Fourier Analysis of Left Ventricular Performance

Abstract

Fourier analysis has been applied to simultaneously obtained ventricular pressure, ascending aortic pressure, and aortic flow in the closed- and open- chest dog and during infusion with isoproterenol, norepinephrine, and phenylephrine. Partial measurements were also obtained from a sheep and a primate. Impedance moduli and phases were calculated from the ventricular (forcing) and aortic (input) side of the aortic valve and compared. Forcing impedance was similar in form but larger than input impedance, and the phase became positive earlier. Ventricular and aortic powers were calculated and expressed as pressure power, kinetic energy power, and reactive power, along with their harmonic distributions. Mean pressure represented 80 to 91% of total load power but only 20 to 51% of total ventricular power. Calculated efficiency varied from 35% with isoproterenol infusion to 100% with norepinephrine, phenylephrine, and open-chest states. Control efficiency was 78%. The concept of impedance matching was investigated; maximal efficiency occurred with optimal matching. Internal resistance was shown to represent an easily measurable quantity which also partially corresponds to the more complex impedance measurement.