Use of a modified van der Pol's oscillator to construct ventricular pressure-volume relations

Ventricular pressure-volume (PV) loops provide information about ventricular function. Methodologic constraints have limited derivation of PV loops to the laboratory. The present study addresses derivation of PV loops from a direct left ventricular pressure measurement and left ventricular volume derived from continuous cardiac output. The measurements were performed in vivo in intact, innervated, normal canine hearts. Data from a total of 5 dogs and 13 different cardiac work states were analyzed. A nonlinear oscillator, a van der Pol's oscillator, described the PV relationships. Comparison of left ventricular stroke work derived from the van der Pol's oscillator model with that obtained from ultrasound transducers sutured directly to the myocardium demonstrated a linear correlation, close to the identity line, with R2 = 0.90. Modelling of LV PV loops by this technique was similar to loops derived by experimental measurements. This technique could lead to increased clinical uses for PV relationships.