Submitted on May 26, 2006
Accepted on December 12, 2006
Contraction-Relaxation Coupling Mechanism Characterization in the Thermodynamic Phase-Plane: Normal vs. Impaired Left Ventricular Ejection Fraction
Yue Wu1, Yingbo Yu2, and Sandor J Kovacs3*
1 Physics, Washington University in St. Louis, St. Louis, Missouri, United States
2 Biomedical Engineering, Washington University in St. Louis, St. Louis, Missouri, United States
3 Internal Medicine, Washington University in St. Louis, St. Louis, Missouri, United States; Physics, Washington University in St. Louis, 1 Brookings Dr., St. Louis, Missouri, 63130, United States
* To whom correspondence should be addressed. E-mail: sjk{at}wuphys.wustl.edu.
We employ the thermodynamic phase-plane (TPP) method to characterize global contraction-relaxation coupling (CRC) between normal vs. impaired left ventricular ejection fraction (LVEF) groups using simultaneous pressure-volume measurements obtained during cardiac catheterization. The cardiac-cycle inscribes a closed loop in the TPP defined by 'potential' (V(dP/dt) - ergs/sec) and 'kinetic' power (P(dV/dt) - ergs/sec) as coordinates. TPP derived indexes 
and 
, define the chamber's contractile and contraction-relaxation coupling attributes, respectively. Data from thirty-three subjects dichotomized as: normal control (n=22, left ventricular ejection fraction (LVEF) > 50%), and impaired LVEF (n=11, LVEF < 50%) were analyzed. Results showed: = 3.0±1.1, = -0.38±0.21 for controls vs. = 5.4±1.6, = -1.14±0.47 for the impaired LVEF group; and for impaired LVEF are significantly higher than 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 utilize 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.
