title: Pressure phase-plane based determination of the onset of left ventricular relaxation.
abstract: Contraction-relaxation coupling is often characterized in terms of its effects on contraction or relaxation parameters, such as the time-constant of isovolumic relaxation (tau). 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 tau, 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.
authors.affiliation: Cardiovascular Biophysics Laboratory, Cardiovascular Division, Washington University Medical Center, 660 South Euclid Ave, Box 8086, St. Louis, MO 63110, USA.
authors.forename: Charles S
authors.initials: CS
authors.lastname: Chung
authors.forename: Sándor J
authors.initials: SJ
authors.lastname: Kovács
mesh_terms: D000328:Adult; D000368:Aged; D005260:Female; D006439:Hemodynamics / Q000502:physiology; D006801:Humans; D008297:Male; D008875:Middle Aged; D009126:Muscle Relaxation / Q000502:physiology*; D016276:Ventricular Function; D017725:Ventricular Pressure / Q000502:physiology