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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Who was awarded the first Nobel Prize for physics in 1901, for his experimental work with radiation?
A) C. E. Kells B) O. Walkhoff C) W. D. Coolidge D) W. C. Roentgen