The cardiovascular system comprises the heart, veins, arteries, and capillaries, which carry blood back and forth from the heart to the lungs (pulmonary circulation) and from the heart to the rest of the body (systemic circulation). The heart works on electrical impulses and produces them constantly, unless stress, fear, or danger is involved, in which case the impulses will increase dramatically. The body's largest artery is the aorta and the largest vein is the vena cava. Veins are thinner than arteries, which resemble rubber bands in that they expand more easily (depending on the amount of blood passing through them). Smaller blood vessels, or capillaries, channel oxygen and blood to tissues. The process is a cycle in which the capillaries deliver oxygen-rich blood to the body and pick up oxygen-poor blood, which is then taken into the veins and finally to the heart to be "rejuvenated" or cleansed.
Cardiovascular disease (CVD), and the resulting complications, is the main cause of death for both males and females in the United States and other technologically advanced countries of the world. It usually is in the top five causes of death in lesser-developed countries. Diseases of the cardiovascular system include those that compromise the pumping ability of the heart, cause failure of the valves, or result in narrowing or hardening of the arteries. In addition, toxins and infectious agents may damage the heart and blood vessels. Injury or failure of the cardiovascular system, especially the heart, also will affect the peripheral tissues that depend on the delivery of nutrients and the removal of wastes through the blood vascular system. CVD is a family of diseases that includes hypertension, atherosclerosis, coronary heart disease, and stroke.
Hypertension (High Blood Pressure)
Blood pressure is a measure of the force of blood against the walls of arteries. It is recorded as two numbers: the systolic pressure over the diastolic pressure. Systolic pressure is the pressure as the heart beats, while diastolic pressure measures the pressure when the heart relaxes between beats.
Blood pressure is normally measured at the brachial artery with a sphygmomanometer (pressure cuff) in millimeters of mercury (mm Hg) and given as systolic over diastolic pressure. Normal blood pressure is less than 120 mm Hg systolic and less than 80 mm Hg diastolic—usually expressed as "120 over 80." However, normal for an individual varies with the height, weight, fitness level, age, and health of a person. Blood pressure is normally maintained within narrow limits, but it can drop during sleep or increase during exercise. Hypertension (HTN), or high blood pressure, occurs when the force of blood passing through blood vessels is above normal. The increase in pressure forces the blood to hit the blood vessel walls. HTN is called "the silent killer" because many people do not know they have the condition. Consistently high blood pressure increases the risk for a stroke or a heart attack. It may be caused by poor diet, obesity, smoking, stress , and inactivity. The Dietary Approach to Stop Hypertension (DASH) project recommends a diet that is low in sodium and high in fruits, vegetables, and low-fat dairy products. Other approaches to controlling HTN include weight loss, smoking cessation, increased physical activity, and stress management.
Atherosclerosis, or hardening of the arteries, is the cause of more than half of all mortality in developed countries and the leading cause of death in the United States. When the coronary arteries are involved, it results in coronary artery disease (CAD). The hardening of the arteries is due to the build up of fatty deposits called plaque, and mineral deposits. As a result, the supply of blood to the heart muscle (myocardium) is reduced and can lead to ischema (deficiency of blood) to the heart, causing chest pain or a myocardial infarction (heart attack). The hardening of the arteries causes an increase in resistance to blood flow, and therefore an increase in blood pressure. Any vessel in the body may be affected by atherosclerosis; however, the aorta and the coronary, carotid, and iliac arteries are most frequently affected. The process begins early in life. Therefore, physicians should obtain risk-factor profiles and a family history for children.
Coronary Artery Disease
Coronary artery disease (CAD) refers to any of the conditions that affect the coronary arteries and reduces blood flow and nutrients to the heart. It is the leading cause of death worldwide for both men and women. Atherosclerosis is the primary cause of CAD. Controlled risk factors associated with CAD include hypertension, cigarette smoking, elevated blood lipids (e.g., cholesterol, triglyceride), a high-fat diet (especially saturated fats and trans-fatty acids), physical inactivity, obesity, diabetes, and stress. Lifestyle changes can assist in prevention of CAD. Uncontrolled risk factors include a family history of CAD, gender (higher in males), and increasing age.
