Denervation Blocked arteries are a major cause of ill health and death.These effects arise when the artery blocked is the sole adequate provider of mutrition and removal of waste products.The result is tissue ischaeaia,a tern referring to inadequste blood flow and its conseqences.As the adverse metabolle effects of ischaemia develop (hypoxia.lactic acidosis.lack of nutrients),the patient experiences pain and loss of function in regions such as the arms and legs,and in the heart -where a richly supply of pain fibres can he activated by metabolic changes. It is possible to experience these effects by putting a blood pressure cuff round your wrist and punping it up to 30-40mmHg above your systolic arterial pressure, thereby cutting off all flow to the hand.At first,there will be only slight disconfort from the tightly applied cuff.After some 10-15 minutes,a moderate ache in the hand is likely,and efforts to use the hand muscles make the pain worse. Discomfort is rapidly relieved by removing the cuff. Renovina the cuff leads to a marked flush in the hand felt as a fullness.as the blood vessels are indeed distended by greatly inereased blood flow,and observed as a pink area strictly limited by a line where the proximal margin of the cuff was situated.This increased blood flow is terned reacrfve Ayperaewfa and illustrates the marked and localized effect of the accumulation of metabolites.It also shows that there are no serious after-effeets of the arterial occlusion in the hand. In general.the peripheries and most tissues can survive considerable periods of ischaemia,unlike the brain,where complete ischaemia leads to unconsciousness in seconds and permanent hrain dange in several minutes.In fact,it is routine in certain operations on the arm or leg to put on a tourmiquet to occlude the circulation and provide a bloodless field for surgery.The occlusion can safely last for an hour or two.After that,there is an increasing risk of tissue damage and general effects when a flood of 'netabolites'is released into the general circulation
Denervation Blocked arteries are a major cause of ill health and death. These effects arise when the artery blocked is the sole adequate provider of nutrition and removal of waste products. The result is tissue ischaemia, a term referring to inadequate blood flow and its consequences. As the adverse metabolic effects of ischaemia develop (hypoxia, lactic acidosis, lack of nutrients), the patient experiences pain and loss of function in regions such as the arms and legs, and in the heart - where a richly supply of pain fibres can be activated by metabolic changes. It is possible to experience these effects by putting a blood pressure cuff round your wrist and pumping it up to 30-40mmHg above your systolic arterial pressure, thereby cutting off all flow to the hand. At first, there will be only slight discomfort from the tightly applied cuff. After some 10-15 minutes, a moderate ache in the hand is likely, and efforts to use the hand muscles make the pain worse. Discomfort is rapidly relieved by removing the cuff. Removing the cuff leads to a marked flush in the hand - felt as a fullness, as the blood vessels are indeed distended by greatly increased blood flow, and observed as a pink area strictly limited by a line where the proximal margin of the cuff was situated. This increased blood flow is termed reactive hyperaemia and illustrates the marked and localized effect of the accumulation of metabolites. It also shows that there are no serious after-effects of the arterial occlusion in the hand. In general, the peripheries and most tissues can survive considerable periods of ischaemia, unlike the brain, where complete ischaemia leads to unconsciousness in seconds and permanent brain damage in several minutes. In fact, it is routine in certain operations on the arm or leg to put on a tourniquet to occlude the circulation and provide a bloodless field for surgery. The occlusion can safely last for an hour or two. After that, there is an increasing risk of tissue damage and general effects when a flood of 'metabolites' is released into the general circulation
