Cardiac Cycle Flashcards
- What is meant by end-diastolic volume?
- What is meant by the end-systolic volume?
Maximum volume of blood in the heart just before the ventricles contract and at this point are relaxed
The residual volume left in the heart following contraction
- Give a definition of stroke volume and how is it calculated?
- How is ejection fraction calculated and what is it’s normal range?
Volume of blood expelled by the heart in any one cardiac cycle
End-diastolic volume - End-systolic volume = Stroke volume
100 x Stroke volume/End-diastolic volume = Ejection fraction Normal: 52-72%
- What would be the ejection fraction range in a patient with heart failure?
30%-35%
what three phases happen under ventricular systole?
what four phases happen under Diastole?
isovolumetric contraction
rapid ejection
slow ejection
isovolumetric relaxation
rapid passive filling
slow passive filling
atrial systole
- What happens during Atrial Systole?
- What wave on ECG signifies the start of Atrial Systole?
- Which heart sound is abnormal but heard during Atrial Systole and why would it be heard?
Atria almost full from passive filling driven by pressure gradient
Atria contract to ‘top up’ volume of blood in the ventricle
P-wave 4th heart sound - S4 Occurs with congestive heart failure, pulmonary embolism or tricuspid incompetence
- Briefly describe how ventricular depolarisation leads to the contraction of ventricular muscle and how is this shown on ECG?
AP arrives at ventricular myocyte
This is sensed by L-type Ca2+ channels which open releasing Ca2+ and also open the internal stores of Ca2+ by Ryanodine receptors Ca2+ is used in the formation of cross-bridges between actin and myosin to cause the sarcomere to shorten This is shown by the QRS complex on ECG
- Which valves are opened or closed during Isovolumetric Contraction?
- How does the volume change during contraction of ventricles in Isovolumetric Contraction?
- What heart sound is heard in Isovolumetric Contraction and why is this heard?
all closed
it doesn’t
S1 'Lub' Due to closure of AV valves and associated vibrations
- What marks the start of the Rapid Ejection phase?
- What happens to the ventricular volume during the Rapid Ejection phase?
- What happens to the aortic pressure during Rapid Ejection?
When the semi-lunar valves open, marking the start of the Rapid Ejection phase Once ventricles contract and ventricular pressure > aortic pressure
decreases
It increases because there is more blood flowing through it and it reaches its maximum blood velocity
but does not increase above the ventricular pressure
- How long after the QRS complex does the Reduced Ejection phase begin?
- What wave on ECG marks the end of systole in the Reduced Ejection phase and why does it occur?
- What occurs in the Reduced Ejection phase?
¬200 milliseconds
T-wave Repolarisation of the muscle leads to decline in ventricular active tension and pressure generation Blood flow from ventricles decreases and ventricular volume decreases more slowly Reduced pressure gradient means aortic and pulmonary valves begin to close
- What happens to the valves during the Isovolumetric Relaxation phase?
- How does the atrial pressure change in the Isovolumetric Relaxation phase?
Aortic and pulmonary valves remain shut
AV valves remain closed until ventricular pressure drops below atrial pressure
Continues to increase
- How is the dichrotic notch caused, shown by the sudden decrease and then increase in aortic pressure?
- How does the volume of the ventricles change in the Isovolumetric Relaxation phase?
- What sound can be heard in the Isovolumetric Relaxation phase and why is it heard?
Caused by the rebound pressure against the aortic valve as distended aortic wall relaxes
it doesn’t
S2 'Dub' Due to closure of the semi-lunar valves
- What is the rate of pressure decline in the ventricles determined by?
- What is this rate called?
The rate of relaxation of the muscle fibres
Relaxation regulated largely by the Ca2+ ATPases in the SR membrane
Lusitropy
- What occurs during the Rapid Passive Filling phase?
- What heart sound is abnormal but heard in the Rapid Passive Filling phase and why is it heard?
- How is Rapid Passive Filling shown on ECG?
Ventricular pressure < Atrial pressure
AV valves open and blood rapidly fills into the ventricles from the atria
S3- May signify turbulent ventricular filling and can be due to severe hypertension or mitral incompetence Occurs during isoelectric (flat) ECG between cardiac cycles
- What does the End Systolic Pressure Volume Line show?
The maximum pressure that can be developed by the ventricle at any given volume
- How does the stroke volume change after an increase in the preload?
- How does the stroke volume change after an increase in the afterload?
It increases
Because there is more blood coming into the heart and so the muscle fibres are stretched more, allowing more space to be taken up in the ventricles
It decreases Greater pressure is required to open the aortic valve Less shortening of muscle fibres as working against the increased afterload
