Interaction of left ventricular contraction and aortic input impedance in experimental and clinical studies.

Implication of aortic input impedance and left ventricular coupling were investigated in three series of studies. In a clinical study, the ascending aortic flow velocity and pressure were simultaneously recorded from a multisensor catheter, and input impedance was calculated from 8 harmonics of aortic pressure and flow. Left ventricular wall stress was calculated from diameters and wall thickness of cineventriculogram and simultaneous recording of left ventricular pressure. In the experimental study, programmable artificial pulsatile pump was used to control pulsatile blood flow in dogs. The pressure-flow relationship in the arterial system had slightly convex curves toward the pressure axis with a critical turning pressure, so the arterial system had low output--high resistance and high output--low resistance characteristics. Therefore, the failed heart should inevitably eject the blood against stiffened vascular beds. Increased work load of the ventricle as expressed by sustained ventricular wall stress was determined mainly by the exaggerated late systolic pressure due to increased input resistance and increased low frequency pulsatile component of the input impedance. These findings are especially important for relieving additional work load of the ischemic heart, which have higher pressure wave reflection.