CVS3: Mechanical properties of the heart 2 Flashcards
What are the two main phases of the heart beat?
DIASTOLE= ventricular relaxation during which the ventricles fill with blood SYSTOLE= ventricular contraction when the blood is pumped into the arteries
What is isovolumetric contraction?
You get contraction but no change in volume so you get a build up of pressure in the ventricles
When do you get an expulsion of blood in isovolumetric contraction?
The ventricles don’t expel blood until the pressure gets to the point where it overcomes the pressure of the after load.
What is the end diastolic volume?
The volume in the ventricles just before the ventricles expel blood
What is the end systolic volume?
The volume in the ventricles after the ventricle has completely contracted and expelled as much blood as it can
What is stroke volume?
EDV- ESV
What is the ejection fraction?
SV/EDV
The proportion of the end diastolic volume that is pumped out of the heart
What are the seven stages of the cardiac cycle?
- Atrial Systole
- Isovolumic contraction
- Rapid ejection
- Reduced ejection
- Isovolumic relaxation
- Rapid ventricular filling
- Reduced ventricular filling
What happens just before atrial systole in terms of blood flow?
Blood flows passively through the open AV valves into the ventricles
What happens during atrial systole in terms of blood flow?
The atria contract, topping off the volume of blood in the ventricles
Which part of the ECG indicates atrial systole?
The P wave= atrial excitation
Why might you hear a sound during atrial systole?
This is an abnormal heart sound called S4 which is caused by valve incompetency which makes the blood flow become turbulent.
When does S4 occur?
- pulmonary embolism
- Congestive heart failure
- Tricuspid incompetence
Which pulse might you feel during atrial systole
Th jugular pulse- due to atrial contraction pushing some blood back up the jugular vein
When is isovolumic contraction?
Between the AV valves closing and the semi-lunar valves opening
What happens during isovolumic contraction?
Ventricles are sealed off
Ventricles contract with no change in volume
What happens to the pressure during isovolumic contraction?
- The volume stays the same because the valves are closed but contraction of ventricles => rapid increase in pressure
What is seen on the ECG during isovolumic contraction?
The QRS complex= ventricular excitation
Which sound is heard during the isovolumic contraction stage and why?
S1 (lub) sound= closing of the AV valves because ventricular pressure> atrial pressure
Is the isovolumic stage isometric or isotonic?
Isometric- muscle fibres aren’t changing length but are generating force and increasing the pressure
What causes the rapid ejection phase?
- The ventricles contracting in a closed chamber causes the ventricular pressure to exceed aortic/ pulmonary pressure (after load)
- so the SL valves open and blood is pumped out
- and ventricular volume decreases
Why causes the ‘c wave’ seen in the atrial pressure?
Right ventricular contraction pushes the tricuspid valve into the atrium and creates a small wave into the jugular vein
What is seen on the ECG and heard during occultation of the rapid ejection phase?
No ECG wave- because electrical excitation has already happened
No heart sounds- no closing of valves
What happens to the pressure during the reduced ejection phase?
The pressure of the ventricles fall below the arterial pressure