Cardiovascular mechanics 2 Flashcards
Describe the 2 phases of the cardiac cycle
▪ Diastole – Ventricular relaxation during which the ventricles fill with blood. o Split into FOUR sub-phases. ▪ Systole – Ventricular contraction when the blood is pumped into the arteries. o Split into TWO sub-phases.
What proportions do systole and diastole represent of each heart beat
Diastole- Lasts approximately 2/3 of each heart beat
Systole lasts approximately 1/3 of each heart beat
Generally, when do valves open
When the pressure of the blood is greater than the back pressure on the valves
What is meant by end diastolic volume
The volume of blood in the ventricles at the end of ventricular filling, just before they are about to contract.
What constitutes the end diastolic volume
This is made up of: o The ESV = ~60ml. o The amount added in atrial diastole (filling without contraction into the ventricle = ~40ml o The amount added by atrial systole (contraction of atria, topping off ventricle volume = ~30ml.
What is meant by end systolic volume
The volume of blood left in the ventricles after they contract.
What is meant by stroke volume
The volume of blood ejected by ventricular contraction.
What is the difference between end diastolic volume and end systolic volume equal to
Stroke volume
What do we measure stroke volume, EDV and ESV in
mL
What are the typical values at rest for EDV,SV and ESV
SV- 70mL
EDV- 130mL
ESV- 60mL
What is meant by the ejection fraction
The proportion of the end diastolic volume that is pumped out of the heart.
What can the ejection fraction be used to assess
How well the ventricles are contracting (the contractility of the heart).
What are the typical values for the ejection fraction at rest
65%, but it can fall as low as 35% in patients with heart failure- they will become breathless with otherwise easy tasks.
How do we calculate the ejection fraction
EF= SV/EDV x 100
How do we calculate cardiac output and what is a typical value for cardiac output at rest
Heart Rate (HR) x Stroke Volume (SV) = approx. 5.04 litres/minute.
How long does each heart beat typically last and what is a typical value for heart rate at rest
(each heart beat approx. 0.8s) = approx. 72 beats/minute.
What do we see on the ECG during atrial systole
P wave on ECG marks start of atrial systole.
The P wave is due to the depolarisation of the atrial cells.
What heart sound can sometimes be heard during atrial systole
During this time, abnormal S4 heart sound can be heard – caused by valve incompetency (bad valve shutting). This can occur due to: o Pulmonary Embolism. o Congestive Heart Failure. o Tricuspid Incompetence.
Describe the movement of blood during atrial systole
Atria already almost full from passive filling driven by pressure gradient. Atria contract to ‘top-up’ the volume of blood in ventricle
Blood has been flowing passively into the ventricles through open AV valves and now the atria contract which tops up the ventricular volume (giving the EDV).
Describe the pressure changes during atrial systole
▪ Atrial pressure shows a small increase due to the contraction – the ‘a’ wave. ▪ There may also be a jugular pulse due to atria contraction pushing some blood back up the jugular vein. Ventricular pressure also increases. But during atrial systole atrial pressure > ventricular pressure. Pressure in the aorta decreases during atrial systole
What happens to the volume of blood in the ventricle during atrial systole
it increases
What do we see on the ECG during isovolumetric contraction
QRS complex marks the start of ventricular depolarisation
In terms of the opening and closing of the valves, what is isovolumetric contraction an interval between
This is the interval between AV valves (tricuspid & mitral) closing and semi-lunar valves (pulmonary & aortic) opening
Which heart sound is associated with isovolumetric contraction
The S1 is heard (“Lub” of the “Lub-Dub”) due to closure of atria-ventricular valves.
What happens to the blood in isovolumetric contraction
▪ This is contraction of the ventricles with NO change in volume (only pressure builds up) i.e. both valves are shut. ▪ Ventricles are contracting isometrically and so muscles fibres are not changing length but are generating force. NO SHORTENING OF THE VENTRICLES
What pressure changes occur during isovolumetric contraction
▪ The AV valve shuts as ventricular pressure exceeds atrial pressure. The ventricular pressure then approaches that of the aortic pressure (without exceeding aortic pressure, aortic valve will NOT open). ▪ When ventricular pressure exceeds aortic pressure (the afterload) the aortic valve opens.
