Dissociation between skeletal muscle microvascular PO2 and hypoxia-induced microvascular inflammation.

Systemic hypoxia (SHx) produces microvascular inflammation in mesenteric, cremasteric, and pial microcirculations. In anesthetized rats, SHx lowers arterial blood pressure (MABP), which may alter microvascular blood flow and microvascular Po(2) (Pm(O(2))) and influence SHx-induced leukocyte-endothelial adherence (LEA). These experiments attempted to determine the individual contributions of the decreases in Pm(O(2)), venular blood flow and shear rate, and MABP to the hypoxia-induced increase in LEA. Cremaster microcirculation of anesthetized rats was visualized by intravital microscopy. Pm(O(2)) was measured by a phosphorescence-quenching method. SHx [inspired Po(2) of 70 Torr for 10 min, MABP of 65 +/- 3 mmHg, arterial Po(2) (Pa(O(2))) of 33 +/- 1 Torr] and cremaster ischemia (MABP of 111 +/- 7 mmHg, Pa(O(2)) of 86 +/- 3 Torr) produced similar Pm(O(2)): 7 +/- 2 and 6 +/- 2 Torr, respectively. However, LEA increased only in SHx (1.9 +/- 0.9 vs. 11.2 +/- 1.1 leukocytes/100 microm, control vs. SHx, P < 0.05). Phentolamine-induced hypotension (MABP of 55 +/- 4 mmHg) in normoxia lowered Pm(O(2)) to 26 +/- 6 Torr but did not increase LEA. Cremaster equilibration with 95% N(2)-5% CO(2) during air breathing (Pa(O(2)) of 80 +/- 1 Torr) lowered Pm(O(2)) to 6 +/- 1 Torr but did not increase LEA. On the other hand, when cremaster Pm(O(2)) was maintained at 60-70 Torr during SHx (Pa(O(2)) of 35 +/- 1 Torr), LEA increased from 2.1 +/- 1.1 to 11.1 +/- 1.5 leukocytes/100 microm (P < 0.05). The results show a dissociation between Pm(O(2)) and LEA and support the idea that SHx results in the release of a mediator responsible for the inflammatory response.     

The laser-assisted end-to-side microvascular anastomosis

A simple method of performing the laser-assisted end-to-side microvascular anastomosis was devised. This technique was tested on 150 Sprague-Dawley rats in two separate series of experiments. In the first, end-to-side anastomoses were performed on the iliac artery under the normal tension due to the elastic recoil of severed vessels. Four stay sutures were placed 90 degrees apart, and the intervals were "spot welded" with a low-wattage CO2 microsurgical laser unit. The patency rate (96 percent) was equivalent to that found in a control group utilizing the conventional all-suture method (92 percent), but there was a significantly higher aneurysm rate (44 versus 11 percent). In a second model, an arterial bypass with very low anastomotic tension was performed around an obstruction created in the carotid artery. This model resulted in turbulent flow but low anastomotic tension. Here the laser-anastomosis patency rate was 98 percent, versus 42 percent for the conventional all-suture method. The placement of fewer sutures in association with turbulent flow in this model may account for the improved patency rate. The avoidance of excessive tension at the anastomotic site reduced the incidence of aneurysms to a negligible level.     

Bipolar coagulation in microvascular surgery

In microvascular surgery and surgery of the hand, hemostasis must be accomplished very precisely to avoid injury to adjacent structures. Bipolar coagulation is one of the more precise techniques, since theoretically, current flows only through tissue that is held between the tips of the forceps. Experiments were done in rats to confirm that bipolar coagulation can be used to control vessel branches without disturbing the parent vessel or adversely affecting an adjacent anastomosis. However, the importance of the characteristics of the bipolar generator require particular attention. The generator used in these experiments produces a continuous-sine-wave current to minimize voltage. In addition, the equipment was designed to sense impedance and to automatically shut down at the point of desiccation, thus avoiding sparking, charring, and adherence of tissue to the forceps.     

Arterial autografts in microvascular surgery

The use of autogenous arterial grafts for long arterial defects in replantation or tissue transfer is recommended. Some grafts are taken from the superficial temporal artery, but the majority are taken from the subscapular arterial tree. The match which can be achieved to vessels in the hand, both proximally and distally, is far superior to that with reversed vein grafts.     

