Ventricular function

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