Figure 14-28 Length-force relationships in intact heart: a
Frank-Starling curve Optimal Length
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Cardiac index for the human being (cardiac output per square
meter of surface area) at different ages
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Effect of Total Peripheral Resistance on the Long-Term Cardiac
Output Level The long-term cardiac output level varies reciprocally
with changes in total peripheral resistance. 4
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The Heart Has Limits for the Cardiac Output That It Can
Achieve! The plateau level of this normal cardiac output curve is
about 13 L/min, 2.5 times the normal cardiac output of about 5
L/min. Factors That Can Cause Hypereffective Heart Only two types
of factors usually can make the heart a better pump than normal.
They are (1) nervous stimulation and (2) hypertrophy of the heart
muscle. Hypoeffective Heart Any factor that decreases the hearts
ability to pump blood causes hypoeffectivity. Some of the factors
that can do this are the following: Coronary artery blockage,
causing a heart attack, Inhibition of nervous excitation of the
heart, Pathological factors that cause abnormal heart rhythm or
rate of heartbeat, Valvular heart disease, Increased arterial
pressure against which the heart must pump, such as in
hypertension, Congenital heart disease, Myocarditis, Cardiac
hypoxia 5 The fig. depicts the normal cardiac output curve, showing
the cardiac output per minute at each level of right atrial
pressure.
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Starting at N, which represents a normal, resting individual: A
= decreased performance due to a reduction in preloadA = decreased
performance due to a reduction in preload B = increased performance
due to an increased preload C represents an increased performance
due almost entirely to increased contractility (close to the
situation during exercise) Points C, D, and E represent different
levels of performance due to changes in preload only; all three
points have the same contractility.
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Q Haemorrhage and volume overload: how does it affects preload,
performance and contractility?
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Vector I: consequences of a loss in preload, e.g., hemorrhage,
venodilators (nitro- glycerin) Vector II: consequences of a loss in
contractility, e.g., congestive heart failure Vector III:
consequences of an acute increase in contractility Vector IV:
consequences of an acute increase in preload, e.g., volume loading
the individual going from the upright to the supine position
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Vascular function curves Defines the changes in central venous
pressure that are caused by changes in cardiac output. It is venous
return creating a filling pressure and preload that normally
determines cardiac output. The vascular function (venous return)
curve depicts the relationship between blood flow through the
vascular system (or venous return) and right atrial pressure.
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cardiac failure What parameter is reduced in cardiac failure?
cardiac contractility How the kidneys are involved in the
compensatory mechanism to cardiac failure. Sympathetic NS acts on
Beta-1 cells in the kidney to release renin secretion. This
increases blood volume and induces venoconstriction
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Q. How does cardiac failure affect CO and RAP? slight fall in
CO Increase RAP
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1.The figure below shows pressure volume loops for two
situations. When compared with loop A, loop B demonstrates (A)
Increased preload (B) Decreased preload (C) Increased contractility
(D) Increased afterload (E) Decreased afterload