Cardiac Performance

Question 1

What is the primary function of the heart?

Answer 1

To eject a sufficient amount of blood into the arterial system to maintain blood pressure that will assure adequate blood flow to all the peripheral tissues

Question 2

How do you calculate stroke volume?

Answer 2

EDV-ESV

Question 3

How do you calculate ejection fraction?

Answer 3

SV/EDV x 100

Question 4

How do you calculate cardiac output?

Answer 4

SV x HR

Question 5

How do you calculate Cardiac Index?

Answer 5

CO/SA

Where SA = body surface area

Question 6

How do you calucalate Left Ventricular Stroke Work (LVSW)

Answer 6

SV x left ventricular pulse pressure

Question 7

Do you need to be able to identify all the steps of heart contraction on a pressure volume loop?

Answer 7

Yes

Question 8

The area inside the pressure/volume loop represents what?

Answer 8

The work done on that bolus of blood (LVSW)

It is literally SV x LVPP

Question 9

How do you calculate the Left ventricular pulse pressure?

Answer 9

Systolic pressure- diastolic pressure

It’s a pulse pressure

Question 10

What is the definition of preload?

Answer 10

Tension (stretch) in ventricular wall at end of diastole (proportional to EDV)

However, we can’t really measure that, so we use End Diastolic Volume in its place.

Preload= EDV

Question 11

What determines resting fiber length?

Answer 11

Preload

Question 12

As preload increases, what happens to stroke volume? Why?

Answer 12

Stroke volume increases due to the muscle being stretched to its optimal length and it ejects more blood

Question 13

What law is this: the strength of the contraction of an isolated cardiac muscle fiber is a function of muscle fiber length (length-tension relationship)

Answer 13

Frank-Starling Law of the Heart

Question 14

When venous return to the right heart increases, what happens to the output of the left heart?

Answer 14

It will also increase

Right and left ventricular outputs are thereby matched

Question 15

With increased HR, what happens to ventricular filling time, and therefore, preload?

Answer 15

Ventricular filling time is reduced, so preload will be reduced.

Question 16

With increased HR, ventricular fill time is reduced, and therefore preload is reduced. What effect does this have on Cardiac output in the ABSENCE of sympathetic stimulation?

Answer 16

Under 150bpm, CO is not affected since the decreased SV is compensated for by the increased HR.

Above 150bpm, CO decreases

Question 17

Increased HR decreases ventricular filling time, and therefore decreases preload. How does this affect Cardaic Output in the PRESENCE of sympathetic stimulation?

Answer 17

Cardiac output can increase dramatically because SV is preserved due to increased contractility.
CO=SV x HR

Question 18

What is this: the ability of ventricle to distend under pressure

Answer 18

Ventricular compliance

Question 19

A highly compliant chamber will undergo a _____ change in volume with a small change in pressure

Answer 19

Large

Question 20

In hypertrophy and ischemia, what happens to compliance?

Answer 20

Compliance is reduced

Question 21

Low compliance has what effect on ventricular pressures and ventricular filling?

Answer 21

High ventricular pressures develop with just a small amount of volume added to the chamber

Filling is retarded (no offense intended with the use of that word)

Question 22

What effect will decreasing intrathoracic pressure have on RV stroke volume?

Answer 22

Increased, which also increase LV preload

Question 23

What effect does increased CVP (Central venous pressure) have on RV stroke volume?

Answer 23

Increased RV stroke volume= increased LV preload

Question 24

If you increase the pressure gradient between the inside and outside of the ventricle (delta P), what will happen to RV filling?

(You increase delta P by either increasing CVP or decreasing intrathoracis pressures ex: inspiration0

Answer 24

Increased RV stroke volume = increased LV preload

Question 25

Atrial systole (kick) has a ____ effect on EDV under normal circumstances?

Answer 25

Small

Question 26

When does the atrial systole (kick) have a very important effect on preload?

Answer 26

When filling time is limited (ex: high heart rate)

Question 27

Under normal conditions, what is the job of the pericardium?

Answer 27

Prevent the LV from being overexpanded Also maintains alignment with major vessels

Question 28

What happens to preload if the pericardium becomes Over filled with fluid?

Answer 28

The hydrostatic pressure on the external surface of the heart will reduce ventricular compliance which reduces EDV and SV (preload is decreased)

Question 29

What is a clinical example of the pericardium being filled with fluid?

Answer 29

Cardiac tamponade

Question 30

What is the definition of Afterload?

Answer 30

Resistance against which the ventricle contracts (For example, in the LV, the major components are arterial pressure, peripheral vascular resistance, arterial wall compliance, mass of the column of blood in the aorta, and the viscosity of the blood)

Question 31

What measurement do we use to estimate afterload?

