4 Mechanical Properties of the Heart II

Question 1

Q: What are the 2 main phases the heart beat is divided into? Subphases?

Answer 1

A: DIASTOLE = ventricular relaxation during which the ventricles fill with blood
-Split into FOUR sub-phases

SYSTOLE = ventricular contraction when the blood is pumped into the arteries
-Split into TWO sub-phases

Question 2

Q: What is end diastolic volume EDV? (2) Dictates? Value?

Answer 2

A: the volume in the ventricles at the end of diastole = max capacity of heart of that cardiac cycle

dictates how stretched the muscle fibres are before the excitatory event

130mL

Question 3

Q: What is end systolic volume ESV? Value?

Answer 3

A: the volume in the ventricles after the ventricle has completely contracted and expelled as much blood as it is going to

60mL

Question 4

Q: What is stroke volume SV? Equation? Value?

Answer 4

A: how much blood has been ejected from the heart in one go

SV = EDV - ESV

70mL

Question 5

Q: What is the ejection fraction? Equation? Normal value at rest? someone with heart failure? Clinical relevance.

Answer 5

A: the proportion of the end diastolic volume that is pumped out of the heart

Ejection Fraction = SV/EDV

• In normal people the ejection fraction at rest is about 65%
• In patients with heart failure, the ejection fraction can drop to around 35%

clinical index of how effective this contraction is

Question 6

Q: Give an overview of the cardiac cycle. (5)

Answer 6

A: 1. diastole allows filling of the ventricles= blood fills heart

2. atrial contraction= fills ventricles with more blood (still part of diastole)
3. isovolumic contraction (ventricles)= allows pressure to develop in both chambers
4. ventricular ejection= when pressure in ventricles is more than pressure in aorta and pulmonary artery
5. relaxation
6. ventricles fill with blood again

Question 7

Q: Describe isovolumic contraction. (2)

Answer 7

A: the pressure builds up in the ventricles but the ventricles don’t expel blood until the pressure gets to the point where it overcomes the pressure of the afterload

(get contraction but there is NO CHANGE IN VOLUME)

Question 8

Q: What is the cardiac cycle?

Answer 8

A: description of mechanical and electrical events, volume changes and sounds associated with the heart beat

Question 9

Q: What are the 7 events of the cardiac cycle?

Answer 9

A: 1. Atrial Systole

2. Isovolumic Contraction
3. Rapid Ejection
4. Reduced Ejection
5. Isovolumic Relaxation
6. Rapid Ventricular Filling
7. Reduced Ventricular Filling

Question 10

Q: Draw a pressure time graph for one heart beat. Include valve opening and closing.

Answer 10

A: REFER

aortic pressure (top)
atrial pressure (bottom)
ventricular pressure (crosses from bottom to top)

bottom left is lub= AV closing

dub= aortic and pulmonary valves close

Question 11

Q: What occurs before atrial systole? Role of atrial systole? How is it seen on an ECG? indicates? (2) Cause?

Answer 11

A: the blood will flow PASSIVELY through the open AV valves into the ventricles
-Atrial Systole tops off the volume of blood in the ventricles

seen as a P wave - indicates atrial excitation= atrial depolarisation
->SA node sends wave of depolarisation across atria

Question 12

Q: During atrial systole, what sound might you hear? Cause? Name 3 conditions it occurs with.

Answer 12

A: you occasionally hear an abnormal heart sound called S4

S4 is usually caused by valve incompetency (valves don’t shut properly making the blood flow become turbulent)

S4 occurs with:

• Pulmonary Embolism
• Congestive Heart Failure
• Tricuspid Incompetence

Question 13

Q: How does pressure change during atrial systole? (3) Relation to pulse?

Answer 13

A: -Atrial pressure shows a small increase due to the contraction
-very little change in the pressure in the aorta and the ventricles

you may feel a small pulse in the jugular at this time due to the atrial contraction pushing some blood back up the jugular vein

Question 14

Q: What is the SA node? Where is it?

Answer 14

A: cardiac pace maker

-just above RA (where vena cava comes in)

Question 15

Q: When does isovolumic contraction occur? Describe the ventricles during this event. (2) Pressure?

Answer 15

A: in between the AV valves closing and the semi-lunar valves opening

• The ventricles are contracting ISOMETRICALLY against closed valves so the muscle fibres ARE NOT CHANGING IN LENGTH but they are generating force and the pressure increases
• The ventricles are completely sealed off during this period
• So the ventricles contract with NO CHANGE IN VOLUME hence it is isovolumic

This contraction against closed valves leads to a rapid increase in pressure

Question 16

Q: How is isovolumic contraction seen on an ECG? signifies? (2)

Answer 16

A: seen as the QRS complex = signifies ventricular excitation = VENTRICULAR DEPOLARISATION

Question 17

Q: What sound is heard during isovolumic contraction?

