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The cardiovascular system is the vehicle and the pathways by which oxygen is delivered to the end-organ tissues. It consists of the heart, arteries, veins, and capillaries, which is where the gas exchange occurs at the end-organ tissues. The heart is the pump that pushes the blood through the blood vessels, specifically arteries, and eventually down to the capillary beds where the oxygen is offloaded into the tissues and the metabolic by-products are on-loaded to be transported through the various filter and excretion processes of the body.
Cardiac output is the amount of blood that is circulated through the body. Cardiac output (CO) is the product of stroke volume multiplied by the heart rate. This is much like the relationship between minute volume and respiratory rate in the respiratory system. Stroke volume has the greatest effect on oxygen delivery. Stroke volume (SV) is the amount of blood pumped out by the left ventricle in one contraction. It depends on the following three variables:
- Preload;
- Afterload, and
- Contractility.
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