3. Cardiovascular mechanics 2 Flashcards
Diastole
Ventricular relaxation
during which ventricles fill with blood
Systole
Ventricular contraction
ventricles generate pressure then eject blood into the arteries
How many sub phases in diastole?
4
How many sub phases in systole
3
End diastolic volume (EDV)
volume of blood in ventricles just before ventricles contract
End systolic volume (ESV)
residual volume of blood in ventricles after contraction
Stroke volume calculation
EDV - ESV
Stroke volume
Volume of blood pumped out of heart in 1 beat
Ejection fraction calculation
(Stroke volume / EDV) X 100
Typical EDV
108 mL
Typical ESV
36 mL
Typical stroke volume
72 mL
Ejection fraction
amount of blood pushed out of heart in relation to amount of blood filling heart
Ejection fraction is a clinical sign of
how well ventricles are contracting
Ejection fraction values normal vs heart failure
Normal = 60-70%
Heart failure= 30-40%
Atrial Systole
Contraction of atria
Atrial systole on ECG
P wave
Atria already almost full from passive filling driven by pressure gradient. They contract…
to ‘top-up’ volume of blood in ventricle
Does atrial systole make a noise?
Not normally, but
4th heart sound – abnormal, occurs with congestive heart failure, pulmonary embolism or tricuspid incompetence
Isovolumetric contraction on ECG
QRS complex
Ventricular depolarisation
Isovolumetric contraction
Contraction of ventricles with no change in volume, but pressure increases
Does Isovolumetric contraction make a noise?
Yes
1st heart sound (‘lub’)
due to closure of AV valves and associated vibrations
Rapid ejection
Ventricles contract, pressure within them exceeds pressure in aorta and pulmonary arteries.
Semilunar valves open, blood pumped out and volumes of ventricles decrease
Type of contraction in rapid ejection
Isotonic
Does rapid ejection make a noise?
No
Reduced ejection
End of systole
Blood flow from ventricles decreases and ventricular volume decreases more slowly
As pressures in ventricles fall below that in arteries, blood begins to flow back causing semilunar valves to close
Reduced ejection on ECG
T wave
Ventricles begin to repolarise
Isovolumetric relaxation
Aortic and pulmonary valves shut, but AV valves remain closed until ventricular pressure drops below atrial pressure. (No change in volume)
Atrial pressure continues to rise
Does isovolumetric relaxation make a noise?
Yes
2nd heart sound (‘dub’)
due to closure of semilunar and associated vibrations
Rapid passive filling
Ventricles start to fill with blood
Rapid passive filling on ECG
isoelectric (flat) between cardiac cycles
Does rapid passive filling make a noise?
Not normally
3rd heart sound – usually abnormal, may signify turbulent ventricular filling
Reduced passive filling
Ventricular volume fills more slowly
Able to fill considerably without contraction of atria
Reduced passive filling AKA
Diastasis
Patterns of pressure changes
Are identical in right and left side of heart
Why are patterns of pressure changes identical in both sides of the heart?
Both ventricles eject the same volume of blood
Which side of the heart pumps blood at a higher pressure?
Left
Pressure volume loops:
Increases in preload results in
increased stroke volume
Pressure volume loops:
Increases in afterload result in
decreased stroke volume
Cardiac output calculation
Heart rate X Stroke volume
Can change CO by changing
HR and SV
SV can be changed by
preload, afterload and contractility
Contractility
Contractile capability (or strength of contraction) of the heart
Measure of contractility
Ejection fraction
What is contractility increased by?
Sympathetic stimulation
