3- Mechanical Propeties 2 Flashcards
What is the EDV, ESV and SV
END DIASTOLIC VOLUME (EDV) = the volume in the ventricles just before
END SYSTOLIC VOLUME (ESV) = the volume in the ventricles after the ventricle has completely contracted and expelled as much blood as it is going to
STROKE VOLUME (SV) = EDV - ESV
What is the ejection fraction
EJECTION FRACTION (EF) = the proportion of the end diastolic volume that is pumped out of the heart (Ejection Fraction = SV/EDV)
What are the 7 steps of the Cardiac cycle
- Atrial Systole
- Isovolumic Contraction
- Rapid Ejection
- Reduced Ejection
- Isovolumic Relaxation
- Rapid Ventricular Filling
- Reduced Ventricular Filling
Describe atrial systole
Depolarisation stimulated by SAN
P wave on ECG
Contraction tops off volume in ventricle
Isovolumetric contraction
AV valves closed (lub)
QRS wave on ECG
Contraction of ventricles with no volume change
Isometric contraction
Ventricular ejection
SL valves open
V. Pressure > aortic/ pulmonary pressure
Reduced ejection
Volume of blood in V. Decreases so pressure decreases
SL begin to close
T wave due to repolarisation
Isovolumetric relaxation
SL closed (dub) Atria have filled with blood but AV valves shut
Rapid ventricular filling
AV valves open, blood flows into ventricles
If there is turbulent ventricular filling, there will be a 3rd sound(ventricular gallop)
Reduced ventricular filling
Ventricular volume increases more slowly
What is the pressure in the systemic and pulmonary systems
120/80. 25/5mmHG
What can cause sound 4
During atrial systole S4 is usually caused by valve incompetency (valves don't shut properly making the blood flow become turbulent) Pulmonary Embolism Congestive Heart Failure Tricuspid Incompetence
What causes the jugular pulse, c wave and v wave
• JUGULAR PULSE - you may feel a small pulse in the jugular at this time due to the atrial contraction pushing some blood back up the jugular vein during atrial systole
The ‘c wave’ seen in the atrial pressure is caused by the right ventricular
contraction pushing the tricuspid valve into the atrium and creating a small wave into the jugular vein during ventricular ejection
‘v wave’ in the atrial pressure is caused by blood pushing the tricuspid valve and giving a second jugular pulse during isovolumetric relaxation
What is the dichrotic notch
DICHROTIC NOTCH - small, sharp increase in aortic pressure due to the rebound pressure against the aortic valve as the distended aortic wall relaxes during isovolumetric relaxation
How is pressure in the right side different to left side of heart
Pressure is less in the right side, but same stroke volume
Describe the pressure volume loop
• You plot VENTRICULAR PRESSURE against VENTRICULAR VOLUME
• Point 1 = End Diastolic Volume (EDV) - the ventricle has a large volume but hasn’t generated any pressure yet
• Point 2 = Isovolumic Contraction - the volume in the ventricle hasn’t changed but there is a large increase in pressure
At this point, the ventricular pressure has got to the same point as the
aortic pressure (afterload) and is just about to overcome it
• Between Point 2 and Point 3 = the ventricle starts to expel blood so the
volume of blood in the ventricle fall and the ventricular pressure rises then falls
• This ends on Point 3 which is the End Systolic Volume (ESV)
• THE DIFFERENCE BETWEEN POINT 3 and POINT 2 IS THE STROKE VOLUME
• Pressure falls in the ventricles due to Isovolumic Relaxation but the volume stays the same so there is a straight line downwards between Point 3 and Point 4
What determines preload and afterload
Volume of blood in ventricles during diastole
Pressure in aortic and pulmonary artery
Considering the Frank-Starling Relationship: what does Increasing preload do
Increases stroke volume: Point 1 and 2 move further to the right because there is more volume returning to the heart and hence the preload increases and End Diastolic Volume increases
The increase in stroke volume is shown by an increase in the distance between point 3 and point 2
Considering the Frank-Starling Relationship: Increasing afterload
Decreases stroke volume
Point 2 moves up, so point 3 and 4 move right, so
Name 3 factors affecting stroke volume
Preload
Afterload
Comtractility
What is cardiac contractility
Definition: Contractile capability (or strength of contraction) of the heart
• Simple measure of cardiac contractility is the EJECTION FRACTION
• Contractility can be increased by sympathetic stimulation
How does exercise affect contractility
Changes in peripheral circulation (e.g.
venoconstriction and muscle pump) means that more blood is returned to the heart and so End Diastolic Volume INCREASES
• So the increase in End Diastolic Volume (EDV) means that point 1 and 2 are pushed further right
• And the increase in contractility means that point 3 and 4 are pushed further to the left
• Thus there is an INCREASE in stroke volume
