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83 Cards in this Set

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Define stroke volume
volume of blood ejected by the ventricle per beat
Stroke volume reflects the ability of the ventricular myocardium to develop?
Tension and shorten
SV is influenced by what three factors?
preload, afterload, contractility
What is the quantitative index of ventricular function?
SV
Define preload
degree of stretch of myocardial fibers prior to contraction
Preload is determined by?
VEDV
Frank-Starling law of the heart represents?
the relationship between preload and SV
Define afterload
force against which the ventricle must work to eject blood
What are components of afterload?
PVR and aortic compliance
Afterload is usually estimated by?
SBP (for the left ventricle)
Change in afterload can affect?
SV
What is one principal determinant of MVO2?
Afterload
Define contractility
index of the force and extent of ventricular contraction
Contractility is determined in part by?
the chemical environment of the cell
Contractility can be evaluated clinically with a?
ventricular pressure-volume loop or by measuring EF
What are some cardiac reserve mechanisms?
Increase HR, preload, contractility, and ventricular hypertrophy
Define cardiac output
the volume of blood pumped by the heart each minute
The afterload on the left ventricle may be considered to be the?
aortic blood pressure, and afterload on the right ventricle may be considered to be the pulmonary artery blood pressure
The afterload determines how much ______ the ventricular wall must develop before cell shortening and ejection can occur
force
An increased afterload will result in a decreased?
SV
When the chamber empties more completely due to an increase in contractility, ______ increases.
stroke volume
What is one major regulator of myocardial contractility?
the activity of the sympathetic nerves that innervate the ventricular muscle cells.
Ventricular function curves, plot?
some index of ventricular function versus some index of preload, permit one to assess the inotropic state (contractility)
Indices of ventricular function include?
1. SV
2. SW
3. Rate of pressure development dP/dt
Define stroke work
is approximated by the product of MAP and SV.
SW= MAP x SV
Indices of preload include?
1. end-diastolic volume
2. end-diastolic pressure
3. MAP (filling pressure)
4. Muscle length/tension
5. Resting force
The ventricular muscle mass increases from?
volume overload and/or pressure overload (increased afterload)
The ventricular cells tend to elongate when there is ?
a volume overload
The ventricular cells tend to thicken when there is?
pressure overload
When muscle cell length is at Lmax, thick and thin filament overlap is?
optimal and force development and rate and extent of shortening are maximal
At shorter cell lengths, thick and thin filament overlap is?
suboptimal and force development and rate and extent of shortening are submaximal
Also, at shorter lengths, there appears to be a decrease in?
the amount of calcium released to the contractile proteins which may contribute to the reduced contractile function when the preload is reduced
When cell length exceeds Lmax and the cells become overstretched, the overlap of thick and thin filaments is?
suboptimal and force development and rate and extent of shortening are also submaximal
What is a measure of preload?
LVEDP
Within limits, an increase in preload will lead to an _______ in stroke volume, if other factors remain unchanged.
increase
When preload changes, does the end-diastolic volume or the end-systolic volume change?
End-diastolic volume *
What is the Frank-Starling phenomenon?
An increase in preload produces an increase in ventricular pump function (SV)
With the Frank-Starling law, it is understood that the right and left ventricular output is?
equal
An increase in preload also leads to a?
-increased MVO2
greater work output and elevated energy usage by the left ventricle
* Afterload and shortening are _______ related.
inversely*
An increase in afterload will lead to a _____ in emptying, and, therefore a _______ in SV.
decrease, decrease
When afterload is increased, the volume ejected by the ventricle is? and what is increased?
reduced and the residual (end-systolic) ventricular volume is increased
What is the compensatory mechanism with an increased afterload?
volume ejected from ventricle is reduced so there is an increase in residual (end-systolic) volume. If volume entering the ventricle during diastole is not changed, the preload for the subsequent contraction is increased and stroke volume tends to return to its original level.
This compensatory mechanism is ______ driven.
preload
When is this preload compensation ineffective?
when aortic pressure rises above 180 mmHg (SBP)
If the heart muscle is not healthy, this compensation may be?
inadequate
With the preload compensation(increased afterload), do both EDV and ESV increase?
yes
T or F. The work of the heart and the oxygen requirements of the heart are increased dramatically by an increase in afterload?
