Mechanical Properties of the Heart 2 Flashcards
State the different phases of the cardiac cycle in order.
Atrial Systole Isovolumic Contraction Rapid Ejection Reduced Ejection Isovolumic Relaxation Rapid Ventricular Filling Reduced Ventricular Filling
What is the Ejection Fraction?
SV/EDV - the proportion of the blood in the heart that is pumped out in one contraction
What ECG change is seen in atrial systole?
on
P wave - atrial depolarisati
What abnormal heart sound could be heard during atrial systole and what could it be a result of?
S4 - this could be due to tricuspid incompetence, pulmonary embolism or congestive heart failure
How does atrial pressure change during atrial contraction?
Atrial pressure shows a small increase - a wave
Describe the pressure and volume changes that take place during isovolumic contraction.
The valves are all closed so there is no change in volume but the pressure increases dramatically.
What heart sound will be heard during isovolumic contraction?
S1 - closing of the atrioventricular valves
What ECG change is seen during isovolumic contraction?
QRS complex - ventricular depolarisation
Describe what happens during rapid ejection.
The ventricular pressure exceeds the aortic and pulmonary pressures so the aortic and pulmonary valves open and blood rapidly flows out into the aorta and pulmonary artery.
What causes the ‘c wave’ in atrial pressure during rapid ejection?
The ventricles contracting pushes the tricuspid valve inwards causing a slight increase in atrial pressure - c wave
Describe the electrical activity and heart sound heard during rapid ejection.
There is no electrical activity - isoelectric line on ECG. No heart sounds are heard.
Describe what happens during reduced ejection.
Marks the end of systole. Ventricular pressure begins to fall
T wave on the ECG due to the repolarisation of the ventricles. There are NO heart sounds because none of the valves are shutting.
What is the dichrotic notch and when does it occur?
The dichrotic notch is caused by the elastic recoil of the aorta causing a small rise in aortic pressure once ventricular contraction has ended.
What changes in pressure occur during isovolumic relaxation?
The atrial pressure increases due to the filling against closed valves - v wave. Volume of the ventricles does not change.
What heart sound can be heard during isovolumic relaxation?
S2 - this is due to the shutting of the aortic and pulmonary valves
What changes in volume and pressure take place during rapid ventricular filling?
There is a gradual increase in ventricular volume but ventricular pressure remains about the same. Atrial pressure decreases.
What abnormal heart sound can be heard during rapid ventricular filling and what could it be a result of?
S3 - can be due to mitral incompetence or severe hypertension
What happens during reduced ventricular filling?
Ventricular volume increases more slowly. This is also called diastasis. There are NO changes on ECG and NO heart sounds.
What diagram can show all this information?
Wiggers diagram
What is the difference between the pressures in the pulmonary circulation and in the systemic circulation?
The pressures in the pulmonary circulation are much lower (though the patterns of pressure changes are the same)
State the average pressures of the systemic circulation and of the pulmonary circulation.
Systemic - 120/80
Pulmonary - 25/5
What is used to measure preload on the left side of the heart?
PAWP - Pulmonary Artery Wedge Pressure
By measuring the pulmonary artery pressure you get an indirect measurement of the left atrial pressure
What do points 1-4 on the pressure-volume loop indicate?
1 = End diastolic volume 2 = Isovolumic contraction (pressure has increased but volume hasn't) 3 = End systolic volume 4 = Isovolumic relaxation (volume doesn't change but pressure has decreased)
Which feature of the pressure-volume loop indicates stroke volume?
Distance between point 2 and point 3
Which points on the pressure-volume loop indicate preload and afterload?
Preload = point 1 (because it indicates the venous return to the heart and hence the stretch on the ventricular muscle) Afterload = point 2 (this is the end of isovolumic contraction when the pressure in the aorta and pulmonary artery (the afterload) is first experienced)
Draw a diagram of the frank-starling relationship combined with a pressure-volume loop.
Starling’s Law = increased muscle fibres length causes increased ventricular contraction
The graph should be force against muscle fibre length (and pressure against volume)
How does the pressure-volume loop change if the venous return to the heart is increased?
Points 1 and 2 move further to the right so the distance between 2 and 3 and hence the stroke volume, increases
How does the pressure-volume loop change if the afterload is increased?
Points 3 and 4 move further to the right so the distance between 2 and 3, and hence the stroke volume, decreases. Also, point 2 and 3 move in a positive y direction so more pressure is required to open the aortic and pulmonary valves.
What three factors can affect cardiac output?
Preload
Afterload
Contractility
What is a simple measure of cardiac contractility?
Ejection Fraction
How does the Frank-Starling Relationship change with increased contractility?
The gradient of the ESV line changes
How does the pressure-volume loop change during exercise?
It becomes wider and the points move further out in all directions. EDV increases and ESV decreases (hence ejection fraction increases)
