Cardiac function Flashcards
Formula for cardiac output
Stroke volume (L/beat) x heart rate (beat/min)
Units for cardiac output
litres/min
What is the normal stroke volume at rest
70ml
What is the normal heart rate at rest
70 beats per minute
What is the normal cardiac output at rest
5L/min
What does control of cardiac output depend on
- Factors affecting heart rate
- Factors affecting stroke volume
What are the factors influencing heart rate
- Sympathetic nervous system
- Pasasympathetic nervous system
- Hormones
- EXtra/intracellular ions
How does the sympathetic nervous system inleucne heart rate
Activation of Beta adrenoceptors causes an increase in heart rate
How does the parasympathetic nervous system incuelce heart rate
Activation of muscarinig receptors causes a decrease in heart rate
How do hormones affect heart rate
Adrenaline acts on Beta adrenoceptors which causes an increase in heart rate
How do extra/intracellular ions affect heart rate
alterations in membrane potential (eg potassium)
What is stroke volume
Volume of blood ejected by each ventricle in a single heart beat
What does stroke volume represent
Difference between the end diastolic volume (EDV) and the end systolic volume (ESV)
Whats the EDV
End diastolic volume =
Amount of blood contained within ventricle when ventricle is fully relaxed
Whats the ESV
ESV= Amount of blood that remains in ventricle after ventricular contraction
What is stroke volume determined by the interaction of
- pre-load
- cardiac contractility
- after-load
Normal value of EDV
140ml
Normal value of ESV
70ml
What is pre-load
how much blood is coming back into the heart from venous system
What is the after-load
How hard it is to pump the blood
What is end diastolic volume dependent on
End diastolic pressure (pre-load)
What is stroke volume primarily influenced by
Venous return (ie venous tone, blood volume, posture, intrathoracic pressure)
What is venous tone
Contraction of veins
What can filling time influence
Stroke volume
