The step response of left ventricular pressure to ejection flow: a system oriented approach

Area of Science:

• Cardiovascular Physiology
• Biomedical Engineering
• Computational Biology

Background:

• Left ventricular pressure is influenced by ventricular volume and ejection flow.
• Ventricular elastance and resistance are key parameters, but decreasing ejection flow introduces elastance depression.
• Existing models may not fully capture the dynamic interplay between flow and ventricular mechanics.

Purpose of the Study:

• To model the effects of elastance, resistance, and elastance depression on left ventricular pressure.
• To develop and validate a three-compartment model for ventricular dynamics.
• To identify novel parameters related to ventricular function during varying ejection flows.

Main Methods:

• A three-compartment model was developed to represent ventricular elastance, resistance, and elastance depression.
• The model was identified using experimental pressure responses from isolated rabbit hearts subjected to controlled flow epochs.
• Flow epochs included constant flow phases and steps of increasing or decreasing flow.

Main Results:

• Elastance remained unchanged with positive or zero flow steps but decreased with negative flow steps.
• A linear relationship was found between elastance deactivation and the pressure difference during negative flow steps.
• Key parameters identified include ventricular active volume, nondepressed elastance, series-elastance, resistance, and a new elastance deactivation factor.

Conclusions:

• The study proposes a new parameter, the elastance depression factor, potentially crucial for understanding heart muscle function.
• The identified parameters align with existing literature, validating the model's core components.
• An nonlinear state-model for the ventricle is proposed, applicable to various physiological flow patterns.