What happens to ventricular volume during isovolumetric contraction
It stays the same
What happens to the pressure of the blood in the aorta and atria during isovolumetric contraction
Pressure in aorta decreases
Pressure in atria decreases, but increases slightly as pressure in ventricles increases. Pressure in atria is initially higher, but then becomes lower as pressure in ventricles increases.
What happens to the valves in the rapid ejection phase
Opening of the aortic & pulmonary valves mark the start of this phase
What happens to the blood in the rapid ejection phase
▪ As ventricles isotonically contract, the ventricular pressure rapidly rises and exceeds aortic pressure (the afterload) and so the semilunar valves open and ventricular volume decreases. ▪ The ‘c’ wave is caused by the pushing of the tricuspid valve into the atrium causing a small pressure increase in the jugular vein – due to the ventricular contraction.
What heart sounds and ECG events are associated with the rapid ejection phase
None.
What happens to the pressure in the atria during the rapid ejection phase
Decreases, but begins to increase again.
Lower than ventricular pressure.
What happens to the pressure in the ventricles and aorta during the rapid ejection phase
They both increase, but pressure in the ventricles is always greater than the pressure in the aorta.
What happens to the ventricular volume during the rapid ejection phase
it decreases rapidly
Why can the closure of vales be heard
We can hear the turbulence associated with the closure of the valves.
What does reduced ejection mark the end of
Systole
What happens to the valves during the reduced ejection phase
Reduced pressure gradient means aortic & pulmonary valves begin to close
What happens to the blood during the reduced ejection phase
▪ As blood has left the ventricles, ventricular volume and pressure begin to decrease → semilunar valves begin to shut as pressure gradient causes backflow from the arteries. The pressure gradient decreases
What causes the semilunar valves to close
As pressures in ventricles fall below that in arteries, blood begins to flow back causing semilunar valves to close
What happens to ventricular volume during the reduced ejection phase
It decreases, but not as quickly as the rapid ejection phase.
What happens to the pressure in the ventricles and aorta during the reduced ejection phase
The pressure in both the ventricles and aorta decreases
Although the ventricular pressure remains higher than that of the aorta, the difference between them decreases (reduced pressure gradient).
What happens to the pressure in the atria during the reduced ejection phase
it increases
What ECG changes are associated with the reduced ejection phase
T wave is due to ventricular re-polarisation
What happens to the aortic and pulmonary valves during isovolumetric relaxation
▪ Aortic and Pulmonary valves have shut. As the pressure in the arteries > pressure in the ventricles.
What happens to the aortic pressure during isovolumetric relaxation
DICHROTIC notch – A small, sharp increase in aortic pressure due to rebound pressure against the aortic valve as the distended aortic wall relaxes.
Which heart sounds are associated with isovolumetric relaxation
2nd heart sound (‘dub’) due to closure of semilunar and associated vibrations
What happens to the atrioventricular valves during isovolumetric relaxation
▪ Atria have filled with blood but due to the AV valves being shut, the atrial pressure rises. ▪ The ‘v’ wave is due to blood pushing the tricuspid valve (this gives the second jugular pulse). ▪
What happens to ventricular volume during the isovolumetric relaxation phase
it remains the same
What happens to the pressure in the atria and ventricles during the isovolumetric relaxation phase
pressure in ventricles decreases
pressure in atria increases
Pressure in atria eventually becomes greater than the pressure in the ventricles (AV valves open).
What happens to the valves in the rapid passive filling phase
Atria-ventricular valves open, ventricles fill.
What happens to the ventricular volume during rapid passive filling phase
Ventricular volume increases while atrial pressure falls.
What is ventricular filling due to during the rapid passive filling phase
This filling is PASSIVE and not isometric.
What happens to the pressure in the aorta during the rapid passive filling phase
Pressure in the aorta decreases
What happens to the atrial and ventricular pressures during the rapid passive filling phase
Both decrease, but pressure in atria is always greater than that of the ventricles
Which heart sound may be associated with the rapid passive filling phase
3rd heart sound – usually abnormal and may signify turbulent ventricular filling
Can be due to severe hypertension or mitral incompetence
Doesn’t close properly- more turbulent flow than normal.