Answer 17

A: The first heart sound occurs during this period - caused by the closing of the AV valves

S1 is the first heart sound - caused by the closing of the AV valves (this is the ‘lub’)

Question 18

Q: When does isovolumic contraction end?

Answer 18

A: You reach a point at which the ventricular pressure EXCEEDS aortic pressure (afterload) and at this point the aortic valve opens and blood starts to be ejected from the ventricles

Once blood begins to be ejected, isovolumic contraction ends

Question 19

Q: What marks the start of rapid ejection? What does rapid ejection involve? (3) What type of contraction?

Answer 19

A: Aortic and pulmonary valves opening

As the ventricles contract in the closed ventricular chamber the ventricular pressure rapidly increases until it exceeds the pressure in the aorta and pulmonary arteries (afterload)

At this point the semi-lunar valves open and the ventricular volume decreases

Once the valves are open, aortic pressure increases in line with the ventricular pressure

isotonic as you get shortening

Question 20

Q: What does rapid ejection look like on the pressure graph? What does it look like on an ECG? Sound?

Answer 20

A: The ‘c wave’ seen in the atrial pressure is caused by the right ventricular contraction pushing the tricuspid valve into the atrium and creating a small wave into the jugular vein

as the excitation process has happened, there is NO ELECTRICAL ACTIVITY on the ECG and there are NO HEART SOUNDS because no valves are closing

Question 21

Q: What does reduced ejection mark the end of? What does it involve? pressure (3).

Answer 21

A: systole

Blood leaves the ventricles and ventricular pressure begins to fall, eventually aortic and pulmonary pressure will exceed the ventricular pressure and so the VALVES WILL BEGIN TO CLOSE

Question 22

Q: What does an ECG show for reduced ejection? Heart sound?

Answer 22

A: ECG - cardiac cells begin to REPOLARISE (action potential went very positive and is now returning to resting potential) - this is seen as a T wave

NO heart sounds because no valves are shutting

Question 23

Q: What does isovolumic relaxation mark? Valves? (3) What does it involve? Volume change?

Answer 23

A: Beginning of diastole

Aortic and pulmonary valves have shut and the AV valves remain shut

• As the AV valves are closed there is NO CHANGE IN VENTRICULAR VOLUME hence it is isovolumic relaxation
• Atria fill but the AV valves are shut hence there is an increase in atrial pressure

Question 24

Q: What are the changes in pressure during isovolumic relaxation? (2) Heart sound?

Answer 24

A: ‘v wave’ in the atrial pressure is caused by blood pushing the tricuspid valve and giving a second jugular pulse

DICHROTIC NOTCH - small, sharp increase in aortic pressure due to the rebound pressure against the aortic valve as the distended aortic wall relaxes

SECOND HEART SOUND is heard when the aortic and pulmonary valves close

Question 25

Q: What is involved in rapid ventricular filling? Volume? Pressure? Energy?

Answer 25

A: AV valves open again and the blood flows rapidly from the atria in to the ventricles Ventricular Volume INCREASES Atrial Pressure DECREASES This filling of the ventricles is PASSIVE as it is not due to atrial systole

Question 26

Q: What heart sound is produced during rapid ventricular filling? signify? Due to? (2) Electrical signalling?

Answer 26

A: S3 is often referred to as VENTRICULAR GALLOP During this period you may hear a THIRD HEART SOUND (S3) which is ABNORMAL and can signify turbulent ventricular filling S3 can be due to severe hypertension or mitral incompetence no electrical event

Question 27

Q: What is reduced ventricular filling? Volume? ECG? Sound?

Answer 27

A: slow filling of the ventricles is also called DIASTASIS Ventricular volume increases more slowly There are NO changes in the ECG and there are NO heart sounds

Question 28

Q: What does the Wiggers diagram show? Includes? (3)

Answer 28

A: standard diagram that is used in teaching cardiac physiology includes: - pressure - ECG - sound etc

Question 29

Q: How does the pressure changes in the left and right side of the heart compare? Despite this?

Answer 29

A: -SAME PATTERNS OF PRESSURE CHANGES -BUT, everything on the right side of the heart occurs at LOWER PRESSURES Despite this lower pressure, the right ventricle ejects the same volume of blood as the left ventricle

Question 30

Q: What are the systemic and pulmonary blood pressure values?

