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 Cardiac Output and HR  

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Ok so my textbook says that Cardiac Output can stay the same within a certain HR range. When HR becomes super fast, the ventricles do not fill properly leading to decreased End Diastolic Volume and when it is super slow, not enough blood is being pump through the system (as a unit of time).

What I don't understand is how an increase or decrease in HR keeps CO normalized??
Is it because an increase in HR= a decrease in SV due to ventricles not filling optimally? But contractility increases with increased HR (Treppe/Staircase effect).

CO = HR x SV ---> does a decrease in HR = increase in SV (and vice versa).



dude,you said it yourself.

CO depends on both.if one increases the other one decreases and CO to some extent remains constant.


in tachycardia there is less time for proper ventricular filling so there is less SV but CO remains normal in some extent due to more beating of heart than normal in each bradycardia there is enough time for ventricular filling so there will be more force of contraction(according to frank starling law"within the physiological limit the greater the length of cardiac muscle fibre the greater will be the force of contraction") so SV will be more.......& CO remains normal.


Q(cardiac output) = HR x SV
btw cardiac output is Q not CO...CO is carbon monoxide

Three factors affect stroke volume: EDV, ESV, and strength of ventricular contraction

EDV (Preload)

ESV (afterload)


Tension = (TP x r)/ Thickness

r= radius

( increased HR)

< ventricular filling = < r = < Tension developed = < contractility = < SV

CO = HR x SV

( increased HR , Decreased SV )

( Decreased HR , Increased SV )

Edited by josedoad on Sep 12, 2013 - 8:53 PM

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