Regression Analysis of the Left-ventricular Isochoric Pressure Decay of the Heart: Four or Five Model Parameters?

BACKGROUND: Isochoric (isovolumic) cardiac pressure decay data were previously described by a four-parametric logistic (tangens hyperbolicus) regression model (Langer model). However, a five-parametric kinematic model (Chung model), according to the differential equation of damped oscillation, was recently introduced to describe the isochoric pressure fall. The present study clarifies (a/) whether these five parameters can be reliably estimated from empirical pressure decay data and if the model excels the four-parametric one, and (b/) whether the kinematic Chung model validly describes these pressure decays. METHODS: High-fidelity intraventricular pressure decay data from 1203 isolated working guinea pig and rat hearts were analyzed by both models. RESULTS: Most cases present with a higher regression error in the five-parametric kinematic model, the median ratio (F value) of its regression variance by those of the four-parametric logistic model is 1.004 (95 per cent confidence interval: 1.002 to 1.006) in in the guinea pig as well as in the rat group. Additionally, the parameters of both models were estimated from the first and second half of the decay phase separately to check for the models' validity.  The five-parametric model yields significantly non-constant parameters more often than the four-parametric model. CONCLUSION: (a) the five parameters of the kinematic Chung model remain underdetermined by the empirical pressure data, and {b) this five-parametric model does not provide a valid description of the isochoric cardiac pressure decay.