chapter  2
44 Pages

Left Ventricular Mechanics

WithDhanjoo N. Ghista, Liang Zhong

CONTENTS 2.1 Introduction and Scope ............................................................................. 24 2.2 Pressure-Drop across a Stenotic Aortic Valve ....................................... 24 2.3 Why Valvular Disorders Can Lead to Myocardial Infarcts?............... 25 2.4 How Myocardial Infarct Impairs Stroke Volume

and Cardiac Output?.................................................................................. 28 2.5 Noninvasive Diagnosis of Diseased Heart (Mitral and Aortic)

Valves, Based on Their Dynamics Modeling, Echo-, and Phonocardiography................................................................ 29 2.5.1 Background...................................................................................... 29 2.5.2 Mitral Valve Biomechanical Model to Detect

Diseased Valve ................................................................................ 29 2.5.2.1 Analysis ............................................................................. 30

2.5.3 Aortic Valve Biomechanical Model to Determine Normal and Diseased Aortic Valve Properties ......................... 32 2.5.3.1 Analysis (Figure 2.5)........................................................ 34

2.6 Diseased LV Myocardial Segment Detection ........................................ 40 2.6.1 Comments ........................................................................................ 43

2.7 Analysis of Blood Flow in the LV (Using Monitored LV Wall-Motion Data to Determine Intra-LV Flow Velocity and Pressure-Gradient Distributions) ..................................................... 45 2.7.1 Finite-Element Analysis of Blood Flow in the LV .................... 45 2.7.2 Analysis for Intra-LV Pressure Distribution .............................. 46 2.7.3 Intra-LV Flow during Diastolic Filling ....................................... 47

2.8 Explaining Left-Ventricular Pressure Dynamics in Terms of LV Passive and Active Elastances (as Measures of LV Pressure Dynamics Response to LV Volume Change and LV Contractility) ... 49 2.8.1 Scope ................................................................................................. 49 2.8.2 Concepts of Passive and Active Elastances ............................... 50

2.8.2.1 Expression for Passive Elastance (Ep) of the LV ........ 50 2.8.2.2 Expression for Active Elastance (Ea) of the LV .......... 51

2.8.3 Clinical Application ....................................................................... 52 2.8.4 Results of Case Studies .................................................................. 55

2.8.4.1 Pressure Dynamics during Filling Phase .................... 56 2.8.4.2 Pressure Dynamics during Ejection Phase .................. 58

2.8.5 Active Elastance as a New Contractility Index ......................... 59 2.8.6 Discussion ........................................................................................ 60

2.9 Conclusion ................................................................................................... 62 References ............................................................................................................. 63

Biomechanics has been associated with major physiological advances and medicine. However, considerable insight into physiology and medicine can also be gained from innovative applications of even relatively basic engineering analyses. In this chapter, we are developing the concept of cardiology to demonstrate how even fundamental engineering disciplines can bring to bear enhanced logic to cardiology, to:

. Determine the pressure-drop across a stenotic aortic valve (AV)

. Demonstrate how AV disorders could lead to myocardial infarct

. Depict likely sites for myocardial ischemias and infarcts

. Explain how myocardial infarct impairs stroke volume and cardiac output

. Obtain quantifiable measures of left-ventricular (LV) stiffness and contractility, so as to provide a measure of impaired LV pumping capacity

We start our journey in the heart, by analyzing the pressure-drop across a stenotic AV. The inlet and outlet to and from the left ventricle is regulated by heart valves. If the AV gets diseased and becomes stenotic, it will result in a big pressure-drop across the valve, which can be evaluated in terms of the LV outflow rate and the dimensions of the outflow tract, using Bernoulli theorem equation, as carried out in Figure 2.1.