Cardiac Cycle

Question 1

What phase are the atria and ventricles in prior to the P Wave? (Diastole or Systole)

Answer 1

Both are in diastole (relaxed)

Question 2

What is the electrical activity of the heart before the P wave? (What phase are the tissues at in their respective APs)

Answer 2

The atria and ventricles are in Phase 4 where all voltage gated channels are closed and K+ leak channels are open and Na/K ATPases are active

The SA and AV nodes are at Phase 4 as well. Funny Na+ channels are slowly depolarizing the tissues (SA node is depolarizing at a faster rate than AV node)

Question 3

What are the physical conditions inside the heart just before the P wave? (Valves, pressure, and blood flow)

Answer 3

The AV valves are open, Aortic and pulmonary valves are closed

Pressure in the atria is greater (4mmHg) than the pressure in the ventricles (0 mmHg)

Blood is flowing from the great veins, through the atria, and into the ventricles. Right before the P wave, the rate of blood flow into the ventricles is at its lowest.

Question 4

What is the Dicrotic Notch?

Answer 4

The point on the aortic pressure curve when the aortic valve closes.

Question 5

What is the state of the cardiac valves whenever it is in an “isovolumetric” phase?

Answer 5

All valves are closed, preventing any change in cardiac blood volume despite changes in pressure

Question 6

What are the normal Blood pressure values (systolic/diastolic) in the right and left ventricles?

Answer 6

Right ventricle: 25/0

Left Ventricle: 120/0

Question 7

How is the rate of dropping aortic diastolic pressure determined?

Answer 7

Blood leaving the aorta enters smaller vessels in the periphery. The rate of the pressure drop in the aorta is thus determined by the peripheral resistance to blood flow

Question 8

What is the “a” wave?

Answer 8

The pressure wave seen in the jugular vein pressure curve that indicates the contraction of the atria. Since there is valve between the great veins and the atria, pressure is reflected backwards.

Question 9

What is the “c” wave?

Answer 9

The pressure wave seen in the jugular vein pressure curve that indicates isovolumetric contraction of the ventricle. The contraction causes a bulging of the tricuspid valve into the atrium which is responsible for this reflection of pressure into the jugular vein.

Question 10

What is the “v” wave?

Answer 10

The pressure wave seen in the jugular vein pressure curve that represents blood returning to the atrium but can’t enter the ventricle (venous blood has continuous flow that is unaffected by ventricular contraction).

Question 11

What is the range of ventricular volume?

Answer 11

120 mL to ~50 mL

Question 12

What are the conditions inside the arteries and veins just before the P wave?

Answer 12

Both the pulmonary artery and aorta are approaching their diastolic pressure values (15 mmHg and 80 mmHg respectively) as blood enters the lungs and periphery.

Venous Pressure is slightly greater than atrial/ventricular pressure (which causes blood to move into the ventricle through the atria).

Question 13

What changes in pressure occur as a result of the P wave?

Answer 13

The atrial pressure increases as they both contract and the ventricular pressure also increases as blood is pushed into them.

Then once the atria begin to relax, so will the ventricles

Question 14

What happens to the atria as a result of the QRS complex?

Answer 14

QRS complex causes the ventricles to contract, causing a rapid increase in ventricular and aortic pressure. The atrial pressure also increases slightly as blood continues to return to the atria.

However, at this point blood does not enter the ventricles as the pressure is too high. It is at this point that we can see the “c” wave in the jugular vein curve.

Question 15

What does the T wave do and when does it occur in regard to ventricular activity?

Answer 15

The T wave indicates ventricular repolarization, which starts before the ventricles begin to relax. As the ventricles relax, the ventricular pressure drops rapidly

Question 16

What occurs during diastole?

Answer 16

Diastole occurs when the chambers are relaxed. The pressure in the ventricles is slightly lower than the atria, allowing blood to flow directly into the ventricles

Towards the end of diastole, the blood flow into the ventricles slows down as it is almost full; the atrial and ventricular pressures slight increase as the cycle is about to enter atrial systole at the instance of the P wave

Question 17

What is the purpose of atrial systole?

Answer 17

Since blood flows into the vetricles prior to atrial contraction, atrial systole is meant to “top off” the ventricles.

Question 18

How is aortic pressure affected by atrial systole?

Answer 18

It isn’t. Atria have no effect on aortic pressure. Through this portion of the cardiac cycle, the aortic pressure is gradually decreasing as blood enters the systemic vessels. Rate of flow plateaus as most of blood enters periphery.

Question 19

What is the condition of the heart at the end of atrial systole?

