Chapter 151

### INTRODUCTION

The cardiac cycle can be divided into alternating periods of myocardial contraction, or systole, and periods of myocardial relaxation, or diastole. Ventricular systolic function is best understood quantitatively in terms of cardiac output (CO) and ejection fraction (EF), whereas the diastolic component of ventricular function relates to the ventricular isovolumetric relaxation time and ventricular capacitance during filling.

### VENTRICULAR FUNCTION CURVES

Ventricular function can also be summarized diagrammatically via ventricular pressure–volume diagrams, by plotting ventricular volume on the x-axis and ventricular pressure on the y-axis. There are primarily two points of interest: (1) the end-diastolic volume (EDV), which reflects diastolic function, including the ability of the ventricular myocardium to relax to fill with blood; and (2) the end-systolic volume (ESV), which reflects systolic function, including the ability of the ventricular myocardium to contract to eject a fraction of the end diastolic ventricular volume. The relationships between ventricular filling, EDV, ventricular ejection, and ESV are depicted in Figure 151-1.

###### FIGURE 151-1

(Reproduced with permission from Hall JE, Guyton AC, Guyton and Hall Textbook of Medical Physiology, 12th ed. Philadelphia, PA: Saunders/Elsevier; 2011.)

### VENTRICULAR SYSTOLIC FUNCTION

One parametric measurement of ventricular systolic function is CO, which refers to the volume of blood pumped by the heart each minute. Generally, as both the right and left ventricle depolarize in synchronous fashion, the pulmonary and systemic COs generated are usually equal. Cardiac output can also be defined mathematically as the product of heart rate (HR) and stroke volume (SV), which is the volume of blood pumped by each ventricle with every depolarization of the myocardium. The following equation summarizes the relationship between CO, HR, and SV: CO = HR × SV. Cardiac output can also be expressed as a cardiac index (CI), to account for individual body size differences and body surface area (BSA) variability, according to the following equation: CI = CO/BSA. The normal range for CI is usually 2.5-4.2 L/min/m2.

A second parametric measurement of ventricular systolic function is the EF, which refers to the percentage of the EDV that is ejected from each ventricle with every depolarization of the myocardium. This relationship can be expressed as a function of the ventricular EDV and ESV according to the following equation: EF = {[EDVESV]/[EDV]} × 100. The normal range for the left ventricular EF is usually 59%-75%.

The effect of ventricular systolic failure can be plotted on a ventricular pressure–volume loop. As the systolic function of the ventricle is failing, there is an increase in EDV and ESV because EF (the ability of the ventricle to eject a fraction of the EDV) is significantly reduced. The overall net effect ...

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