Effect of venous return, length-tension relationship, and afterload on stroke volume

Question 1

What will ventricular dialation give rise to?

Answer 1

Gives rise to an increase in ventricular compliance or the slope of LVEDPVR is less steep.

Question 2

What does dilated ventricle enhances?

Answer 2

Venous return.

Question 3

For the ventricular hypertrophy what decrease will there be in?

Answer 3

Ventricular compliance.

Question 4

What effect does venous return have on preload?

Answer 4

An increase in VR will increase ventricular filling and therefore increase preload.

- Also an increase in end-diastolic volume.
       - Will cause an increase in end-diastolic pressure for any given heart.

Question 5

For a given heart the lesser the compliance, the slower the?

Answer 5

Venous return.

Question 6

A decrease in preload caused by a decrease in compliance will lead to an increase in?

Answer 6

EDP.

Question 7

An increase in EDP implies the heart must?

Answer 7

Contract more forcefully to counteract the increase in EDP in order to eject the blood. With a decrease in SV

Question 8

Increase in venous return will?

Answer 8

• Increase preload.

-Stretch the myocardial contractile myocytes.

• Increase force of contraction.
• Increase stroke volume.
• Increase cardiac output with a given HR.

Question 9

What is the Frank-Starling mechanism?

Answer 9

Ensures the outputs of both the ventricles are matched over time and to prevent the shift of blood between pulmonary and systemic circulations.

Question 10

Increase in EDV will increase?

Answer 10

Ventricular developed force.

Question 11

What does too much or too little overlap of thick and thin filaments results in?

Answer 11

Decreased tension.

Question 12

What happens if an increase in SV by increasing the venous return or preload alone would cause?

Answer 12

An increase in contractility of a given heart then a decrease in ESV is expected.

Question 13

What does the length-tension relationship illustrates?

Answer 13

It illustrates relationship between changes of the initial length of a myocyte to the contractile force developed by the heart muscle.

     - The length-tension relationship explains why an increase in EDV will result in an increase in SV with no change in ESV.

Question 14

With an increase in preload there is?

Answer 14

an increase in active tension.
- Will be accompanied by an increase in the velocity of tension development.

Question 15

How does the duration of contraction and the time from peak tension back to baseline remains the same?

Answer 15

With an increase in muscle length by stretching.

Question 16

What is a sequence of the length-tension relationship?

Answer 16

• Increase in preload.
• Increase in stretching of muscle.

-Increase in active tension
development.

• Resulting an increase in
  dL/dt (increase in the rate
  of muscle shortening).
• Increase in force of contraction Increase in SV.

Question 17

What is afterload?

Answer 17

• Afterload can be defined as the ventricular wall tension (stress) developed during ventricular ejection (systole).
• Can also be defined as the load against which the heart must counteract before blood can be ejected out.

Question 18

The magnitude of the ventricular wall tension developed is directly related to?

Answer 18

Resistance, impedance or pressure that the ventricle must be able to overcome before blood can be ejected.

Question 19

What is one of the major components of afterload for the left ventricle?

Answer 19

Aortic pressure.

Question 20

How can ventricular wall stress be estimated?

Answer 20

By the Laplace’s law for a sphere.

  - Wall stress is proportional to the product of the intra-ventricular pressure (p) and ventricular radius (r), divided by the wall thickness (h).
* σ α (p * r) / 2h *

Question 21

What can be observed from the Laplace’s law?

Answer 21

1) σ increases in response to a higher pressure load (p) e.g.) Hypertension.

2) σ increases in response to an increase in the ventricular chamber size (r) e.g.) an ↑ in pre-load.

3) An increase in ventricular wall thickness (h) will reduce wall stress (σ) and therefore reduce the afterload e.g.) Left ventricular hypertrophy.

Question 22

Ventricular hypertrophy as an adaptive mechanism:

Answer 22

→ To offset an increase in wall stress.

→ Usually induced by the increase in afterload
e.g.) aortic stenosis or hypertension.

Question 23

For heart failure e.g.) congestive heart failure (CHF):

Answer 23

• With left ventricular dysfunction, there is an increase in LVESV resulting in a secondary increase in preload.

→ Frank-Starling mechanism fail to compensate the
increase in pre-load due the decrease in contractile function of the heart giving rise to an enlarged heart (cardiomegaly).

Question 24

What does Frank-Starling curve describe?

Answer 24

The relationship between
LVEDV/LVEDP (preload) to SV

Question 25

An increase in afterload shifts the Frank-Starling curve to?

Answer 25

Down and to the right.

Question 26

Due to the an increase in afterload?

Answer 26

The heart have to generate a much higher pressure in order to eject the same volume of blood.

Question 27

An increase in afterload will decrease the?

Answer 27

Velocity of fiber shortening during contraction.

Question 28

A decrease in Velocity of muscle fiber shortening will result in?

Answer 28

A decrease in SV.

Question 29

What does the y-intercept in the force-velocity relationship curve represent?

Answer 29

• Represents an extrapolated value for the maximum velocity (Vmax) that can be achieved by the muscle fiber in the absence of any load.

Question 30

Vmax is an indicator for?

Answer 30

• The inotropic condition of a contractile muscle in a given physiological condition.

Question 31

What does the x-intercept in the force-velocity relationship curve represent?

Answer 31

• Represents the maximum force that the heart can generate at a given preload condition.

Question 32

For a given heart at a given inotropic condition, any
elevation in preload will result in?

Answer 32

• An increase in afterload, but with no effect on the Vmax.

Question 33

Changes in afterload produces?

Answer 33

Secondary changes in preload.

Question 34

When there is an increase in
afterload (e.g. increase in aortic pressure) the ventricle has to generate a?

Answer 34

• A higher pressure in order to open the aortic valve.

Question 35

Higher afterload will?

Answer 35

• Decrease ejection velocity of blood resulting a decrease in SV and an increase in ESV.

Question 36

The increase in ESV in the
ventricle will be?

Answer 36

• Added with the normal venous return, result an increase in EDV.
  • However, the increase in ESV due to the increase in afterload is greater than the increase in EDV such that the difference between EDV and ESV (stroke volume) is decreased.

Question 37

Steady state will be reached after?

Answer 37

Several beats such that cardiac output equals to the venous return.