The influence of vacular function on left ventricular contraction/relaxation coupling

Indexes of ventricular function have conventionally been classified into indexes of systolic (contractile) or diastolic (relaxation/stiffness) function. Systolic indexes include maximum elastance (Emax) or equivalently the end-systolic pressure volume relation (ESPVR) and left ventricular ejection fraction (LVEF). Diastolic indexes include the time constant of isovolumic relaxation (τ) and the end-diastolic pressure-volume relation (EDPVR). The conceptualization of ventricular contraction/relaxation coupling presents a challenge when mechanical events of the cardiac cycle are depicted in conventional pressure (P) or volume (V) terms. Additional conceptual difficulty arises when ventricular/vascular coupling is considered using P, V variables. In this preliminary work, we introduce the concept of thermodynamic phase-plane (TPP) defined by the PdV and VdP axes. TPP allows all cardiac mechanical events and their coupling to the vasculature to be geometrically depicted and simultaneously analyzed. Conventional systolic and diastolic function indexes are easily recovered, novel indexes of contraction-relaxation coupling are discernible and the influence of vascular function can be assessed.