The thermodynamics of diastole: kinematic modeling-based derivation of the P-V loop to transmitral flow energy relation with in vivo validation

Mossahebi S, Shmuylovich L, Kovacs SJ. The thermodynamics of diastole: kinematic modeling-based derivation of the P-V loop to transmitral flow energy relation with in vivo validation. Am J Physiol Heart Circ Physiol 300: H514-H521, 2011. First published November 12, 2010; doi: 10.1152/ajpheart.00814.2010.-Pressure-volume (P-V) loop-based analysis facilitates thermodynamic assessment of left ventricular function in terms of work and energy. Typically these quantities are calculated for a cardiac cycle using the entire P-V loop, although thermodynamic analysis may be applied to a selected phase of the cardiac cycle, specifically, diastole. Diastolic function is routinely quantified by analysis of transmitral Doppler E-wave contours. The first law of thermodynamics requires that energy (epsilon) computed from the Doppler E-wave (epsilon(E-wave)) and the same portion of the P-V loop (epsilon(P-V E-wave)) be equivalent. These energies have not been previously derived nor have their predicted equivalence been experimentally validated. To test the hypothesis that epsilon(P-V E-wave) and epsilon(E-wave) are equivalent, we used a validated kinematic model of filling to derive epsilon(E-wave) in terms of chamber stiffness, relaxation/viscoelasticity, and load. For validation, simultaneous (conductance catheter) P-V and echocadiographic data from 12 subjects (205 total cardiac cycles) having a range of diastolic function were analyzed. For each E-wave, epsilon(E-wave) was compared with epsilon(P-V E-wave) calculated from simultaneous P-V data. Linear regression yielded the following: epsilon(P-V E-wave) = alpha epsilon(E-wave) + b (R-2 = 0.67), where alpha = 0.95 and b = 6e(-5). We conclude that E-wave-derived energy for suction-initiated early rapid filling eE-wave, quantitated via kinematic modeling, is equivalent to invasive P-V-defined filling energy. Hence, the thermodynamics of diastole via epsilon(E-wave) generate a novel mechanism-based index of diastolic function suitable for in vivo phenotypic characterization.