Cardiac Cycle Flashcards
What is the normal pressure of the right atrium?
2 mm Hg
What is the systolic pressure of the right ventricle?
25 mm Hg
What is the diastolic pressure of the right ventricle?
0 mm Hg
What causes ventricular filling?
small pressure differential (1-2 mm Hg on right and 5 mm Hg on the left) between the atria and ventricles during diastole.
What is the flow of blood?
enters the right atrium via the superior and inferior vena cava, passes through the tricuspid valve (right AV valve) to the right ventricle, through the pulmonary valve, through the pulmonary artery, to the lungs, back through the pulmonary veins, into the left atrium, through the mitral valve (left AV valve), into the left ventricle, and out through the aortic valve to the aorta and systemic circulation.
What are the pressures of the pulmonary artery?
systolic 20/ diastolic 6
What is the systolic pressure of the left ventricle?
120 mm Hg
What is the diastolic pressure of the left ventricle?
0 mm Hg
What is the pressure (systolic/diastolic) of the aorta?
120/80 mm Hg
If you heart rate is 75 beats/min, how long is one cardiac cycle?
(60 sec/min)* (1 min/75 beats)= 0.8 sec
How long is systole in relation to the cardiac cycle?
about a 1/3 of the time (so if cardiac cycle is 0.8 sec/beat then systole= 0.27 sec). Ejection itself= 0.22 sec.
Where does the cardiac cycle spend most of its time?
diastole= 0.53 sec.
Into what is systole divided?
Isovolumetric contraction= 0.05 sec
Ejection= 0.22 sec (rapid and reduced).
What is isovolumetric contraction?
the time during systole in which there is no change in volume as both mitral and aortic valves are closed, right before contraction.
Into what is diastole divided?
isovolumetric relaxation= 0.12 sec
Filling= 0.41 sec (rapid and reduced)
What is isovolumetric relaxation?
the time during diastole in which there is no change in volume as both mitral and aortic valves are closed, right before ventricular filling.
Where does the heart spend most of its time in systole and diastole?
systole= ejection diastole= filling
In late diastole, is atrial or ventricular pressure higher?
atrial (so the blood can flow through the mitral valve into the ventricle).
What happens to aortic pressure during late diastole?
it decreases as blood fills capillaries and veins throughout the body.
What causes the mitral valve to close?
as soon as the ventricular pressure increases beyond the atrial pressure (beginning of systole).
What cause the first heart sound (S1)?
mitral and tricuspid valves closing.
Why does the ventricular pressure rise so rapidly at the beginning of systole?
because the ventricle is isometrically contracting against 2 closed valves (mitral and aortic).
Where is the rate of rise in pressure (dPdT) the highest?
during systolic isometric contraction.
What causes the aortic valve to open?
when ventricular pressure exceeds the aortic pressure. This marks ejection.
What is the marker for ventricular systole?
mitral valve closing
What is the first phase of ejection?
rapid ejection phase
What happens in the latter part of systole?
the ventricle begins to relax and the ventricular and aortic pressures fall, as the ventricle begins to repolarize (T wave).
What happens as the ventricular pressure falls below the aortic pressure?
the aortic valve closes (second heart sound “S2”), indicating the beginning of ventricular diastole.
What forms the dicrotic notch of the aorta?
at the end of systole when the blood flows backward closing the aortic valve, recoil occurs, causing an initial increase in aortic pressure.
What causes the mitral valve to open?
when the intraventricular pressure falls below the atrial pressure.
What generates the third heart sound “S3”?
the initial rapid movement of blood from the atria to the ventricle during the rapid filling phase of diastole.
What happens at the end of diastole?
the atria depolarize (P wave) and contract adding a final volume of blood to the ventricles.
What generates the fourth heart sound “S4”?
the movement of blood from the atria to the ventricles in late diastole when the atria contract.
Where is ATRIAL systole?
during ventricular diastole.
Does most ventricular filling occur before or after atrial systole?
BEFORE. Atrial systole is to squeeze the last little bit into the ventricles at the end of ventricular diastole.
What is the a wave of atrial pressure?
increase in atrial pressure due to atria contracting
What is the c wave of atrial pressure?
increase in atrial pressure due to isovolumetric contraction
What is the x descent of atrial pressure?
decrease in atrial pressure due to rapid ejection of ventricular volume.
What is the v wave of atrial pressure?
increase in the atrial pressure as the atria fill with blood during ventricular systole.
What is the y descent of atrial pressure?
decrease in atrial pressure as blood moves from the atria to the ventricles during rapid filling of ventricular diastole.
What is the volume of ventricular blood near the end of diastole, before the atria contract, and after they contract?
before= about 150 ml
after= about 160 ml
*so only a change of about 10 ml
When does the role of atrial systole become important and why?
when your heart rate rises because diastolic time decreases, meaning the ventricles have less time to fill.
Does most ventricular blood filling occur passively or actively during ventricular diastole?
passively (150 ml) compared to the 10 ml extra from atrial systole.
How much does ventricular volume change during the rapid and reduced ejection phases of ventricular systole, respectively?
rapid ejection= 60 ml
reduced ejection= 20 ml
How much blood is ejected during ventricular systole?
about half of its total volume (80 ml). This is the ejection fraction
What is the ejection fraction?
the volume of blood that is ejected (stroke volume)/ total end diastolic volume. (normal is about 55%).
What events are associated with the P wave on the EKG?
(mitral valve is already opened) S3 sound before P wave, atrial depolarization, and S4 sound during ventricular active filling
What events are associated with the QRS complex?
ventricular depolarization, mitral valve closes, S1 sound
What event is associated with the PR interval?
AV node conduction and down the purkinje system
What events are associated with the T wave?
ventricular repolarization, aortic valve closes (S2 sound), and the mitral valve opens at the end of the T wave
What events are associated with the QT interval?
ejection phase, and aortic valve opens
What are the 3 major differences between the left and right side of the heart?
- pulmonary arterial pressure is much less than aortic pressure (20/6 vs. 120/80).
- diastolic filling lasts a little longer on the right side because the tricuspid valve opens before the mitral and the tricuspid closes after the mitral valve.
- ejection phase on the right side lasts a little longer because the pulmonary valve opens before the aortic and closes after the aortic valve.
Why does the right atrium contract slightly before the left atrium?
because the SA node is on the right and will depolarize this side first.
Why does the mitral valve close a little before the tricuspid?
due to pressure that is greater on the left closing the valve sooner.
Why does the pulmonic valve open before the aortic?
because the right ventricle is pumping against a much lower pressure than the left.
Is isovolumetric contraction in the right side of the heart (time between tricuspid closing and pulmonic opening), longer or shorter than the left side (mitral closing and aortic opening)?
shorter
Can you distinguish the mitral valve closing before the tricuspid valve?
NO, because they are so close together they sound like 1 sound.
Does the aortic or pulmonic valve close first?
the aortic, due to greater pressure.
Is duration of ejection longer on the left or the right?
right because of lower pressure and valves remaining open a little longer.
Can you distinguish the aortic valve closing before the pulmonic valve?
sometimes, and this would be known as a “split S2.”
More likely to pick it up during inspiration than expiration because during inspiration intrathoracic pressure decreases, thus increasing venous return (fill up the heart a bit more) causing it to eject a little longer.
