Lecture 6 Flashcards
What happens to blood in the heart during systole and diastole?
Systole: Ejects blood
Diastole: Fills w blood
What is preload
Tension or load on the ventricular muscles when it begins to contract/at the end of diastole
(Changes in myocardial muscle fibre length)
What is afterload
The force the muscle must overcome to open the valves and to eject a given volume of blood)
-Systemic vascular resistance/peripheral resistance = best marker for afterload
What is contractibility
Change in performance at a given preload or afterload
Isometric contractions
How does stretching a cardiac muscle affect the
tension (force) it can develop?
- Will increase passive tension
- Will increase the active tension up to a certain point
What is Lmax?
the optimum muscle length at which max tension can occur
Cardiac muscle usually around 85% Lmax
What does increasing preload do?
Increases force of contraction
What does increasing resting muscle fibre length do
Increases force of contraction
Isometric tension:
What can increase Tension-Length Profile upward?
Sympathetic stimulation
Ex: Norepinephrine, B1 activation
Define Inotropism
A change in active force
development in the absence of a change in preload
Explain the length-tension relationship
Increasing the resting length of a myocardial fibre will
increase the tension developed when the fibre
contracts
What effect does sympathetic simulation have?
- It increases force/tension at a particular length
- increases force of contraction
- Shifts isometric peak up and to the left
(Increases extent of shortening on a muscle)
What effect does afterload and preload have on shortening velocity?
Force-Velocity relationship
Increasing afterload:
-Smaller the shortening velocity (Ability for muscle to shorten is less)
Increasing preload:
-Greater the shortening velocity (Ability for muscle to shorten is more)
What effects do positive inotropes have
- Increase contractility = increase Vmax = improve rate of crossbridge cycling
- Increase the amount of shortening possible
Define inotropic state
Contractile ability of the heart
What are the major influential factors affecting stroke volume?
1) Preload
2) Afterlaod
3) Intropic state
As End diastolic volume increases stroke volume _____?
Increases
What’s Staring’s law of the heart?
Increasing preload = Increase stroke volume by increasing end diastolic volume
Cardiac performance curve
-A ventricular curve w/
Y-axis: Stroke volume
X-axis: Right atrial pressure
Functions of myocardial muscle fibre length
1) Central venous pressure
2) End diastolic volume
3) End diastolic pressure
4) Right atrial pressure
Functions of force of contraction
1) ventricular pressure
2) cardiac output
3) stroke work
4) cardiac output
Ventricular function curve
-Any graph whose x-axis is a function of myocardial muscle fibre length and whose y-axis is a reflection of contractile energy
What situations increase afterload?
1) Increasing aortic pressure
2) Increasing systemic vascular/total peripheral resistance
3) Aortic stenosis (Pressure overload on the left ventricle)
Explain Laplace’s Law of the dilated heart
Tension (Stress)= Pressure x radius/2xh (wall thickness)
-Dilated hearts need greater tension to generate same pressure = working harder = increased afterload
Explain laplace’s law and hypertrophy
Thickening of the walls of the ventricles through hypertrophy to combat to increase tension making ejection of blood easier
(Common in athletes)
What are some positive inotropes?
1) B receptor agonists
- Isoprenaline
- Dobutamine
2) Cardiac Glycosides
- Digoxin (Increases cytoscolic ca+ = increase contractibility)
