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Vasospasm include the vasodilators nitric oxide (no) and prostacyclin (pgi2) which become underactive, and the vasoconstrictors endothelin-1 (et-1) and thromboxane a2 (txa2) which become overactive. buy cheap viagra Potassium channels are also thought to play an important role, heme oxygenase[ see articles in the key references section]. There is also a structural component to cerebral vasospasm. when will a generic for viagra be available This takes the form of an inflammatory reaction in the vessel wall. In addition to the destruction of the vessel wall cells [especially the endothelial cells and adventitial nerve fibers which normally play a key role in relaxing the artery (i. compare viagra vs viagra E. viagra pills , in vasodilatation)], the vessel wall is invaded by white blood cells ("white cell infiltration"), while the smooth muscle layer can actually become thickened ("myoproliferation") and the adventitial and smooth muscle layers can even become more stiff or fibrotic ("fibrosis"). best price for real viagra These changes, in addition to the functional changes described above, serve to maintain cerebral vasospasm in the longer term [ see articles in the key references section]. Mechanism of cerebral vasospasm: figure 2 illustrates the basic mechanism underlying cerebral vasospasm. difference between viagra viagra and viagra A section of the artery wall is shown, similar to the cross-section seen elsewhere ( take me to brain artery structure right now). viagra online without prescription Say the part of the wall shown above represents the wall of a brain aneurysm that has just ruptured. viagra canada Blood (shown in red-brown) now gushes from its normal compartment in the lumen of the blood vessel through the ruptured wall (see 1 in the figure) and into the space surrounding the brain artery known as the subarachnoid space. buy viagra Here it forms a clot (2) which contains a lot of red blood cells and, eventually, their breakdown products. A key breakdown product is oxyhemoglobin, and when it forms, it generates free radicals (curved black arrows originating from 2) which damage cells in all layers of the blood vessel wall, including the endothelium (3), smooth muscle (4), and adventitia. when will a generic for viagra be available In the adventitia, fibroblasts (5) and nerve fibers (6) are damaged. secure canadian pharmacy online cheap viagra A brisk inflammatory reaction follows. Overall, the blood vessel overcontracts, its lumen shuts down, and local blood flow is impaired. This entire process culminates in cerebral vasospasm. 4. viagra to take effect Why is cerebral vasospasm a problem? The essential problem with vasospasm is that it causes an artery to shut down. Since a brain artery's function is to transport blood (and all its nutrients) to a specific part of the brain, then it follows that vasospasm leads to loss of the ability of the artery to carry out its normal function. As a result, the part of the brain formerly supplied by that artery effectively starves (ischemia) and may die ("infarction" or "stroke"). As mentioned above, although cerebral vasospasm is a transient. when will a generic for viagra be available