The crucial point about unblocking arteries is that it can be highly beneficial within a few hours of complete occlusion.but thereafter the chances of complete or even partial recorery steadily decline.The major sites where unblocking arteries is a common and important procedure are the heart and the legs,and these will be considered in turn. The heart Unblocking the coronary arteries is needed in two situations.The first is when a noderately narrowed artery can maintain flow at rest but not in exercise-indicated by amgin of effort (cardiac pain,often in the chest,related to exercise).The second is an acute emergency when a sudden complete blockage,often a coronary throwbosis,leads to a hearr attack with severe chest pain at rest and a risk of sudden death.A heart attack,or ocardial infarction.and its treatment are described on page 616;the treatment of less-sudden narrowing will be considered here. Narrowing is likely to have been found in an X-ray of the coronary arteries (coromary angjograe)undertaken because the patient has angina of effort,with evidence of ischsenia found during a cardiac treadnill test.The narrowing can often be relieved by angioplasty (angio,a vessel:plasty,reconstruction).Here.a cardiac catheter (flexible tube)is passed into the narrowed coronary artery.The catheter is inserted via a major artery such as a femoral,passed up the aorta and into the coronary artery orifice just distal to the aortic valve.The tip of the catheter is passed into the narrowed region,and a balloon surrounding the last few centinetres of the catheter is inflated to a high pressure of several atmospheres to crush the material obstructing the lunen.The dispersed material does not usually cause any harm.Often,a small tube.or stemt,is inserted to maintain patency of the lunen it is expanded at the site soreshat like opening an urbrella.Finally. if it is not possible to reopen the vessel in this way (perhaps because a comsiderable length of artery is severely cbstructed)a coronary artery bypass grafr is made. A segnent of the patient's own blood vessels is used.A leg vein can carry out this function its wall gradually becores thickened hy srooth muscle (arterialized)-
The crucial point about unblocking arteries is that it can be highly beneficial within a few hours of complete occlusion, but thereafter the chances of complete or even partial recovery steadily decline. The major sites where unblocking arteries is a common and important procedure are the heart and the legs, and these will be considered in turn. The heart Unblocking the coronary arteries is needed in two situations. The first is when a moderately narrowed artery can maintain flow at rest but not in exercise - indicated by angina of effort (cardiac pain, often in the chest, related to exercise). The second is an acute emergency when a sudden complete blockage, often a coronary thrombosis, leads to a heart attack, with severe chest pain at rest and a risk of sudden death. A heart attack, or myocardial infarction, and its treatment are described on page 616; the treatment of less-sudden narrowing will be considered here. Narrowing is likely to have been found in an X-ray of the coronary arteries (coronary angiogram) undertaken because the patient has angina of effort, with evidence of ischaemia found during a cardiac treadmill test. The narrowing can often be relieved by angioplasty (angio, a vessel; plasty, reconstruction). Here, a cardiac catheter (flexible tube) is passed into the narrowed coronary artery. The catheter is inserted via a major artery such as a femoral, passed up the aorta and into the coronary artery orifice just distal to the aortic valve. The tip of the catheter is passed into the narrowed region, and a balloon surrounding the last few centimetres of the catheter is inflated to a high pressure of several atmospheres to crush the material obstructing the lumen. The dispersed material does not usually cause any harm. Often, a small tube, or stent, is inserted to maintain patency of the lumen - it is expanded at the site somewhat like opening an umbrella. Finally, if it is not possible to reopen the vessel in this way (perhaps because a considerable length of artery is severely obstructed) a coronary artery bypass graft is made. A segment of the patient's own blood vessels is used. A leg vein can carry out this function - its wall gradually becomes thickened by smooth muscle (arterialized) -
or a nearby internal mamary artery may be used.In both cases,collateral circulations compensate for the vessel renoved. The legs Problems with inadequate circulation in the legs are also quite oftem dealt with by a bypass,e.g of the popliteal artery.Sometines,a large enbolus (dislodged clot)blocks leg arteries and can be removed surgically.As with the heart,if the arterial supply to a leg or legs is suddenly and completely cut off.the tissue can survive for some hours before local tissue death (amgrene)develops
or a nearby internal mammary artery may be used. In both cases, collateral circulations compensate for the vessel removed. The legs Problems with inadequate circulation in the legs are also quite often dealt with by a bypass, e.g. of the popliteal artery. Sometimes, a large embolus (dislodged clot) blocks leg arteries and can be removed surgically. As with the heart, if the arterial supply to a leg or legs is suddenly and completely cut off, the tissue can survive for some hours before local tissue death (gangrene) develops