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Thermodynamic phase plane analysis of ventricular contraction and relaxation
Mustafa Karamanoglu1, Sándor J Kovács
1Cardiovascular Biophysics Laboratory, Washington University School of Medicine, Washington University in St Louis, 660 South Euclid Ave, Box 8086, St, Louis, MO 63110, USA. mustafa.karamanoglu@medtronic.com
Background:
Ventricular function has conventionally been characterized using indexes of systolic (contractile) or diastolic (relaxation/stiffness) function. Systolic indexes include maximum elastance or equivalently the end-systolic pressure volume relation and left ventricular ejection fraction. Diastolic indexes include the time constant of isovolumic relaxation - and the end-diastolic pressure-volume relation. 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.
Methods:
We introduce the concept of thermodynamic phase-plane, TPP, defined by the PdV and VdP axes.
Results:
TPP allows all cardiac mechanical events and their coupling to the vasculature to be geometrically depicted and simultaneously analyzed.
Conclusion:
Conventional systolic and diastolic function indexes are easily recovered and novel indexes of contraction-relaxation coupling are discernible.
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