Answer 31

Mean arterial pressure | DP + 1/3 PP PP in the aorta btw

Question 32

If you increase afterload, what happens to SV?

Answer 32

Decreased SV

Question 33

With increased afterload, the aortic valve opens (sooner/later) and closes (sooner/later)

Answer 33

Opens later Closes sooner Causes increased ESV (more blood left in the heart at the end of systole) and a reduced SV

Question 34

How does the heart compensate for increased afterload (which would normally cause increased ESV and decreased SV)

Answer 34

It is compensated for by the Frank starling mechanism. The Right heart doesn’t know that the LV is having trouble ejecting the blood into the aorta, so it will deliver a normal amount of blood to the LV, causing it to stretch, which allows the LV to generate more force. SV is restored to normal.

Question 35

What effect does aortic stenosis have on afterload

Answer 35

Increased afterload

Question 36

What effect does elevated arterial pressure (hypertension) have on afterload?

Answer 36

Increased afterload

Question 37

How does the heart compensate for increased afterload?

Answer 37

It fills more during diastole=more stretch=bigger force of contraction ***frank starling mechanism***

Question 38

What is the definition of contractility?

Answer 38

The ability of the heart to do work at any given fiber length (Independent of preload and afterload)

Question 39

What types of factors affect contractility?

Answer 39

ANS acitivty (mainly SNS) Circulating hormones (ie. epinephrine) Catecholamins increase Ca+ influx and availability = more cross bridges=more force

Question 40

what is the primary contributor to afterload?

Answer 40

The pressure in the aorta

Question 41

What does the area in the loop in a pressure/volume loop represent?

Answer 41

Ventricular stroke work

Question 42

Why does the heart get bigger after a long period of hypertension?

Answer 42

To increase the frank starling method of compensation -heart is bigger=larger volume of blood in ventricle=more forceful contraction

Question 43

How does norepinephrine affect contractility?

Answer 43

It stimulate B1 receptors, which increases contractility, and increases the SV at a given EDV. This is an **increase in ejection fraction** **postive inotropic effect**

Question 44

With SNS stimulation, what happens to the length of systole?

Answer 44

It is shortened, so that time for diastole is not shorter, and the filling time is maintained

Question 45

What effect will increasing contractility have on ejection fraction and ESV?

Answer 45

Ejection fraction will increase ESV will decrease (less blood in ventricle at end of systole)

Question 46

As contractility increases what is the effect on: Ejection velocity Stroke volume ESV

Answer 46

Ejection velocity increases Stroke volume increases ESV decreases *****TEST QUESTION******

Question 47

How do we estimate contractility?

Answer 47

By estimating the ejection fraction using ultrasound/echocardiogram.

Question 48

How do you calculate ejection fraction

Answer 48

SV/EDV x100

Question 49

What is a normal ejection fraction?

Answer 49

Normal 50-75%

Question 50

What is Treppe?

Answer 50

As HR increases, Ca++ accumulates, which increases contractility Helps to maintain cardiac output at very fast HRs

Question 51

Is maximum HR a function of age or training?

Answer 51

Age

Question 52

As exercise intensity increases, HR increases linearly. Does SV also increase linearly?

Answer 52

No, it is linear at low intensities, but *plateaus at about 40-60% of VO2 max

Question 53

Is the heart muscle aerobic or anaerobic?

Answer 53

Highly aerobic

Question 54

Does the efficiency of heart muscle increase or decrease with exercise

Answer 54

Increases

Question 55

What type of work increases during exercise: volume work (moving blood-preload) or pressure work (working against afterload)?

Answer 55

Volume work increases. | Volume work is energetically less costly than pressure work

Question 56

What is Left Ventricular Stroke Work? | How do you calculate it in a lab situation vs in the clinic?

Answer 56

It is the work done by the left ventricle in one stroke LVSW= SV x LVPP Only IF you have the values of the pressures in the left ventricle, which would be difficult to do in the clinic. In the clinic, you would estimate LVPP with MAP LVSW= SV x MAP (MAP = diastolic Pressure + 1/3 pulse pressure)

Question 57

What is left ventricular minute work and how do you calculate it?

Answer 57

It is the amount of work done by the left ventricle in one minute LVMW=LVSW x HR BUT you might not always have the LVPP requreied to calculate LVSW, so you would estimate LVPP by using MAP LVMW= SV x MAP x HR ``` (MAP= diastolic press + 1/3 Pulse pressure) (LVSW= SV x LVPP) ```