Q:

What is cardiac preload?

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Quick Answer

Cardiac preload refers to pressure in the left or right ventricles immediately after end-diastole or before systole, notes the Columbia Center for New Media Teaching and Learning. Cardiac preload stretches heart muscles, which are also known as cardiomyocytes, to their fullest extent depending on physiological demands.

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Full Answer

Cardiac preload is one component of the Frank-Starling relationship, notes CCNMTL. According to the Frank-Starling relationship, the volume of blood in the right or left ventricles determines heart pressure. In turn, heart pressure determines the extent to which cardiomyocytes stretch. The greater the muscle stretch, the more powerful the contraction during systole and the bigger the volume of blood pumped to the rest of the body.

Cardiac preload is just one of four factors that determine cardiac output. Cardiac output refers to the volume of blood pumped out from the heart every minute. The second factor is heart rate, measured in beats per minute. Faster heart rates typically lead to greater cardiac output. The third factor is contractility, which refers to the strength of the ventricles. Greater contractility, which can be stimulated using drugs such as epinephrine, generally leads to higher cardiac output. The final factor that determines cardiac output is afterload. Afterload is the force that resists blood ejection from ventricles. The heart typically pumps out 67 percent of the blood it receives from the body, notes CCNMTL. Increased afterload usually leads to lower cardiac output and decreased afterload to higher cardiac output.

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