Lecture 12 - Cardiac Function Flashcards
What affect does the fact that AFTERLOAD is not constant, have on the shape of the ejection phase of the P-V loop?
since after load is not constant,
the PV loop at ejection is NOT FLAT
- curved due to changing after load in aorta
(rapid & reduced ejection)
What is the ejection fraction of the Ventricle? State the components of the nominator and denominator
EF = (EDV - ESV)/ EDV * 100
Ejection fraction is the fraction of blood ejected during one stroke of the heart in relation to the total left ventricular END- DIASTOLIC Volume
- stroke volume/ end-diastolic volume
What clinical index is the ejection fraction used for?
CONTRACTILITY
What is a normal ejection fraction?
60%
What affect does preload have on:
- resting tension
- On maximum tension development
- Shortening
- Increasing preload - increases resting tension
- Maximum tension development is NOT changed by an increase in preload
- MORE SHORTENING
- move up the resting tension curve, which allows for a greater change in muscle length (increased muscle shortening)
What affect does an increase in preload have on:
- EDP
- Stroke Volume
- ESP
- End-Diastolic Pressure INCREASES when preload increases
- Stroke volume increases
- NO CHANGE on end systolic pressure
What affect does changing the after load have on
- Tension Development
- Shortening
- Increases the Tension Development
- moves from one value on peak Isometric tension curve to a higher value on the curve - Decreases shortening
What affect does changing the after load have on:
- Pressure Development Before Ejection
- Stroke Volume
- Increased pressure development
- increased energy used - Decrease in Stroke Volume
- blocking a tube that is trying to force water out - result is less water can go out
END-SYSTOLIC VOLUME changes to a higher value -
What affect does changing the Contractility have on the muscle/tension graph?
SHIFT UP AND LEFT w/ an increase in contracttility
- More muscle shortening
- after load and preload not changed
What affect does changing contractility have on the PV graph?
- Stroke Volume
- Ejection velocity
- Increased Stroke Volume
2. Increased Ejection Velocity
What are 3 ways to maximize shortening of muscle or STROKE volume in the heart?
- Increase preload
- Decrease after load
- Increase contractility
What is heart failure?
Condition in which the heart fails to provide cardiac output sufficient to meet the needs of the body.
What are 2 types of Heart failure?
- Systolic
2. Diastolic
What changes in Systolic & Diastolic Heart Failure? How is the curve of the diastolic and diastolic graph changed?
- Systolic - decrease in contractility
- curve shifted down - Diastolic - decrease in compliance
- curve shifted up (decrease compliance increases the slope and thus increases the pressure exerted on the ventricle)
What 4 changes in Stroke Volume as a result of changes in Preload
- Pressure Gradient
- Time for Ventricular Filling
- Ventricular COmpliance
- Atrial Function
How does changing the pressure gradient result in a change in the preload? How does it affect the end-diastolic pressure as a result?
- if there is a decrease in the pressure gradient between the atria and ventricles, there is less passive outflow to fill the ventricle
- this increases end-diastolic pressure and decreases ventricular filling
How can time for ventricular filling change, resulting in a change in the preload?
- increasing the heart rate, decreases ventricular filling time
How can ventricular compliance change, resulting in a change in the preload?
Less compliance results in a decrease in filling
How can Atrial Function change, resulting in a change in the preload?
Decreased atrial function due to ATRIAL FIBRILLATION decreases the filling time
How can contractility be changed in the heart?
- Sympathetic nerve activity increases contractility (enhances relaxation via Ca increases)
- Drugs (digitalis)
- increases contractility, by inhibiting Na/K pump and causing the Na/Ca pump to leave more Calcium in - Disease (loss of myocardium/ dysfunctional myocardium)
What are three common changes in after load that change the stroke volume?
- Aortic pressure
- Ventricular Outflow Resistance
- Ventricular Size
What is a way of increasing aortic pressure? What is the result?
- Hypertension (disease)
- increase in AFTERLOAD
What is a way of increasing ventricular outflow tract resistance?What is the result?
- STENOSIS!!! - valvular stenosis to be specific
2. Increase in after load
How is ventricular size (wall tension) change the after load?
Increasing the ventricular size (dilated hearts) results in higher wall tension
therefore a LARGER AFTERLOAD
- hard to overcome
How does changing heart rate affect:
- Contractility
- Ventricular FIlling time
- Increased HR - INCREASES contractility due to the force- frequency relationship
- increase stimulation of L-Type calcium channels, Na/K ATP as does not keep up with influx of Na - less time for CALCIUM HANDLING - Increased HR - Decreases ventricular filling time
What 3 factors influence HR?
- Pacemaker Function
- AV Nodal COnduction
- ventricular Arrhythmias
How can pacemaker function be changed?
- activation of latent pacemaker changes the ventricular rate
- enhancing or depressing the pacemaker function with Autonomics (changing slope, the maximum diastolic potential, or threshold of diastolic depolarization)
How can AV nodal Conduction be changed?
- 2nd or 3rd degree heart block
2. Atrial Fibrillation and Atrial FLutter
can progress to affect ventricles
Ventricular Arrhythmias do not affect heart rate. True or False.
FALSE
How does load affect the following:
- velocity of shortening in the ventricle? (ejection velocity)
- Amount of Shortening in the ventricle? (stroke volume)
- Increasing the load decreases the velocity of shortening
2. increasing load - decreases shortening
How does a change in contractility affect:
- Velocity of Shortening
- Amount of Shortening
- in cardiac muscle
- Increased contractility increases velocity of shortening
2. Increasing contractility INCREASES amount of shortening as well
