007/BF00386186.
When perfusion pressure is reduced, red blood cell flow in the capillaries of skeletal muscle ceases at a positive pressure difference across the vascular bed, while arterioles dilate and venules are not constricted. This flow cessation (i.e., cessation of red blood cell flow) and luminal diameter changes in capillaries following femoral arterial pressure reduction were investigated in the rabbit tenuissimus muscle in situ (n = 42) using intravital video microscopy. Arterial pressure was reduced by occlusion of the aorta distal to the renal arteries. During the experiments, leg and muscle were placed in a sealed box. The muscle was exposed to low PO2 by leading a gas mixture deprived of O2 through the box. Locally at the muscle surface, i.e., under the microscope objective, PO2 was varied by varying the PO2 in the superfusion solution. In all experiments, the remainder of the muscle was kept at low (< 20 mm Hg) PO2. The incidence of flow cessation was virtually zero at low local (< 20 mm Hg) PO2 and became almost 100% at local values above 70 mm Hg. Initial equivalent capillary diameters were 3.1-5.8 microm (median 4.0 microm) and did not correlate with local O2 tension. During aorta occlusion, capillary diameters significantly (P < 0.0001) decreased by a median value of 8% at all local PO2 values; in 14 out of 54 capillaries local diameter became less than 2.8 microm. The extent of diameter reduction did not correlate with PO2. In the 14 capillaries in which the diameter became less than 2.8 microm flow cessation occurred in only four cases. The minimal diameter reached was always at the site of an endothelial nucleus. The capillary diameter reductions are probably due to passive recoil. In the 48 capillaries in which flow ceased, only in four cases did a red blood cell stop at the site of the nucleus. We conclude that capillary diameter reductions (local and generalized) lead to a considerable increase in capillary resistance which contributes to the occurrence of flow cessation but cannot solely explain it.
当灌注压降低时，骨骼肌毛细血管中的红细胞流动在血管床两端存在正压差时就会停止，而小动脉扩张，小静脉不收缩。利用活体视频显微镜，在原位兔缝匠肌（n = 42）中研究了股动脉压降低后毛细血管中的这种血流停止（即红细胞流动停止）和管腔直径变化。通过阻断肾动脉远端的主动脉来降低动脉压。在实验过程中，腿部和肌肉被置于一个密封箱中。通过让一种不含氧气的混合气体通过箱子，使肌肉暴露于低氧分压环境。在肌肉表面局部，即在显微镜物镜下，通过改变灌注溶液中的氧分压来改变氧分压。在所有实验中，肌肉的其余部分保持在低（<20 mmHg）氧分压。在局部低（<20 mmHg）氧分压时，血流停止的发生率实际上为零，而在局部氧分压高于70 mmHg时几乎达到100%。初始等效毛细血管直径为3.1 - 5.8微米（中位数4.0微米），与局部氧张力无关。在主动脉阻断期间，在所有局部氧分压值下，毛细血管直径均显著（P < 0.0001）减小，中位数减小8%；在54根毛细血管中有14根局部直径小于2.8微米。直径减小的程度与氧分压无关。在直径小于2.8微米的14根毛细血管中，只有4根出现了血流停止。达到的最小直径总是在内皮细胞核所在部位。毛细血管直径减小可能是由于被动弹性回缩。在血流停止的48根毛细血管中，只有4根红细胞在细胞核部位停止。我们得出结论，毛细血管直径减小（局部和全身性）会导致毛细血管阻力显著增加，这有助于血流停止的发生，但不能单独解释它。
