Control of Cardiac Output Flashcards
cardiac output formula
CO = HR x SV
stroke volume formula
SV = end diastolic vol - end systolic vol
typical CO at rest
5 l/min
typical maximal CO for untrained and trained individuals
untrained: ~23 l/min
trained: ~30 l/min
explain intrinsic control of CO
varying the length of cardiac muscle fibres depending on EDV (length-tension relationship)
explain extrinsic control of CO
varying the extent of sympathetic stimulation
what is the Frank-Starling law of the heart, why is it the case
increased venous return results in increased SV
increased EDV means the muscle fibres are more stretched and they generate greater force
what are the advantages of the length-tension relationship of CO
equalise output of either side of the heart
when larger CO is needed, venous return is increased via NS resulting in greater SV
what is the cellular basis of the length tension relationship of CO
greater initial length increases the sensitivity of contractile proteins and Ca2+ release from sarcoplasmic reticulum
define preload
the degree of ventricular stretch when the heart is at the end of diastole
define afterload
the work the heart needs to exert to eject the blood during systole
what is the effect of increased arterial blood pressure
ventricles must generate sufficient pressure to overcome pressure in major arteries and open semilunar valves
define contractility
the force of the heart muscle which contributes to SV
what is dP/dt
why is it a useful index of contractility
max rate of rise of pressure
independent of afterload as it is measured during isometric contraction phase
aortic and AV valves are shut
global assessment of contractility
