1. What is the difference in quality between an S4 and the first major component of a split S1, i.e., the M1?
ANS: When the S4 is loud, it is difficult to tell the difference in quality between an S4 and an M1, but when soft, the S4 has fewer high frequencies, so that it is often inaudible when the diaphragm is pressed hard against the chest. The M1 is usually heard almost as well with the diaphragm as with the bell, regardless of whether it is loud or soft.
The use of a diaphragm will eliminate most soft S4s and may bring out the narrow, sharp, clicking physiological split of Sj.
2. How can the site of auscultation tell you whether you are listening to an S4-Sj rather than to a split Mj-Aj or Ml-Tl?
ANS: The S4 is very sensitive to proximity and tends to disappear anywhere away from the apex beat. Therefore, a split Sj that sounds the same at the left sternal border as at the apex has an Mj as the first component.
3. How can postural volume changes differentiate an S4 from an Mj-Aj?
ANS: Because the S4 is very sensitive to blood volume changes, standing will generally make it disappear. The Mj-Aj may even become more apparent on standing because the Mj-Aj interval represents isovolumic contraction time, which can be prolonged by standing, and wide splits are more obvious to the ear.
Note: A general principle to help you distinguish an S4 from an Mj is that it is easy to get rid of an S4. If the first component of what sounds like a split Sj disappears on decreasing blood volumes, on increasing stethoscope pressure, or by moving away from the apex, you are dealing with an S4. If the S4 is so loud that none of the above maneuvers diminish it, it will usually be palpable as an atrial hump or A wave on the apex beat's pulse contour with the patient in the left lateral decubitus position.
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