Cardiac Cycle Flashcards
What are the 2 phases of a heart beat?
Systole + Diastole
What is systole?
Ventricular contraction - ventricles generate pressure + eject blood into arteries
What is diastole?
Ventricular relaxation - ventricles fill with blood
How long does diastole last?
Approx. 2/3 of heart beat
How long does systole last?
Approx. 1/3 of beat
How many sub phases is diastole split into?
4
How many sub phases is systole split into?
3
What sub phase does the cardiac cycle start with?
Atrial systole
What are the 4 sub phases of diastole?
- Isovolumetric Relaxation
- Rapid Passive Filling
- Slow Passive Filling
- Atrial Systole
What are the 3 sub phases of systole?
- Isovolumetric Contraction
- Rapid Ejection
- Slow Ejection
What is end-diastolic volume?
the volume of blood in the ventricles before contraction
What is end-systolic volume?
the volume of blood in the ventricles after contraction
What is stroke volume?
the volume of blood pumped from the left ventricle per beat
How is stroke volume calculated?
end-diastolic volume - end-systolic volume
What is ejection fraction?
k
How is ejection fraction calculated?
(100*stroke volume) / end-diastolic volume
What heart sound does atrial systole produce?
4th heart sound, but only abnormally - occurs w/ congestive heart failure, pulmonary embolism, tricuspid incompetence
What is isovolumetric contraction?
interval between AV valves closing and SL valves opening + contraction of ventricles with no change in volume
What signifies isovolumetric contraction on an ECG?
QRS complex
What heart sound does isovolumetric contraction produce?
1st heart sound (“lub”) - due to closing of AV valves and associated vibrations
What is rapid ejection?
ventricles contract pressure within them which exceeds pressure in aorta and pulmonary arteries + SL valves open, blood is pumped out and the volumes of ventricles decrease
What signifies rapid ejection on an ECG?
gap between QRS complex + start of T wave (opening of SL valves also marks start of this phase)
What heart sound does rapid ejection produce?
no heart sounds
What is reduced ejection?
- reduced pressure gradient means SL valves start closing
- blood flow from ventricles decreases + ventricular volume decreases more slowly
- as pressures in ventricles < arteries, blood begins to flow back causing SL valves close
What is reduced ejection?
- reduced pressure gradient means SL valves start closing
- blood flow from ventricles decreases + ventricular volume decreases more slowly
- as pressures in ventricles < arteries, blood begins to flow back causing SL valves close
What does reduced ejection signify?
end of sytole
What heart sound does reduced ejection produce?
no heart sounds
What is isovolumetric relaxation?
SL valves CLOSE + atrial pressure continues to rise (AV valves only open when atrial pressure > ventricular pressure)
What is the dichrotic notch?
an upstroke in aortic pressure when its descending - due to rebound pressure on the closed aortic valve as distended aortic wall relaxes
What heart sound does isovolumetric relaxation produce?
2nd heart sound (“dub”) - due to SL valves closing + associated vibrations
What is rapid passive filling?
AV valves open + blood rapidly flows from atria to ventricles
What signifies rapid passive filling on an ECG?
occurs in the isoelectric (flat) part of ECG after T wave
What heart sounds are heard with rapid passive filling?
3rd heart sound - usually abnormal + may signify turbulent ventricular filling
What could cause an abnormal 3rd heart sound?
turbulent ventricular filling - could be caused by severe hypertension or mitral incompetence
What is reduced passive filling?
ventricular volume fills more slowly, ventricles still fill considerably without contraction of atria
What is reduced passive filling also called?
diastasis
How does pressure compare from the right to the left of the heart?
can reach a max of 120mg in the left side, can reach a max of 25mg in the right
How do patterns of pressure changes compare from the right to the left of the heart?
essentially identical
How does stroke volume compare from the right to the left of the heart?
both eject same volume despite lower pressures in the right
Why does the right ventricle pump the same amount of blood as the left?
pumps into a lower pressure circuit
What is the pressure difference in the systemic circuit vs. pulmonary circuit?
systemic circuit - 120/80
pulmonary circuit - 25/5
Describe a general pressure volume loop shape (from A to D).
From A, heads up to B, curves to the left to C, drops down to D
What are graph axis and points ABCD for a general pressure volume loop?
x-axis = left ventricular volume y-axis = left ventricular pressure A = end-diastolic volume B = aortic pressure encountered C = end-systolic pressure
What determines the preload that stretches the resting ventricular muscle?
blood filling the ventricles during diastole
What blood pressures represent afterload?
blood pressures in greater vessels (aorta + PA)
What blood pressures represent afterload?
blood pressures in greater vessels (aorta + PA)
How can stroke volume be measured using the pressure volume loop?
horizontal linear distance between lines AB + CD
How does stroke volume change with preload?
increase in preload = increase in stroke volume
How does stroke volume change with afterload?
increase in afterload = decreases in stroke volume
How is cardiac output calculated?
cardiac output = heart rate x stroke volume
What 3 factors affect stroke volume?
preload, afterload, contractility
What is contractility?
contractile capability (strength of contraction) of the heart
How is contractility measured simply?
ejection fraction
How can contractility be increased?
sympathetic stimulation
How does increase in contractility affect ESPVR lines?
ESPVR line gets steeper than normal
How does decrease in contractility affect ESPVR lines?
ESPVR line gets less steep than normal
How does sympathetic stimulation increase contractility?
phosphorylate the Ca entry channel and Ca release channel => more release + more force
