the cardiac cycle

Question 1

what is the cardiac cycle?

Answer 1

• diastole = ventricles relax and fill with blood
• systole = ventricles contract and pump blood into the aorta (LV) and pulmonary artery (RV)
• at a HR of 75bpm, diastole is 0.5 sec and systole is 0.3 sec

Question 2

what events occur during the cardiac cycle?

Answer 2

1. passive filling
2. atrial contraction
3. isovolumetric ventricular contraction
4. ventricular ejection
5. isovolumetric ventricular relaxation

Question 3

what happens during passive filling?

Answer 3

• pressure in the atria and ventricles close to zero
• AV valves open so venous return flows into the ventricles
• aortic pressure = 80mmHg, and aortic valve is closed
• same happens in right side but pressure is lower
• ventricles become 80% full

Question 4

what happens during atrial contraction?

Answer 4

• the P-wave in the ECG signals atrial depolarisation
• the atria contracts between the P-wave and the QRS
• atrial contraction complete the EDV

Question 5

what happens during isovolumetric ventricular contraction?

Answer 5

• starts after the QRS in the ECG
• ventricular pressure rises
• when the VP exceeds atrial pressure, the AV valves shut
• this produces the first heart sounds (LUB)
• the aortic valve is still shut
• the tension rises around a closed volume “isovolumetric”
• the ventricular pressure rises very steeply

Question 6

what is ventricular ejection?

Answer 6

• when the ventriuclar pressure exceeds aorta/pulmonary artery pressure
• aortic/pulmonary valve open (silent event)
• SV is ejected by each ventricle, leaving behind the ESV
• aortic pressure rises
• T-wave in ECG signals ventricular repolarisation
• ventricles relax and ventricular pressure starts to fall
• when the VP falls below aortic/pulmonary, the valves shut
• this produces DUB
• the valve vibration produced the dicrotic notch in aortic pressure curve

Question 7

what is isovolumetric ventricular relaxation?

Answer 7

• closure of aortic/pulmonary valves signals the start of the isovolmumetric ventricular relaxation
• ventricle is again a closed box, as the AV valve is shut
• the tension falls around a closed volume
• when the ventricular pressure falls below atrial pressure, AV valves ioen (silent) and a new cycle will start

Question 8

when is S1 heard?

Answer 8

• S1 - caused by closure of nitral and tricuspid valves “lub”, heard in the beginning of systole

Question 9

when is S2 heard?

Answer 9

• S2 - caused by closure of aortic and pulomnary valves “dub”, heard at the beginning of diastole

Question 10

what are the jugular venous pressures?

Answer 10

• JVP occurs after right atrial pressure waves
• a = atrial contraction
• c = bulging of tricuspic valve into atrium during ventricular contraction
• v = rise of atrial pressure during atrial filling: release as AV vales open