Pressure phase-plane based determination of the onset of left ventricular relaxation

Charles S. Chung, Sándor J. Kovács

Research output: Contribution to journalArticlepeer-review

6 Scopus citations


Contraction-relaxation coupling is often characterized in terms of its effects on contraction or relaxation parameters, such as the time-constant of isovolumic relaxation (τ). While thermodynamics-based LV function characterization methods exist, landmark relaxation-onset determination studies used surgical methods. One classic, open-chest preparation study found that relaxation-onset occurs during early ejection, i.e. 34% of systolic time, TSYS, defined as the time from end-diastolic pressure to peak negative dP/dt. Because ventricular pumping is a steady state system, the laws of thermodynamics and nonlinear dynamics require that energy generation (during contraction) and energy utilization (during relaxation) must be balanced in a time-averaged (steady-state) sense. We calculated both energy generation and energy utilization, via novel pressure phase-plane (PPP) based parameters, including isovolumic stiffness analogs, in 29 subjects, 20 cardiac cycles per subject (580 beats). Results in control subjects show that relaxation-onset occurs near or prior to 34% of TSYS. In hearts with sever dysfunction including prolonged τ, relaxation-onset commences after 50% of TSYS (p < 0.05). We conclude that PPP-based analysis can characterize relaxation-onset in vivo in thermodynamic and nonlinear dynamics terms without requiring an open-chest preparation, and may facilitate characterization of cellular mechanisms of relaxation-onset at the organ system level.

Original languageEnglish
Pages (from-to)162-171
Number of pages10
JournalCardiovascular Engineering
Issue number4
StatePublished - Dec 2007


  • Diastole
  • Hemodynamics
  • Limit cycle
  • Pressure phase plane
  • Relaxation


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