Lecture 10: Cardiac Cycles and Sounds

Question 1

What comes first electrical event or mechanical event?

Answer 1

Electrical (depolarization/repolarization)

Question 2

What officially begins the cardiac cycle and what does this represent?

Answer 2

P wave. Atrial depolarization by SA node

Question 3

How is the atrium depolarized?

Answer 3

SA node sends electrical impulse to AV node, depolarizing the cells of the atrium so it can contract

Question 4

What is the PR interval, what does it represent and why is this important physiologically?

Answer 4

Delay of AP in the AV node. Ventricle basically waits for the atrium to finish it’s thing before doing anything so ventricular and atrial contraction don’t occur at the same time

Question 5

How is the ventricle depolarized? What direction does this happen and why?

Answer 5

• AV Node is helped by bundles and Purkinje fibers to send impulses throughout the thick ventricle.
• Apex up. Efficient for ejecting blood from ventricle to vessel (ventricle has to squeeze the blood upwards)

Question 6

What does the QRS complex represent?

Answer 6

Ventricular depolarization

Question 7

What does the time delay between the QRS (depolarization) and the increase in ventricular pressure (contraction) represent?

Answer 7

Time lag between electrical and mechanical event

Question 8

What does T wave represent?

Answer 8

Ventricular repolarization, this will be followed by ventricle relaxation

Question 9

What does the X and Y axes of an ECG represent?

Answer 9

X: time (P wave to P wave)
Y: depends, can represent volume or pressure in the atrium, ventricle or aorta

Question 10

What is the maximum time between 1 P-wave and the next?

Answer 10

1 second (=60 BPM, lowest normal HR)

Question 11

What needs to happen to pass the blood from one chamber to another?

Answer 11

Pressure from the previous chamber needs to exceed the pressure of the next chamber (e.g atrium to ventricle, ventricle to vessel)

Question 12

Draw the graph for left ventricular volume during one cardiac cycle. Label the significant events during this curve

Answer 12

Ok

Question 13

Draw the graph of the pressure curves for the atrial, ventricular and aortic pressure during one cardiac cycle. Label the significant events during this curve.

Answer 13

Ok

Question 14

What curve for pressure has the highest span? Why is that?

Answer 14

Ventricular pressure curve. V pressure needs to be lower than A pressure to get blood, and needs to be higher than aortic pressure to release blood. So it fluctuates a lot.

Question 15

What is necessary to open the valves?

What is necessary to close the valves?

Answer 15

Pressure in the previous chamber overcomes the diastolic pressure of the next vessel/chamber allowing blood to pass to the next destination

Pressure in the next chamber overcomes the pressure from the previous chamber/

Question 16

What is the dicrotic notch and what causes it?

Answer 16

Small spike in aortic pressure at the end of systole.

Caused by closing of the aortic valve which pushes some blood to the aorta

Question 17

Draw the curve of the jugular venous pressure during one cardiac cycle. Label the significant events during this curve.

Answer 17

Ok

Question 18

What is the a wave? 
What is the c wave? 
What is the V wave? 
What is x descent?
What is y descent?

Answer 18

atrial contraction
tricuspid valve closure
venous filling
atrial relaxation (interrupted by c wave) 
atrial emptying

Question 19

What does atrial systole mean?

Answer 19

A pressure > V pressure. Blood moves from A to V.

Question 20

Is aortic pressure higher or lower than A and V pressure?

Answer 20

Higher, because the the higher pressure is needed to eject the blood to the system

Question 21

What are the normal aortic and pulmonary arterial pressures?

Answer 21

Aortic: 120/70

Pulmonary A: 25/15

Question 22

What causes heart sounds?

Draw the locations of the 4 heart sounds on the Wiggers diagram

Answer 22

Blood hits some part of the heart and causes audible vibrations

Ok

Question 23

What causes the 1st heart sound?

Answer 23

bicuspid valves close and blood hits the closed valve

Question 24

What causes the second sound?

Answer 24

aortic valves close and blood loses its forward momentum and backflows from the vessel and hits the closed valve behind it

Question 25

What causes the 3rd sound? Can you hear this in adults?

Answer 25

Blood rapidly fills the ventricles

Not always

Question 26

What causes the 4th sound? Can you hear this in adults?

Answer 26

Last bit of blood is passed from A to V

Question 27

What causes a heart murmur?

Answer 27

Blood goes the wrong direction or its flow is obstructed

Question 28

If you have a systolic murmur, what is going on if …
Wrong direction:
Obstruction of flow:

Answer 28

Bicuspid valve is defective and causes blood to go back to left atrium
Aorta or pulmonary artery stenosis (blood stuck in ventricle)

Question 29

If you have a diastolic murmur, what is going on if…
Wrong direction:
Obstruction of flow:

Answer 29

Semilunar valves are defective so blood returns to the ventricle
Blood cannot get into the ventricles because of stenosis