Although the figures are foreboding, substantial progress has occurred during the last 40 years. The death rate for cardiovascular diseases has declined by approximately 51 % since 1950.Although an impressive accomplishment, it is somewhat diminished by the fact that cardiovascular diseases remain by far the leading cause of death in the united states. Two types in particular, coronary heart disease and strokes, are the first and third leading causes of death. More than 50% of the premature deaths in our society are attributed to lifestyle habits. Authorities therefore agree that preventive measures emphasizing risk reduction strategies that involve lifestyle changes will produce the most dramatic benefits in the fight against heart disease. Also contributing to the downward trend in the death rate from cardiovascular disease are more sophisticated diagnostics, improved treatment, and prompt recognition of impending heart attacks. Circulation is better understood if you are familiar with the basic anatomy and function of the heart. The heart consists of cardiac muscle and weighs between 8 and 10 ounces. It is about the size of a fist and lies in the center of the chest. The heart is divided into two halves, or pumps, by a wall and each half is subdivided into an upper chamber (the atrium) and a lower chamber (the ventricle). The right heart, or pulmonary pump, receives deoxygenated blood from the tissues and transports it to the lungs so that carbon dioxide can be exchanged for a fresh supply of oxygen. From the lungs, the oxygen rich blood is sent to the left heart, or systemic pump, so that the oxygenated blood can be transported to all the tissues of the body. Both pumps work simultaneously. The systemic pump carries the heavier workload of the two and thus has a more muscular ventricular wall.

The arteries carry oxygenated blood away from the heart while the veins carry deoxygenated blood to the heart. There are two exceptions.

• First, the pulmonary artery carries deoxygenated blood from the right heart to the lungs to exchange carbon dioxide for a fresh supply of oxygen.
• Second, the pulmonary vein carries fully oxygenated blood from the lungs to the left heart for distribution throughout the body.

The primary function of circulation is to provide a constant supply of blood and nutrients to the cells while removing their waste products. Under ordinary circumstances, the interruption of blood flow for as little as 4 to 6 minutes can result in irreversible brain damage due to oxygen deprivation.

The average heart beats 70 to 80 times per minute at rest. Endurance athletes often have resting heart rates in the 30 and 40 beat range, whereas some over weight and sedentary smokers have resting heart rates in the 90s. The low heart rates of endurance athletes reflect physiological adaptations to training that represent normal values for this group. The framing ham heart disease study showed that a rapid resting heart rate increased the risk of death from heart attack. Mortality increased progressively with higher resting heart rates, especially among men.

The heart is auto regulatory, that is, it contains an intrinsic conduction system that is fully capable of establishing and maintaining the heart beat without outside neural stimulation. The heart’s beating rate and rhythm is established by the sinoatrial node (SA node, or pacemaker). The atria contract, forcing blood into the ventricles as the electrical impulse travels from the SA node to the atrioventricular node (AV node), which is located between the right atrium and right ventricle. The electrical impulse pauses for one tenth of a second at the A V node to allow the ventricles to fill with blood and then resumes down the system and spreads throughout the ventricular walls. The ventricles contract during this time, ejecting blood from these chambers.

Blood that enters the chambers of the heart does not directly nourish the heart muscle because there are no direct circulatory routes from the heart’s chambers into its muscular walls. Instead, blood must first be ejected from the heart to the aorta (the largest artery in the body) then to the coronary arteries that supply the myocardium (heart muscle) with blood and oxygen. The majority of blood is received by the myocardium during diastole (when the heart is between beats) because the blood vessels dilate during this time, increasing their capacity to accept and deliver blood. The left coronary artery supplies a major portion of the myocardium with blood, whereas the right coronary artery serves less of it. Both vessels divide and subdivide downstream and eventually culminate in a dense network of capillaries (the smallest blood vessels in the body). Blood supply to the myocardium is so important that every muscle fiber is supplied by at least one capillary. The coronary veins return deoxygenated blood to the right atrium so that it can enter pulmonary circulation. The veins bring deoxygenated blood from all tissues back to the right atrium.

Blood plasma is a clear, yellowish fluid that carries approximately 100 chemicals. Plasma represents 55% of the blood contents. The remaining 45% consists of blood solids the erythrocytes (red blood cells), the leukocytes (white blood cells), and the blood platelets. The red blood cells are the most abundant of the blood solids, composing about 99% of the total. Attached to hemoglobin, an iron containing protein, the red blood cells carry oxygen and carbon dioxide to and from the tissues of the body. The white blood cells are an important part of the body’s defense system against invading micro organisms and other foreign substances. The blood platelets are involved in the complex processes that lead to the formation of clots for repairing damaged blood vessels.