the cardiac cycle

Question 1

what is the cardiac cycle

Answer 1

the sequence of pressure and volume changes that take place during cardiac activity
the mechanical events of the cardiac cycle are brought about by rhythmic changes in cardiac electrical activity
consists of alternate periods of systole and diastole (the atria and ventricles go through separate cycles)

Question 2

what is systole

Answer 2

contraction and emptying
0.3 sec at rest
0.15 sec at max HR

Question 3

what is diastole

Answer 3

relaxation and filling
0.55 sec at rest
0.15 sec at max HR

Question 4

what is the mechanism of valve action

Answer 4

when pressure is greater behind the valve, it opens
when pressure is greater infront of the valve, it closes > it is a one way valve so does not open in the opposite direction

Question 5

what is the ECG

Answer 5

a record of the overall spread of electrical activity through the heart

Question 6

what are the phases of the cardiac cycle

Answer 6

mid diastole
late diastole
end of diastole/early systole
ejection period
end of ventricular systole
filling period

Question 7

what is mid diastole

Answer 7

atrial and ventricular pressures low
ventricles contain approx 80% of final filled volume
aortic and pulmonary valves are closed
aortic pressure hihg

Question 8

what is late diastole

Answer 8

P wave of ECG
towards end of Pwave atria contract - increasing atrial pressure - most of the blood in the atria is propelled into ventricles - adds approx 20% to ventricular filling - accompanied by a small increase in ventricular pressure
volume in each ventricle at the end of diastole is approx 130ml standing and 160ml laying

Question 9

what is the end of diastole/early systole

Answer 9

QRS complex of ECG - start of ventricular depolarisation
ventricles contract at end of QRS complex - early systole
rapid increase in ventricular pressure
AV valves snap shut - first heart sound
ventricles contract but both AV and aortic valves are shut - no blood can enter or leave
isovolumetric/isometric phase

Question 10

what is the ejection period

Answer 10

ventricular pressure exceeds arterial pressure, aortic and pulmonary valves open
blood is ejected into the aorta and pulmonary artery
aortic pressure rises from diastolic minimum of 80mmHg to systolic peak of 120mmHg

Question 11

what is the end of ventricular systole

Answer 11

T wave signals ventricular repolarisation
ventricles start to relax - ventricular pressure falls below aortic pressure - aortic valve shuts - second heart sound - and dicrotic notch (incisura) on aortic pressure record
AV valves also shut - no blood can enter or leave
isometric ventricular relaxation

Question 12

what is the filling period

Answer 12

ventricular pressure falls below atrial pressure
AV valves open
major part of ventricular filling
blood which entered atria during ventricual systole is released into ventricle by opening of AV valves
atrial and ventricular pressures fall sharply and ventricular volume increase rapidly

Question 13

what are the major phases of the cardiac cycle

Answer 13

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

Question 14

what are the heart sounds

Answer 14

are generated by heart action
detected using a phonocardiogram
there are two distinct heart sounds;
- the 1st coincides with the beginning of systole > produced by the closure of AV valves
- the 2nd begins with the onset of diastole > closure of the aortic and pulmonary (semilunar) valves
abnormal sounds in pathological conditions are known as murmurs.