A new active contraction model for the myocardium using a modified hill model.

Area of Science:

• * Biophysics and Computational Biology
• * Cardiovascular Physiology and Modeling

Background:

• * Existing myocardial contraction models often lack comprehensive integration of phenomenological and micro-structural mechanisms.
• * Accurate modeling of cardiac dynamics requires capturing complex interactions at the sarcomere level.

Purpose of the Study:

• * To develop and validate a new hybrid active contraction model for myocardial dynamics.
• * To combine the strengths of the phenomenological Hill model and the micro-structurally motivated active strain approach.
• * To enhance the capability for personalized cardiac modeling.

Main Methods:

• * Developed a hybrid model with parallel passive and active branches, incorporating a serial passive element for force transmission.
• * Formulated active stress using the active strain approach, multiplicatively decomposing contractile element stretch.
• * Incorporated length-dependence and force-velocity relationships into the active strain formulation and generalized to 3D.

Main Results:

• * The hybrid model demonstrated high descriptive capability for isometric and isotonic contractions.
• * Validated simulation of physiologically accurate human cardiac dynamics.
• * Highlighted the crucial role and tight interaction of length-dependence and force-velocity in active strain.

Conclusions:

• * The proposed hybrid model offers a significant advancement over existing active strain approaches.
• * The model accurately predicts cardiac mechanical behavior and has potential for personalized cardiac applications.
• * Provides insights into multi-scale coupling in active contraction based on the sliding filament theory.