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Contraction-relaxation coupling mechanism characterization in the thermodynamic phase plane: normal vs. impaired left ventricular ejection fraction

¹Cardiovascular Biophysics Laboratory, Department of Physics, ²Department of Biomedical Engineering, and ³Cardiovascular Division, Department of Internal Medicine, Washington University, St. Louis, Missouri

Submitted 26 May 2006 ; accepted in final form 12 December 2006

Using simultaneous pressure-volume measurements obtained during cardiac catheterization, we employ the thermodynamic phase-plane (TPP) method to characterize global contraction-relaxation coupling (CRC) between normal and impaired left ventricular (LV) ejection fraction (LVEF) groups. The cardiac cycle inscribes a closed loop in the TPP defined by the coordinates "potential" power [V(dP/dt), ergs/s] and "kinetic" power [P(dV/dt), ergs/s]. The TPP-derived indexes and define the chamber's contractile and CRC attributes, respectively. Data from 33 subjects dichotomized as normal control (n = 22, >50% LVEF) and impaired LVEF (n = 11, <50% LVEF) were analyzed. The results were as follows: = 3.0 ± 1.1 and = –0.38 ± 0.21 for controls and = 5.4 ± 1.6 and = –1.14 ± 0.47 for the impaired LVEF group; and are significantly higher for impaired LVEF than for control (P < 0.001 for both). As increased, decreased (r = –0.69) for all subjects. Hence, ventricles with impaired LVEF are thermodynamically less efficient because they require more potential power per unit of delivered kinetic power than controls. We conclude that TPP-derived indexes of CRC facilitate assessment of chamber efficiency in thermodynamic terms and elucidate the dominant differentiating features in terms of CRC indexes.

left ventricular function; cardiac power; mathematical modeling