Relative Loudness Pitch and Duration of the S1 and S2

1. When is it difficult to distinguish an S1 from S2 by stethoscope alone?

ANS: When systole almost equals diastole in duration. This is called a "ticktack" rhythm (like the ticking of a clock) or embryocardia (like the fetal heart sounds).

2. What causes ticktack rhythm?

ANS: Anything that shortens diastole more than it does systole, as in tachycardia. As the heart rate increases, both systole and diastole are shortened, but diastole is shortened relatively more than systole.

Note: a. The heart rate in the first year of life may be as high as 190, and in the second year up to 160. In the fourth year it can normally be 130. Even at the time of puberty it may be as high as 100 normally. This in the adult would be called a tachycardia. b. Severe AR may also produce a ticktack rhythm because it can prolong systole in relation to diastole.

3. How may the relative loudness of the S1 and S2 help to distinguish one from the other?

ANS: The S2 is normally louder than the S1 at the second right or left interspace (i.e., at the base of the heart), possibly because this is where the aortic and pulmonary valve structures are closest to the chest wall. At the apex the S1 is usually louder than the S2.

Note: The apex area is not as reliable as the base for distinguishing an S1 from an S2 by loudness, because with a long P-R interval or with myocardial damage, the S1 may be very soft.

4. How can you tell at the bedside which heart sound is the S2 when relative loud-ness is of no help?

ANS: a. The S2 is higher in pitch as well as sharper and shorter than the S, because it is usually single on expiration. The S1 is relatively rough because of its three components and its dominant low and medium frequencies. This is implied by the term "lub-dup," which is often used to mimic the sound of the S1-S2. b. Palpate the carotid while listening with the stethoscope. The S1 will be heard just before the carotid impulse is felt. The carotid has the same relationship to the S1 as an early systolic murmur (i.e., if we use the letter C to represent the carotid impulse, then the rhythm goes "1-C-2, 1-C-2"). This is due to the slight delay between the beginning of ventricular contraction, which produces the Sj, and the arrival of the carotid impulse in the neck.

The tap of the carotid pulse on your fingers is felt after and not with the first heart sound.

c. Place the stethoscope or a finger over the apex beat, and note the outward impulse that occurs during systole. It should bulge outward with or just after the Sj. The stethoscope itself will rise during systole, and this will tell you which sound is the Sj. The Sj will appear to "produce" the rise in apical impulse.

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