1. Draw a simultaneous normal left ventricular (LV) and left atrial (LA) pressure curve. At what point on the curve does the mitral valve open? ANS: The mitral valve opens when LV pressure drops below LA pressure. The normal peak LA pressure is about 10 mmHg. Therefore, when LV pressure drops to about 9 mmHg, the mitral valve should open.
Note: LV early expansion has an active suction effect related to the degree of cardiac function or inotropism.
Note that the left atrial V-wave rise is abruptly interrupted by LV pressure falling below left atrial pressure and opening the mitral valve.
2. Draw an LV, LA, and simultaneous aortic pressure curve. Which left-sided event produces a sound just before the mitral valve opens? (See p. 156)
ANS: Closure of the aortic valve produces the A2 about 100 ms (0.10 s) before the mitral valve opens. This 100-ms interval takes about as long as it takes to say "pa-pa" as quickly as possible.
3. What is usually necessary before the opening of the mitral valve becomes audible?
ANS: At least some mitral stenosis (MS), which is due primarily to fibrous thickening and often to calcification of the margins of the mitral leaf lets, especially the large anterior leaflet. The mitral valve belly may act like a sail that billows downward into a dome in diastole as the LV attempts to "suck" LA blood into the LV cavity. This sudden diastolic doming caused the anterior leaflet to bulge downward with a snap.
Note: Excessive flow through the mitral valve in early diastole as in VSD, MR, and thyrotoxicosis can also cause an opening snap.
4. Why is the audible opening of the mitral valve called an opening snap (OS)?
ANS: Because most of the time the sound is a short, high-frequency, crisp crack, click, or snap.
valve incisura and occurs shortly before the LV pressure drops below left atrial pressure, to open the mitral valve. The interval between the aortic valve closure (A2) and the opening of the mitral valve is the isovolumic relaxation time.
5. Why must it be the anterior leaflet that is responsible for the OS of MS?
ANS: The anterior leaflet is three times broader than the posterior leaflet.
6. What do we call the interval between the closing of the aortic valve and the opening of the mitral valve?
ANS: The isovolumic relaxation period.
7. What is the auscultatory term for the isovolumic relaxation interval between the aortic closure sound and the OS sound?
ANS: The A2-OS interval, or simply the 2-OS interval.
The A2 is simultaneous with the aortic
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