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| 題 名 | Regional Variations in Structural and Functional Adaptations in Cerebral Vasculature in Chronic Hypertension=長期高血壓狀態腦血管之構造及功能上之調適現象呈現區域性之變化 |
|---|---|
| 作 者 | 王家儀; | 書刊名 | 醫學研究 |
| 卷 期 | 11: 附輯1 民80.04 |
| 頁 次 | 頁79-100 |
| 分類號 | 398.25 |
| 關鍵詞 | 功能; 長期; 高血壓; 區域性; 腦血管; 構造; 調適現象; 變化; |
| 語 文 | 英文(English) |
| 中文摘要 | 腦循環有幾項特徵異於體循環,例如腦血流之自我調節功能特別靈敏,對於血中化學變化(如pH,血中氧及二氧化碳濃度)也很敏感,交感神經的影響力較小(但高血壓時例外)以及血腦屏障(Blood-Brain Barrier)通常具有保護功能。現有之文獻顯示腦血流自我調節之機轉有區域性之變化,例如腦幹之自我調節功能較大腦皮質靈敏,另一與體循環不同之特徵是:在體循環小動脈是血管阻力的主要來源,而在腦循環則大動脈是產生血管阻力的主要位置。 長期高血壓狀態可引起一些功能性的調適現象,例如腦血流自我調節之曲線會右移至較高的血壓範圍,也就是在高血壓時腦血流自我調節之血壓上限會提高,使之更能適應高血壓,但下限亦提高,以致於若此時突然降低血壓反而危險。在高血壓狀態,交感神經對腦血管之影響力加強,使腦血管收縮,因而減少腦血流,保護腦部不致過度灌流。以上皆是一些功能上的調適現象。 腦血管構造上的調適現象,一般已知的變化是腦軟膜大血管壁之中膜層增厚,管腔直徑變窄,但腦部實質組織內微血管是否產生變化,則尚無人研究。我們最近研究自發性高血壓大白鼠腦血管構造上之變化,發現軟膜大血管產生之變化,視所在解剖位置而有程度上之差異,而腦深層組織微血管(包括微動脈、微靜脈及微血管),則大致無變化,顯示腦循環構造上之調適變化發生在大血管,以產生主要之血管阻力,減少腦血流,以致於‘下游區’的微小血管及腦組織可受到適當之保護。 |
| 英文摘要 | Cerebral circulation differs from systemic circulation in the following aspects: 1). Autoregulatory mechanisms are particularly efficient and effective. 2). While cerebral circulation is very sensitive to chemical changes in blood, sympathetic influence is only minimal (except in the hypertensive state). 3). While in the systemic circulation the arterioles provide the major source of resistance, larger arteries in the brain contribute significantly to total vascular resistance. 4). The existence of a functionally intact blood-brain-barrier also protects the brain from potentially harmful materials. Chronic hypertension leads to functional adaptive changes. Such functional changes can be summarized by describing the effects of hypertension on each of the above features of cerebral circulation. For example, the autoregulatory range shifts to a higher pressure so that higher systemic pressures can be tolerated. However, the lower limit is also shifted higher, therefore a sudden drop in systemic pressure could be dangerous. Experimental evidence suggests that there are regional differences in autoregulatory mechanisms, for instance, they are more effective in the brain stem system in normotension is minimal, sympathetic influence becomes more prominent in hypertension. Therefore, the brain is protected from hyperperfusion through vasoconstriction which limits the flow. These is also regional variation in hypertensive disruption of BBB. Structural adaptations in chronic hypertension include wall hypertrophy and lumen narrowing in the pial arteries. No studies have been previously directed at parenchymal microvessels. Results of our recent morphometric studies suggest that in the sponstaneously hypertensive rat regional differences exist in structural alterations in the large pial vessels. No significant structural alterations were observed in the parenchymal microvessels (including small arterioles, venules and capillaries). These results indicate that major structural adaptations occur in the larger vessels. The resistance generated in the "upstream" large arteries will restrict flow so that the "downstream" microvessels and brain tissues can be properly protected. |
本系統中英文摘要資訊取自各篇刊載內容。