Control of cardiac output Flashcards
How do you calculate cardiac output?
CO = HR x SV
How do you calculate stroke volume?
End diastole volume - end systole volume
How can the force of contraction be increased?
Increasing the Ca2+ sensitivity of the contractile apparatus
Increasing the cellular concentration of Ca2+
What is Starling’s law of the heart?
“Force of ventricular contraction is dependent on the length of ventricular muscle fibres in diastole”
Intrinsic property of cardiac muscle
Isolated muscle cells stretching the sarcomere increase force of contraction
Length dependent increase in Ca2+ sensitivity results in greater number of cross bridges
How is end diastole volume regulated?
Venous return
Central venous pressure
What factors affect venous return to the right ventricle?
Blood volume Skeletal muscle pump Respiratory pump Venous tone Gravity
How does blood volume affect venous return?
Increased blood volume due to renal failure increases venous return
Decreased blood volume due to dehydration or haemorrhage leads to reduced venous return
How does the skeletal muscle pump affect venous return?
Skeletal muscle contraction increases venous return
How does the respiratory pump affect venous return?
Inspiration decreases thoracic pressure and increases abdominal pressure
How does venous tone affect venous return?
Increase in sympathetic activity will evoke venoconstriction
Venoconstriction reduces the volume of blood in the veins at a given pressure
Venoconstriction increases venous return
How does gravity affect venous return?
Supine Uniform distribution of blood across the body Standing Redistribution of blood due to gravity Venous pooling in lower extremities Reduction in thoracic blood volume Venous return is reduced
What is a pre-load factor?
Any factor which influences the stretch of cardiac muscle cells before contraction
What other factors affect EDV?
Atrial contraction
Heart rates over 180 beats/min
How is end systole volume regulated?
Increased contractility
How do we increase contractility?
Increased sympathetic nerve activity
Increased Ca2+ influx
Increased no. of cross bridge formation
