The dicrotic notch recorded in the aorta immediately follows what mechanical event of the car-diac cycle?
a. Closure of the aortic valve
b. Closure of the atrioventricular valves
c. Isovolume contraction
d. Opening of the aortic valve
ANS: A
Rather than immediately dropping off, aortic and pulmonary pressures rise again after the semi-lunar valves close. Note the feature termed the dicrotic notch, which is caused by the elastic re-coil of the arteries. This recoil provides the extra "push" that helps maintain the head of pressure created by the ventricles.
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