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6. When the bell of the stethoscope is applied to the skin, the enclosed skin
forms a diaphragm. With increased pressure, the skin diaphragm is made
more taut and its natural period of oscillation increases. This improves the
response to higher skin diaphragm. As a result, the lower-frequency
components of the heart sounds are attenuated, whereas the higher
frequencies are still well heard.
This important maneuver of being able to diminish the intensity of low-pitched
sounds, by pressure on the bell has several implications and applications:
1. To hear faint, low-pitched sounds, the examiner must apply the bell lightly to
the chest wall.
2. By noting what happens to a sound or murmur when the bell is first applied
lightly, and then with pressure, the examiner can judge, to a certain degree,
the pitch of a sound or murmur.
3. The high-pitched systolic murmur of mitral regurgitation is less likely to be
affected by pressure than medium-pitched, innocent systolic murmurs.
4. With pressure, the faint, high-pitched, systolic murmur of mitral regurgitation
is less affected than the first heart sound, and the masking effect of the first
heart sound is thus diminished. The same is true of the high-pitched, early
diastolic murmur of aortic regurgitation and accentuated second heart sound.
5. In some very noisy hearts with both systolic and diastolic murmurs because
of the amount of sound in systole, it is difficult to be sure if there is a low-
pitched diastolic murmur. With pressure, the total sound is diminished and
the low-pitched murmur in diastole may disappear. By holding the bell
alternately lightly and heavily and by concentrating on diastole, the examiner
can detect the diastolic rumble
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