Cardiac Muscle Mechanics Flashcards
What are the 4 determinants of cardiac output?
Heart Rate
Preload
Afterload
Contractility
What is preload?
Preload is the load on the heart BEFORE contraction -> tension
What is after load?
Afterload is the load on the heart after contraction -> any FORCE that resists muscle shortening
What is contractility?
Amount of force generation of the heart and is [Ca2+] dependent
What is isometric contraction?
Contraction without shortening. It occurs as the heart blood pressure increases until it overcomes the aortic pressure.
What is isotonic contraction?
It is contraction with shortening and it occurs after the aortic pressure is overcome and the heart contracts to pump blood out.
What is diastolic tension?
It is tension based on the stretching of the preload and is related to the compliance of the heart.
What is systolic tension?
It is isometric tension generated at a particular preload, and increases in preload will increase the systolic tension. It is related to the contractility of the heart.
What is compliance and how does it affect the resting tension curve?
Compliance is the measure of how much volume changes alter the pressure. The heart has a low compliance as small volume changes cause large pressure changes. It determines the diastolic slope of the filling curve.
How does contractility affect the active tension curve?
Contractility increases will shift the curve up and left as the muscle can generate more tension but it can also generate more tension at the same muscle length as it can shorten more than before.
How does preload determine isometric tension development?
Preload stretches cardiac muscle which creates better actin-myosin overlap and increase the sensitivity to Ca2+ leading to an increased tension development.
How do increases in contractility affect peak isometric tension?
It will increase the peak isometric tension and reduce the relaxation time needed.
What is the force-velocity relationship?
The force generated determines the velocity of muscle shortening.
How do changes in the preload affect the force-velocity relationship?
Increases in preload will shift the curve up and right, but will not increase the maximum velocity. At any given after load, increased preload increases the velocity of shortening.
How do changes in the after load affect the force-velocity relationship?
Increasing the after load will decrease the velocity of contraction. The muscle contracts with maximum velocity at 0 force and with 0 velocity and maximum force.
