The relative intensity of these sounds may also be helpful. S1 is usually louder than S2 at the apex; more reliably, S2 is usually louder than S1 at the base.
Even experienced clinicians are sometimes uncertain about the timing of what they hear, especially when they encounter extra heart sounds and murmurs. "Inching" can then be helpful. Return to a place on the chest—most often the base—where it is easy to identify S1 and S2. Get their rhythm clearly in mind. Then inch your stethoscope down the chest in steps until you hear the new sound.
Auscultation alone, however, can be misleading. The intensities of S1 and S2, For example, S1 is decreased in for example, may be abnormal. At rapid heart rates, moreover, diastole first-degree heart block, and S2 is shortens, and at about a rate of 120 the durations of systole and diastole be- decreased in aortic stenosis. come indistinguishable. Use palpation of either the carotid pulse or the apical impulse to guide the timing of your observations. Both occur in early systole, right after the first heart sound.
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