CVS3: Mechanical properties of the heart 2 Flashcards
What are the two main phases of the heart beat?
DIASTOLE= ventricular relaxation during which the ventricles fill with blood SYSTOLE= ventricular contraction when the blood is pumped into the arteries
What is isovolumetric contraction?
You get contraction but no change in volume so you get a build up of pressure in the ventricles
When do you get an expulsion of blood in isovolumetric contraction?
The ventricles don’t expel blood until the pressure gets to the point where it overcomes the pressure of the after load.
What is the end diastolic volume?
The volume in the ventricles just before the ventricles expel blood
What is the end systolic volume?
The volume in the ventricles after the ventricle has completely contracted and expelled as much blood as it can
What is stroke volume?
EDV- ESV
What is the ejection fraction?
SV/EDV
The proportion of the end diastolic volume that is pumped out of the heart
What are the seven stages of the cardiac cycle?
- Atrial Systole
- Isovolumic contraction
- Rapid ejection
- Reduced ejection
- Isovolumic relaxation
- Rapid ventricular filling
- Reduced ventricular filling
What happens just before atrial systole in terms of blood flow?
Blood flows passively through the open AV valves into the ventricles
What happens during atrial systole in terms of blood flow?
The atria contract, topping off the volume of blood in the ventricles
Which part of the ECG indicates atrial systole?
The P wave= atrial excitation
Why might you hear a sound during atrial systole?
This is an abnormal heart sound called S4 which is caused by valve incompetency which makes the blood flow become turbulent.
When does S4 occur?
- pulmonary embolism
- Congestive heart failure
- Tricuspid incompetence
Which pulse might you feel during atrial systole
Th jugular pulse- due to atrial contraction pushing some blood back up the jugular vein
When is isovolumic contraction?
Between the AV valves closing and the semi-lunar valves opening
What happens during isovolumic contraction?
Ventricles are sealed off
Ventricles contract with no change in volume
What happens to the pressure during isovolumic contraction?
- The volume stays the same because the valves are closed but contraction of ventricles => rapid increase in pressure
What is seen on the ECG during isovolumic contraction?
The QRS complex= ventricular excitation
Which sound is heard during the isovolumic contraction stage and why?
S1 (lub) sound= closing of the AV valves because ventricular pressure> atrial pressure
Is the isovolumic stage isometric or isotonic?
Isometric- muscle fibres aren’t changing length but are generating force and increasing the pressure
What causes the rapid ejection phase?
- The ventricles contracting in a closed chamber causes the ventricular pressure to exceed aortic/ pulmonary pressure (after load)
- so the SL valves open and blood is pumped out
- and ventricular volume decreases
Why causes the ‘c wave’ seen in the atrial pressure?
Right ventricular contraction pushes the tricuspid valve into the atrium and creates a small wave into the jugular vein
What is seen on the ECG and heard during occultation of the rapid ejection phase?
No ECG wave- because electrical excitation has already happened
No heart sounds- no closing of valves
What happens to the pressure during the reduced ejection phase?
The pressure of the ventricles fall below the arterial pressure
What is the result of the fall in ventricular pressure?
Ventricular pressure < Arterial pressure = blood begins to flow back causing the SL valves to begin closing
What is seen on an ECG and heard during oscultation of the reduced ejection stage?
ECG: cardiac cells begin to REPOLARISE (AP returns to resting potential) = T wave
Sounds: NO SOUND (valves haven’t closed yet)
What happens to the valves during isovolumic relaxation?
- aortic/ pulmonary valves close
- AV valves remain closed
Why is this stage called isovolumic relaxation?
AV valves are closed so no change in volume
What happens to the atrial pressure during isovolumic relaxation?
Atria fills with blood but AV valves are shut so you get an INCREASE in atrial pressure
What causes the v wave in the isovolumic relaxation stage?
Blood pushing the the tricuspid valve giving a second jugular pulse
What causes the dichrotic notch in atrial pressure?
