FIGURE 5-18 Combined cardiac and systemic function curves: effects of chronic heart failure. The normal operating intercept (point A) is shifted to point B when cardiac function alone is depressed by loss of inotropy. Compensatory increases in total blood volume (Vol) and systemic vascular resistance (SVR), along with reduced venous compliance (CV), shifts the systemic function to the right and decreases the slope. The new combined intercept (point C) represents partial compensation in cardiac output at the expense of a large increase in right atrial pressure (PRA).
return) depends on both cardiac and systemic vascular function. Cardiac stimulation in a normal heart has only a modest effect on cardiac output; however, if systemic function is additionally altered by decreasing venous compliance and systemic vascular resistance, the cardiac output is able to increase. Without changes in systemic function, cardiac output is limited by the return of blood to the heart and ventricular filling.
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