Effect of venous return, length-tension relationship, and afterload on stroke volume Flashcards
What will ventricular dialation give rise to?
Gives rise to an increase in ventricular compliance or the slope of LVEDPVR is less steep.
What does dilated ventricle enhances?
Venous return.
For the ventricular hypertrophy what decrease will there be in?
Ventricular compliance.
What effect does venous return have on preload?
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.
For a given heart the lesser the compliance, the slower the?
Venous return.
A decrease in preload caused by a decrease in compliance will lead to an increase in?
EDP.
An increase in EDP implies the heart must?
Contract more forcefully to counteract the increase in EDP in order to eject the blood. With a decrease in SV
Increase in venous return will?
- Increase preload.
-Stretch the myocardial contractile myocytes.
- Increase force of contraction.
- Increase stroke volume.
- Increase cardiac output with a given HR.
What is the Frank-Starling mechanism?
Ensures the outputs of both the ventricles are matched over time and to prevent the shift of blood between pulmonary and systemic circulations.
Increase in EDV will increase?
Ventricular developed force.
What does too much or too little overlap of thick and thin filaments results in?
Decreased tension.
What happens if an increase in SV by increasing the venous return or preload alone would cause?
An increase in contractility of a given heart then a decrease in ESV is expected.
What does the length-tension relationship illustrates?
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.
With an increase in preload there is?
an increase in active tension.
- Will be accompanied by an increase in the velocity of tension development.
How does the duration of contraction and the time from peak tension back to baseline remains the same?
With an increase in muscle length by stretching.
What is a sequence of the length-tension relationship?
- 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.
What is afterload?
- 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.
The magnitude of the ventricular wall tension developed is directly related to?
Resistance, impedance or pressure that the ventricle must be able to overcome before blood can be ejected.
What is one of the major components of afterload for the left ventricle?
Aortic pressure.
How can ventricular wall stress be estimated?
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 *
What can be observed from the Laplace’s law?
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.
Ventricular hypertrophy as an adaptive mechanism:
→ To offset an increase in wall stress.
→ Usually induced by the increase in afterload
e.g.) aortic stenosis or hypertension.
For heart failure e.g.) congestive heart failure (CHF):
- 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).
What does Frank-Starling curve describe?
The relationship between
LVEDV/LVEDP (preload) to SV
An increase in afterload shifts the Frank-Starling curve to?
Down and to the right.
Due to the an increase in afterload?
The heart have to generate a much higher pressure in order to eject the same volume of blood.
An increase in afterload will decrease the?
Velocity of fiber shortening during contraction.
A decrease in Velocity of muscle fiber shortening will result in?
A decrease in SV.
What does the y-intercept in the force-velocity relationship curve represent?
- Represents an extrapolated value for the maximum velocity (Vmax) that can be achieved by the muscle fiber in the absence of any load.
Vmax is an indicator for?
- The inotropic condition of a contractile muscle in a given physiological condition.
What does the x-intercept in the force-velocity relationship curve represent?
- Represents the maximum force that the heart can generate at a given preload condition.
For a given heart at a given inotropic condition, any
elevation in preload will result in?
- An increase in afterload, but with no effect on the Vmax.
Changes in afterload produces?
Secondary changes in preload.
When there is an increase in
afterload (e.g. increase in aortic pressure) the ventricle has to generate a?
- A higher pressure in order to open the aortic valve.
Higher afterload will?
- Decrease ejection velocity of blood resulting a decrease in SV and an increase in ESV.
The increase in ESV in the
ventricle will be?
- 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.
Steady state will be reached after?
Several beats such that cardiac output equals to the venous return.
