Iancu RV, Jones SW, Harvey RD. Compartmentation of cAMP signaling in cardiac myocytes. Biophys J. 2007;92:3317.
Liu Y, Bubolz AH, Mendoza S, et al. H2O2 is the transferrable factor mediating flow-induced dilation in human coronary arterioles. Circ Res. 2011;108:566.
predominate over those in the aorta, and they respond more vigorously to changes in pressure (stretch) than to elevated or reduced nonpulsatile pressure.
9.
Peripheral chemoreceptors (carotid and aortic bodies) and central chemoreceptors in the medulla oblongata are stimulated by a decrease in blood PaO2 and by an increase in blood PCO2. Stimulation of these chemoreceptors increases the rate and depth of respiration, but it also produces peripheral vasoconstriction. Cardiopulmonary baroreceptors are also present in the cardiac chambers and large pulmonary vessels. They have less influence on blood pressure but do participate in regulation of blood volume.
10.
Peripheral resistance and hence blood pressure are affected by stimuli that arise in the skin, viscera, lungs, and brain. The combined effect of neural and local metabolic factors distributes blood to active tissues and diverts it from inactive tissues. In vital structures, such as in the heart and brain and in contracting skeletal muscle, the metabolic factors predominate.
Llewellyn-Smith IJ, Verberne AJM, eds. Central Regulation of Autonomic Functions. New York: Oxford University Press; 2011.
Timmers HJ, Wieling W, Karemaker JM, et al. Cardiovascular responses to stress after carotid baroreceptor denervation in humans. Ann N Y Acad Sci. 2004;1018:515.
Zhang P, Mende U. Regulators of G-protein signaling in the heart and their potential as therapeutic targets. Circ Res. 2011;109: 320.
Upon completion of this chapter, the student should be able to answer the following questions: 1.
What are the four major factors that determine cardiac output? Which two of these factors are said to be “coupling factors,” and what is the reason for that description?
2.
What is a cardiac function curve, and how is it related to the Frank-Starling mechanism?
3.
What is a vascular function curve, and how is it affected by changes in total peripheral resistance, blood volume, and venous tone?
4.
Why does the operating point of the cardiovascular system occur at the intersection of the vascular and cardiac function curves?
5.
How does evaluation of the cardiac function curve and the vascular function curve enable clinicians to determine the effect of changes in blood volume, vascular tone, and contractility on cardiac output?
6.
What mechanisms in the central nervous system, heart, and systemic vasculature allow cardiac output to increase to the necessary levels during vigorous exercise?
7.
What are the cardiovascular consequences of hemorrhage, and what are the compensatory mechanisms that tend to restore arterial pressure and cardiac output?
Regulation of Cardiac Output and Blood Pressure
Four factors control cardiac output: heart rate, myocardial contractility, preload, and afterload (
Fig. 19.1). Heart rate and myocardial contractility are strictly cardiac factors, although they are controlled by various neural and humoral mechanisms. Preload and afterload are factors that are mutually dependent on function of the heart and the vasculature and are important determinants of cardiac output. Preload and afterload are themselves determined by cardiac output and by certain vascular characteristics. Preload and afterload are called coupling factors because they constitute a functional coupling between the heart and blood vessels.
To understand regulation of cardiac output, the nature of the coupling between the heart and the vascular system must be appreciated.