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):

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Blood Pressure Health

Blood Pressure Health

Your heart pumps blood throughout your body using a network of tubing called arteries and capillaries which return the blood back to your heart via your veins. Blood pressure is the force of the blood pushing against the walls of your arteries as your heart beats.Learn more...

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