Ventricular Function Flashcards
resting tension
the amount of tension that develops passively by stretching muscle
active tension
the amount of tension that is developed by the muscle by an active process (contraction) at a particular length
preload
force placed on muscle before contraction beings (pre)
muscle is passive as preload is applied
causes muscle to passively lengthen
intact heart, preload is the volume that fills the chamber during the diastolic phase
isometric contraction
contraction without change in length
isotonic contraction
contraction with shortening and constant muscle tone
effects of increasing preload on isometric contraction
increasing preload increases amount of tension developed
time to peak tension unchanged
increases dT/dt
optimal length
the sarcomere length that produces the maximal tension development - due to better crossbridge alignment
length dependent calcium sensitivity
as length of muscle increases, so does the sensitivity to calcium
contractility
a change in force development, independent of change in muscle length due to load
changing contractility alters the amount of tension developed and the time to peak tension (isometric)
increasing preload at constant afterload and contractility
- Decreases the time to the onset of shortening. (Note the dotted vertical lines in A)
- Increases the amount of shortening. (A, B, C)
- Increases shortening velocity. (Note differences in dL/dt in A). Shortening velocity increases with increased preload.
- Does not affect the maximum tension reached (This is determined by the afterload!).
increasing afterload at constant preload and contractility
- Increasing afterload decreases the amount of shortening
- Increasing afterload decreases the velocity of shortening
- Increasing afterload increases the total tension developed in the muscle.
What happens to Vmax when contractility is increased?
increased
ejection fraction equation
EF= { EDV-ESV } / EDV * 100
preload in the heart
stretches cardiac muscle passively toward its optimal length
passively positions contractile elements for interaction
alters calcium sensitivity
equivalent to EDV
afterload in the heart
opposes shortening (ejection)
analogous to arterial pressure
in some diseases, also due to obstrictive structures such as aortic valve stenosis or hypertrophied muscle
