Aortic input impedance in normal man: relationship to pressure wave forms.

SUMMARY The relationship between the shape of the ascending aortic pressure wave form and aortic input impedance was studied in 18 patients who underwent elective cardiac catheterization but in whom no heart dis-ease was found. Ascending aortic flow velocity and pressure were simultaneously recorded from a multisensor catheter with an electromagnetic velocity probe and a pressure sensor mounted at the same location. Another pressure sensor at the catheter tip provided left ventricular pressure or a second aortic pressure to determine pulse-wave velocity. Fick cardiac outputs were used to scale the velocity signal to instantaneous volumetric flow. Input impedance was calculated from 10 harmonics of aortic pressure and flow. For each patient, im-pedance moduli and phases from a minimum of 15 beats during a steady state were averaged. Peripheral resistance was 1137 ± 39 dyn-sec-cm ' (4 SEM) and characteristic impedance was 47 4 4 dyn-sec-cm-; pulse-wave velocity was 6.68 ± 0.32 m-sec-'. In all patients, a well-defined systolic inflection point divided the aortic pressure wave form into an early and late systolic phase. The patients were classified into three groups: group A (n = 7) patients whose late systolic pressure exceeded early systolic pressure; group B (n = 7) pa-tients whose early and late systolic pressures were nearly equal; group C (n = 4)- patients whose early systolic pressure exceeded late systolic pressure. Group A and B patients all demonstrated oscillations of the impedance moduli about the characteristic impedance. Group C patients demonstrated flatter impedance spec-