Heart Physics & Heart as a Pump

Question 1

CO=______ x ______

Answer 1

HR times stroke Volume

Question 2

What three things affect stroke volume?

Answer 2

inotropy (contractility)
preload
afterload

Question 3

What are the numbers for average:
HR?
SV?
CO?

Answer 3

HR- 70 beats per min
SV- 70ml/beat
CO- 4.9L/min

Question 4

What is the difference between stroke volume and cardiac output?

Answer 4

CO=volume of blood pumped per minute by the left ventricle

SV=volume of blood pumped per beat

Question 5

Cardiac Output must equal what?

Answer 5

venous return to the heart

Question 6

what happens if the CO is not the same for the left and right sides of the heart?

Answer 6

edema (peripheral or pulmonary-can you guess when each would be?) if the volumes are not closely matched.

Also this is bad if you were not aware.

Question 7

What are the four phases of the cardiac cycle (these are also the four main changes in pressure and volume)?

Answer 7

Diastole
Isovolumetric contraction phase
Ejection Phase
Isovolumetric relaxation phase

Question 8

Describe the changes in pressure and volume that occur in the DIASTOLE phase and how it happens (all of these will be for the left side of the heart).

Answer 8

By the end of diastole (L vent.) the left atrium is filled with blood. atrium begins to contract and atrial pressure increases. This is seen as the a wave in both atrial and ventricular pressure. It is seen in both because the mitral valve is open allowing blood to flow freely (and pressure to distribute).

Question 9

Describe the changes in pressure and volume that occur in the ISOVOLUMETRIC CONTRACTION phase and how it happens.

Answer 9

the wave of depolarization which triggered the atrium to contract now reaches the ventricle. As it begins to contract, pressure in the ventricle immediately exceeds that found in the atrium (which is now relaxing) and the mitral valve closes. Aortic pressure is still high however (about 80 mmHg) and so the aortic valve stays shut. Ventricular pressure dramatically increases during this stage because both valves are shut and the blood has no place to go (this is why its called isovolumetric).

Question 10

Describe the changes in pressure and volume that occur in the EJECTION phase and how it happens.

Answer 10

The ventricle continues to contract and eventually exceeds that in the aorta. When this happens the aortic valve opens and the blood flows through. As ventricle relaxes the ventricular pressure falls below the aortic pressure and the aortic valve eventually closes. This process is delayed a couple milliseconds because the blood flowing out prevents it from closing.

Question 11

Describe the changes in pressure and volume that occur in the ISOVOLUMETRIC RELAXATION phase and how it happens.

Answer 11

Both valves are now closed and the ventricle continues to relax causing pressure to fall rapidly. Eventually pressure falls below that of the atrium and the mitral valve opens and blood begins to flow into the ventricle freely. A new cycle begins. A new era dawns.

There is a good graph of this on the slides (slide 5).

It should be noted that things are the same for the R side of the heart too.

Question 12

The end diastolic pressure-volume relationship represents what? define what this thing is.

Answer 12

preload- ventricular wall tension at the end of diastole (law of laplace)

more generally preload is the length to which a muscle is stretched before shortening.

the EDPVR curve becomes steeper with decreasing compliance.

Question 13

The Systolic pressure-volume relationship approximately represents what? define that thing.

Answer 13

afterload- the ventricular wall stress during contraction. What the ventricule has to push against in the aorta to move its contents there.

Question 14

What is the active tension or starling curve?

Answer 14

it is the difference in pressure between peak systolic pressure and end diastolic pressure curves. Good picture of this on PDF. Note that it has an ascending and a descending limb meaning that the difference between the two curves increases and then decreases.

Question 15

What is the Frank Starling law of the heart?

Answer 15

three ways to say:

1. heart responds to an increase in EDV by increasing the force of contraction
2. healthy heart always functions on the ascending limb of the ventricular function curve
3. what goes in must come out. Cardiac output must equal venous return and cardiac output from R and L ventricles must equal each other.

Question 16

What is a PV loop diagram?

Answer 16

a graphical representation of the relationship between vent. pressure and volume during the cardiac cycle. they show how diffs in preload, afterload, and contractility affect cardiac performance.

Question 17

what is the filling phase on the PV diagram?

Answer 17

bottom part of the loop (point a to c on diagram in PDF). Represents from mitral valve opening to mitral valve closing. The first part of this line represents end systolic volume (this is not zero, there is always some blood left in the heart) and the last part represents end diastolic volume. This curve is also the end diastolic pressure-volume relationship (seen previously).

Question 18

What is the isovolumetric contraction phase on the PV diagram?

Answer 18

ventricle contracting, valves closed so only pressure increases. no change in volume (points c-d in diagram). The constant volume during this phase is the end diastolic volume (EDV).

Question 19

what is the ejection phase on the PV diagram?

Answer 19

Aortic valve opening to aortic valve closing (points d-f). pressure increases and then slowly decreases because pressure is still increasing as blood begins to leave and then blood begins exiting more rapidly.

Question 20

What is the isovolumetric relaxation phase on the PV diagram?

Answer 20

both valves close and ventricular volume stays constant as ventricular pressure decreases (points f-a). when falls below atrial pressure the ventricle begins filling again.

Sorry I know I probably should have just bought the pro version and put the picture in here… oh well. what is done is done my son.

Question 21

How do you measure the peak systolic pressure on the PV diagram?

Answer 21

the peak of the ejection phase line.

Question 22

How to measure stroke volume on pv curve?

Answer 22

difference between end systolic volume and end diastolic volume (it is also just the width of the pv diagram).

Question 23

How do you calculate ejection fraction?

Answer 23

EF=SV/EDV

normal ejection fraction is 50-70%

Question 24

How do you calculate stroke work?

Answer 24

energy per beat (joules). Find by calculating the area inside the PV loop diagram. NOT the same for the Left and Right sides.

Question 25

What factors can affect preload?

Answer 25

• ventricular compliance (especially reduced compliance)- can cause a lower EDV which directly affects preload.
• afterload

Other things that affect it are mostly logical: blood volume, filling pressure, filling time, resistance to filling etc. anything that could change the amount of blood in the heart right before it contracts.

Question 26

increasing EDV does what to SV and stroke work?

Answer 26

increases. It is important to not that if contractility is not changed SV and SW return to normal on the next beat because EDV will return to normal.

Question 27

What affects afterload?

Answer 27

wall thickness and ventricular radius and aortic pressure.

Question 28

An increase in afterload causes what?

Answer 28

increase in ESV
decrease in EF, SV
EDV unchanged

Question 29

An increase in inotropy corresponds with changes in what?

Answer 29

increased SV and EF
decreased ESV
This also results in a new starling curve.
These effects will not correct on the next beat unless the inotropy is changed by something.