CAM201: Cardiac Cycle Flashcards
What are the phases of the cardiac cycle?
1) Diastasis (passive filling of ventricle)
2) Atrial Systole
3) Isovolumic Contraction
4) Ejection Phase
5) Isovolumic relaxation
Describe what is happening, including the pressures, during Diastasis
During diastasis, atrial pressure exceeds ventricular pressure. Thus, the AV valve is open, and the ventricle fills with blood from the atria passively.
The MV is closed because aortic pressure exceeds ventricle pressure
At the onset of Diastasis, A= 5, V= 2, Aorta= 80
Describe what is happening, including the pressures, during Atrial Systole
During Atrial systole, the atrial myocardium has depolarised, resulting in atrial contraction. This forces the last bolus of blood into the ventricle.
Throughout diastole and atrial systole, the ventricle’s volume is increasing, but the pressure in the ventricle is not increasing significantly.
During atrial contraction: A= 10, V= 5, Aorta= 80
Describe what is happening during Isovulumic Contraction, including the pressures
Durin Isovolumic contraction, the ventricle myocardium has depolarised, so it is contracting. The sudden increase in V pressure causes the AV valves to snap shut (this is the S1 heart sound - closure of mitral and tricuspid valves)
The ventricle’s contraction causes an increase in pressure within the ventricle (by decreasing the overall volume of the ventricle) without a change in blood volume.
During Isovolumic Contraction: A=2, V=60+, Aorta=80
Describe what happens during the ejection phase, including pressure changes
During the Ejection phase, the ventricular contraction has risen Ventricular pressure to the point where it exceeds Aortic pressure, thus forcing open the Aortic valve, and ejecting blood.
Whilst ejection of blood is occurring, contraction continues, thus the pressure does continue to rise for a bit, whilst the volume decreases. After a bit, the pressure starts decreasing again…
During Ejection: A= 3, V= 130, Aorta= 120
Describe what happens during Isovolumetric Relaxation, including pressure changes
At the end of the ejection phase, the V pressure falls to the point where the aortic pressure exceeds this. This snaps shut the MV (S2 heart sound - MV/TV closing).
Then, Isovolumetric Relaxation occurs: both valves are shut, and the Ventricle myocardium relaxes. Thus, there is a decrease in pressure without a change in volume.
Isovolumic Relaxation: A= 5, V= 60-, Aorta= 90
What follows Isovolumic relaxation?
Diastasis follows, once the ventricle has lowered its pressure to the point where atrial pressure exceeds ventricle pressure
