Lecture 3: Cardiac Cycle & Heart Sounds Flashcards
Systole
Contraction of the heart
Systole can be divided into?
- Atrial systole (atria contracting)
- Ventricular systole (ventricles contracting)
Diastole
Relaxation of the heart; common to refer to ventricular diastole, but the atria do relax too.
Blood pressure is always written as?
Systolic/Diastolic
Unlike skeletal muscle cardiac muscle can generate its own?
Action potentials
In the heart, the specialized tissue of the _______ and the _______ spontaneously depolarize and generate the action potential that causes contraction of cardiac muscle
SA node and AV node
In a healthy heart the ________ is the only source of excitation of the ventricles?
The AV node
Under normal conditions which node reaches threshold faster; and is therefore referred to as what?
The SA node; serves as the pacemaker
What does sinus rhythm refer to?
The SA node is driving the heart (pacemaker)
What two things occur after the SA node generates the AP?
1) AP depolarized the atria using gap junctions
2) AP travels to the AV node via an internodal pathway.
What kind of cells are found in the internodal pathway?
Specialized cardiac muscle cells that are good at conduction; not quite nerve, but functon similarly
What’s the condunction velocity in the AV node like; what does this cause?
Slows so there is a ‘pause’ between depolarization of the atria and that of the ventricles. Leads to a delay before ventricular contraction
Once the AV node transmits the AP to the ventricles, what helps further carry this AP for depolarization?
Specialized cardiac muscle (the bundle branches and purkinje fibers)
The bundle branches and purkinje fibers transmit the AP and depolarize which parts of the ventricle?
1) Septum
2) Free walls of both ventricles starting from the apex back up
What helps spread the AP through the atria once the SA node fires?
Gap junctions
The last to depolarize is the first to?
Repolarize
Since the atria depolarize first, they contract fist, which causes?
Increased pressure in the atria, driving blood from the atria to the ventricles through the open valves.
The ventricular pressure _______ as blood is pushed from the atria into the ventricles?
increases
After the atria contract and begin to relax, the ventricles?
Start to contract
Which part of the ventricle contracts first; causes it to?
The septum since it was depolarized first, causes it to ‘stiffen.’
Which part of the ventricle contracts second and what does this lead to?
The walls of the ventricles, squeezing blood in the chambers, and increasing the pressure in the ventricles.
Why is the atrial pressure increasing during ventricular systole?
Blood continues to return to the heart (venous return) during the period of ventricular systole, but can’t move into the ventricles because of the ventricular contraction. This causes the atrial pressure to increase.
What are the pressures in the ventricle at the lowest and the highest?
Lowest = 0 mmHg
Highest = 120 mmHg
Why is the aortic pressure quite a bit above the atrial and ventricular pressures?
The amount of blood leaving the aorta is being controlled by the smooth muscle in the vasculature.
Almost immediately, the ventricular pressure exceeds the atrial pressure, causing what?
The AV valves to close, preventing blood from flowing back into the atria
The contraction of the ventricles continues, building pressure in the ventricles, but is blood being ejected now?
No - the pressure in the ventricle must exceed the pressure in the pulmonary artery and aorta before the valves leaving the ventricles will open.
While the ventricular pressure is increasing dramatically, but blood is not being pumped out yet, what is happening to the ventricular volume; known as?
Remains constant; isovolumetric contraction (iso = same; volumetric = volume)
Arterial blood pressure is measured at 118/68; while the pulmonary arterial pressure is 26/14. What is the minimum pressure in the left ventricle when the aortic valve opens?
68
What is normal aortic pressure?
120/70
What is normal pulmonary artery pressure?
25/15
The ventricular pressure must exceed what to open the valve?
Diastolic pressure on each side
What occurs once the ventricular pressure exceeds that in the artery and the valve is forced open?
Blood is ejected from the ventricle into the artery
Once the aortic valve opens and blood is ejected from the ventricle, what is seen on the graph of the cardiac cycle (ventricular volume/pressure and atrial pressure); marks the end of which period?
