Cardiac Pressurevolume Curves

Ventricular function can be analyzed and graphically displayed with a pressure-volume diagram. Both systolic and di-astolic pressure-volume relationships during a single cardiac cycle are displayed in Fig. 2. Pressure-volume assessment of myocardial function on intact myocardium involves multiple factors, such as preload, afterload, heart rate, and contractility. The area inside the pressure-volume loop is an estimate of the myocardial energy (work = pressure x volume) utilized for each stroke volume (stroke volume = end-diastolic volume - end-systolic volume). The shape of the normal pressure-volume loop changes with alterations in myocardial compliance, contractility, and/or valvular and myocardial disease.

Pressure-volume loops are displayed by plotting ventricular pressure (y axis) against ventricular volume (x axis) during a single cardiac cycle (Fig. 2). Points and segments along the pressure-volume loop correlate with specific mechanical events of the ventricle. The width of the pressure-volume loop is the stroke volume. Myocardial contractility is represented by the slope of the end-systolic pressure-volume relationship; this relationship defines the maximal pressure generated over time with a given myocardial contractility state. Contractility is proportional to change in pressure over time (dP/dt). The passive ventricular filling during diastole is defined by the end-dias-tolic pressure-volume relationship, and ventricular compliance is inversely proportional to the slope of the end-diastolic pressure-volume relationship.

The effect of heart rate on the pressure-volume relationship cannot be assessed with a single pressure-volume loop. Instead, multiple pressure-volume loops must be obtained to assess effects of heart rate on the pressure-volume loop. By altering variables such as afterload, contractility, and preload, the mechanical events and pressure-volume relationship are displayed.

The pressure-volume diagram shows events of a single cardiac cycle (Fig. 2):


Essentials of Human Physiology

Essentials of Human Physiology

This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.

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