Answer 30

A: SYSTEMIC = 120/80 mmHg Pulmonary = 25/5 mmHg systolic/diastolic

Question 31

Q: How can you measure pressure changes in the heart? (3)

Answer 31

A: A catheter can be inserted into a large vein and worked up into the right atrium and the right ventricle and you can have a pressure tip on it which allows you to measure changes in pressure You can insert a catheter with a balloon on the end into the pulmonary artery and inflate the balloon so that no blood can go past it Distal to the balloon, you can measure pressure changes further up the pulmonary system which is linked to the left atrium

Question 32

Q: When is PAWP elevated? (2)

Answer 32

A: if you've got problems on the left side of the heart (particularly the left atrium) or problems with the mitral valve

Question 33

Q: What is PAWP?

Answer 33

A: by measuring pressure on the right side of the heart, you can measure the preload on the LEFT side of the heart This is PULMONARY ARTERY WEDGE PRESSURE (PAWP)

Question 34

Q: How do you get a pressure volume loop? Draw and label. (4)

Answer 34

A: plot VENTRICULAR PRESSURE against VENTRICULAR VOLUME (plot anticlockwise from bottom right) 1. End Diastolic Volume (EDV)= ventricle has large volume and low pressure - > contraction 2. Isovolumic Contraction = volume in the ventricle is same and pressure has increased 3. End Systolic Volume (ESV) -> Pressure falls in the ventricles due to Isovolumic Relaxation but the volume stays the same so there is a straight line downwards 4.

Question 35

Q: On a pressure volume loop, what is the difference between points 2 and 3?

Answer 35

A: stroke volume

Question 36

Q: Identify preload and afterload on the pressure-volume loop.

Answer 36

A: Blood filling the ventricles during diastole determines the preload that stretches the resting ventricle = therefore is point 1= EDV blood pressures in great vessels (aorta and pulmonary artery) represent afterload (just after point 2 when the left ventricle encounters the aortic pressure when the aortic valve begins to open)

Question 37

Q: How does the pressure volume loop fit into the Frank-Starling Relationship? What is point 3?

Answer 37

A: REFER TO GRAPH- instead of force we have pressure and instead of length we have volume - these are the in vivo correlates in the Frank-Starling Relationship End Systolic Volume so the active force curve at this point represents the End-Systolic PV Line

Question 38

Q: Considering the Frank-Starling Relationship, what happens when you increase preload? EDV? SV?

Answer 38

A: increase the amount of blood flowing back to heart (more preload) = increase stretch on muscle = increased pressure volume loop size by point 1 and 2 move further right End Diastolic Volume increases as well as stroke volume = shown by an increase in the distance between point 3 and point 2

Question 39

Q: Considering the Frank-Starling Relationship, what happens when you increase afterload? Point 2? Point 1? EDV? SV?

Answer 39

A: increase the afterload = decrease amount of shortening (= stroke volume decreases) (points 3 and 4 move right) -> more pressure is needed to open the aortic valve so Point 2 moves in a positive y direction Point 1 remains the same because the End Diastolic Volume is the same

Question 40

Q: What happens to afterload if you have high blood pressure? result?

Answer 40

A: the afterload is increased so the ventricular muscle has to work harder to eject the blood against the higher pressure

Question 41

Q: How do you calculate cardiac output? What's it affected by? (3)

Answer 41

A: heart rate x stroke volume stroke volume is affected by preload, afterload (venous return and arterial pressure) and contractility (heart beat strength) eg using adrenaline

Question 42

Q: Define cardiac contractility. Simple measure of it is? How can it be increased?

Answer 42

A: Contractile capability (or strength of contraction) of the heart ejection fraction sympathetic stimulation

Question 43

Q: What do you get as cardiac contractility changes? eg if it increases? Draw 3 graphs for control, increased and decreased contractility.

Answer 43

A: family of Frank-Starling Relations more blood is pumped out hence the stroke volume increases and Point 3 moves further to the left REFER TO VOL PRES GRAPH

Question 44

Q: How does exercise affect contractility? Describe the graph change (frank-starling). Stroke volume?

Answer 44

A: contractility is INCREASED due to increased sympathetic activity -Changes in peripheral circulation (e.g. venoconstriction and muscle pump) means that more blood is returned to the heart and so End Diastolic Volume INCREASES -So the increase in End Diastolic Volume (EDV) means that point 1 and 2 are pushed further right -And the increase in contractility means that point 3 and 4 are pushed further to the left =>Thus there is an INCREASE in stroke volume