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2 Fundamentals of Information, Signal and System Theory

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elektrocardiogram

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phonocardiogram

blood pressure, blood flow

imaging

Fig. 2.7: Human heart with the common vital signs from which possible diagnoses can be derived.

"heart" in the respective form (cf. Figure 2.7). These signals are therefore called state

variables or variables of a system. In addition to the signals of the electrical conduction

system of the heart and the muscle contractions themselves, signals such as pressure

and flow changes of the blood circulation and the associated flow sounds as well as the

sounds of the heart valves can also be measured as acoustic signals. Figure 2.7 shows

the most common vital signals of the human heart from which possible diagnoses

can be derived. Figure 2.8 shows an overview of the signals of the heart: The pressure

curve in the aorta and in the left ventricle as well as the volume of the ventricle indicate

flow-related diseases, the electrocardiogram gives hints about the electromechanical

functioning of the conduction system and the phonocardiogram about the function of

the heart valves.

Each of these signals contains only a part of the total information and is also often

only partially known in relation to the biophysical system of the heart. The individual

signals thus encode, only very specific partial information of the system state with an

only partially known code. For example, if there is an aortic valve defect or a conduc-

tion block in the conduction system of the heart, only certain parts in the signal change

accordingly. In the first case, one will probably hardly notice a change in the ECG, but

the heart tones will sound different. In the second case, the contraction of the vent-