6.3 Signals of the Cardiovascular System

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time t / s

Fig. 6.37: Phonocardiogram on a healthy heart with 20 s duration (top): First and second heartbeats

alternate in a regular sequence, with the interval between first and second heartbeats being shorter

than between second and first. Section of phonocardiogram showing three heartbeats (bottom).

pumping capacity of the heart, which in a healthy heart is accompanied by an in-

crease in the strength and frequency of contractions. The second heart sound is

produced by the synchronous closing of the aortic and pulmonary valves and marks

the end of blood ejection. The amplitude of the two heart sounds varies with the re-

spective measurement position, which is indicated by the number of the intercostal

space and the lateral distance to the sternum (breastbone) according to convention.

Thus, measurement position 2R2 denotes a point in the second intercostal space, right

side, 2 cm from the sternum. At this position, the aortic valve can be easily heard. 4L4

means accordingly: fourth intercostal space, left side, 4 cm from the sternum. This

corresponds to a point centrally located over the heart. Other common measurement

positions are 2L2 and apex (apex of the heart, in the region of the left costal arch).

Both the time course and the spectral composition of the heart sounds contain dia-