L11 Heart- Cardiac Muscle Mechanics Flashcards
Define the four determinants of cardiac output.
Heart rate
Preload
After load
Contractility
How does heart rate affect cardiac output?
Increased HR= increased cardiac output
How does preload affect cardiac output?
Increase in preload= increase stretch= increase cardiac output/stroke V
How does afterload affect cardiac output?
Increase afterload (BP)= decrease cardiac output/ stroke V
How does contractility affect cardiac output?
Increase contractility= Increase cardiac output/ stroke V
Define isometric contraction.
Contraction WITHOUT shortening (no change in length)
-Muscle unable to generate enough force to meet the afterload
Define isotonic contraction.
Contraction WITH shortening and constant force (no change in force)
-Muscle is able to generate enough force to meet afterload
Define resting (diastolic) tension.
Amount of tension that develops passively by stretching the muscle (increasing preload)
- Preload is ventricular filling volume (end-diastolic V)
- Slope of resting tension curve is primarily determined by muscle compliance
Define active (systolic) tension.
Amount of isometric tension that is developed by muscle contraction at a particular muscle length (preload)
- Systolic tension curve represents stroke V
- Slope of active tension curve is primarily determined by contractility
Define the length-tension relationship of cardiac muscle.
1
Define compliance.
Change in volume (length) in relation to change in pressure (tension)
change in V = Change in length
__________ _____________
Change in P Change in tension
-How much does something move when you push on it? How much does something stretch when you apply tension?
How does compliance affect the slope of the resting tension curve?
1
Define contractility.
I
How does contractility affect the slope of the active tension curve?
1
Define how contractility affects peak isometric tension development and relaxation.
1
Define how contractility affects the amount of isotonic muscle shortening.
1
Define the force-velocity relationship.
1
How is the force-velocity relationship affected by changes in preload?
1
How is the force-velocity relationship affected by changes in afterload?
1
How is the force-velocity relationship affected by changes in contractility?
1
How is stroke volume affected by changes in preload?
1
How is stroke volume affected by changes in afterload?
1
How is stroke volume affected by changes in contractility?
1
Define preload
Load on the muscle BEFORE contraction is initiated, how much blood is in the heart before contraction
-Dependent on ventricular filling (end-diastolic V)
Define afterload
Load on the muscle AFTER contraction is initiated, any force that resists muscle shortening, BP
-Arterial pressure is the force that resists L ventricle contraction
Define contractility
Inherent ability of actin and myosin to form cross-bridges and generate contractile force
- Primarily determined by intracellular Ca
- More intracellular Ca= more cross bridge formation= stronger contraction
- Increased contractility (postive inotropic effect) shifts slope of active tension curve up and left
- Decreased contractility (negative inotropic effect) shifts slope of active tension curve down and right
During a normal cardiac cycle, cardiac muscle initially generates _______ tension and then ______ contractions.
Isometric, isotonic
What is the equation for cardiac output?
HR x stroke V