3rd heart sound – usually abnormal and may signify turbulent ventricular filling
Often referred to as ‘Ventricular Gallop’.
Describe the ECG events associated with the rapid passive filling phase
Occurs during isoelectric (flat) ECG between cardiac cycles
What is the reduced passive filling phase sometimes known as
This phase can be called diastasis
What happens to ventricular volume during the reduced passive filling phase
it increases, but more slowly than that of the rapid passive filling phase
What ECG events and heart sounds are associated with the reduced passive filling phase
None
What happens to the pressure in the aorta during the reduced passive filling phase
it decreases
What happens to the pressures in the atria and ventricles during the reduced passive filling phase
Both increase slightly. But pressure in atria is always greater than that of the ventricle.
Describe the differences in pulmonary circuit pressures on the right side and left side of the heart
The same pattern of pressure changes occurs in the right side of the heart BUT the right side of the heart displays lower pressures. ▪ Despite the lower pressure, the SV is the same.
Why do both sides of the heart eject the same amount of blood despite the differences in pressure
Because the pressure changes are the same on both sides.
What are the blood pressure values for the systemic and pulmonary circuit
o Systemic = 120/80 mmHg. o Pulmonary = 25/5 mmHg.
What is meant by pulmonary artery wedge pressure
o This measures pressures in the heart so by measuring in the pulmonary artery (right side), you can measure the preload on the left side of the heart (as the sides are linked by the pulmonary circuit). o PAWP is elevated with problems in the left side of the heart.
Describe the typical pressure values on the left side of the heat
LA- 8-10
LV- 125/5
Aorta- 120/80
Describe the typical pressure values on the right side of the heart
RA- 0-8
RV- 25/5
PA- 25/12
What can pressure-volume loops be a sign of
Contractility of the heart
What is a pressure-volume loop a graph of
The graph is ventricular pressure vs ventricular volume.
Describe the different points on the pressure-volume loop
- The EDV – The ventricles are full but haven’t generated any isotonic pressure. 2. Isovolumic contraction – The volume hasn’t changed but the isotonic contraction generates a large increase in pressure. 3. The afterload pressure is reached (aortic pressure) and then ventricle begins to expel blood into the aorta (pressure rise and fall). This ends at the ESV. 2 → 3 = SV! 4. Pressure falls due to Isovolumic relaxation.
Describe the in vivo correlates of the pressure-volume loop with the frank-starling relationship
Instead of force, it is pressure and instead of length, it is volume. These are the in vivo correlates in the Frank-Starling relationship.
What does point 3 on the pressure-volume loop represent
Point 3 – Represents the ESV so the active force curve tangent at this point represents the End-Systolic PV line.
Explain what happens to the pressure-volume loop when afterload is increased
▪ Increasing afterload decreases amount of shortening. o I.E. I cannot lift a 2-ton weight so not much shortening will occur in my own muscles. ▪ When afterload increases, more pressure is needed to open the aortic valve so point 2 moves in y-direction. ▪ Point 1 remains the same as the EDV is the same. ▪ Increase in afterload also means less shortening can occur so the stroke volume decreases.
What happens to the pressure-volume loop when preload is increased
Point 1 and 2 move to the right, hence SV increases.
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 the AFTERLOAD
What can stroke volume be altered by
o Preload – volume of blood returning to the heart. o Afterload – arterial pressure. o Contractility – how forcefully the heart contracts (e.g. using adrenaline).
Describe contractility
Definition: Contractile capability (or strength of contraction) of the heart
Simple measure: Ejection fraction
Increased by: Sympathetic stimulation- during exercise (adrenaline)
What does an increase in contractility result in
Increase in contractility (active force) increases the stroke volume so point 3 moves further left.
What happens to the pressure-volume loop during exercise
During exercise – contractility is increased due to increased sympathetic activity. o Changes in the peripheral circulation (e.g. vasoconstriction) cause more blood to return to heart so EDV (preload) increases – Point 1&2 move to the right. o Increase in contractility moves points 3&4 to the left so an increase in SV occurs in total.
What is meant by ventricular compliance
The ability of the ventricles to fill with blood