Reparative regeneration of microvascular anastomosis

Dynamics of reparative regeneration of the sutural anastomosis of the abdominal aorta has been studied in 90 white mice during the time from 1 day up to 1 year. The operation has been performed by means of microsurgical technique. Histological, histochemical, electron microscopic and radioautographic (3H-thymidine and 3H-uridine labelling) methods have been used. By the 7th day fibrin is organized on the adventitia, the scar along the resection line is formed, endothelial lining and middle layer of the vascular wall are restored. As sources of regeneration in the anastomosis serve cellular elements preserved in the lesion margins. Further maturation of the formed structures and formation of the initial thickening by migrating smooth muscle cells of the middle layer take place. Completeness and typicity depend on preservation of the elastic carcass in the middle layer and adventitia.     

Neutrophil-dependent mediation of microvascular permeability

Macromolecular extravasation induced by the chemoattractants N-formyl-methionylleucylphenylalanine (FMLP), complement fragment C5a, and leukotriene B4 (LTB4) has been reported to be neutrophil dependent. A review of experimental evidence argues against mechanical disruption of the endothelial barrier as a likely mechanism for enhanced microvascular permeability. Other proposed mechanisms attribute macromolecular efflux to extracellular liberation of granule constituents or granule-independent neutrophil release products (e.g., oxygen radicals) that can undermine vascular integrity by direct or indirect actions on endothelial cells or other components of vascular walls (glycocalyx, basement membrane). The cytotoxic potential of neutrophil-release products on endothelial cells prompts consideration of a transcellular pathway for macromolecular transport. Further studies are needed to clarify the precise nature of endothelial injury and its resolution to better understand the physiology behind the transient effects of these mediators on vascular permeability.     

Vitronectin decreases microvascular endothelial cell apoptosis

Angiogenesis after tissue injury occurs in a matrix environment consisting of fibrin, fibronectin, and vitronectin as the major extracellular matrix (ECM) constituents. ECM-integrin interactions is critical for angiogenesis and failure to bind a ligand to certain integrin receptors (α_vβ₃ or α_vβ₅) inhibits angiogenesis. The ligand that binds to α_vβ₃ or α_vβ₅ integrin receptors during microvascular angiogenesis has not been identified. Our hypothesis is that provisional matrix molecules provide the environmental context cues to microvascular endothelial cells and promote angiogenesis by decreased programmed cell death. Using cultured human microvascular endothelial cells, we show that vitronectin, in comparison to growth on alternative provisional matrix molecules (fibronectin, fibrinogen plus thrombin), collagen I, and basement membrane molecules (collagen IV), significantly reduces microvascular endothelial cell death in vitro. This reduction was observed using morphologic criteria, TdT-mediated dUTP nick end labeling (TUNEL) assay, histone release into the cytoplasm, and thymidine release into the supernatant. Though our data confirm that vitronectin may bind to more than one integrin receptor to reduce MEC apoptosis, binding to the α_v component appears to be the critical integrin subcomponent for reducing apoptosis. J. Cell. Physiol. 175:149–155, 1998. © 1998 Wiley-Liss, Inc.     

脑缺血后的脑微血管变化

大脑微血管具有独特的组织结构,这种结构对脑组织起到了保护性屏障作用,局部脑缺血可以引起这种屏障功能破坏,导致血液成分渗出,以及与炎症反应密切相关的整合素表达明显增加,促使炎性细胞以及血小板等向缺血局部聚集和迁移,从而造成局部微血管阻塞。同时,血管内皮细胞基质金属蛋白酶表达明显增加,内皮细胞和星形胶质细胞表面的结构整合素以及对应的基质配体丢失,使微血管细胞间的紧密联系破坏。以上这些变化伴随着神经细胞的损伤,同时,与血管生成和神经发生相关的受体上调,缺血局部区域出现血管生成和神经发生现象,这些过程可能与缺血后期脑功能的恢复相关。本文主要就脑缺血以后脑微血管的变化进行了综述,并对其中的问题以及今后脑血管病研究的发展进行了探讨。     

Analytical characterization of microvascular resistance distribution

The bat wing is used as an experimental preparation and as a self-contained vascular bed. The number, dimensions, and distribution of the vessels of the real vascular bed are included into an analyzable, representative geometric configuration. Based on theoretical analysis and experimental data, equations are developed and utilized to characterize the pressure-flow relationships for each branching order of the vascular field. The geometric configuration and associated describing equations are used to determine the resistance distribution of the microvascular bed. The predicted values are compared with experimentally determined quantities in normal and hypertensive animals.