CVS 3 - Mechanical Properties of the Heart 2 Flashcards
Describe the 2 phases of heartbeat.
- Diastole - ventricular relaxation (ventricles fill with blood). 4 sub-phases.
- Systole - ventricular contraction (blood pumped into arteries). 2 sub-phases.
Formula for SV?
SV = (End-diastolic volume) - (end-systolic volume)
Formula for Ejection Fraction?
EF = SV / EDV
Which phase is part of diastole?
Atrial contraction. It allows topping up of the ventricular volume
What is isovolumetric contraction?
Period of contraction with no change in volume.
Occurs in systole.
Pressure builds up in ventricles but ventricles don’t expel blood until pressure exceeds after load pressure. This is followed by ventricular ejection. Relaxation then starts again.
Define EDV, ESV, SV, EF.
- End Diastolic Volume = volume in ventricles just before contraction
- End Systolic Volume = volume in ventricles after ventricle has fully contracted and expelled maximal blood
- SV = EDV - ESV
- Ejection Fraction - proportion of EDV pumped out of heart.
EF = SV/EDV
EF is about 65% in normal people, as low as 35% in heart failure patients.
What are the 7 events of the cardiac cycle?
- Atrial systole
- Isovolumetric contraction
- Rapid ejection
- Reduced ejection
- Isovolumic relaxation
- Rapid ventricular filling
- Reduced ventricular filling
Describe atrial systole
- Just before AS, blood passively flows into ventricles via AV valves.
- AS tops of the volume of blood into ventricles
- Atrial pressure shows small increase due to contraction
- Very little pressure change in aorta and ventricles.
Describe ECG features in AS.
- Seen as P wave - indicates atrial excitation/atrial depolarisation
- May occasionally hear abormal S4 sound. Could indicate: Pulmonary embolism/Congestive heart failure/Tricuspid incompetence).
- Jugular pulse may be felt due to atrial contraction pushing some blood back unto jugular vein.
P WAVE = ATRIAL DEPOLARISATION
Describe isovolumic (isovolumetric) contraction.
- Occurs between AV valves closing and semi-lunar valves opening
- Ventricles completely sealed off in this period
- Ventricles contract against closed valves - so no change in volume
- Rapid pressure increase
- First heart sound occurs during this period (AV valves closing).
- Isometric contraction of ventricles - no change in length but force generated
- When ventricular pressure exceeds aortic pressure (after load), aortic valve opens.
- Ventricular depolarisation/excitation occurs - QRS complex
Which ECG complex signifies ventricular depolarisation/excitation?
QRS complex.
Describe the rapid ejection phase.
- Starts when mitral and pulmonary valves open.
- C wave seen in atrial pressure graph caused by RV contraction, which pushed the tricuspid valve into atrium, which then creates a small wave into jugular vein.
- No electrical activity on ECG and no heart sounds as no valves closing.
Describe the reduced ejection phase.
- Marks end of systole
- Blood leaves ventricles and ventricular pressure decreases. Once Pv < Pa , valves close
- T wave, which shows ventricular repolarisation.
Describe isovolumic relaxation.
- Beginning of diastole
- AV valves and pulmonary valves shut.
- (AV valves shut so) no change in ventricular volume.
- Increase in atrial pressure.
- “V wave” in atrial pressure due to blood pushing tricuspid valve and giving second jugular pulse
- Second heart sound heard when aortic and pulmonary valves close.
- DICHROTIC NOTCH - small, sharp increase in aortic pressure due to rebound pressure against aortic valve as distended aortic valve relaxes.
Describe rapid ventricular filling.
- AV valves reopen, blood flows from A to V (passive filling).
- Atrial pressure decreases.
- S3 may be heard - abnormal, may signify turbulent ventricular filling.
What does an S3 indicate?
aka Ventricular Gallop
Mitral incompetence or severe hypertension
Describe reduced ventricular filling.
- Slow filling of ventricles = diastasis
- Ventricular volume increases slowly
- No ECG changes or heart sound changes
Although the RHS occurs at lower pressures, what is constant between the RHS and LHS?
Both eject the same volume of blood.
What are ideal blood pressure values.
Systemic = 120/80
Pulmonary = 25/5
Measuring pressure changes on the RHS allows what?
To measure preload of the LHS.
This is called Pulmonary Artery Wedge Pressure (PAWP)
In which cases is PAWP elevated?
If there are problems with the LHS or mitral valve.
Explain pressure volume loops.
- EDV. Ventricle has large volume but no pressure yet.
- Isovolumic contraction. Volume in ventricle unchanged but large increase in pressure. (Pv is same as aortic pressure and just about to overcome it)
- Between point 2 and 3, blood expelled. Ventricle pressure increases then decreases. 3 = ESV
- Pressure decreases but volume stays the same due to isovolumic relaxation.
How to calculate stroke volume from a pressure-volume loop?
Difference between 2 and 3.
Where is preload and afterload located on a pressure volume loop?
Preload - point 1
Afterload - just after point 2
What does increasing preload do to the stroke volume?
Increasing preload increases stroke volume.
- Points 1 and 2 shifted right as more volume (Greater EDV).
- More preload means greater contraction.
- Bigger difference between points 2 and 3 on PV loop, so greater SV.
What does increasing after load do to stroke volume?
Increased Afterload = Decreased SV
- Increased after load = less shortening
- Hypertension = increased after load, ventricular muscle must work harder to eject blood against higher pressure.
- More pressure needed to open aortic valve, so point 2 moves higher up (in y axis).
- Point 1 remains the same.
- Less shortening due to increased after load.
- Point 3 is now higher up on the Frank-Starling graph (pressure volume graph), so difference between points 2 and 3 is smaller = smaller SV.
SEE Pg 20 Lazs NOTES
How can CO be changed?
CO= HR x SV
SV can be changed by:
- Increasing preload
- Decreasing afterload
- Altering the contractility (e.g. by using adrenaline)
Define contractility.
Contractile capability of the heart. Measured by Ejection Fraction.
Can be increased by sympathetic stimulation.
What effect does increased contractility have on a pressure volume loop?
More blood is pumped out, so SV increases as point 3 moves further to the left.
(in the PV graph, increased contractility makes a steeper gradient)
What changes occur during exercise?
- Contractility is increased due to increased sympathetic activity. This pushes points 3 and 4 to the left.
- Changes in peripheral circulation (e.g. venoconstriction and muscle pump) means increased EDV. This pushes points 1 and 2 further to the right.
- Difference between points 2 and 3 is greater, so greater SV.
