Mechanical properties of the heart 2 Flashcards
What are the two main phases of the cardiac cycle?
diastole and systole
What is end diastolic volume?
The volume of blood in the ventricle at the end of ventricular filling - around 130ml
What does the end diastolic volume consist of?
End systolic volume
Amount added in atrial systole
Amount added into atrial diastole
What is end systolic volume?
The volume left in the ventricle at the end of contraction - around 60ml
What is stroke volume?
The volume of blood ejected by ventricular contraction - around 70ml
How can stroke volume be calculated?
EDV-ESV
What is ejection fraction and how can it be calculated?
The proportion of the end diastolic volume that is pumped out of the heart
SV/EDV
What is normal ejection fraction and what happens to it in a person with heart failure?
normal - 65%
can drop to 35% in someone with heart failure
What is a normal heart rate?
72 bpm
What is normal cardiac output?
5.04L/min
Describe what happens during atrial systole
- include the anatomy, pressure changes and any ECG/heart sound (abnormal)
Anatomy:
The blood is in the atria and it contracts
Pressure changes:
The atrial pressure shows a small increase (a wave), there may also be a jugular pulse to to atrial contraction pushing some blood back up the jugular vein
ECG:
P wave marks atrial systole
Heart sounds:
Abnormal s4 sound can be heard causes by valve incompetency. This could be due to pulmonary embolism, congestive heart failure or tricuspid incompetence
Describe what happens during isovolumic contraction
- include the anatomy, pressure changes and any ECG/heart sound
Anatomy:
Contraction of ventricles with no change in volume, only pressure build up (both valves are closed). Muscles don’t change length
Pressure changes:
The AV valve shuts when ventricular pressure exceeds atrial. The ventricular pressure approaches that of aortic without exceeding it so aortic valve doesn’t open. Only when pressure exceeds afterload it opens.
ECG:
QRS complex marks ventricular depolarisation
Heart sounds:
S1 sound heard, the lub sound caused by AV valves closing
Describe what happens during rapid ejection
- include the anatomy, pressure changes and any ECG/heart sound
Anatomy:
Aortic and Pulmonary valves open.
Pressure Changes
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
ECG Changes & Heart Sounds:
None
Describe what happens during reduced ejection
- include the anatomy, pressure changes and any ECG/heart sound
Anatomy:
Aortic and Pulmonary valves begin to close - end of systole, blood leaves ventricles slowly
Pressure Changes:
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.
ECG Changes:
T wave is due to ventricular re-polarisation
Heart sounds:
None
Describe what happens during isovolumic relaxation
- include the anatomy, pressure changes and any ECG/heart sound
Anatomy:
Aortic and Pulmonary valves have shut.
Pressure Changes:
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).
DICHROTIC notch – A small, sharp increase in aortic pressure due to rebound pressure against the aortic valve as the distended aortic wall relaxes.
ECG Changes:
None
Heart Sounds:
The S2 sound is heard when the aortic and pulmonary valves shut - dub
Describe what happens during rapid ventricular filling
- include the anatomy, pressure changes and any ECG/heart sound
Anatomy:
AV valves open, ventricles fill.
Pressure Changes:
Ventricular volume increases while atrial pressure falls.
This filling is passive and not isometric.
ECG Changes:
None
Heart Sounds:
An abnormal S3 may be heard which signifies turbulent ventricular filling.
Can be due to severe hypertension or mitral incompetence.
Describe what happens during reduced ventricular filling
- include the anatomy, pressure changes and any ECG/heart sound
Anatomy
Also called ‘Diastasis’
Pressure Changes:
Ventricular volume increases more slowly.
ECG Changes & Heart Sounds:
None
What are the 7 stages of the cardiac cycle?
- Atrial systole
- Isovolumic contraction
- Rapid ejection
- Reduced ejection (both ejections can be counted as one)
- Isovolumic relaxation
- Rapid ventricular filling
- Reduced ventricular filling
Pressure Volume Loops
The graph is ventricular pressure vs ventricular volume.
- The EDV – The ventricles are full but haven’t generated any isotonic pressure.
- Isovolumic contraction – The volume hasn’t changed but the isotonic contraction generates a large increase in pressure.
- 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 to 3 = SV!
- Pressure falls due to Isovolumic relaxation.
Frank Starling Relationship In Vivo
 Instead of force, it is pressure and instead of length, it is volume. These are the in vivo correlates in the Frank-Starling relationship.
Point 3 – Represents the ESV so the active force curve tangent at this point represents the End-Systolic PV line.
Ventricular volume vs ventricular pressure loop
- When afterload increases, more pressure is needed to open the aortic valve so point 2 on pressure volume loop (second highest point representing afterload) moves in y-direction
- Point 1 (third highest point is preload) remains the same as the EDV is the same
How can the contractility of the heart be increased?
increased by sympathetic stimulation
How can the stroke volume be changed?
change preload, afterload and contractility
How is the pressure volume loop affected during exercise to increase SV and CO?
- Increase in contractility (active force) increases the stroke volume so point 3 moves further left.
- During exercise contractility is increased due to increased sympathetic activity.
- 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.
- Increase in contractility moves points 3&4 to the left so an increase in SV occurs in total.
