Curva de Presion y Volumen Cardiaco Ciclo
Curva de Presion y Volumen Cardiaco Ciclo
Curva de Presion y Volumen Cardiaco Ciclo
Chapter
Cardiac Pressure–Volume Loops
31
Describe the left ventricular pressure– Ventricular ejection, in which the stroke volume
(SV) is ejected into the aorta.
volume loop Isovolumetric relaxation, a vertical line
The left ventricular pressure–volume loop provides a representing the fall in intraventricular pressure
useful representation of left ventricular performance without a change in ventricular volume.
through the cardiac cycle (Figure 31.1; see also Diastolic ventricular filling, in which the ventricle
Chapter 28, Figure 28.1). fills with blood ready for the next contraction.
In a normal left ventricle (LV), the pressure–
volume loop is approximately rectangular and can
be divided into four phases: How does the pressure–volume loop
Isovolumetric contraction, a vertical line change when preload is increased?
representing the increase in intraventricular Preload can be thought of as the volume of blood
pressure without a change in ventricular volume. within the ventricle prior to contraction (see
120
Systolic BP
Left ventricular pressure (mmHg)
80
contraction
Isovolumetric
relaxation
60
40
0
0 20 40 60 80 100 120 140 160
Left ventricular end- Left ventricular volume (mL)
diastolic pressure Stroke volume
End-systolic volume
136
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Chapter 31: Cardiac Pressure–Volume Loops
Chapter 29). For the LV, it is the left ventricular end- the shortening of cardiac myocytes. As afterload
diastolic volume (LVEDV). According to Starling’s increases (e.g. due to an increase in diastolic aortic
law, an increase in preload results in a greater dia- pressure), both the rate and extent of sarcomere
stolic stretch of the contractile myocardial fibres (see shortening decrease, resulting in a reduction in SV:
Chapter 30). The stretched sarcomeres contract more As a reduced volume of blood is ejected from the
forcefully, thus increasing SV (Figure 31.2). LV, the LVESV is increased.
Figure 31.2 illustrates a number of important features: In turn, the addition of the venous return leads to
The width of the pressure–volume loop, which an increase in LVEDV.
represents SV, is increased due to the increase in According to Starling’s law, an increase in LVEDV
LVEDV. The left ventricular end-systolic volume causes an increase in myocardial contractility.
(LVESV) increases slightly due to an increase in Thus, SV increases, returning LVEDV to near
afterload (aortic pressure) caused by the greater normal.
cardiac output.
Overall, the increase in LVESV is greater than that of
The end-diastolic pressure–volume relationship LVEDV. SV is slightly decreased, and the left ven-
(EDPVR) line reflects the passive diastolic tricular pressure–volume loop looks taller and thinner
compliance of the LV. Beyond a certain preload, (Figure 31.3a).
left ventricular end-diastolic pressure (LVEDP)
increases sharply, reflecting the nonlinear
compliance of the left ventricular wall. This is due How does an increase in myocardial
to the elastic proteins and connective tissue within contractility alter the pressure–
the myocardium reaching their elastic limit.
volume loop?
Myocardial contractility may be altered extrinsically by
How does the pressure–volume loop the autonomic nervous system, circulating hormones
change when afterload is increased? or positively inotropic drugs. It is therefore independ-
Afterload is the stress developed in the left ventricular ent of preload and afterload. Graphically, increased
wall during ejection, and it reflects the force opposing contractility (positive inotropy) increases the gradient
120
Left ventricular pressure (mmHg)
100
80
60
40 LVEDP
increased EDPVR
20
Higher end-diastolic volume
0
0 20 40 60 80 100 120 140 160 180 200
Left ventricular volume (mL)
Stroke volume increased
Figure 31.2 Effect of increased preload on the pressure–volume loop (BP = blood pressure; EDPVR = end-diastolic pressure–volume
relationship; LVEDP = left ventricular end-diastolic pressure).
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Section 3: Cardiovascular Physiology
160 160
Increased Increased contractility
systolic and
140 140
diastolic BP
Left ventricular pressure (mmHg)
100 100
80 80
60 60
40 40 LVEDV is
EDPVR
LVESV is lower slightly lower
20 20
0 0
0 20 40 60 80 100 120 140 160 180 200 0 20 40 60 80 100 120 140 160
Stroke volume Left ventricular Stroke volume Left ventricular
is reduced volume (mL) is increased volume (mL)
Figure 31.3 Effect of (a) increased afterload and (b) increased contractility on the pressure–volume loop (BP = blood pressure).
120
Following the addition of venous return, LVEDV is
reduced. As positive inotropy decreases LVESV more 100 Area = external work
than LVEDV, overall SV is increased.
80
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Chapter 31: Cardiac Pressure–Volume Loops
The total work done – that is, the sum of external and Increased afterload may not increase external
internal work – is known as the pressure–volume area work significantly, but does increase internal work
(PVA). PVA correlates surprisingly well with the myo- (Figure 31.3a); thus, myocardial O2 demand
cardial O2 consumption for the heart. Note: whilst increases.
mechanical work accounts for most of the heart’s Increased myocardial contractility may not
energy expenditure, basal metabolism accounts for a increase internal work, but does increase external
small percentage, resulting in a small discrepancy work (Figure 31.3b). Overall, myocardial O2
between PVA and myocardial O2 consumption. consumption is increased.
Looking back at Figures 31.2 and 31.3, it can be
seen that: How does the pressure–volume loop of
Increased preload leads to increased external work
(Figure 31.2); thus, myocardial O2 demand is higher. the right ventricle compare with that of
the left?
The right ventricular pressure–volume loop has a
characteristic triangular shape (Figure 31.5). Some
Right ventricular pressure (mmHg)
120 120
Left ventricular pressure (mmHg)
Left ventricular pressure (mmHg)
100 100
Increased LVEDP,
80 80 reduced LVEDV
60 60
EDPVR
40 EDPVR 40
20 20 Reduced left
Increased
ventricular
EDV
compliance
0 0
0 20 40 60 80 100 120 140 160 180 200 0 20 40 60 80 100 120 140 160 180 200
Left ventricular Stroke volume Left ventricular
Stroke volume volume (mL) volume (mL)
reduced reduced
Figure 31.6 Left ventricular (a) systolic failure and (b) diastolic failure.
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Section 3: Cardiovascular Physiology
In the RV, stroke work makes up a greater contractility (reduced gradient of the ESPVR line) and
proportion of the total work than the LV does. an increase in LVEDV. A subnormal SV is ejected
The RV is therefore more susceptible to failure from the LV, resulting in a higher than normal
in the presence of pulmonary hypertension LVESV (Figure 31.6a).
than the LV is in the presence of systemic Left ventricular diastolic failure is due to reduced
hypertension. left ventricular compliance. The EDPVR line follows
a different course, but the contractility of the LV
How does the left ventricular pressure– (the ESPVR line) is unchanged. Overall, SV is reduced
(Figure 31.6b).
volume loop change in heart failure?
As discussed in Chapter 30, left ventricular failure is Further reading
classified as systolic, diastolic or mixed. Left ventricu- R. E. Klabunde. Cardiovascular Physiology Concepts, 2nd
lar systolic failure results in a reduction in myocardial edition. Philadelphia, Lippincott Williams & Wilkins, 2011.
140
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