Left Ventricular Contractility Indices

CONTENTS 3.1 Scope ............................................................................................................. 68 3.2 Left Ventricular Shape Factor Based Contractility Index .................... 68 3.2.1 LV Model Geometry Development ............................................. 69 3.2.2 Determination of LV Model Wall Stress..................................... 70 3.2.3 Normalized Wall Stress based Shape Factor Index .................. 71 3.2.4 Optimal Left Ventricle Shape Factor and Corresponding Shape Factor Index 2 ...................................................................... 73 3.2.5 Optimally Shaped LV(s) Compared to Abnormally Shaped LV(s) for Different Age Groups .............. 77 3.2.6 Clinical Applications ...................................................................... 78 3.2.6.1 Measurements .................................................................. 78 3.2.6.2 Subjects .............................................................................. 78 3.2.6.3 Results ............................................................................... 78 3.2.7 Comparison with Traditional Invasive LV (dP=dt)max ............ 84 3.2.8 Discussion and Conclusion ........................................................... 84 3.3 Left Ventricular Sarcomere Contractile Characteristics and Associated Power Index .................................................................... 85 3.3.1 Left Ventricle Cylindrical Model (Incorporating the Myocardial Fibers within Its Wall) .............................................. 85 3.3.2 Myocardial Structural Unit (MSU) Model ................................. 87 3.3.3 Determination of Fiber Density, Length, and Force; Fiber Angle a and MSU Force (Ft); Torque Produced on the LV due to Fiber Activation ............................ 88 3.3.3.1 Fiber Density, Length, and Force .................................. 88 3.3.3.2 Determining the Fiber Pitch Angle a ........................... 90 3.3.3.3 Torque Imparted to the LV by Fiber Contraction ..... 91 3.3.4 Dynamics of a Myocardial Structural Unit ................................ 92 3.3.4.1 Governing Equation of MSU Dynamics and Its Solution ................................................................ 92 3.3.4.2 Phase I: Solving Equation 3.31 for Isovolumic Contraction Phase (during 0< t< t).......................... 95 Ghista/Applied Biomedical Engineering Mechanics DK8315_C003 Final Proof page 67 29.5.2008 12:00am Compositor Name: MSubramanian