Cardiac cycle

Question 1

What is a cardiac cycle?

Answer 1

All events that occur from the beginning of one heart beat to the beginning of the next

Question 2

What occurs during diastole and systole?

Answer 2

• Diastole: the heart ventricles are relaxed and fill with blood
• Systole: the heart ventricles contract and pump blood into the: aorta (LV) and pulmonary artery (RV)

Question 3

At a heart rate of 75bpm, how long does both the diastole and systolic phase last?

Answer 3

diastole = 0.5sec
systole= 0.3 sec
so diastole lasts almost twice as long as systole

Question 4

What are the 5 events during the cardiac cycle?

Answer 4

• Passive Filling
• Atrial Contraction
• Isovolumetric ventricular Contraction
• Ventricular Ejection
• Isovolumetric ventricular Relaxation

Question 5

Describe passive filling.

Answer 5

• Pressure in atria and ventricles close to zero
• AV valves open so venous return flows into the ventricles
• Aortic pressure ~ 80 mmHg, and aortic valve is closed
• Similar events happen in the right side of the heart, but the pressures (right ventricular and pulmonary artery) are much lower
• Ventricles become ~ 80% full by passive filling

Question 6

What is atrial contraction ?

Answer 6

Completes the end diastolic volume and is represented in the ECG between the P-wave (atrial depolarisation) and the QRS wave

Question 7

Describe isovolumetric ventricular contraction.

Answer 7

• Ventricular contraction starts after the QRS (signals ventricular depolarization) in the ECG
• Ventricular pressure rises
• When the ventricular pressure exceeds atrial pressure the AV VALVES SHUT
• This produces the FIRST HEART SOUND (LUB)
• The aortic valve is still shut, so no blood can enter or leave the ventricle
• The tension rises around a closed volume “Isovolumetric Contraction”
• The ventricular pressure rises very steeply

Question 8

What produces the first heart sound?

Answer 8

The “LUB” is produced by the closure of mitral and tricupsid valves

Question 9

Describe ventricular ejection?

Answer 9

-When the ventricular pressure exceeds aorta/pulmonary artery pressure
-Aortic/pulmonary valve open - Remember this is a silent event
-Stroke Volume (SV) is ejected by each ventricle, leaving behind the End Systolic Volume (ESV)
-SV = EDV – ESV
= 135 – 65 = 70 ml
-Aortic pressure rises
-The T-wave in the ECG signals ventricular repolarization
-The ventricles relax and the ventricular pressure start to fall
-When the ventricular pressure falls below aortic/pulmonary pressure: aortic/pulmonary valves shut
-This produces the SECOND HEART SOUND (DUB)
-The valve vibration produces the dicrotic notch in aortic pressure curve

Question 10

What produces the second heart sound?

Answer 10

The “DUB” sound -When ventricular pressure falls below aortic/pulmonary pressure , the aortic/pulmonary valves shut

Question 11

Describe the isovolumetric ventricular relaxation ?

Answer 11

• Closure of aortic/and pulmonary valves signals the start of the isovolumetric ventricular relaxation
• Ventricle is again a closed box, as the AV valve is shut
• The tension falls around a closed volume “Isovolumetric Relaxation”
• When the ventricular pressure falls below atrial pressure, AV valves open (Remember this is a silent event), and the heart starts a new cycle

Question 12

Why does arterial pressure does not fall to 0?

Answer 12

Due to elastic properties of arteries , they stretch when contracted and when they recoil so recoiling moves blood forward

Question 13

When does jugular venous pulse occur?

Answer 13

Occurs after right atrial pressure waves (indirect measurement ofd central venous pressure )