Conceito de pré carga e pós carga em cardiologia
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Conceito de pré carga e pós carga em cardiologia


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fashion. Defined in words, therefore, preload
represents all the factors that contribute to pas-
sive ventricular wall stress (or tension) at the
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TABLE 1
Summary of published definitions of preload and afterload
Reference Preload Definition Afterload Definition
Textbook of Medical
Physiology (9)
\u201c. . . the degree of tension on the muscle when it
begins to contract . . . is the preload . . .\u201d
(p. 115)
\u201cFor cardiac contraction, the preload is usually
considered to be the end-diastolic pressure
when the ventricle has become filled.\u201d
(p. 115)
\u201c. . . the load against which the muscle exerts its
contractile force . . . is called the afterload.\u201d
(p. 115)
\u201cThe afterload of the ventricle is the pressure in
the artery leading from the ventricle.\u201d (p. 115)
Physiology (2) \u201c. . . the resting muscle is stretched by a preload,
which in the intact heart represents the end of
filling of the left ventricle during diastole (in
other words, it represents the end diastolic
volume).\u201d (p. 366)
\u201cDuring ejection, the afterload is represented by
aortic and intraventricular pressures, which
are virtually equal to each other.\u201d (p. 366)
Best and Taylor\u2019s
Physiological Basis of
Medical Practice (31)
\u201cThe end-diastolic pressure in the ventricle can
also be equated to the preload.\u201d (p. 220)
\u201cIn the whole heart the preload should
constitute the tension in the wall at the end of
diastole (which determines the resting fiber
length), but for practical purposes the
ventricular end-diastolic volume of the
ventricular end-diastolic pressure is used to
indicate the preload.\u201d (p. 227)
\u201cAfterload 5 wall tension (stress). Diagram
showing how the systolic wall tension or wall
stress (which represents the afterload in the
myocardial fibers during left ventricular
ejection) is affected by the geometry of the
left ventricle (LV).\u201d (p. 220, legend of Figure
2.111)
Review of Medical Physiology
(6)
\u201cIn vivo, the preload is the degree to which the
myocardium is stretched before it
contracts . . .\u201d (p. 546)
\u201c. . . and the afterload is the resistance against
which blood is expelled.\u201d
(p. 546)
Essential Medical Physiology
(14)
\u201cThe filling pressure is often termed the preload
because this is the load on the muscle fibers
before contraction.\u201d (p. 192)
\u201cThe afterload for the contraction is the aortic
pressure . . .\u201d (p. 192)
Medical Physiology (23) \u201cAt the end of diastole the intraventricular
pressure is analogous to the \u2018preload\u2019 in a
simple muscle strip preparation (i.e., the
weight that is suspended from such a strip to
stretch it to the desired initial length).\u201d
(p. 994)
\u201cDuring ejection the aortic pressure is related to
the \u2018afterload,\u2019 or weight that the muscle
[strip] is required to lift.\u201d
(p. 994)
Human Physiology (26) \u201cThe preload is given by the end-diastolic
pressure . . .\u201d (p. 387)
\u201c. . . and the afterload by the diastolic arterial
pressure.\u201d (p. 387)
Human Physiology:
Foundations and Frontiers
(21)
\u201cIn the case of the heart, the preload is the
right atrial pressure . . .\u201d (p. 376)
\u201cIn the case of the heart, . . . the afterload is
the aortic pressure.\u201d (p. 376)
Textbook of Physiology:
Circulation, Respiration,
Body Fluids, Metabolism,
and Endocrinology (24)
\u201cThe end-diastolic filling pressure or maximal
diastolic volume (preload) is the most
important determinant of stroke volume.\u201d
(p. 973)
\u201cThe second intrinsic factor that determines the
stroke volume is the aortic pressure or
afterload.\u201d (p. 974)
Physiology (3) \u201cThe force required to stretch the muscle . . . is
called the preload. The term preload is also
used to indicate the length of the sarcomere or
muscle before contraction.\u201d (p. 43)
