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Aortic Pressure Curve
When the left ventricle contracts, the ventricular pres-sure increases rapidly until the aortic valve opens. Then, after the valve opens, the pressure in the ventricle rises much less rapidly, as shown in Figure 9–5, because blood immediately flows out of the ventricle into the aorta and then into the systemic distribution arteries.
The entry of blood into the arteries causes the walls of these arteries to stretch and the pressure to increase to about 120 mm Hg.
Next, at the end of systole, after the left ventricle stops ejecting blood and the aortic valve closes, the elastic walls of the arteries maintain a high pressure in the arteries, even during diastole.
A so-called incisura occurs in the aortic pressure curve when the aortic valve closes. This is caused by a short period of backward flow of blood immediately before closure of the valve, followed by sudden cessa-tion of the backflow.
After the aortic valve has closed, the pressure in the aorta decreases slowly throughout diastole because the blood stored in the distended elastic arteries flows continually through the peripheral vessels back to the veins. Before the ventricle contracts again, the aortic pressure usually has fallen to about 80 mm Hg (dias-tolic pressure), which is two thirds the maximal pres-sure of 120 mm Hg (systolic pressure) that occurs in the aorta during ventricular contraction.
The pressure curves in the right ventricle and pul-monary artery are similar to those in the aorta, exceptthat the pressures are only about one sixth as great.
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