True
When the contractile function of the myocardium is depressed, the heart cannot adequately respond to an increase in afterload and what falls?
SV
An increase in contractility produces?
an increase in rate of force development (dP/dt), and an increase in the rate and extent of shortening
An increase in contractility will tend to also increase?
the emptying of the ventricular chamber, thus, increase ESV and SV.
When contractility increases, preload (venous return) typically?
remains unchanged or is increased.
What happens to the pressure-volume loop with increasing SV when contracility is increased?
shift to left
What is responsible for the increased venous return in response to an increase in contracitility?
venoconstriction, sympathetically mediated
The sympathetic nerves that terminate on the heart release what neurotransmitter?
NE
NE does what to the ventricular muscle cells?
produce an increase in contractility
Activation of SNS leads to?
1. Increased contractility
2. Increased diastolic filling (increased preload) which results from venoconstriction
3. Increased HR which results from the action of NE on the SA node.
What other factors could increase contractility (5)?
1. Increased ECF calcium concentration
2. Increased plasma levels of Epi and NE
3. Increased SNS activity
4. Decreased extracellular hydrogen ion concentration
5. Many drugs (including digitalis)
What factors can decrease contractility (6)?
1. Decreased ECF calcium
2. Depressed plasma levels of Epi and NE
3. Decreased SNS activity
4. Increased extracellular hydrogen ion concentration
5. Many drugs
6. Decreased O2 supply (hypoxia, hypoxemia)
What are the cardiac reserve mechanisms?
1. Increased HR
2. Increased SV (Increased EDV=increased preload, decreased ESV=increased contractility)
3. Increased ventricular mass (hypertrophy)
Hypertrophy generally occurs in response to a?
pathophysiological condition
What are the two types of hypertrophy?
1. Chamber dilation
2. Wall thickening
Chamber dilation occurs when?
the ventricle is required to pump excessive quantities of blood (volume overloaded)
Wall thickening occurs when?
the ventricle is required to pump against a high afterload (pressure overloaded)
What can cause chamber dilation?
incompetence of either the mitral or aortic valves
If the mitral or aortic valve is incompetent, why does this cause hypertrophy?
the ventricle is required to pump large quantities of blood per stroke if a significant amount of regurgitation is present
In chamber dilation, hypertrophy occurs predominantly as a consequence of?
cell elongation (eccentric hypertrophy)
Cell elongation, causes the radius of the chamber to?
increase
With chamber dilation, the ventricular mass may _____, however, there is not generally a ______ in ventricular wall thickness
triple, large increase
The oxygen requirements of the ventricle may be?
elevated markedly, the work of the ventricle is increase, which increases oxygen usage, and there is also more tissue to supply
In chamber dilation, diastolic wall tension is?
enhanced, T= P x radius
Is the normal 1:1 ratio of myocardial fibers to capillaries maintained with chamber dilation?
yes, just elongation of fibers and capillaries
Concentric hypertrophy
occurs as a consequence of cell thickening, diameters of individual fibers increase
Wall thickening occurs when?
the left ventricle is required to pump against an elevated afterload (pressure overloaded)
What can cause concentric hypertrophy?
Aortic stenosis or chronically elevated arterial BP (hypertension)
Does the radius increase with concentric hypertrophy?
not generally
The pumping ability of the left ventricle is enhanced because of its?
greater wall thickness
Do oxygen requirements increase with concentric hypertrophy?
yes, and oxygen delivery may be reduced.
The greater ventricular mass requires an increased oxygen supply, the diffusion distances for oxygen are?
increased, and the work of ejection is increased
What occurs from the prolonged or chronic elevation in afterload?
eventually it leads to a severe depression in contractility which may be caused by a defect in the cellular handling or calcium ions
Which way does the ventricular function curve shift in response to 1. increased contractility and
2. decreased contractility
1. Shifts up and to the left
2. Shifts down and to the right
Which way does the ventricular function curve shift in response to 1. increased afterload and
2. decreased afterload
1. Down and to the right
2. Up and to the left
Is it more difficult to maintain a normal stroke volume if afterload is increased or decreased?
increased, afterload reduction is a common and important therapeutic measure