Which statement regarding heart sounds is correct?
A. S1 and S2 sound equally loud over the entire cardiac area.
B. S1 and S2 sound fainter at the apex.
C. S1 and S2 sound fainter at the base.
D. S1 is loudest at the apex, and S2 is loudest at the base.
Correct Answer: D. S1 is loudest at the apex, and S2 is loudest at the base.
The S1 sound—the “lub” sound—is loudest at the apex of the heart. It sounds longer, lower, and louder there than the S2 sounds. The S2—the “dub” sound—is loudest at the base. It sounds shorter, sharper, higher, and louder there than S1. Heart sounds are created from blood flowing through the heart chambers as the cardiac valves open and close during the cardiac cycle. Vibrations of these structures from the blood flow create audible sounds — the more turbulent the blood flow, the more vibrations that get created.
Option A: The S1 heart sound is produced as the mitral and tricuspid valves close in systole. This structural and hemodynamic change creates vibrations that are audible at the chest wall. The mitral valve closing is the louder component of S1. It also occurs sooner because of the left ventricle contracts earlier in systole.
Option B: Changes in the intensity of S1 are more attributable to forces acting on the mitral valve. Such causes include a change in left ventricular contractility, mitral structure, or the PR interval. However, under normal resting conditions, the mitral and tricuspid sounds occur close enough together not to be discernible. The most common reasons for a split S1 are things that delay right ventricular contraction, like a right bundle branch block.
Option C: The S2 heart sound is produced with the closing of the aortic and pulmonic valves in diastole. The aortic valve closes sooner than the pulmonic valve, and it is the louder component of S2; this occurs because the pressures in the aorta are higher than the pulmonary artery.