cardiac perf

Question 1

Cardiac Output

Answer 1

volume of blood ejected by the heart per unit time

= heart rate (HR) x stroke volume (SV)

Question 2

stroke volume

Answer 2

volume of blood pumped per contraction

SV = EDV- ESV

Question 3

end-diastolic volume

Answer 3

volume of blood in ventricle before contraction

Question 4

end-systolic volume

Answer 4

volume of blood in ventricle after contraction

Question 5

preload

Answer 5

• volume of blood (load) inside the heart chamber before contraction
• fiber length or tension when the heart contracts

Question 6

what influences preload

Answer 6

• venous return, EDV
• ventricular filling time
• ventricular compliance
• atrial systole

Question 7

what is Frank-Starling’s Law of the Heart

Answer 7

• stretching cardiac muscle fibers increases strength of contraction
• stretch dependent on the extent of ventricular filling or preload

Question 8

cardiac muscle length-tension relationship

Answer 8

unlike skeletal muscle, cardiac muscle does not normally function at the peak of the length-tension relationship; stretching cardiac muscle fibers increases strength of contraction

*neither summation nor recruitment occurs

Question 9

what causes an increase in tension in cardiac muscles? List steps.

Answer 9

1. overlap of thick and thin filaments
2. increases Ca2+ sensitivity of myofilaments
3. enhanced CA2+-induced CA2+ release (stretch activated Ca2+ channels)

Question 10

Why is the length tension relationship different between skeletal and cardiac muscle?

Answer 10

• cardiac muscle is
  
  • stiffer than skeletal muscle
  • high resting tension
  • small changes in length produce large changes in tension

Question 11

how are fiber length and stroke related

Answer 11

• increase in LV-end diastolic fiber length = greater force of contraction = greater SV

Question 12

what does preload dictate

Answer 12

ventricular filling pressure

Question 13

how does ventricular filling time impact end diastolic volume and stroke volume

Answer 13

• as heart rate increases
  
  • filling of ventricles will decrease
  • EDV and SV will decrease

Question 14

what is ventricle filling pressure

Answer 14

the pressure that builds up in the ventricle as the ventricle is being filled with blood

• typically equivalent to the mean atrial pressure
• more blood = more pressure

Question 15

what is ventricular compliance

Answer 15

the heart’s ability to distend under pressure

C= change in volume/change in pressure

Question 16

what happens to ventricular compliance during heart disease

Answer 16

• compliance decreases as ventricles can “stiffen”

Question 17

what happens to SV during heart disease

Answer 17

• decreased compliance causes
  
  • decrease in end-diastolic fiber length
  • decreased SV

Question 18

why is atrial systole more important at elevated heart rates (i.e. exercise)

Answer 18

• atrial systole accounts for 10-20% of ventricular filling at rest
• accounts for up to 40% of SV at elevated heart rates

Question 19

what is afterload

Answer 19

• resistance against which the ventricle contracts

OR

• the pressure the ventricle must generate to eject blood

Question 20

Name some factors that affect afterload

Answer 20

oppose ventricular ejection

• peripheral resistance
• blood viscosity
• valvular dysfunction

Question 21

afterload is equated to what

Answer 21

aortic pressure

Question 22

give equation for relationship between mean arterial pressure, diastolic pressure and systolic pressure

Answer 22

MAP = diastolic pressure + 1/3 (systolic pressure - diastolic pressure)

Question 23

pressure and volume loops provides information about what

Answer 23

ventricular performance

Question 24

what 4 phases are represented in the pressure and volume loop

Answer 24

Question 25

what is occuring during isovolumetric contraction

Answer 25

* contraction against a closed chamber and fixed volume of blood * mital valve and aortic valve closed * ventricular volume is constant * LVP increases dramatically

Question 26

what is occuring during ventricular ejection (top of PV loop)

Answer 26

* LVP becomes greater than aortic pressure and aortic valve opens * blood is ejected

Question 27

what occurs to LV pressure and volume during ventricular ejection

Answer 27

* LVP remains high because of contracting ventricle * LV volume decreases dramatically

Question 28

What is occuring during isovolumetric relaxation (left side of PV loop)

Answer 28

* systole ends, ventricle relaxes * LVP drops below aortic pressure =\> aortic valve closes * ventricular blood volume remains constant * closed valves = fixed volume

Question 29

what initiates ventricular filling (bottom part of PV loop)

Answer 29

* LV pressure falls below atrial pressure * mitral valve opens

Question 30

what happens to volume of ventricle during ventricular filling (bottom part of PV loop)

Answer 30

* ventricle fills with blood; volume increases back to its EDV

Question 31

how does the pressure volume loop change with _increased preload_

Answer 31

* increase in venous return * greater filling of LV * greater end diastolic fiber length * **stroke volume is increased**

Question 32

what changes are made to the pressure volume loop with _increased afterload_

Answer 32

* increased aortic pressure * LV must eject blood against a greater pressure * LV pressure must increase to a level higher than aortic pressure * aortic valve opens later and closes sooner * **ESV is increased =\> SV is reduced**

Question 33

What changes are made to the P/V loop with increased contractility (sympathetic stimulation)

Answer 33

* LV develops greater tension and pressure * _LV ejects a greater volume of blood during systole_ * less blood remains in ventricle * **SV is increased** as expense of a **decreased ESV**

Question 34

define work as related to the myocardium

Answer 34

* work = force (pressure) x distance (stroke volume) * work is stroke work = work the heart performs on each beat

Question 35

what is the equation for stroke work

Answer 35

stroke volume x MAP (afterload)

Question 36

what is cardiac work

Answer 36

left ventricular work per unit time

Question 37

what is the equation for cardiac work

Answer 37

cardiac work = cardiac output x MAP cardiac work = stroke work x heart rate

Question 38

look at last lecture slide

Answer 38

* increased filling * decreased afterload * increased preload * increase ventricular pressure * increased stroke volume * increased contractility