Week 18: The Cardiac Cycle Flashcards
What is the cardiac cycle?
the sequence of pressure and volume changes that takes place during cardiac activity
What brings about the mechanical events in the cardiac cycle?
by rhythmic changes in cardiac electrical activity
how to calculate max heart rate?
220 bpm- age in years
When does a valve open?
pressure is greater behind the valve than in front
when does a valve close?
when pressure is greater in fronton way valve=closes
What is the ECG a record of?
overall spread of electrical activity through the heart.
Electrical activity is the precursor for mechanical activity
When is the AV valve open?
When the Atria are depolarising between P and S on ECG
When is the left ventricle at its peak blood volume?
Between, S and shortly after. After depolarisation (R)
When is the left ventricle at its lowest blood volume?
Midpoint of T (repolarisation) and when the corn ends
When does mid-diastole occur?
between T and P sections.
after ventricular depolarisation and before atrial depolarisation
When does the atria fill up with blood?
between T and P.
Mid-diastole
When do the ventricles fill passively? (passive filling)
during mid-diastole when AV vales are open. accounts for 80% of final diastolic volume
Why are the aortic and pulmonary valves closed during mid-diastole?
higher pressure in the arteries compared to ventricular pressure
What happens to the ECG curve during late diastole?
P wave of ECG occurs
When do the atria contract?
towards end of P wave- increase atrial pressure
What happens when the atria contract?
most of the blood in the atria is propelled into ventricles, adds 20% to ventricular filling
What happens to ventricular pressure when atria force blood into them?
increase pressure slightly
What are some basic steps in late diastole?
1) SA node reached threshold, AP generated.
2) AP conducted across arterial tissue of heart via internodal pathway
3) Causing atrial muscle to collectively depolarise, rise to P wave
4) Increase atrial pressure, squeeze bait more blood into ventricles
When does diastole end on ECG?
onset of ventricular contraction/depolarisation
What happens during end of diastole/early systole?
ventricles contract at the endow QRS complex.
What happens to ventricular pressure during early systole?
rapid increase in pressure
What happens to valves during early systole?
AV valves snap shut- first heart sound
AV and aortic valves are shut … nothing in and nothing leaves
What is the phase called when both aortic and AV valves are closed?
isovulumetric or isometric phase
What happens to the valves ejection period?
ventricular pressure exceeds arterial pressure, aortic and pulmonary valve pulmonary valves open.
What is the pressure difference in the pulmonary artery for ejection period?
8mmHg to 25 mmHg during systole
What makes the second heart sound?
closing of the aortic valve during end of ventricular systole
What makes the first heart sound?
closing AV valves of the during early systole
What is the end of ventricular systole on ECG?
down slope of T wave
What happens during end of ventricular systole?
ventricles relax, ventricular pressure falls below aortic pressure.
aortic valves shut
What does the second heart sound cause?
blip/notch on the aortic pressure curve.
called a dicrotic notch
What happens to the valves in the end pf ventricular systole?
AV valve also shut, no blood in or out.
isomeric ventricular relaxation
What happens during filling period?
ventricular pressure falls below atrial pressure
AV valve opens
Blood which entered during ventricular systole is released into the ventricles by opening of AV valve
What are the changes in pressure and volume during filling period?
Atrial and ventricular pressures fall sharply and ventricular volume increases rapidly
What are the 5 phases in the cardiac cycle?
1) filling period
2) atrial contraction
3) isovolumetric ventricular contraction
4) ejection
5) isovolumetric ventricular relaxation
What is used to detect the heart sounds?
phonocardiogram
What are abnormal sounds in pathological conditions called?
murmurs
