Research Of Relationship Between Vascular Radial Compliance And Main Histological Characteristics Of Common Carotid Artery In Pig

In recent years, with the popularity of bypass graft surgery in patients with cardiovascular disease, autologous vascular donors obviously lack and allograft vessels have the problem of immune exclusion, the development and clinical use of artificial blood vessels is highly concerned. Currently, polyester or PTFE production of artificial blood vessels are mainly used for large diameter (D≥6mm) treatment of vascular reconstruction. The disadvantage of applying small caliber artificial vascular prosthesis (D≤6mm) is its poor long-term patency rates accompanied by infection, intima thickness and thrombopoiesis, the deep reason of this is that artificial vascular transplantion and vascular compliance in vivo are mismatching. Peripheral vascular grafting with saphenous vein’s five-year patency rate was88%and ten-year patency rate was50%, which spurred further developing tissue engineer blood vessels or artificial blood vessels that have similar biological properties of nature blood vessels (with the characteristics of the nature vascular endothelial surface including antithrombotic, shrinkage, compliance and remodeling capacity). Tissue engineer is committed to improving the above-mentioned disadvantages of the artificial blood vessels, but, there are still many issues to be resolved before eventually used clinically. At home and abroad, researching on small-caliber vascular substitutes including collagen fibers with nature materials, artificial vascular structures, has problems of biomechanics and blood vessels not match in body. Synthetic materals has poor biocompatibility in vivo tissue, the thickness of artificial vascular tube wall and the diameter size of vessels affect compliance greatly. With the problem of biomechanics mismatch, both at home and abroad, investors tested different proportions of silk, collagen fibers and finally made out artificial blood vessels with the biomechanics similar to the great saphenous, but the ratio of different components on the production of artificial blood vessels is trialed. There is no adequate histological basis that can be quickly extended to the production of other small-caliber vascular in body. As we all know:blood vessels in body even if in the same diameter, different parts of vascular wall structure and biological characteristics may also be different.Typical artery include intima, media and adventitia parts, separated by internal and external elastic lamina. The intima primarily formed by the endothelial cells and the basement membrane, the medial consist of smooth muscle cells, collagen fibers and elastic fibers, while the adventitia mainly has connective tissue especially collagen fibers produced by fibroblasts. The inner layer of circulatory system is a continuous, single-cell layer within the cortex, the endothelial cells are able to sense shear stress changes in the blood flow, participate in leukocyte adhesion, aggregation and small molecule signals transduction in the blood. Those special important effects are achieved primarily through the surface of the endothelial cells toward lumen. The biofilm of Monolayers-endodermis is an extremely important multifunctional organ, it not only reduce the resistance to blood flow, but also has a selective permeability, and the ability to monitor, integrate, sense vasogenic signal, it can also generate multibiologically active substances; So the normal state has an important role for the maintenance of the normal vascular physiology activities. Vascular intima maintains the contraction of the blood vessels, diastolic elastic biomechanical properties, while adventitia limits excessive blood vessels dilation. Porcine common carotid artery without branch is the ideal experimental material to study arterial expansion-diastolic abilities. In histology, common carotid artery proximal segment likes the elastic arteries, distal performs transitional artery; In the former:smooth muscle cells showing circumferential arrangement between the coarse curly elastic fibers and collagen fibers, accompanied by fine collagen fibers surrounding smooth muscle cells. While, in the distal, collagen fibers concentrated with small elastic lamina; vascular adventitia has large number of fibroblasts. Collagen fibers, elastic fibers both distribute along the long axis of vessels.Atherosclerosis, hypertension and diabetes with vascular lesions etc, in the process of these diseases, hardness increases while compliance reduces in blood vessels. Studies show that the vascular disease associated with vascular endothelial cell dysfunction, elements formed by vascular membrane are changed both at RNA level and protein level, and this process is closely related to the matrix metalloproteinases(MMPs) and the tissue inhibitors of metalloproteinase (TIMPs) the transformation growth factor-β1(TGFβ-1), etc. Vascular endothelial cells sense vasogenic signals; smooth muscle cells, collagen fibers and elastic fibers in film work together and participate in vascular biomechanics; the adventitia main play a role to constrict blood vessels from excessive expansion. Smooth muscle cells maintain the tension of blood vessels; elastic fibers keep the vessels at recoil state, type I collagen fibers limit excessive expansion of vessel wall, while type III collagen fibers, similar to elastic fibers, have the ability to keep vessel recoil. A lot of researches on different component of the diseased vessel wall have been done, but there has been little research on the relationship between basic vascular structure and biomechanics. Research about vascular structure not only helps to understand the basis for the development of disease status, more conducive to the progress of the study of vascular substitutes. The view of this experiment is to do the following studies:1:Firstly, six adult healthy pigs (aged6months) go through general anesthesia before anterior median incision to take bilateral common carotid arteries (CCA) in the neck, the left CCAs of all the animal were fixed on the Bose bio-dynamic monitor to detect the three pressure segments (low pressure:50mmHg～90mmHg, normal pressure:80mmHg-120mmHg, high pressure:110mmHg～150mmHg). Pressure-diameter relationship was got through linear regression analysis of vascular compliance at different pressure sections. The right CCAs of all the animals were done by H.E staining, elastic fibers dyed, Massion staining, Sirius red saturated picric acid staining, a-actin staining.Statistical analysis of respective components of the vascular changes in the proximal and the distal segment of the CCA, suggesting that the relationship between the different tangible histological components and the vascular compliance. Results:proximal lumen area, medial thickness and elastic fibers area percentage were significantly greater than that of the distal vessel; numbers of smooth muscle cells in the membrane unit area of the proximal and distal was no significant difference. Collagen fiber content was no significant difference in the proximal and the distal segments, while type I collagen fibers area percentage of the proximal was more than that in distal CCA, type III collagen fibers is more in the distal than that of in proximal CCA. Maximum vascular compliance was got in normal pressure segment. These results indicate that changes in the distribution of the parting of collagen fibers and elastic fibers along the carotid artery play important roles in vascular compliance changes.2:Three adult pigs at physiological pressure were perfused by heparin physiological saline and neutral formalin in situ, the corresponding vascular segment (different segments of aorta, pulmonary artery, coronary artery, internal thoracic artery and common carotid artery were removed, their morphological characteristic of endothelial cells were observed under scanning electron microscope. Results:in a straight vessel segments, endothelial cells generally fusiform nucleus slightly elevated, consistent with the direction of the long axis of the cell and blood flow. In the vascular bending area, the cells are or look like slightly oval; such as in the pulmonary artery, it is ovoid while in the aortic, endothelial cells have rich microvilli. In coronary, we observed multiple leukocyte adhesion in the endothelial surface, in the right coronary, posterior interventricular branch, there was a local cell in the regenerated status. In internal thoracic artery, carotid artery and coronary, we observed a kind of cells which are adhesive to the endothelial surface with a round, oval, and triangle forms of cell body and long prolongations, the number of prolongation varies from two to six, some of many prolongation have bifurcation. Conclusion:endothelial cell morphology, length of the arrangement, microvillus, the density and quantity depend on different sites, shear stress may be an important factor contributing to these differences. Microvilli not only expand cell surface area but may also have the function to reduce flow shocks. Telocyte is a new type of mesenchymal cells recently found in a variety of tissues (vascular membrane, trachea, myocardial interstial, skeletal, muscle interstitial, gastrointestinal tract, skin, etc), but it has not been found in blood, Cells with prolongations in the blood which we have found was analyzed by international telocyte well-known scientist Professor Peposcu, he thought that the cell is telocyte in blood and its true origin, biological characteristics and its functions worth further research.