lecture 3: machanical properties of the heart : episode 2 Flashcards
what are the two main phases of the heart beat?
systole
diastole
what is diastole?
this is ventricular relaxation during which ventricles fill up with blood
4 sub phases
what is systole?
this is ventricular contraction when the blood is pumped into the arteries
2 sub phases
what is the isovolumetric ventricular contraction?
the pressure builds up in the ventricles during early systole but the ventricles only expel the blood when the pressure reaches the point where it overcomes the pressure of the after load
this period of time is known as the isovolumetric ventricular contraction
what is the end diastolic volume?
this is the volume of the ventricle at the end of ventricular filling
around 130 ml
what is the end systolic volume?
this is the volume left in the ventricle at the end of contraction
around 60ml
what is the stroke volume?
this is the volume of blood that is ejected by ventricular contraction
what is the ejection fraction?
- this is the proportion of the end diastolic volume that is pumped out
this is normally 65%
heart failure means 35%
what is the heart rate?
72 beats / min
what was the cardiac output?
heart rate x stroke volume = 5.04 litres/min
- what is the anatomy of atrial systole?
- blood has passively been flowing through the valve into the ventricle
- but as atrial contraction happens this tops up the ventricular volume
- what is the pressure change of atrial systole?
- atrial pressure shows a small increase due to the contraction
- there might also be a small jugular pulse due to the atria contraction pushing some blood back up the jugular vein
- what is the ECG change and heart sound of atrial systole?
- P WAVE
during this time we can hear the S4 heart sound which is caused by valve incompetency
what causes valve incompetency ?
- pulmonary embolism
- congestive heart failure
- tricuspid incompetence
- what is the anatomy of isovolumetric contraction?
- this is the contraction of the ventricles with no change in volume
- contraction of ventricles against closed valves
- AV valves closing and the semi-lunar valves opening
- the ventricles are contracting isometrically so the muscle fibres are not changing length but they are generating force
- what is the pressure change of isovolumetric contraction?
- the AV valve will shut as the ventricular pressure overtakes the atrial pressure
- the ventricular pressure is reaching the aortic pressure
- when the ventricular pressure is greater than the aortic pressure the aortic valve opens
- what are the ECG changes and heart sounds of the isovolumetric contraction?
- QRS complex marks the ventricular depolarisation
- S1 (LUB) is heard due to the closure of atria ventricular vales
- what is the anatomy of rapid ejection?
the aortic and pulmonary valve opens
- what is the pressure change of rapid ejection?
- the ventricles isotonically contract
- the ventricular pressure rapidly increases and exceeds the aortic pressure so the semilunar valves open and ventricular volume decreases
- the tricuspid valve is pushed into the atrium which causes a small increase in pressure in the jugular vein - c wave
- what is the anatomy of reduced ejection?
the aortic and pulmonary valve start to close
- what is the pressure change of reduced ejection?
- as the blood has left the ventricles the ventricular volume and pressure begins to decrease
- this means the semilunar valves to shut as the pressure gradient means blood starts to blood backwards from the arteries
- what are the ECG changes and heart sounds of reduced ejection?
the T wave is due to ventricular re polarisation
- what is the anatomy of isovolumetric relaxation?
- the aortic and pulmonary valves have shut
- what are the pressure changes of isovolumentric relaxation?
- the atria have been filled with blood but due to the atrioventricular valves being shut the atrial pressure starts to rise
- v wave is due to blood pushing the tricuspid valve which gives the second jugular pulse
- there is a sharp increase in aortic pressure due to rebound pressure against the aortic valve as the aortic wall relaxes
- what are the ECG changes and heart sounds of isovolumic relaxation?
- the S2 sound is heard when the aortic and pulmonary valves shut
- what is the anatomy of rapid ventricular filling?
- atria ventricular valves open and the ventricles fill
- what are the pressure changes of rapid ventricular filling?
- ventricular volume increases while atrial pressure falls
- this time the filling is passive NOT isometric
- what are the ECG changes and heart sounds of rapid ventricular filling?
- an abnormal S3 sound might be heard which suggests turbulent ventricular filling
what could turbulent ventricular filling be caused by?
- severe hypertension
- mitral incompetence
what is the anatomy of reduced ventricular filling?
diastasis: where the initial passive filling of the heart’s ventricles has slowed down, but before the atria contract to complete the active filling.
what are the pressure changes of reduced ventricular filling?
the ventricular volume increases more slowly
what is the difference between the left and the right side of the heart in terms of pressure?
- the same pattern of pressure changes occurs in the right side of the heart
- but the right side of the heart displays lower pressures than the left side of the heart
what does the pulmonary artery wedge pressure measure?
- this measures the pressures in the heart by measuring in the pulmonary artery in the right side
- measure the preload on the left side
why does there PAWP become elevated?
problems with the left side of the heart
what does a pressure volume loop compare?
ventricular pressure vs ventricular volume
what is the EDV point?
this is when the ventricles are full but they haven’t generated any isotonic pressure
what is isovolumic contraction?
this is when the volume hasn’t changed but they isotonic contraction generates a large increase in pressure
why does the pressure fall?
this is due to isovolumic relaxation
how does increasing pre load affect the stroke volume
increase in pre load
increase in SV
what relationship does pressure and volume correlate with?
the frank starling relationship
what does increasing the after load do?
this decreases the stroke volume
because increasing the after load decreases the amount of shortening
what is the equation for cardiac output?
stroke volume x heart rate
how do we change the stroke volume in this equation?
- change the preload
- change the after load
- change the contractility
what is contractility?
- this is how forcefully the heart contracts
what is the measure of contractility?
- the simple measure is the ejection fraction
what increases contractility?
sympathetic stimulation