Rebound pressure against the aortic valve as the distended aortic wall relaxes
What are the key events in the rapid ventricular filling stage?
- AV valves opening
- blood flow from atria to ventricles (passive- no contraction)
- increase in ventricular volume
- decrease in atrial pressue
What might be heard during the rapid ventricular filling stage? and what does this indicate
S3 might be heard= abnormal heart sound.
Caused by turbulent ventricular filling
What is S3 also called?
Ventricular gallop
Which conditions cause S3?
- severe hypertension
- mitral incompetence
What happens during the reduced ventricular filling stage?
- Slow filling of ventricles
- gradual increase in volume of ventricles
What is the reduced vetricular filling stage also known as?
Diastasis
Which diagram can be used to present the cardiac cycle information?
The Wiggers diagram
Compare and contrast the pulmonary and systemic circulation
SAME:
- same pattern of pressure changes
- same volume of blood ejected
DIFFERENT:
- On the right side, have lower pressures than left
What is the pulmonary artery wedge pressure?
- lodging a balloon catheter into the pulmonary artery
- blocking off the artery so no blood can go past
- by measuring pressure on right side of the heart, you can measure preload on left side of the heart
What are the x and y axes of the pressure- volume loops?
x= ventricular volume y= ventricular pressure
What is the first point on the pressure-volume loop?
End diastolic volume= high volume in ventricles but hasn’t generated any pressure
What is the second point on the pressure- volume loop?
Isovolumic contraction= volume doesn’t change but pressure generated increases
What is the third point on the pressure volume loop?
End systolic volume= ventricles have contracted and start to expel blood. The volume of blood in the ventricles begins to fall and the ventricular pressure rises then falls
What is the fourth point on the pressure volume loop?
Isovolumic relaxation= pressure in ventricles decreases but volume stays the same
How do you calculate the stroke volume from a pressure volume loop?
Volume of Point 2 - volume of point 3
What determines preload?
Preload= determines the stretch on muscles. Blood filling ventricles during diastole determines the preload.
How can we determine preload from a pressure-volume loop?
Point 1 (EDV) gives an idea of preload because it is the volume of blood filling the ventricles and stretching the resting ventricular muscle
What determines after load?
Its is the pressure in the aorta that the ventricle has to overcome to eject blood
How can after load be determined from a pressure volume loop?
Afterload is JUST AFTER point 2 when the left ventricle encounters the aortic pressure when the aortic valve begin to open
What form the axes for the Frank-Starling relationship in vivo?
x-axis: Instead of muscle fibre length we have volume
y-axis: Instead of force we have pressure
What happens to stroke volume if we increase preload?
Points 1 and 2 are higher so distance between P3 and P2 increases= SV increases and EDV increases.
Greater preload= more contraction
What happens to stroke volume if we increase afterload?
- Increasing afterload= decreases the amount of shortening.
- More pressure needed to open the aortic valve so P2 moves up the graph (in y-direction)
- So stroke volume decreases
When might after load increase?
If you have high blood pressure (hypertension)
Which three factors affects stroke volume?
Changing the amount of blood that returns to the heart:
1. Preload
2. Afterload
Altering how forcefully the heart contracts (by using adrenaline)
3. Contractility
Define cardiac contractility
Contractile capability (strength of contraction) of the heart
Which measure can be used to determine cardiac contractility? And what increases cardiac contractility?
Ejection fraction
Sympathetic stimulation
What happens to the in vivo Frank Starling relationship when contractility is increased?
More blood is pumped out
SV increases
P3 moves further to the left
What happens to contractility and EDV during exercise?
- contractility increases because of an increase in sympathetic activity
- venoconstriction and muscle pump means EDV increase and more blood is returned to the heart
What happens to the Frank Starling relationship during exercise?
- P1 and 2 move further to the right because EDV increases
- P3 and 4 move further to the left because of the increase in contractility
- Difference between P2 and P3 increases= increase in SV