Stroke, or a cerebrovascular accident (CVA), occurs when the brain does not receive sufficient oxygen-rich blood through blood vessels or when a blood vessel bursts. A stroke may result from blockage of the blood vessels due to a blood clot (ischemic) or from ruptures of the blood vessels (hemorrhagic bursts). Uncontrolled hypertension is a major risk factor for strokes.
The symptoms of CVD develop over many years and often do not manifest themselves until old age. Autopsies of young servicemen indicate significant accumulation of plaque and hardening of the arteries (atherosclerosis). Thus, primary prevention for CVD must begin in early childhood. Preventing premature CVD (before age 60) is crucial. Heart attacks between the ages of forty and sixty are primarily due to lifestyle factors.
Smoking, high blood cholesterol, high blood pressure, and lack of physical activity are the most serious risk factors for CVD and heart attack. Controlling one of these risk factors can help control others. For example, regular exercise can help control cholesterol, blood pressure, weight, and stress levels. Smoking is the most preventable risk factor. Smokers have twice the risk for heart attack that nonsmokers have. Tobacco use alters the blood chemistry and increases blood clotting. Nearly one-fifth of all deaths are due to tobacco use, and a smoker lives an average of seven to eight fewer years than a nonsmoker.
The worldwide increase in obesity and type 2 diabetes (in both children and adults) point to a high-fat, high-calorie diet and a sedentary lifestyle. Poverty increases the risk for poor dietary habits and poor access to healthful foods. Many of the world's urban poor have more access to highly processed foods, convenience foods, and fast foods than to fresh fruits and vegetables. But even in the most wealthy and technologically advanced countries, the affluent are choosing to eat more fast foods and processed foods that are high in fat, cholesterol, and sodium. For optimal health, health professionals recommend:
- Maintaining a healthy weight, with a body mass index (BMI) of 18.5–24.9.
- Limiting dietary fat to 30 percent or less of total calories—10 percent saturated fat, 10 percent polyunsaturated fat, and 10 percent monounsaturated fats. Consumers should be aware that ounce for ounce, all sources of fat have approximately the same amounts of calories.
- Limiting saturated fats to 10 percent of calories. Saturated fats come primarily from animal sources (e.g., high-fat dairy and meats), but also are found in coconut and palm oil.
- Limiting polyunsaturated fats to 10 percent of calories. Polyunsaturated fats come primarily from vegetable oils (e.g., corn oil, safflower oil).
- Limiting monounsaturated fats to 10 percent of calories. Monounsaturated fats may have a protective role in heart disease. Excellent sources of monounsaturated fats include olive oils, nuts, avocado, and canola oil.
- Increasing intake of omega-3 fatty acids. Two to four grams daily of omega-3 fatty acids may lower risk for CVD by reducing blood clotting, making platelets less sticky, and lowering triglycerides. Patients should inform their physician if they are using omega-3 supplements, since they may increase the risk of bleeding. Excellent sources of
- omega-3 include fatty fish (such as salmon and sardines), fish oils, and flax seed.
- Limiting sodium intake to 2,400 milligrams per day.
- Increasing potassium intake to at least 3,500 milligrams per day.
- Eating at least five servings a day of fruits and vegetables.
- Eating a plant-based diet consisting primarily of whole grains, fruits, and vegetables is also recommended.
- Eating at least 25 grams of fiber daily.
- Eating 25 grams of soy protein daily.
In addition to diet modification, research is increasingly focused on the role of physical activity in preventing CVD. People who are not physically active have twice the risk of heart disease as those who are active. More than half of U.S. adults do not achieve recommended levels of physical activity. Studies indicate a correlation between the amount of television viewing, playing videos, and other sedentary activities and increased rates of childhood obesity. In general, the more sedentary the activities, the more high-fat and sugary foods are consumed. At least thirty minutes of moderate physical activity, five times a week, is recommended. Moderate physical activity slows down the narrowing of the blood vessels, due to contraction of the smooth muscles in the vessel walls. It also increases coronary blood flow, strengthens the heart muscles, and reduces stress.
