Loudness Of The S3

1. Which chest piece and degree of stethoscope pressure best brings out the S3?

ANS: The bell, applied with light to moderate pressure so that the low frequencies will not be damped out.

2. What increases the loudness of the S3, inspiration or expiration?

ANS: Either. Expiration can make the S3 louder by squeezing blood out of the lungs into the left atrium and ventricle, and by bringing the stethoscope closer to the heart. Inspiration can make it louder by increasing sympathetic tone to the heart and via a sinus arrhythmia speeding up the heart rate and blood flow through the valve.

Note: Either inspiration or expiration can make the S3 louder by causing the apex beat to emerge between the ribs. In some patients the apex beat comes out between the ribs on inspiration, and in others it does so on expiration.

3. Because the proximity of the apex beat to the stethoscope appears to be a factor in intensifying the loudness of the S3, how can you bring the apex beat closer to the chest wall?

ANS: By turning the patient into the left lateral decubitus position.

In the left lateral decubitus position shown, the apex of the heart is brought as close to the stethoscope as possible. This is an absolute necessity for hearing a soft S3, because it is sensitive to proximity.

4. What proof is there that ventricular volume and flow control the audibility of the S3?

ANS: a. Conditions that increase the volume of flow make the S3 louder, i.e., exercise or mitral regurgitation. b. Conditions that decrease flow to the heart and decrease ventricular volume cause decreased audibility of the S3, e.g., standing up, venous tourniquets, or the water-loss effect of diuretics.

Note: One of the characteristics that is most confusing to the beginner when listening to a soft S3 is its intermittent audibility, i.e., it waxes and wanes in and out of one's hearing threshold. This probably occurs because its loudness is very sensitive to slight changes in proximity and volume caused by respiration.

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Blood Pressure Health

Your heart pumps blood throughout your body using a network of tubing called arteries and capillaries which return the blood back to your heart via your veins. Blood pressure is the force of the blood pushing against the walls of your arteries as your heart beats.Learn more...

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