Blood Pressure And Cardiac Performance

Resistance develops as the blood travels through the circulatory system. This resistance is known as blood pressure. The average systemic arterial pressure

(blood pressure) is 120/80 mmHg. The higher the resistance, the higher the blood pressure.

The total volume of blood expelled by the heart in a minute is referred to as cardiac output. The average cardiac output is 4 to 8 L/min. The amount of blood ejected from the left ventricle during each heartbeat is called the stroke volume. The average stroke volume is 70 mL/beat.

As blood flows into the ventricles the ventricles fill and stretch. The force in which blood flows into the ventricle is called preload. The force used to contract the ventricle is called the heart's contractility. The resistance to blood ejected by the ventricle is called the afterload. Afterload is the opposing pressure in the aorta and systemic circulation to the contraction of the ventricle.

Drugs can be used to ease the workload of the heart by increasing or decreasing the preload and afterload resulting in adjusting the stroke volume and cardiac output. Vasodilators decrease the preload and afterload decreasing arterial pressure and cardiac output. Vasopressors increase the preload and afterload increasing the arterial pressure and cardiac output.

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