14: Regulation of cardiac output Flashcards
Cardiac output equation
CO= SVxHR
Cardiac output
Varies with O2 demands
Same as flow
Stroke volume
SV= end diastolic volume - end systolic volume
Main regulator of heart rate
ratio of parasym to symp inputs
Chronotropic
Heart rate
What increases chronotropic effects
Norepinephrine binding to B-1 androgenic receptors in SA
What decreases choronotropic effects
ACh binding to muscarinic receptors on pacemaker cells
Why does cardiac output not increase at a linear rate as heart rate increases
Stroke volume decreases
Lusitropic effects
Increase and decrease rate of relaxation
What is the cause of positive Lusitropic effect
better cross bridge formation for Ca
Inotropic changes
Changes in contractility
intrinsic regulation of inotropic effects
mechanical properties of cardiac muscle
extrinsic regulation of inotropic effects
sympathetic innervation
hormonal
blood gas
pH
Active tension of sarcomeres is dependent on
Starting length of sarcomeres at time of activation
Actin-myosin overlap
Total tension =
Passive tension + active tension
Isometric
No blood movement
Isotonic
blood movement
What determines if a stretch will be active or passive
External constraints
What are examples of external constraints in the heart
End dyistolic volume
Aortic pressure
Preload
Stretch on the cardiac muscle that occurs during the relaxed state
End diastolic volme
Volume load during diastole
What does preload determine
the force generated y the cardiac muscle for the subsequent contraction
Frank-Starling mechanism
Stroke volume increases if the EDV increases and everything else is constant
Equalize outputs between right and left ventricles
Isotonic contraction phase
Total muscle force exceeds the external load and muscle begins to shorten
What force does the ventricles need to overcome during isontonic contraction
Aortic pressure
What is the end systolic volume dependent on
afterload and contractility
What does an increase in aortic pressure do to stroke volume
Decrease stroke volume
Contractility
performance of the heart at a give preload and afterload
What determines contractililty
Changes in intracellular Ca and a rate of contractile protein interaction
How is cardiac muscle contractility gaded
Extrinsic mechanisms
4 hormonal influences on myocardial function
- Epinephrine
- Thyroid hormone
- Increases in CO2
- Myocardial ischemia