Answer 19

1) Atria begin to relax and both atrial and ventricular pressure decrease slightly
2) AV valves are both open
3) Aortic and pulmonic valves are closed
4) QRS complex has probably occurred or is occurring

Question 20

What is the condition of the heart at the beginning of ventricular systole?

Answer 20

1) QRS has already happened
2) The rapid increase in ventricular pressure forcefully closes the AV valves
3) Aortic/Pulmonary valves are closed (aortic/pulomnary artery pressure is greater than ventricular pressure, thus no blood is ejected yet). Also there is no change in aortic pressure yet
4) 1st heart sound occurs

Question 21

When does the 1st heart sound occur, and what is the source of the sound?

Answer 21

1st heart sound occurs right after the AV valves close. It is caused by blood entering the atrium hits the now closed AV valve. This is the loudest of the heart sounds.

Question 22

What happens during isovolumetric contraction?

Answer 22

1) Pressure rapidly rises, but no blood is ejected
2) AV valves bulge backwards (causing the “c” wave seen in the jugular vein pressure curve).
3) The aortic pressure is still decreasing at this point unaffected by the increasing ventricular pressure

Question 23

What is the pressure (systolic/diastolic) of the aorta and pulmonary artery respectively?

Answer 23

Aorta: 120/80

Pulmonary Artery: 25/15

Question 24

At what pressure will the aortic valve and pulmonary valves open, respectively?

Answer 24

Aortic Valve opens at Diastolic pressure: >80 mmHg

Pulmonary artery opens at its diastolic pressure: >15 mmHg

Question 25

What changes in pressure occur during ejection of the blood?

Answer 25

The ventricular pressure continues to increase temporarily, but then begins to decrease as blood volume in the ventricles decrease.

Atrial pressure is increasing during ejection as blood is returning to the atria.

The T wave occurs, causing repolarization of the ventricles.

Question 26

What causes the aortic/pulmonary vessels to close?

Answer 26

As the ventricles relax, the ventricular pressure rapidly decreases. Once the ventricular pressure falls below the aortic/pulmonary artery pressure, the valves close

Question 27

At what point does the second heart sound occur and what is the source of it?

Answer 27

The 2nd heart sound occurs just after the aortic/pulmonary valves close. The sound comes from the back flow of blood in these vessels when the pressure from the ventricle is cut-off abruptly.

Question 28

What is the state of the heart during isovolumetric relaxation?

Answer 28

AV valves are closed

Aortic/Pulmonar Valves are closed

Ventricle is relaxing and pressure is dropping rapidly

Aortic pressure is decreasing at a slower rate

Isovolumetric relaxation ends once the ventricular pressure drops below the atrial pressure, at which point the AV valves will open and blood will rush into the ventricle.

Question 29

Are the ventricles empty after contraction occurs?

Answer 29

No, the ventricles can never completely remove all the blood they contain

Question 30

When does the 3rd heart sound occur and what is the source of the sound?

Answer 30

The 3rd heart sound occurs after the AV valves open. The rapid filling of the ventricles creates a quiet sound not normally heard in adults, but can be heard in children with a stethoscope.

Question 31

What is diastasis?

Answer 31

The period of slow filling at the end of diastole as ventricular and atrial pressure become nearly equal.

Blood flow into the ventricles might actually stop if it becomes full (stasis).

Question 32

What phase does the heart spend the most time in?

Answer 32

Diastole

Question 33

If the heart rate changes, which phase decreases the time it consumes in the cycle?

Answer 33

Diastole. Systole is at a nearly fixed rate and cannot change much at all. When the heart rate increases, diastole decreases.

Question 34

When does the 4th heart sound occur and what is the source of the sound?

Answer 34

The 4th heart sound occurs just after the P wave as the atria contract ejecting blood into the already mostly full ventricle.

This is the softest of the heart sounds, cannot be heard in an adult.

Question 35

Which ventricle pumps more blood/minute?

Answer 35

Both ventricles pump an equal amount of blood/minute

Question 36

When would you hear a systolic murmur?

Answer 36

Between the 1st and 2nd heart sounds (lub and dub)

Specifically, during ventricular systole

Caused by stenosis of the pulmonary/aortic valves

OR

Caused by regurgitation of the AV valves (blood forced back into the atria)

Question 37

When would you hear a diastolic murmur?

Answer 37

Occurs after S2,and fades before S1.

Specifically during diastole (duh)

Caused by stenosis of AV valves (makes it difficult for blood to enter ventricles)

OR

Caused by Aortic/pulmonic regurgitation (allows blood back into ventricles from the aorta/ pulmonary artery.