Estimation of ventricular source parameters and its load matching state in vivo

Ventriculo-arterial coupling states were estimated by calculating left ventricular hydromotive pressure (Ps), source impedance (Zs) and input impedance (Zl) in 24 mongrel dogs with Fourier transforms of ventricular pressure and aortic flow immediately before and after instantaneous changes of arterial load. Calculated Ps (Psc) were compared with measured left ventricular isovolumic pressures (Psm) in various inotropic and loading states. Psc waveforms coinciding closely with those of Psm were obtained by cutting off higher frequencies within the fifth to tenth harmonics prior to the inverse Fourier transformation. The regression equation was Psc = 1.08 Psm +0.68 (r = 0.978). In control conditions, the ratio of Zs (0) / Zl (0) (function of frequency, 0 = zero Hz) was close to the ratio of ejection phase to one whole cardiac cycle, and the ratio of peak Psm to left ventricular ejection pressure was 1.85 +/- 0.25 SD. These results imply the presence of a ventriculo-arterial load matching state in control conditions.