The central arterial pulses. Experiments on a hybrid model of the heart and the arterial system.

In order to examine the contours of central aortic and coronary flow pulses as well as those of pressure and flow pulses along the aorta, a hybrid model of the arterial system and the heart was designed. The digitally programmed model of the aortic system is an inhomogeneous transmission line with adjustable reflection factors at the end and at three intermediate locations. For the reflection factor at the entrance different values may be chosen for the ejection time and the diastole. The influence of a stenosis and of frequency-independent damping may be examined. The model of the ventricle is the analog solution of a system consisting of an internal isometric pressure source and an internal resistance and capacitance. The model of the coronary artery is the analog solution of a windkessel model of the system. The digital and analog models are interlocked by AD and DA converters. All programs can be executed in real time. The characteristic contour of the aortic flow is determined by the relation between the internal impedance of the ventricle and the magnitude of the characteristic impedance of the aorta. Furthermore, the influence of reflections within the arterial system is shown to be quite remarkable. Natural pressue pulses can be simulated by the model under normal and pathological conditions including aortic coarctation. The contour of the left coronary artery flow is determined on the one hand by the fraction of the ventricular pressure which acts as a counterpressure at the site of the peripheral resistance, and by the time constant of the coronary windkessel on the other hand.