Blood vessels, calcifications

The most widely studied synthetic polymers for blood contact applications are polyether urethane ureas ( Biomer (Ethicon)). These materials have been used in artificial hearts, as coatings for lead wires in pacemakers, have been used and are being considered for blood vessel prostheses. The success of these materials is believed to be due to preferential adsorption of albumin rather than globulin or fibrinogen which promote a clotting response. However, these materials are hydrophobic and questions of long-term effectiveness are unresolved. Particularly, these materials may shed emboli or may be susceptible to surface calcification. Thus, it may be desirable to have synthetic polymers which are hydrophilic and better resemble blood vessels [475]. 

Q13 Arterial emboli, which can block blood vessels and cause ischaemia or infarction in the tissues they affect, tend to originate in the left heart and are associated with valvular disease and dysrhythmias. Mitral stenosis is associated with abnormal atrial rhythm, particularly atrial fibrillation. Fibrillation and other rhythm abnormalities in the atria favour blood coagulation, resulting in production of thromboemboli which can move to distant parts of the circulation, such as the cerebral circulation. Thrombi could also form on surfaces of valves distorted by calcification and other abnormalities. In view of the risks of thromboembolism, it is usual to provide anticoagulant therapy to patients with mitral valve problems and atrial fibrillation. 

Intoxication with vitamin D causes weakness, nausea, loss of appetite, headache, abdominal pains, cramps, and diarrhea. More seriously, it also causes hypercalcemia, with plasma concentrations of calcium between 2.75 to 4.5 mmol per L, compared with the normal range of 2.2 to 2.5 mmol per L. At plasma concentrations of calcium above 3.75 mmol per L, vascular smooth muscle may contract abnormally, leading to hypertension and hypertensive encephalopathy. Hypercalciuria may also result in the precipitation of calcium phosphate in the renal tubules and hence the development of urinary calculi. Hypercalcemia can also result in calcinosis - the calcification of soft tissues, including kidneys, heart, lungs, and blood vessels. This is assumed to be the result of increased calcium uptake into tissues in response to excessive plasma concentrations of the vitamin and its metabolites. 

Diseases of elastic tissue are few compared with those that affect collagen, and in these destruction of preformed elastic fibers appears to occur only in localized areas, particularly in the walls of blood vessels and in the skin. In arteriosclerosis loss of elasticity and breakdown in the structure of the elastic elements in the media of arteries is accompanied by calcification of the media and the development of calcified plaques in the intima. Since calcification of the media may be seen to occur without the development of atheromata, it is thought that this change may be associated in the first place with age. Other age-related changes looked for have been changes in the gross content of elastin in the media and changes in the amino acid... 

Some individuals develop hypertension in response to vitamin D, which in some of them may be directly related to hypercalcemia and which may be reversible when renal function is normalized (12). Metastatic calcification is observed in various tissues (13), but arterial calcification is the most usual. In some patients undergoing dialysis, calcification of the blood vessels has been so extensive that cannulation could not be performed (14). 

Ectopic calcifications in the blood vessels, brain, subcutaneous tissue, muscles, and cartilage (calcium phosphate is an insoluble salt) (see Figure 75). 

Unidentified Hyaline sclerosis and calcification of blood vessels Necrosis of heart muscle Cardiac aneurysm Liver damage (32, 36, 37, 49) (36, 37) (37) (36, 37, 49)... 

CT may be able to demonstrate those collateralized territories, it cannot provide further information on the quahty of collateral blood flow (Fig. 21.8). MR perfusion imaging can prove whether collateral blood flow is sufficient or insufficient (Fig. 21.9). In cases of recurrence of chest pain in patients post-CABG, CT bypass CTA is perfectly suited to assess bypass graft patency (Fig. 21.10) the judgment of the native vessels though is substantially hampered by the fact that coronary vessels may exhibit an accelerated atherosclerosis and calcification. In addition, CTA is limited in its accuracy in small distal coronary segments. Early after CABG, CT assessment of bypass patency may be of clinical value. 

---