The Heart and the Circulatory System

IntroductionAnatomy of the Heart Circulatory SystemBlood VesselsBlood Supply Problems

Circulatory Problems No discussion of the circulatory system would be complete without mentioning some of the problems that can occur. As mentioned earlier, several problems can occur with the valves of the heart. Valvular stenosis is the result of diseases such as rheumatic fever, which causes the opening through the valve to become so narrow that blood can flow through only with difficulty. The result can be blood damming up behind the valve. Valvular regurgitation occurs when the valves become so worn that they cannot close completely, and blood flows back into the atria or the ventricles. If the blood can flow backward, the efficiency of the cardiac stroke is drastically reduced. The coronary arteries are also subject to problems. Atherosclerosis is a degenerative disease that results in narrowing of the coronary arteries. This is caused by fatty deposits, most notably cholesterol, on the interior walls of the coronary arteries. When the walls become narrowed or occluded, they reduce the blood flow to the heart muscle. If the artery remains open to some degree, the reduced blood flow is noticed when the heart is under stress during periods of rapid heartbeat. The resulting pain is called angina. When the artery is completely closed or occluded, a section of the heart muscle can no longer get oxygenated blood, and begins to die. This is called a heart attack. Only quickly restoring the blood flow can reduce the amount of heart muscle that will die. At times, the walls of the systemic arteries become weakened. When this occurs, the wall may balloon outward, much like a weak spot in the radiator hose. This called an aneurysm, and is an extremely dangerous condition. Like a radiator hose under pressure, the wall can rupture. Blood can then spill out of the circulatory system into the body cavity. If an aneurysm ruptures in the aorta, death is almost certain. The systemic veins also can have problems. When the valves in the veins break down, blood can pool in the lower legs, causing varicose veins. Clots can also form in veins of the legs. These clots can break loose and flow to the lungs, causing a pulmonary embolism and possible death. The capillary beds are not without their problems. True capillaries do not have any smooth muscle in their walls. They have no way to control excess pressure other than a small muscle, the precapillary sphincter. A precapillary sphincter encircles each capillary branch at the point where it branches from the arteriole. Contraction of the precapillary sphincter can close the branches off to blood flow. If the sphincter is damaged or can not contract, blood can flow into the capillary bed at high pressures. When capillary pressures are high (and this can be the result of gravity), fluid passes out of the capillaries into the interstitial space, and edema or fluid swelling is the result. This can be seen in people who have to stand all day. Their feet and ankles often swell from the excess fluid accumulating there. Capillaries are fragile and can be damaged easily. It is often ruptured capillaries in the skin that cause bruises when one falls or sustains a blow. Since the advent of modern medical research, physicians have made quantum leaps in their understanding of the heart and in ways to treat cardiovascular disorders. When we hear of breakthroughs in cardiac medicine, we often think of radical treatments such as heart transplants or artificial hearts. The first heart transplant took place in 1967. It was performed by the South African surgeon Dr. Christiaan Barnard. The patient lived just 18 days. The first U.S. transplant took place in 1968. The rate of transplants increased in the 1970's, but most patients died within a year. The drugs given to fight rejection of the heart also lowered the body's resistance to infections. It was these infections that often killed the patients. Then, in the 1980's physicians began using the drug cyclosporine to fight rejection. Patients taking cyclosporine had a much greater rate of survival. In 1982, the first artificial heart was implanted into Barney Clark by the American surgeon Dr. William DeVries. Due to complications, Clark lived only 112 days. As of this writing, the use of the artificial heart is not approved in the United States. While these two methods both sound less than successful, you must remember that they are last resort treatments. They are not typical of the success rates that other, more common, treatments have enjoyed. Most cardiovascular emergencies are directly caused by coronary artery disease. As noted earlier, coronary arteries can become clogged or occluded, leading to damage to the heart muscle supplied by the artery. There are three methods for treating coronary artery disease. They may be used individually or in combination with the each other. Medication can be given to control the blood flow to the heart. This is not always effective. Another method, coronary bypass surgery, involves replacing a blocked coronary artery with either a vein from the leg or with a thoracic artery from the chest wall. This method requires that the patient's chest be opened. The heart must be stopped, then restarted after the new vessels are connected. Another technique, although not new (it was first performed in 1977 by a Swiss physician), is a highly successful treatment called percutaneous transluminal coronary angioplasty, or balloon angioplasty by most laypersons. In this procedure, the patient remains awake. Under local anesthesia, tubes called catheters are inserted into an artery and vein in the groin. Next, a tiny, flexible guide wire is maneuvered through the arteries, eventually passing through the narrowed opening in the occluded coronary artery. Next, another catheter with a balloon near the end is run along the guide wire. When the balloon is in place, it is inflated and deflated several times, enlarging the opening of the artery and increasing the blood flow. When the surgeon is satisfied with the size of the opening, the catheters are removed. The patient remains in the hospital for a few days, but can resume normal activities in a matter of weeks. Other current cardiovascular research involves drugs that control the blood pressure or heart rate, artificial blood substitutes, and devices implanted in the wall of the heart that can detect changes in the rate or patterns of contraction of the ventricles and correct them before a heart attack occurs. Modem cardiovascular medicine and our understanding of the heart and circulation have certainly come a long way since the days of Pliny, Galen, and Harvey. While we jest about broken hearts in romances, or having the heart needed to work hard to win an event, we all know that the heart and the circulatory system are not related to emotions, the soul, or intellect. Without the four-chambered heart and double circuit circulatory system, mammals would not have been able to successfully evolve, for this type of circulation gave rise to the warm-bloodedness needed to out compete the slower responding reptiles. Our own circulatory system has evolved to feed large amounts of blood to our brains, letting the brain develop and evolve into the organ it is today. Modern medical research on the heart has changed the face of the future. Advances in cardiovascular surgery and cardiac care have given thousands of people the opportunity to live on after the attack of disease, often for decades. What once would have killed can now be not only survived, but even prevented. All because an English physician in the 1600's decided that maybe everything was not as he had been taught, and had the "heart" to try something different.