Cardiac Cycle

Question 1

Know how does the pressure-volume curve look like for heart during systole

Also know the when does the mitral valve close and the aortic valve close and how to define the ventricular systole

Also know where the End Diastolic Volume (EDV) and the End Systolic Volume (ESV) lie on the graph

Answer 1

Ventricular systole is defined as the time when the mitral valve closes to the point where the aortic valve closes

Question 2

Pressures that we are supposed to know

Answer 2

1. Pressure when aortic valve opens: 80 mm Hg
2. Pressure when aortic valve close: 115 mm Hg
3. Peak pressure in the heart: 120

Question 3

Ejection fraction and stroke volume

Answer 3

Stroke volume = EDV - ESV

Ejection fraction = Stroke volume/EDV, normally it is around 0.5 to 0.7

Question 4

What is the main driving force for left ventricular filling

Answer 4

It will be due to ventricular repolarization when the ventricle is expanding. Atrial contraction only contributes 10% to 20% to ventricular filling which can be seen in the graph (the point corresponds to the P wave which is atrial contraction)

Question 5

When does atrial contraction has a bigger role

Answer 5

During exercise when the heart rate is increased, which causes the time for diastole to get shortened

Question 6

Define the AV node delay

Answer 6

During the PR segment of EKG the AV node cells are depolarizing which causes the action potential to travel to the ventricular myocytes. The conduction velocity for this action potential is slow so that the atria can complete contracting and fill the ventricle completely. This is called the AV node delay

Question 7

Isovolemic phase

Answer 7

There are 2 phase isovolemic contraction and isovolemic relaxation. The contraction happens before systole and relaxation before diastole.

Normally mitral valve has very low resistance and it opens or closes in very slight changes in pressure.

During the beginning of systole the ventricles are just about to contract, increasing the pressure of the ventricles. Mitral valve closes and the aortic valve is still closed, this phase is called the isovolemic phase.

Know the point in graph as to when does it take place

Question 8

Interesting question, what causes the pressure to rise during the generation of action potential in ventricular myocytes

Answer 8

During phase 2 Ca enters the ventricles cells causing cross bridges to form and myosin heads to bind, producing a power stroke. This leads to increase in pressure in the ventricles. Know when does this happen in the graph (in the inner gray thin strip area)

Question 9

What happens to Ca levels in isovolemic relaxation

Answer 9

The concentration of Ca inside the cells decrease as Ca exits out of the cells.

Question 10

Compare left and right heart ventricles graphs

Answer 10

The right side generates less pressure, the volume has to be the same since the circuit is in series. Also the valves are different.

Question 11

How does the resistance compare for systemic and pulmonic circulation

Answer 11

Peak pressure in the right ventricle is 1/5th of the left ventricle so 1/5th resistance is in the pulmonic circulation as compared to systemic circulation

Question 12

How does the pressures compare in the left and right atria

Answer 12

About the same, the pressure in the right atria is slightly lower (about 10 mm Hg lower)

Question 13

Explain the timing of the valves in systole

Answer 13

Pressure in the left and right atria is almost the same

When QRS complex occurs the left ventricle empties out faster than the right ventricle, so the mitral valve closes first but this sound cannot be heard.

Similarly when the pressure starts to rise, the pulmonic valve will open at a much lower pressure than the aortic valve so the pulmonic valve opens slightly before the aortic valve

Question 14

Expalin the timing of the valves in diastole

Answer 14

The exact reverse of systole occurs in diastole

1. Aortic valve closes first
2. Then pulmonic valve closes
3. Tricuspid valve opens then
4. Finally Mitral valve opens

Question 15

Where does most of the resistance to blood flow takes place

Answer 15

Arteries, 90%

Question 16

What is the significance of change in pressure in the left ventricle and the corresponding change in pressure in the aorta

Answer 16

The pressure in the left ventricle and in the aorta rises in parallel once the aortic valve opens. This signifies that the resistance provided by the aortic valve is incredibly small

Question 17

Difference between diastolic pressure and end diastolic pressure

Answer 17

EDV is between 0 and 10 mm Hg, this is the pressure at the end of ventricular diastole whereas on the other hand DP is 80 mm Hg and it is located in the arteries by definition

Question 18

When does diastolic pressure occurs

Answer 18

Right in the beginning of systole, look at the red dot in the graph that is the DP in the aorta

Question 19

When does S1 and S2 occur on EKG

Answer 19

S1 on QRS complex and S2 on T wave

Question 20

What does S3 and S4 signify

Answer 20

S3 is heard during ventricular filling, signifies ventricular hypertrophy and heart failure, S4 signifes atrial hypertrophy

Question 21

What are the venous waves

Answer 21

A wave is porduced by atrial contraction, occurs at the end of diastole

C wave occurs due to bulging of tricuspid valve into the right atrium during ventricular contraction

V wave: right atrial pressure gradually increases after the C wave to a peak which is called the v wave and it is due to atrial filling by venous return due to ventricular systole (some more filling then occurs in diastole)

Question 22

Splitting of S2

Answer 22

The closure of the pulmonic wave is delayed which causes physiological splitting of S2

Question 23

Wide splitting

Answer 23

It is caused by:

1. Right bundle branch block: slower depolarization of the right ventricle
2. Pulmonic Stenosis: Stiff pulmonic wave prolongs ejection time as it offers more resistance to blood flow

Question 24

What is paradoxical splitting

Answer 24

It is the exact opposite of wide splitting, the aortic valve closes at a later time. The causes are

1. Left Bundle branch block: the conduction defect results in a longer time to depoalrize the left ventricle and so it takes longer to eject blood
2. Aortic valve stenosis: High resistance due to stiff valve results in longer ejection time

Question 25

How do you differentiate between pradoxical splitting as opposed to wide splitting

Answer 25

Paradoxical splitting occurs during expiration whereas wide splitting occurs during inspiration

Question 26

Some normal values to remember

Answer 26

1. Left Ventricle EDV = 120 to 140 ml
2. Left Ventricular ESV = 40 to 60 ml
3. Left ventricle stroke volume = 60 to 100 ml
4. Left ventricle ejection fraction = 0.5 to 0.7
5. CO = 5 to 6 l/min

Cardiac Index = 2.6 to 4.2 l/min/sq meter body surface area

Question 27

Know the pressures in the different chambers of the heart

Answer 27

1. Normal blood pressure is 120/80 so in the left ventricle max pressure should be 120, EDP should be same as max pressure in LA which is 10.
2. The pressure in the pulmonic circulation is 1/5th of that of systemic so it should be 24/16 mm Hg
3. Pressure in the right atrium is less than left atrium (it is 8 in RA and 10 in LA) = thats why the congenital anomalies involving shunts move from left to right
4. Max pressure in the veins is 10