What is the clinical evidence from this study?

Study design: Other. Population: Left ventricular pressure-volume relation modeling (n=5). Intervention: Six isochrone models (LinFix, LinFree, Langew, Sigm, Shroff, Burkh) vs. Measured PV-loops. Primary outcome: Akaike information criterion (AIC) and Hamming distance.

What does this research mean for the field?

A linear model with a varying volume intercept (LinFree) provides the best fit for simulating the instantaneous left ventricular pressure-volume relation, demonstrating that a linear model is sufficient for realistic simulations despite the known nonlinearity of the PV relation. Novelty: ClaimNovelty.NOVEL_FINDING. Consensus alignment: ConsensusAlignment.NEUTRAL.

June 24, 2009Open Access

Modeling the Instantaneous Pressure–Volume Relation of the Left Ventricle: A Comparison of Six Models

Key Result

A linear model with varying volume intercept (LinFree) provided the best fit for simulating the instantaneous left ventricular pressure-volume relation, though all six models performed similarly for PV-loop shape (Hamming distance 20-23%).

Structured PICO

Population

5 closed-chest sheep (35.0-46.0 kg) undergoing vena cava occlusion to vary preload

Intervention

Six mathematical models of the left ventricular pressure-volume relation (LinFix, LinFree, Langew, Sigm, Shroff, Burkh)

Comparator

Measured pressure-volume loops in the sheep

Outcome

Goodness of fit assessed by Akaike information criterion (AIC) and Hamming distance (geometric shape similarity)surrogate

For realistic simulation of the instantaneous left ventricular pressure-volume relation, a linear model with a free volume intercept is sufficient and performs best among the tested models.

Limitations

Load-dependence of the force-length relation implies violation of the basic assumption that instantaneous PV-relations are load-independent.
The models do not simulate the behavior of the isovolumic phases observed in measured data.
The use of a fixed source resistance Rv resulted in sometimes incomplete filling.
The Langew model requires an arbitrary choice of maximum physiological volume (Vm).
The AIC score calculation critically depends on the parameterization.

Abstract

Simulations are useful to study the heart's ability to generate flow and the interaction between contractility and loading conditions. The left ventricular pressure-volume (PV) relation has been shown to be nonlinear, but it is unknown whether a linear model is accurate enough for simulations. Six models were fitted to the PV-data measured in five sheep and the estimated parameters were used to simulate PV-loops. Simulated and measured PV-loops were compared with the Akaike information criterion (AIC) and the Hamming distance, a measure for geometric shape similarity. The compared models were: a time-varying elastance model with fixed volume intercept (LinFix); a time-varying elastance model with varying volume intercept (LinFree); a Langewouter's pressure-dependent elasticity model (Langew); a sigmoidal model (Sigm); a time-varying elastance model with a systolic flow-dependent resistance (Shroff) and a model with a linear systolic and an exponential diastolic relation (Burkh). Overall, the best model is LinFree (lowest AIC), closely followed by Langew. The remaining models rank: Sigm, Shroff, LinFix and Burkh. If only the shape of the PV-loops is important, all models perform nearly identically (Hamming distance between 20 and 23%). For realistic simulation of the instantaneous PV-relation a linear model suffices.

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