Cardiac output
Say it: KAR-dee-ak OWT-put
Cardiac output is the volume of blood each ventricle of the heart pumps in one minute, equal to heart rate multiplied by stroke volume.
Definition
What is cardiac output?
Cardiac output is the amount of blood pumped by each ventricle of the heart in one minute, usually given in liters per minute. It equals heart rate, the number of beats per minute, multiplied by stroke volume, the volume ejected with each beat. Stroke volume is the difference between how much blood the ventricle holds at the end of filling and how much is left after it contracts. A resting adult with a heart rate of about 75 beats per minute and a stroke volume of about 70 milliliters has a cardiac output of roughly 5 liters per minute.
The body changes cardiac output by adjusting both factors. Heart rate is set by the autonomic nervous system: sympathetic nerves and epinephrine speed it up, while the vagus nerve slows it. Stroke volume depends on preload, the stretch of the ventricle before it contracts, since a more stretched ventricle beats more forcefully (the Frank-Starling mechanism); on contractility, the strength of each contraction; and on afterload, the resistance the ventricle must pump against. During hard exercise, a healthy young adult's cardiac output can rise four- to fivefold.
Cardiac output, together with the resistance of the blood vessels, sets blood pressure, and a low cardiac output is a feature of heart failure and some forms of shock.
Word parts
Where does the term “cardiac output” come from?
- cardi-
- heartGreek kardia
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- HeartThe heart is the hollow, muscular organ in the chest whose four chambers pump blood through the lungs and then around the rest of the body.
- Blood pressureBlood pressure is the force that circulating blood exerts on the walls of the arteries, recorded as systolic over diastolic pressure in mm Hg.
- Autonomic nervous systemThe autonomic nervous system is the division of the nervous system that runs involuntary functions such as heart rate, digestion and gland secretion.
- ShockShock is a life-threatening state in which the circulation fails to bring tissues the oxygen and nutrients their cells need.
- HomeostasisHomeostasis is the body's ability to keep internal conditions, such as temperature, blood glucose and pH, steady while conditions around it change.
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