- Ventricular volume decreases (blood leaving)
- Atrial pressure decreases (valve not bulging back anymore)
- Ends the period of isovolumetric contraction.
How does cardiac muscle differ from that of skeletal in how AP’s are generated?
Specialized tissue of SA and AV node can spontaneously depolarize and generate an AP
The AP travels from the SA node to the AV node via what?
The internodal pathway
What creates the first heart sound, “lub?”
The AV valve closes and blood in the atria bounces off the valve as it tried to enter the ventricle
What number must the pressure in the ventricle exceed before opening of the pulmonary or aortic valves occurs and blood can be ejected?
The ventricular pressure must exceed the diastolic pressure on each side to open the valve.
What is occuring here?
Closing of the aortic valve producing the Dicrotic notch in the aortic pressure wave
*Atrial pressure shows a similar wiggle*
The second heart sound is produced by what?
Closing of the aortic and pulmonary valves causes some of the blood to backflow towards the ventricles and bounce off the closed valves
Why does the blood “backflow” when the valves close?
Upon closure of the valves, the force driving the blood forward (pressure in ventricle) is “cut-off” and gravity is free to pull the blood back down.
What is isovolumetric relaxation?
Period after closing of the pulmonary and aortic valves where no blood enters or leaves the ventricles while they are relaxing (the AV valves are also still closed).
What is occuring in this image?
Atrial pressure is exceeding ventricular, AV valves open, blood begins to move into the ventricle.
What pressure does the L and R ventricle have to be at for the blood to enter from the atria?
The ventricular pressure must be LOWER than all other pressures during diastole (close to zero) for blood to move from high pressure to low pressure
Why does blood flow very rapidly into the ventricles once the AV opens back up?
Due to the ventricular pressure and volume being very low
Why does the aortic pressure continue to gradullay drop?
Blood continues leaving the aorta and flowing into smaller vessels in the periphery (peripheral run-off)
What determines the rate of peripheral run-off as blood leaves aorta into the periphery?
Resistance to blood flow
Label A-D
A) Mitral Valve closes
B) Aortic Valve opens
C) Aortic Valve closes
D) Mitral Valve opens
What is producing the small drop in atrial pressure here?
The aortic valve is opening, so blood can now be pumped out of the ventricles. This relieves some of the pressure of the blood in the ventricle that is pushing back on the AV valves causing an increase in atrial pressure
Most of the ventricular contraction occurs when?
During the ST segment
Isovolumetric relaxation occurs where on the ECG?
The end of the T-wave
Where on the ECG is atrial repolarization occuring?
At somepoint during the QRS complex
What point of jugular pressure is indicated by the arrow?
The ‘A’ wave - pressure wave created by atrial contraction - pressure reflected backwards due to there being no valve between the atria and great veins
What point of jugular pressure is indicated by the arrow?
The ‘C’ wave - pressure created during isovolumetric contraction in ventricles - there is bulging of the wall back into the atria
What point of jugular pressure is indicated by the arrow?
The ‘V’ wave - pressure wave created as blood returns back to the heart, but cannot enter the ventricle (AV valve still closed)
What creates the third heart sound?
Blood rushing into the ventricle during the rapid filling phase.
Atrial Pressue > Ventricular Pressure
2 reasons that a murmur is heard?
1) Blood is moving in a direction it shouldn’t be
2) Blood is having a hard time moving in the direction it should
*Valve issues*
A systolic murmur would be heard between which heart sounds?
S1 and S2
What causes a systolic murmur?
1) Blood moving back into the atria (mitral regurgitation)
2) Blood unable to get into the aorta/pulmonary artery due to stenosis.
Where would you hear a diastolic murmur when listening to the heart?
Right after S2 and before the next S1.
What causes a diastolic murmur?
1) Blood moving back into the aorta or pulmonary artery, caused by aortic regurgitation
2) Blood can’t get into the ventricle, stenosis.
