Cardiac cycle Flashcards
How long does diastole last?
Approx 2/3 of each beat
How long does systole last?
approx 1/3 of each beat
So what happens in ventricular relaxation?
- Ventricles fill with blood
- split into 4
So what happens in ventricular contraction?
- Ventricles generate pressure then eject blood into arteries
- Split into 3 phases
What is the series of a heart beat ?
- Atrial systole
- Isovolumetric contraction (end dualistic volume)
- Rapid ejection
- Slow ejection (end systolic volume)
- Isovolumetric relaxation
- Rapid passive filling
- Slow passive filling
How do you work out stroke volume?
end dialostic volume - end systolic volume
How do you work out ejection fraction?
100xstroke volume divided by end dualistic volume
Which wave on a ECG for atrial systole?
P wave
What happens in atrial systole?
- Atria already almost full from passive filling driven by pressure gradient. Atria contract to ‘top-up’ the volume of blood in ventricle
- 4th heart sound – abnormal, occurs with congestive heart failure, pulmonary embolism or tricuspid incompetenc
What is shown on ECG for isovolumetric contraction?
QRS complex (marks Start of ventricular depolarisation)
What happens in isovolumetric contraction?
- This is the interval between AV valves (tricuspid & mitral) closing and semi-lunar valves (pulmonary & aortic) opening
- Contraction of ventricles with no change in volume
- 1st heart sound (‘lub’) due to closure of AV valves and associated vibrations
Where does rapid passive filling happen?
Occurs during isoelectric (flat) ECG between cardiac cycles
What happens during rapid passive filling?
-Once AV valves open blood in the atria flows rapidly into the ventricles.
-3rd heart sound – usually abnormal and may signify turbulent ventricular filling
Can be due to severe hypertension or mitral incompetence
What happens in rapid ejection?
- Opening of the aortic & pulmonary valves mark the start of this phase
- As ventricles contract pressure within them exceeds pressure in aorta and pulmonary arteries. Semilunar valves open, blood pumped out and the volumes of ventricles decrease.
- No heart sounds for this phase
What happens in reduced ejection?
- This phase marks the end of systole
- Reduced pressure gradient means aortic & pulmonary valves begin to close
- Blood flow from ventricles decreases and ventricular volume decreases more slowly
4 .As pressures in ventricles fall below that in arteries, blood begins to flow back causing semilunar valves to close
-T wave as start to repolarise?
What happens in isovolumetric relaxation?
- The aortic & pulmonary valves shut, but the AV valves remain closed until ventricular pressure drops below atrial pressure.
- Atrial pressure continues to rise. Dichrotic notch (green line) caused by rebound pressure against aortic valve as distended aortic wall relaxes.
- 2nd heart sound (‘dub’) due to closure of semilunar and associated vibrations
What happens in reduced passive filling?
- This phase can be called diastasis
- Ventricular volume fills more slowly
- The ventricles are able to fill considerably without the contraction of the atria
What a re the patterns of pressure changes in right and left?
- The patterns of pressure changes in the right heart are essentially identical to those of the left
- Quantitatively, the pressures in the right heart and pulmonary circulation are much lower (peak of systole – 25mmHg in pulmonary artery)
- Despite lower pressures right ventricle ejects same volume of blood as left (it is simply pumping the same quantity of blood into a lower pressure circuit)!
How do you determine pulmonary circuit pressure?
Catheter in pulmonary artery
and pull it make and measure pressure
What is pressure in systemic circuit?
High pressure - 120/80 mmHg
What is pressure in pulmonary circuit?
Low pressure - 25/5mmHg
How does the pressure volume loop change with preload and afterload?
- Changes
- PVL only for left ventricle!!
What happens at preload in the pressure volume loop (A)?
- Lub
- Mitral valve closes (and tricuspid)
- End diastolic
What happens between A and B on pressure volume loop?
Isovolumetric contraction
What happens at B on PVL?
- Aortic valve opens
- Pulse pressure is measured between B and C
What happens at C on PVL?
- Dub S2
- Aortic valve closes (and pull)
- End systolic
What happens at D on PVL?
- Mitral valve opens
- Between A and D is stroke volume
- A to A is 0.9s
What determines preload?
-Blood filling the ventricles during diastole determines the Preload that stretches the resting ventricular muscle
What determines afterload?
-The blood pressures in great vessels (aorta and pulmonary artery) represent afterload
What does increase in preload result in?
Increases in stroke volume (this is frank starling relationship)
What do you do if you increase afterload?
- Decrease stroke volume
- As afterload increase, the amount of shortening that occurs decreases
How doe you work out cardiac output?
Heart rate x stroke volume
What is stroke volume affected by?
- preload
- Afterload
- contractility: increase through engagement of autonomic NS and stimulation of sympathetic nervous system which changes amount of Ca2+ influx in and so changes force
What is contractility?
-Contractile capability (or strength of contraction) of the heart
-Simple measure: Ejection fraction
-Increased by: Sympathetic stimulation
As contractility changes, a ‘family’ of Frank-Starling relations become apparent
