[Aortic pressure and velocity signals processing: application to human aorta characterization (author's transl)]

The input to and characteristic impedances of the ascending aorta and the mean, pulsatile and maximum hydraulic powers generated by the left ventricle have been determined in 16 patients by simultaneous measurements of aortic pressure (by miniature transducer), velocity (by electromagnetic probe) and diameter (by cineangiography). Eight patients had normal blood pressure and eight were hypertensive. Harmonics of pressure and flow were calculated by processing the signals for 40 cycles, taking into account the frequency response of the velocity probe (Figs. 1 and 2). 1. The invariance of input impedance with heart frequency confirms the linearity of the arterial system under resting conditions (Fig. 3). 2. The characteristic impedances calculated by averaging the input impedance modulus above 2 Hz (Fig. 5) and from cineangiography are in good agreement for normotensive patients but discrepancies arise for hypertensive patients (Fig. 4). 3. Comparison of input impedance spectra (Fig. 6) reveals that in hypertensive patients the point of minimum modulus and zero phase is shifted towards higher frequencies while the characteristic impedance is higher. 4. The hydraulic power generated by the left ventricle is higher for hypertensive patients (Table I) and the increase in pulsatile power is almost entirely due to the increase in pressure harmonics (Figs. 7 and 8). These results suggest that the aorta plays an important role in left ventricular performance and that it may be characterized by its input impedance spectrum.