Cardiac output-1

Cardiac output (COP) is the quantity of blood pumped into the aorta each minute by the heart, or it is the output of the heart per unit of time (stroke volume × heart rate), which equals to the quantity of blood that flows through the circulation. Cardiac output is one of the most important factors to consider in relation to the circulation because it is the sum of the blood flows to all the tissues of the body.
As mentioned previously, the amount of blood pumped out of the heart per beat, the stroke volume, is about 70 ml from each ventricle in
a resting man of average size in the supine position; so COP averages about 5 L/min (70 ml × 72 BPM). In women, the value of COP averages about 4.9 L/min.
Venous return is the quantity of blood flowing from the veins into the right atrium each minute. The venous return and COP must equal each other.
When one states that cardiac output is controlled by venous return, this means that it is not the heart itself that is normally the primary controller of cardiac output. Instead, it is the various factors of the peripheral circulation that affect flow of blood into the heart from the veins, called venous return, that are the primary controllers.
Cardiac output varies widely with the level of activity of the body. Factors that have direct effect on cardiac output are (1) the basic level of body metabolism, (2) exercise, (3) age and (4) the size of the body. The effects of various conditions on cardiac output are summarized in table (1).
Cardiac index
Experiments have shown that the cardiac output increases approximately in proportion to the surface area of the body. Therefore, cardiac output is frequently stated in terms of the cardiac index, which is the cardiac output per square meter of body surface area. The average human being who weighs 70 kilograms has a body surface area of about 1.7 square meters, which means that the normal average cardiac index for adults is about 3 L/min/m2 of body surface area.