2.4.1 Cardiac Cycle

Question 1

What is arterial pressure determined by?

Answer 1

Arterial pressure is proportional to the volume of blood within the arterial system. During ejection when inflow is greater than outflow of blood from arteries to veins, arterial pressure increases.

Question 2

What is occurring during atrial contraction?

Answer 2

It is initiated near the end of diastole once atrial depolarization occurs. Atrial contraction only increases atrial pressure slightly and increases ventricular volume by about 10-20%.

Question 3

What do each of these arrow stand for?

Answer 3

Question 4

Answer 4

B

Question 5

What is wide splitting of S2? What are some things that can cause it?

Answer 5

Question 6

What do the heart sounds of S1, S2, S3 and S4 indicatie?

Answer 6

Question 7

What are some causes of increased pressure in the right atria?

Answer 7

Tricuspid stenosis, RV failure, and Cardiac Tamponade

Question 8

What causes the physiological splitting of S2 during inspiration?

Answer 8

Venous return to the right heart is a flow, and therefore it is dependent on the pressure gradient driving the flow and resistance. pressure is increased then venous return to the right ventricle will increase. During inspiration, decreased right atrial pressure increases venous return to the right heart. Filling of the right ventricle is increased which causes a greater stroke volume on the next beat (Starling’s Law). The pulmonic valve remains open longer than normal during ejection of this greater stroke volume and so pulmonic valve closure is delayed relative to aortic valve closure on inspiration.

Question 9

What is the formula for Ejection Fraction and what are the normal ranges in humans?

Answer 9

EF = Stroke volume / EDV

Normal range is 0.5 to 0.7 and this is an index of contractility of the heart

Question 10

How does the cardiac cycle compare between the right and left heart?

Answer 10

Question 11

What is occurring during the isovolumic ventricular relaxation phase of the cardiac cycle?

Answer 11

This period when the aortic valve is closing and ventricular pressure is falling rapidly. Ventricular volume cannot change since mitral valve is also closed. S2 signals the onset of diastole. Calcium levels in myocytes are decreasing.

Question 12

When does systemic arterial diastolic pressure occur?

Answer 12

During systole

Question 13

What is ESV and what does it represent?

Answer 13

End-systolic volume - the ventricular volume at the end of ejection

Question 14

Answer 14

D

Question 15

What are the events that occur when the QRS complex occurs?

Answer 15

Mitral and tricuspid valves close (S1)

Pulmonic and Aortic valves opening

Question 16

Answer 16

B

Question 17

A cardiac cycle is defined as?

Answer 17

One complete sequence of contraction and relaxation of the heart

Question 18

Answer 18

D

Question 19

What is paradoxical splitting of S2 and what are some causes?

Answer 19

Question 20

Since the right and left heart are in series what does this mean for the amount of blood they must pump over a minute?

Answer 20

They must pump the same amount - cardiac output must equal pulmonary blood flow

Question 21

What do the red and blue shaded areas represent respectfully?

Answer 21

Red - Ventricular diastole - begins at the time of aortic valve closure and lasts until mitral valve closure

Blue - Ventricular systole - begins at the time of mitral valve closure and lasts until aortic valve closure

Question 22

When ventricular contraction occurs, what happens to the pressure in the ventricles compared to the pressure in the artia? How does this affect the mitral and tricuspid valves?

Answer 22

When the ventricles contract the pressure within them increases and becomes greater than atrial pressure. This results in the closing of the mitral and tricuspid valves to keep blood from flowing back to the atria.

Question 23

Answer 23

A

Question 24

Since there is a much lower pressure difference in the right side of the heart, how can it achieve the same level of vascular flow as the left side of the heart?

Answer 24

The level in resistance in the right side of the heart is substantially less than the left side.

Question 25

What is indicated by the pressure in the ventricle and the corresponding artery being the same during ejection?

Answer 25

This indicates that the aortic and pulmonic valves have very little resistance to blood flow

Question 26

What is occurring during the process of ventricular filling?

Answer 26

When ventricular pressure falls below atrial pressure the mitral valve opens and blood flows from the atrium to the ventricle. Rapid filling occurs in the ventricle as blood flows from atrium to ventricle, causing atrial pressure to drop. Most of the filling is due to the pressure gradient being higher in the atrium than the ventricle.

Question 27

When are the tricuspid and mitral valves open?

Answer 27

When atrial pressures are greater than ventricular pressures - allowing the blood to flow from the atria to the ventricles.

Question 28

What are some causes of reduced pressure in the Right Atria?

Answer 28

Hypovolemia and impaired venous return to the heart

Question 29

When can the distinct sound of the aortic valve closing before the pulmonic valve closing be heard?

Answer 29

Upon inspiration by the patient

Question 30

When would atrial contraction become more important for ventricular filling?

Answer 30

During high heart rate, because there is a reduced diastolic filling time

Question 31

How can you determine stroke volume from ESV and EDV?

Answer 31

SV = EDV - ESV

Question 32

How does arterial diastolic pressure compare to ventricular end diastolic pressure?

Answer 32

DP: This is the pressure in the aorta at the time right before the opening of the aortic valve - tends to be roughly 80mmHg EDP: This is the pressure in the ventricle at the end of diastole - normally 0-10 mmHg

Question 33

Explain what the venous waves indicate.

Answer 33

Question 34

What is occurring during isovolumic ventricular contraction?

Answer 34

This is the onset of ventricular systole. This begins once an action potential passes through the AV node and initiates ventricular depolarization; triggered by QRS complex. Contraction causes intraventricular pressure to rise above atrial pressure causing the mitral valve to close. Since the aortic valve is also closed, pressure rises rapidly without a change in volume.

Question 35

What is EDV and what does it represent?

Answer 35

End-diastolic volume - the ventricular volume at the end of filling

Question 36

What accounts for the slight differences is the openings of the pulmonic vs aortic valves? What accounts for this in the closing of the mitral and tricuspid valves?

Answer 36

Upon depolarization of the ventricles, the pressure in the left ventricle will rise much faster (due to larger muscle) than the right ventricle. This will cause the mitral valve to close slightly before the tricuspid valve. The pulmonic valve will open at a much lower pressure than the aortic valve so the pulmonic valve will open slightly before the aortic.

Question 37

What is occurring during the ventricular ejection phase of the cardiac cycle?

Answer 37

Ejection begins when ventricular pressure rises above the aortic pressure - opening the aortic valve. There are two phases. Rapid ejection phase - Immediately after the aortic valve opens, blood rapidly enters the aorta and causes arterial pressure to rise. Slow ejection phase - after ventricular and aortic pressures reach maxium the rate of ejection and both pressures decrease. The peak systolic pressure is nearly the same in the ventricle and aorta because there is **little resistance** to flow in the aortic valve. Pressure declines throughout the slow ejection phase because the **force of contraction is decreasing as ventricular volume gets smaller and due to ventricular repolarization** (signified by the onset of the T wave). Eventually **intraventricular pressure falls below aortic pressure, which results in aortic valve closure.**

Question 38

What is stroke volume?

Answer 38

The volume ejected in a single beat