Physiology And Nomenclature For The S2

1.What produces the normal second heart sound (S2)?

ANS: Events associated with closure of the aortic and pulmonary valves.

Note: Valve "closure" itself probably produces no noise. Echocardiography shows that the sounds occur slightly after the coaptation of the leaflets. Shortly after apposition the sealed cusps are made tense and then vibrate (stretch and recoil) due to the rapid force of aortic or pulmonary artery recoil [1].

2. Which valve normally closes first, the aortic or the pulmonary valve?

ANS: The aortic valve. (It is crucial to remember this.) The sequence is A, P (i.e., aortic and pulmonary), as in Atlantic and Pacific. The A comes first, as in the alphabet. We shall call the aortic component of the second sound A2 and the pulmonary component P2.

3. What is the old meaning of A2 and P2 (to which we shall not refer in this book)?

ANS: A2 used to mean the total S2 in the traditional "aortic area" (second right interspace). P2 used to mean the total S2 in the traditional "pulmonary area" (second left interspace). We now use A2 to mean only the aortic component of the S2, and P2 to mean the pulmonary component of the S2.

A2 is the aortic valve closure component of the S2. P2 is the pulmonary valve closure component of the S2. Note that the S2 occurs near the end of the T wave of the ECG; i.e., the T wave is a systolic event.

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Your heart pumps blood throughout your body using a network of tubing called arteries and capillaries which return the blood back to your heart via your veins. Blood pressure is the force of the blood pushing against the walls of your arteries as your heart beats.Learn more...

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