Cardiac cycle
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How do we calculate arterial blood pressure?
ABP = SV x HR x TPR
What may change the cardiac cycle?
Exercise Heart failure
What can be used to measure pressure changes?
Cardiac catheter Echocardiography
What is the chain of events in the cardiac cycle?
Electrical activity Mechanical activity Pressure changes Volume changes
Whats the average duration of the cardiac cycle?
850ms
What is the average duration of diastole?
600ms
What is the average duration of systole?
200ms
What increases pressure in a chamber?
The muscle around it contracting
What variables affect pressure changes?
Thickness of the muscle
What opens valves?
A positive pressure gradient
Where does blood move?
Down a pressure gradient From high pressure to low pressure
What is the first stage of the cardiac cycle?
Ventricular pressure falls below atrial pressure Mitral valve opens Atrial blood flows into ventricle “Rapid filling” Aortic valve remains closed as aortic pressure is greater than ventricular pressure
What happens at the end of ventricular diastole?
Atrial systole
What is the result of atrial systole?
A little more blood added to the ventricles 5ml of 120-130ml
What is the second stage of the cardiac cycle?
Ventricular systole Ventricular pressure higher than atrial pressure Mitral valve closes Aortic valve still closed "Isovolumetric contraction"
What is meant by isovolumetric contraction?
Contracting the same volume of liquid No change of volume All valves closed
What is the third phase of the cardiac cycle?
Ventricular ejection Ventricular pressure higher than aortic pressure Aortic valve opens
How come the aortic valve doesn’t shut soon after open?
Regardless of the pressure gradient, momentum keeps the aortic valve open
What is the fourth phase of the cardiac cycle?
Ventricular diastole Aortic valve closes Mitral valve still closed This is called isovolumetric relaxation
What is the end systolic volume and what is its role?
50ml of blood In case of need to rapidly increase stroke volume
What are normal pressures in the aorta?
120/80
What are normal pressures in the pulmonary artery?
25/10
What are normal pressures in the right atrium?
4
What are normal pressures in the right ventricle?
25/4