Assessment of left ventricular viscoelastic components based on ventricular harmonic behavior

Area of Science:

• Cardiovascular Mechanics
• Biomedical Engineering
• Cardiac Physiology

Background:

• Assessing left ventricular (LV) function, particularly contractility, remains a challenge in cardiac mechanics.
• Traditional methods rely on pressure-volume (P-V) relationships, requiring invasive instrumentation.
• Existing P-V diagrams, while interpretable, are difficult to obtain non-invasively.

Purpose of the Study:

• To introduce a novel technique for estimating LV viscoelastic properties, encompassing both elastic and viscous components.
• To develop a method applicable non-invasively for assessing cardiac mechanics.
• To analyze the oscillatory behavior of the ventricular chamber for parameter estimation.

Main Methods:

• Modeled long axis displacement of the mitral annulus plane as a linear damped oscillator with time-varying coefficients.
• Represented elastic deformations using a time-varying spring and viscous components with a time-varying viscous damper.
• Estimated time-varying model parameters using a Recursive Linear Least Squares (RLLS) technique in ten healthy sheep.

Main Results:

• Left ventricular (LV) stiffness ranged from 61.86-136 dyne/gxcm (end-systole) and 1.25-21.02 dyne/gxcm (end-diastole).
• Averaged stiffness and damping coefficients during a cardiac cycle were estimated at 58.63+/-12.8 dyne/gxcm and 0 dynexs/gxcm, respectively.
• Linear regression confirmed agreement between estimated parameters and measured stiffness values.

Conclusions:

• Estimated elastic coefficients align with those from force-displacement diagrams.
• The trend of estimated parameter changes is consistent with previous P-V diagram studies.
• The model utilizes long axis displacement, obtainable non-invasively via tissue Doppler or MR imaging.