Effects of High Blood Pressure on the Cardiovascular System Term Paper

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High blood pressure or hypertension is defined as a consistent recording of systolic blood pressure of 140mm HG or greater, and a diastolic blood pressure recording of 90mm HG or greater. High blood pressure is the most common circulatory disorder among human beings. Hypertension occurs all over the world, mostly in middle-aged or elderly men and women. Nearly half of all Americans who reach the age of 74 develop high blood pressure. Table 1. Below provides a classification of blood pressure for adults. As indicated in Table 1, hypertension can be classified as normal, pre-hypertensive, Stage 1, or Stage 2 (National Institutes of Health). Cardiac output, and total peripheral resistance determines blood pressure. Cardiac output is the total volume of blood pumped by the heart per minute, and total peripheral resistance is the force that the heart must work against to pump the blood. Cardiac output is a central factor that is determined by the heart rate, and stroke volume, where total peripheral resistance is a peripheral factor determined by vascular resistance.

It is estimated that 50 million Americans have high blood pressure. The prevalence of high blood pressure is higher for African-Americans than any other race. In addition, hypertension is more prevalent in lower SES groups and more prevalent men. In addition, the prevalence of high blood pressure increases with age. Hypertension is often associated with obesity, increased salt intake, heavy alcohol intake, decreased physical activity, and psychosocial stress.

Hypertension can be categorized as either primary hypertension or secondary hypertension. Primary hypertension accounts for approximately 90% of all cases of high blood pressure, and is idiopathic in nature. Secondary hypertension accounts for approximately the remaining 10% of all cases of high blood pressure and is normally caused by kidney disorders, adrenal tumors, drugs or toxemia in he final trimester of pregnancy.

Table 1. Categories for Blood Pressure Levels in Adults

(In mmHg, millimeters of mercury)

Category

Systolic

(Top number)

Diastolic

(Bottom number)

Normal

Less than 120

Less than 80

Prehypertension

120-139

80-89

High Blood Pressure

Systolic

Diastolic

Stage 1

140-159

90-99

Stage 2

160 or higher

100 or higher

Hypertension can have widespread effects on multiple organs within the body, including the brain, kidneys, and eyes. However, the effects of hypertension on these organs are secondary to the effects of hypertension on the cardiovascular system. That is, the changes that occur in the cardiovascular system due to hypertension lead to the deleterious effects observed in the brain, kidneys and eyes. Therefore, this paper will focus on the effects of hypertension on the cardiovascular system.

Hypertensive damage to the cardiovascular system occurs in either the myocardium (heart) or arterial system. In general, hypertension increases the risk of heart attacks, congestive heart failure, peripheral vascular disease, and stroke. Even moderately elevated blood pressure can be dangerous. The effects of high blood pressure on the arterial system will be examined first, followed by a discussion of the effects of high blood pressure on the myocardium.

Hypertension and the arterial system

High blood pressure accelerates hardening of the arteries and arterioles, leading to an increased incidence of atherosclerosis along with increased calcium deposits in the coronary arteries (Lu et al.). For reasons that are not completely clear, hypertension hastens hardening of the arteries, a process known as arteriosclerosis, or atherosclerosis. The terms are basically synonymous. Atherosclerosis refers to a buildup of plaque on the inside lining (intima), of the artery.

Although the underlying mechanisms leading to atherosclerosis resulting from high blood pressure are not clearly understood, one theory holds that the increased pressure of the blood flow damages the intima and makes it more susceptible to narrowing by deposits of plaque and cholesterol. More specifically, the endothelial lining of the artery is damaged. Because of the damage to the endothelium, fats, cholesterol, platelets, cellular waste products, calcium and other substances are deposited in the artery wall. The deposit of these substances may stimulate artery wall cells to produce other substances that result in further buildup of cells.

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These cells and surrounding material thicken the endothelium significantly. The artery's diameter shrinks and blood flow decreases, reducing the oxygen supply. The end result is a narrowing of the lumen of the artery, with a subsequent reduction of blood flow and a resulting aggravation of the pressure problem. Often a blood clot may form near this plaque and block the artery completely, which may stop blood flow altogether.

In the elderly population, atherosclerosis results from aging processes. With increasing age, arterial compliance (elasticity) decreases resulting in stiffer arterial walls. Thus, during systole (pumping of the blood from the heart into the arterial tree), the arteries do not expand to accommodate the volume of blood pumped causing increased peripheral resistance to blood flow. Here again the heart must exert additional force to pump the blood through the narrowed arteries. The resulting high blood pressure further injures the arterial walls and worsens the atherosclerosis.

Over time, the constant pressure of blood flowing through a weakened artery can cause a section of its wall to enlarge and form a bulge, called an aneurysm. An aneurysm can rupture and lead to death from significant internal bleeding. Aneurysms can form in any artery throughout your body, but they're most common in the aorta. The majority of aortic aneurysms occur in the abdominal aorta, or the descending thoracic aorta.

Thus atherosclerosis can lead disease states in multiple organ systems throughout the body. In coronary arteries the result can be angina or a heart attack. If atherosclerotic narrowing of the arteries occurs in the brain, stroke can result. In addition, narrowing of the arterial lumen increases the total peripheral resistance, which increases the afterload on the heart, resulting in an increased workload on the myocardium.

Hypertension and the heart

Ventricular hypertrophy and cardiomyopathy are common myocardial consequences of high blood pressure. In addition, valvular heart disease can result from high blood pressure. Hypertension forces the heart to pump harder in order to force the blood through narrowed arteries. As a result, the heart actually enlarges. It increases in thickness (hypertrophy) because of the additional stress and also stretches (cardiomyopathy) because of the larger volume of fluid it must accommodate. Cardiomyopathy is a disease of the heart muscle. The known causes of cardiomyopathy are many, and include coronary artery disease and valvular heart disease, both of which may result from hypertension. There are three major types of cardiomyopathy. 1. Dilated cardiomyopathy. This type involves enlargement of one or more of your heart's chambers. 2. Hypertrophic cardiomyopathy. This form involves thickening of your heart's muscle. 3. Restrictive cardiomyopathy. This type results in your heart muscle becoming more rigid. Resulting complications may result from each of these myopathies, including blood clots, heart arrhythmias, and cardiac arrest (Giles).

Blood clots are mostly associated with dilated or restrictive cardiomyopathy, which result from turbulent blood flow in the lower portion of heart chambers that eventually clot. Once these clots are expelled form the heart, and enter the blood circulatory system, they can obstruct the blood flow to vital organs, including the heart and brain. Clots that develop in the right atrium or right ventricle may travel to the lungs leading to a pulmonary infarction. Cardiac arrhythmias are mostly associated with dilated cardiomyopathy. The increased size of the myocardium may lead to interruptions in the electrical impulses that control the heart rhythm. In severe cases, arrhythmias may lead to cardiac arrest. Most notably ventricular fibrillation is one of the most dangerous arrhythmias. This arrhythmia can lead to ineffective pumping of blood to the myocardium itself resulting in cellular death of heart tissue, and eventual death.

When the heart stretches too far, the muscle tissue is damaged, and the heart can no longer pump efficiently. The damage is irreversible, and once symptoms are noticed, a great deal of damage may have….....

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