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6 Applications and Methods in Biosignal Processing

Fig. 6.38: Spectrum of the phonocardiogram from Figure 6.37.

gnostic information. Examples of heart sounds conspicuous in the time domain are

the systolic or a third heart sound in the diastolic phase. A systolic murmur is a noise

between the first and second heart sounds and may be a indication of aortic or pul-

monary valve regurgitation. A third heart sound may be associated with ventricular

dilatation due to chronic heart failure. A complete review of heart murmurs and their

origin can be found in [31]. The spectral composition of heart murmurs (Figure 6.38)

provides additional information. For example, if the systolic murmur has strong high-

frequency components above 400 Hz, this can be attributed to increased transvalvular

flow velocity due to a heart valve stenosis.

As mentioned in the section 4.3, phonocardiography has been largely displaced

in the cardiological functional diagnostics superseded by ultrasound imaging sono-

graphy. However, the particular simplicity of use in conjunction with modern meth-

ods of remote data transmission opens up new fields of application for phonocardio-

graphy. For example, heart patients can use an electronic stethoscope to record heart

sounds themselves and send them to experts for further evaluation. This enables close

monitoring in the home environment, which is particularly advantageous for monit-

oring disease progression.

Furthermore, a method for the automatic determination of the left ventricular

ejection time (LVET) will be presented. LVET is an important cardiological parameter

and is used as such or normalized to the heart rate to assess cardiac output. At normal

cardiac pumping rate and a heart rate of approximately 70 beats per minute, LVET

is 260 to 320 ms. If the contractility of the heart muscle and thus the pumping capa-

city is reduced due to disease, the organism reacts by prolonging the pumping pro-

cess, which increases the LVET. In patients with chronic heart failure and poor pump-

ing capacity (ejection fraction < 35 %), LVET values up to more than 450 ms can be

found. With massively impaired pump function, LVET may then shorten again because

the pumping process stops prematurely. Thus, LVET comes into consideration for the