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Cardiovascular Physiology 2, 1: Atrial pressure higher than ventricular…
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1: Atrial pressure higher than ventricular pressure, blood flow passively into ventricles
2: Ventricular volume rising
3: SA node fire and impulse spread through atria (P wave)
4: Atrial pressure increase
5,6: Volume in ventricles increase leading to an increase in ventricular pressure
7: Atrial contraction complete.
End diastolic volume (EDV) ~ 135ml
Impulse passes through AV node
8: QRS – ventricular excitation
9: Sharp increase in ventricular pressure
1st heart sound: AV valves close
9-12: Isovolumetric ventricular contraction – All valves close, no change in volume or muscle length, pressure continue to increase
12: Ventricular pressure > aortic pressure (aortic valves open and blood ejected)
13: Aortic pressure increase as blood is pumped into aorta faster than blood can drain off smaller vessels at the other end
14: Ventricular volume decrease
15: End systolic volume (ESV) – blood not
pumped out totally
16: T wave – ventricular repolarisation
17: Ventricles relax, pressure drops
18 & 2nd heart sound: ventricular pressure < aortic pressure, aortic valve close.
19: All valves closed again. Isovolumetric relaxation
20: Chamber volume remains constant
21: Ventricular pressure < atrial pressure (AV valves open)
22: Atria pressure increasing due to constant flow of blood from veins
23: Pool of blood in atria rush into ventricles when AV valves open (rapid filling)
24: Filling of blood slow down
25: SA node fire and impulse spread through
atria again (P wave).
Cardiac cycle repeat
Heart cannot be empty, otherwise there'll be a vacuum in the heart.