Collateral blood supply

The collateral blood supply to the brain is described by Liebeskind (2003). Common sites of collateral blood supply to and within the brain are ... 

Patients with chronic ischemic heart disease may demonstrate varying degrees of endothelial dysfunction and ischemia depending on the status of their endothelium and the presence and robustness of collateral blood supply. From a clinical perspective, this is most easily manifested by the various physiologic parameters of exercise capacity. 

These microspheres are precisely calibrated, spherical, hydrophilic, microporous beads made of tris-acryl co-polymer coated with gelatin. They come in defined range of sizes, ranging from 40 to 1200 pm in diameter. Their smooth hydrophilic surface, deformability and minimal aggregation tendency have been shown to result in a lower rate of catheter occlusion and more distal penetration into the small vessels [32]. Their efficacy has been evaluated in several conditions, and vdien compared to the standard polyvinyl alcohol particles (PVA) particles, a deeper penetration and embolization of smaller and more peripheral vessels may be achieved. This distal embolization may limit the development of any collateral blood supply. Also, in a study where PVA particles and tris-acryl microspheres of similar size were compared, the level of vascular occlusion with calibrated tris-acryl microspheres precisely correlated with particle size whereas the level of vascular occlusion with PVA particles did not. Another study has demonstrated that in embolized tumors. 

The stomach and duodenum have a rich collateral blood supply and hence embolization of branches of the coeliac axis can be performed with a low risk of infarction of the viscera. Conversely, the extensive vascular supply may make embolization more difficult to achieve. Thus, in addition to coils, a small particulate embolic agent is often required for a more distal block. A co-axial catheter system is likely to be necessary for this. The method of embolization depends on the angiographic findings but occlusion of the artery needs to be performed on either side of the abnormality (eroded artery or aneurysm) to achieve haemostasis. Ischaemia may be provoked... 

Differences in segmental arterial supply probably also impact on the risk of infarction. The rectum is likely to tolerate embolization better than other regions since it has a dual blood supply with the superior hemorrhoidal artery off of the inferior mesenteric artery and middle hemorrhoidal arteries arising from the internal iliac circulation. This translates into increased potential for collateral blood flow and thus decreased risk of ischemia. The cecum may be more prone to ischemia since there is not a well developed arcade along the mesenteric border of the cecum and instead there are separate anterior and posterior cecal branches. The tissue supplied by these individual branches may be more susceptible to ischemia and in fact infarction of the cecum (even after microcatheter embolization) has been reported [13]. 

The anatomy of uterine fibroids and uterine artery embolization (UAE) consists of the fibroids, their position in the uterus, and the vasculature associated with the uterus. The vasculature of the ovarian arteries is also important because of the potential for collateral blood flow from the ovarian arteries supplying the fibroids. Communication between the uterine arteries and the ovarian arteries are also important because of the risk of embolization of the ovaries through uterine-ovarian anastomoses. 

The blood supply to the capitellum is via end arterioles from the inferior ulnar collateral artery crossing the olecranon fossa posteriorly into the lateral condyle to the ossific nucleus of the capitellum. This predisposes to avascular necrosis following displaced capitellar fractures. 

Michels N (1966) Newer anatomy of the liver and its variant blood supply and collateral circulation. Am J Surg 112 337-347... 

Arterial Blood Supply 312 Arteria Radicularis Magna 312 Potential Arterial Collaterals 313 Venous Drainage 313... 

The evidence for a beneficial effect of nitrates on collateral circulation in the heart has been summarized.14 And the interesting proposal has been made that nitrates, by dilating mainly the large coronary arteries, improve the blood supply to Ischemic areas, while other coronary vasodilators, by acting primarily on smaller vessels, could actually divert blood from the ischemic regions.22... 

The first important question is whether or not the injured vessel can be sacrificed. The answer to this partially depends on whether you would expect the tissue distal to the target artery to remain viable or become ischemic after embolization. If sufficient collaterals are available, the tissue supplied by the target vessel may not be affected. So for example, embolizing a gastric branch to stop post-gastros-tomy bleeding (Fig. 7.3) is unlikely to cause any ischemia due to the rich collateral supply around the stomach. Tissue distal to the injured vessel may also be safe from ischemia if there is an alternate blood supply. For example, portal venous flow into the liver allows safe embolization of even major trunks of the hepatic artery. 

The liver receives a dual blood supply fromboth the hepatic arteries and the portal vein. Although good collateral flow exists, necrosis can occur if enough arterial supply is occluded at the time of embolization. Therefore, it is wise to assess the direction of blood flow in the portal vein because hepatofugal flow may increase the risk of infarction. One should be cautious and superselective when embolizing in the presence of portal vein thrombosis. 

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