\u201cThe afterload represents an impediment to the
shortening of muscle fibers or to ejection in
the heart. The afterload for the ventricles is
the arterial pressure . . .\u201d (p. 163)
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TABLE 1\u2014Continued
Summary of published definitions of preload and afterload
Reference Preload Definition Afterload Definition
Circulatory Physiology (28) \u201c. . . during diastole a greater influx of blood into
the ventricle will cause the ensuing
contraction to be more forceful. This may be
thought of as a \u2018preload\u2019 stimulus since it was
applied before contraction began.\u201d (p. 76)
\u201c. . . he [Starling] controlled the right atrial
pressure (and thereby the right ventricular
diastolic pressure or preload) . . .\u201d (p. 76)
\u201cHe [Starling] also controlled the aortic pressure
(or afterload) by means of an artificial aortic
resistance.\u201d (p. 76)
Cardiovascular Physiology
(22)
\u201cDuring diastolic ventricular filling, for example,
the progressive increases in ventricular
pressure and volume combine to increase
muscle tension (T 5 P z r) . . .\u201d (p. 55)
\u201cEnd-diastolic pressure is referred to as
ventricular preload because it sets the resting
tension of the cardiac muscle fibers at the end
of diastole.\u201d (p. 55)
\u201cSystemic arterial pressure is often referred to as
the ventricular afterload because it
determines the tension which must be
developed by cardiac muscle fibers before
they can shorten.\u201d (p. 56)
Cardiovascular Physiology
(1)
\u201c. . . the preload refers to the stretch of the left
ventricle just before the onset of contraction
(the so-called end-diastolic volume) . . .\u201d
(p. 65)
\u201c. . . and the afterload refers to the aortic
pressure during the period when the aortic
valve is open.\u201d (p. 65)
Physiology of the Heart and
Circulation (18)
\u201cIt is customary to refer to this length [just
before contraction] in terms of the force or
preload required to stretch the muscle to its
precontraction length.\u201d (p. 77)
\u201cIn summary, cardiac afterload . . . is the left
ventricular myocardial force necessary to
overcome opposition to ventricular ejection.
In the clinical setting, as a rough index, it is
frequently related to aortic pressure.\u201d (p. 177)
An Introduction to
Cardiovascular Physiology
(15)
\u201cTo study the effect of stretch, the relaxed
muscle is stretched to a known length by
means of a small weight or preload . . .\u201d
(p. 78)
\u201cThe afterload is the stress, S [force per unit
cross-sectional area of wall], during systole,
and from the statement S 5 Pr/2w we see
that it depends not only on the arterial
pressure but also on chamber radius and wall
thickness.\u201d (p. 89)
Modern Cardiovascular
Physiology (11)
\u201cThis volume [end-diastolic volume] is often
termed preload because it is a load applied to
the muscle fibers before they contract.\u201d (p. 9)
\u201cThis resistance [to outflow] is termed the
afterload, since it is applied after contraction
is initiated.\u201d (p. 11)
Cardiovascular Physiology
(20)
\u201c. . . the upper end of the muscle is anchored,
and a weight (preload) is suspended from the
lower end. The resting force is equal to the
weight attached . . .\u201d (p. 94)
\u201cPreload, the force just prior to contraction
(Chapter 3), is related in the ventricle to end-
diastolic pressure.\u201d (p. 118)
\u201cThe afterload on an intact ventricle is
consequently not a simple quantity, and
authorities do not agree on how it should be
measured or expressed.\u201d
(p. 118)
\u201cThe input impedance of the systemic or
pulmonary arteries is the most appropriate
measure of ventricular afterload, but it is
complicated to analyze and takes the form of
a frequency-dependent spectrum (Chapter 6).
The choice is thus between a simple variable
like mean aortic pressure, which is an
indirect, partial representation of the real
afterload, and the more complete but
complicated analysis involving in computing
impedance.\u201d (p. 118)
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TABLE 1\u2014Continued