6.3 Signals of the Cardiovascular System

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SJM, AKE

SJM, AKE

Fig. 6.43: Closing sound of a normal two-leaflet prosthesis (left) and with thrombus adhesion (right):

The impact noise of one of the two leaflets is clearly attenuated by the thrombus in the right image.

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Frequency f / kHz

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intact

thrombosis

Fig. 6.44: Spectrum of a normal impact sound of a mechanical heart valve (blue) and in the presence

of thrombus (red).

pact sound. Since the two valve leaflets are never exactly perpendicular in the blood

stream, the two valve leaflets close with a short time lag of up to 12 ms, which is why

two impact noises can be found in the sound image. Shortly before the impact, there is

a weak hinge noise, which is caused by the rotation of the flap leaflets in their housing

suspension.

If a thrombus obstructs the hard impact of a valve leaflet, as in Figure 6.41, the

amplitude of the closing sound is strongly damped (Figure 6.43). A thrombus also al-

ters the spectrum of the valve closure sound (cf. Figure 6.44). In particular, the high

frequency components above about 11 kHz largely disappear. In the spectrum, the es-

sential difference to conventional phonocardiography becomes clear, because there

the bandwidth reaches only up to a maximum of 1.2 kHz. Noise analysis in the time