Worldwide, HTN is linked to about 50 percent of CVDs and approximately 75 million "lost healthy life years" each year. Thus, controlling HTN may greatly reduce the risk of disability and death from CVD. Secondary prevention involves treating the signs and symptoms of CVD. These strategies include management of hypertension, cholesterol, and other blood lipids. Dietary and lifestyle modification are tried first. However, medication may also be prescribed, depending on other clinical factors. Compliance with a medication regimen is extremely important, as is the monitoring of blood pressure and blood lipids. Recommended total serum cholesterol should not exceed 200 milligrams per deciliter (mg/dl); low-density lipoproteins (LDLs or "bad cholesterol") should not exceed 100 mg/dl, and high-density lipoproteins (HDLs or "good cholesterol") should not be lower than 40 mg/dl.
Surgical intervention may restore cardiovascular function. Vessels may be opened by angioplasty or repaired by the use of grafts or stents, heart valves can be repaired or replaced with artificial valves, and pacemakers or drugs may aid heart function. A heart transplant may be an individual's last resort. Many large-scale international studies have focused on preventing cardiovascular disease through smoking cessation, healthful eating, physical activity, hypertension and cholesterol control, health education, and media campaigns. These include the Stanford Three City, the Stanford Five City Projects, the Framingham Heart Study, the Bogalusa Heart Study, the Multiple Risk Factor Intervention Trial (MRFIT), Active Australia, the Whickham Study (based on the Framingham model), and the North Karelia Study (Finland). Small, gradual changes in diet and exercise and smoking cessation are the best way to produce long-term effects.
Bauman, A.; Bellow, B.; Owen, N.; and Vita, P. (2001). "Impact of an Australian Mass Media Campaign Targeting Physical Activity in 1998." American Journal of Preventive Medicine 21:41–47.
Bijnen, F. C.; Caspersen, C. J.; Feskens, E. J.; Saris, W. H.; Mosterd, W. L.; and Kromhout, D. (1998). "Physical Activity and 10-Year Mortality from Cardiovascular Diseases and All Causes." Archives of Internal Medicine 158(14):1499–1505.
Elward, K., and Larson, E. K. (1992). "Benefits of Exercise for Older Adults: A Review of Existing Evidence and Current Recommendations for the General Population." Journal of Clinical Gerontology Medicine 8(1):35–50.
Fortman, S. P., and Varady, A. N. (2000). "Effects of a Community-Wide Health Education Program on Cardiovascular Disease Morbidity and Mortality: The Stanford Five-City Project." American Journal of Epidemiology 152:316–323.
Fox, S. I. (1999). Human Physiology, 6th edition. Boston: McGraw-Hill.
Insel, P. M., and Roth, W. T. (2004). "Cardiovascular Disease and Cancer." In Core Concepts in Health, 9th (brief) edition. Boston: McGraw-Hill.
American Heart Association/American Stroke Association. "Heart Disease and Stroke Statistics—2003 Update." Available from <http://www.americanheart.org>
American Heart Association. "Common Cardiovascular Diseases." Available from <http://americanheart.org/stroke>
Bogalusa Heart Study (n.d.). Tulane Center for Cardiovascular Health. Available from <http://www.som.tulane.edu/cardiohealth>
HeartCenterOnline. "Coronary Artery." Available from <http://www.heartcenteronline.com/myheartdr>
National Heart, Lung, and Blood Institute. "Framingham Heart Study: 50 Years of Research Success." Available from <http://www.nhlbi.nih.gov>
National Institutes of Health, National Cancer Institute. "Action Guide for Healthy Eating." Available from <http://www.5aday.nci.nih.gov/actionguide>
National Public Health Partnership of Australia. "Developing an Active Australia: A Framework for Action for Physical Activity and Health." Available from <http://www.health.gov.au/pubhlth>
World Health Organization. "Cardiovascular Death and Disability Can Be Reduced More than 50 Percent." Available from <http://www.who.int/mediacentre>