Cardiac Function Part 1: Cardiac Pump Performance

Question 1

functions of the heart

Answer 1

• generate adequate arterial blood pressure to meet needs of tissues/organs
• nutrients, water, oxygen, thermoregulation
• maintain normal/low venous pressure to help remove metabolic waste products

Question 2

heart failure

Answer 2

• lack of adequate arterial BP and therefore flow/CO to meet the needs of the tissues/organs: nutrients, water, etc
• excessive venous pressure & lack of adequate metabolic waste removal

Question 3

systole

Answer 3

emptying/contraction of ventricle

Question 4

diastole

Answer 4

filling of ventricle

Question 5

what defines the onset of systole?

Answer 5

mitral/tricuspid valve closure (first heart sound)

Question 6

what defines the onset of diastole?

Answer 6

aortic/pulmonic valve closure

Question 7

stroke volume

Answer 7

EDV (end diastolic volume) - ESV (end systolic volume)
the volume of blood EJECTED from ventricle in one cycle

Question 8

what is the ejection fraction?

Answer 8

SV / EDV (maximum) = the % of blood that leaves the ventricle with each cycle
a low ejection fraction tells you your ventricle isn’t functioning well

Question 9

what is normal ejection fraction?

Answer 9

> 50-60%
if your ejection fraction is very low, this tells you that something is wrong and your ventricle isn’t functioning well

Question 10

how is cardiac performance assessed?

Answer 10

volume, pressure, and flow (echo!)

Question 11

CO

Answer 11

cardiac output = stroke volume x heart rate

Question 12

what is cardiac output?

Answer 12

• total volume of blood pumped into Ao and PA in 1 min (L/min)

Question 13

T/F: the CO of the left ventricle is greater than the right ventricle

Answer 13

false- CO is equal for right and left ventricles

Question 14

T/F: the CO is equal for right and left ventricle, as is stroke volume

Answer 14

true

Question 15

how is CO measured?

Answer 15

catheter in the pulmonary artery: usually access thru jugular vein

can estimate with echo or U/S

Question 16

what is cardiac index?

Answer 16

cardiac output NORMALIZED to body size: especially used is body surface area

Question 17

when heart rate is really fast, what happens to filling time?

Answer 17

it decreases

Question 18

will heart rate increase or decrease filling?

Answer 18

decrease filling
yet increases contractility

Question 19

preload

Answer 19

diastolic wall stress/pressure just prior to contraction (related to sarcomere length)

Question 20

afterload

Answer 20

systolic wall stress or pressure (load or force on contracting cardiomyocytes)

Question 21

contractility/inotropy

Answer 21

degree muscle fibers shorten INDEPENDENT of load

Question 22

relaxation/lusitropy

Answer 22

ventricular compliance and diastolic function

Question 23

as you increase heart rate, what happens to stroke volume?

Answer 23

it decreases because you are decreasing diastolic filling time

Question 24

as you increase heart rate, what happens to contractility?

Answer 24

it increases

Question 25

which of the following best describes the relationship between heart rate and stroke volume? (SAMPLE EXAM QUESTION) a. increased heart rate results in decreased contractility, which reduces stroke volume b. decreased heart rate results in decreased ventricular filling time, which decreases stroke volume c. increased heart rate results in decreased ventricular filling time, which decreases stroke volume d. decreased heart rate results in increased contractility, which increases stroke volume

Answer 25

c

Question 26

what affects preload?

Answer 26

many things, but most important is total blood volume aka VENOUS RETURN

Question 27

preload and frank- starling's law

Answer 27

increased end diastolic volume & thus pressure (up to a point) INCREASES stroke volume (INDEPENDENT OF CONTRACTILITY) ie, what the heart sees, it pumps! assumes afterload and contractility remain constant

Question 28

intrinsic property of cardiomyocytes (think frank starling)

Answer 28

1. increased sarcomere length 2. optimizes overlap of actin & myosin and Ca2+ sensitivity 3. increases rate of cross-bridge complex formation and velocity of myofiber shortening

Question 29

if you decrease preload and decrease EDV, what happens to stroke volume?

Answer 29

it decreases

Question 30

if afterload and contractility remain constant, a change in preload affects what 2 parameters

Answer 30

EDV and thus SV

Question 31

systolic wall stress/pressure is named

Answer 31

afterload: impedence to ejection

Question 32

what affects afterload?

Answer 32

***systemic vascular resistance!!*** and thus arterial blood pressure ie how much resistance do the arterioles have: how constricted are they, how easy is it to eject blood out of the ventricle - compliance of aorta and arteries (ie stiff aorta makes it harder for blood to leave ventricle) - left ventricular outflow tract anatomy: subaortic valve stenosis - numerous others

Question 33

LaPlace's Law

Answer 33

afterload related wall stress = (pressure on ventricle x radius of ventricle) / (2 x wall thickness)

Question 34

what ventricle has the most high pressures?

Answer 34

left ventricle, 4-5x higher than R: explained by LaPlace's law pressures much higher in left, so to normalize wall stress need to increase wall thickness in left ventricle relative to the right

Question 35

normal RV wall thickeness =

Answer 35

1/2 to 1/3 LV wall thickness

Question 36

what effect do vasodilators have on afterload?

Answer 36

decrease it, use to treat heart failure

Question 37

what is inotropy

Answer 37

contractility

Question 38

what is contractility

Answer 38

degree/velocity muscle fibers shorten INDEPENDENT of load (preload afterload) aka squeeziness of the ventricle

Question 39

how is contractility regulated?

Answer 39

ANS

Question 40

muscles need what ion to contract more effectively?

Answer 40

calcium!

Question 41

positive inotropes increase what ?

Answer 41

increase Ca2+ influx or sensitivity to Ca2+

Question 42

what are indices of systolic function?

Answer 42

1. ejection fraction 2. shortening fraction

Question 43

what is the gold standard measure of contractility?

Answer 43

ESPVR line: slope of end systolic pressure volume relation

Question 44

increased contractility has what effect on stroke volume?

Answer 44

increases stroke volume by DECREASING ESV

Question 45

how does increased preload and afterload affect contractilty?

Answer 45

it does not affect it!

Question 46

ventricular compliance =

Answer 46

change in volume / change in pressure

Question 47

MVO2

Answer 47

myocardial oxygen demand/consumption

Question 48

what determines MVO2?

Answer 48

1. heart rate: increased HR increased MVO2 2. wall stress/pressure: increased pressure increases MVO2 - hypertrophied hearts are energy inefficient 3. contractility: increased inotropy increases MVO2

Question 49

what drugs decrease MVO2?

Answer 49

beta adrenergic blockers: cardioprotective drugs: slow everything down