Aortic input impedance in heart failure.

Abstract

SUMMARY The input impedance of the systemic circulation was calculated from recordings of pulsatile pressure and flow in the ascending aorta of 20 patients. Ten patients had clinical and hemodynamic evidence of heart failure. The other 10 subjects had no clinical evidence of heart failure and were used as a control group. In the heart failure patients, both input resistance and characteristic impedance (index of aortic distensibility) were significantly increased compared to pressureand age-matched control subjects. Oscillations of impedance moduli, represented by the difference between maximum and minimum moduli, were also significantly increased in the heart failure patients compared with the control subjects. The increased characteristic input impedance in these heart failure patients suggests that the human aorta is stiffer in heart failure, and the larger oscillations in the impedance spectrum indicate an increase in pressure and flow wave reflections. From reflected wave theory in elastic tubes, reflected pressure waves add to the amplitude of incident pressure waves at the entrance of the system, whereas reflected flow waves subtract from the magnitude of the forward flow. Thus, changes in aortic distensibility could have an important influence on the pulsatile function of the failing left ventricle.THE AORTA AND LARGE ARTERIES of the systemic circuit are not rigid pipes, but constitute a distensible elastic buffering chamber. These elastic properties permit a damping mechanism through which pulsatile blood flow waves ejected from the left ventricle are converted to a near-constant blood flow for resistance vessels to distribute to systemic capillaries. Elastic properties of these large vessels can be modified by autonomic nervous effects on vascular smooth muscle cells with only minor changes in vessel dimensions.' Recent studies in our laboratories suggest that age and the presence of atherosclerosis may also be important in modifying the elastic properties of large vessels.2In heart failure, previous studies have emphasized abnormal ventricular and peripheral hemodynamic

Characteristics of vascular hydraulic load in patients with heart failure.

“…10 Although the normal mean characteristic impedance in that study was similar to our normal control group, mean ZL in their patients with heart failure was significantly elevated at 131 + 27 dyne-sec-cm -. In a more recent report, mean aortic characteristic impedance in subjects with heart failure and cardiomyopathy was quite similar to our mean data."…”

“…10 The possibility of increased arterial wall sodium content with a secondary decrease in distensibility raises the intriguing possibility of altering arterial elastic properties in patients with heart failure with diuretic therapy. All of our patients with heart failure were studied after appropriate medical therapy and were in a clinically stable condition at the time of catheterization.…”

“…4 Although it is generally agreed that the 0 Hz, or DC, component of impedance, systemic vascular resistance, is elevated in patients with congestive heart failure both at rest and during exercise,5-9 there is conflicting evidence with regard to abnormalities in the pulsatile component of the vascular load. 10. "I Furthermore, experimental data suggest that arterial wave reflections decrease with systemic vasodilation and increase with vasoconstriction.'…”

Interaction between pulse wave velocity, augmentation index, pulse pressure and left ventricular function in chronic heart failure

“…Regarding proximal arterial stiffness, conflicting results have been published. Using characteristic impedance as a direct marker of arterial stiffness, Mitchell et al 29 and Pepine et al 30 found an increase in proximal arterial stiffness, whereas Merillon et al 31 and Kromer et al 32 did not. These conflicting results are probably partly due to methodological differences, but no data are available for patients with very low EF.…”

Effects of aging on changing arterial compliance and left ventricular load in a northern Chinese urban community.

“…'-' In comparisons of changing load under different circumstances, vascular impedance is usually expressed as characteristic impedance.3 5 7-9 Characteristic impedance has been used also as an index of arterial distensibility and this (when expressed in appropriate units) has been shown to change in different disease conditions with different drugs and with increasing age. , [9][10][11][12][13][14][15] Characteristic impedance of an arterial segment is directly related to regional arterial pulse wave velocity (PWV). 0 Regional PWV can be determined from the time delay between the foot of pulse waves recorded in proximal and distal sites and the distance between recording sites.…”