L9 - control of cardiac output

Question 1

what is cardiac output

Answer 1

vol of blood ejected by heart per min

Question 2

what is the equation relating CO , SV and HR

Answer 2

CO = HR x SV

Question 3

average HR
average SV
average CO

Answer 3

72bpm
70ml per beat
5L/min/side

Question 4

what is meant by the heart being a permissive pump

Answer 4

it only pumps what comes back to it

CO = venous return

Question 5

what is the major determinant of CO

Answer 5

venous return

Question 6

what is preload

Answer 6

‘filling pressure of heart’

pressure into atria from vena cava/pulmonary vein

Question 7

what is afterload

Answer 7

pressure against which the heart has to pump

eg pressure in aorta/pulmonary artery

Question 8

what is the frank starling mechanism

Answer 8

more blood in the ventricles at the end if diastole (relaxing, filling) = bigger stroke volume
affects preload

Question 9

purpose of frank starling mechanism

Answer 9

matches RV and LV output

Question 10

average preload pressure

Answer 10

3-8 mmhg

Question 11

what are the two explanations for the starling relationship

Answer 11

1. length tension relationship

2. Ca2+ sensitivity

Question 12

explain the length tension relationship

Answer 12

more stretch of striated muscle = stronger contraction

stretching sarcomere to a point where the most cross bridges can be formed = stronger contraction

Question 13

explain Ca2+ sensitivity in relation to starling relationship

Answer 13

cardiac muscle filament sensitivity to Ca increases with stretch

Question 14

what can affect the starling relationship and how

by affecting stroke volume

Answer 14

SNS stimulation (A/NA)
inotropic drugs 

by increasing contractility (at any sarcomere length)

Question 15

what is a positive inotrope

Answer 15

something that increases contractility at given fibre length

Question 16

what is a negative inotrope

Answer 16

something that decreases contractility at a given fibre length

Question 17

do inotropes affect preload of afterload

Answer 17

preload

Question 18

effect of afterload on CO

Answer 18

very little effect

Question 19

what is the main determinant of SV - (CO)

Answer 19

preload

Question 20

what effect does the SNS have on HR

Answer 20

1. A/NA increases funny current
2. this increases rate of diastolic depolarisation of SA node
3. increases HR

Question 21

what effect does PSNS have on HR

Answer 21

1. ACh decreases funny current
2. slower diastolic depolarisation of SA node
3. slower HR

Question 22

what is a positively chronotropic agent

Answer 22

increases HR

Question 23

what is a negatively chronotropic agent

Answer 23

decreases HR

Question 24

what is 
inotropy
chronotropy 
luistropy
referring to

Answer 24

contractility
HR
rate of relaxation

Question 25

what does a +ve luistropic agent do -ve luistropic agent do

Answer 25

increases rate of relaxation | decreases rate of reaction

Question 26

effect of dynamic exercise on : 1. skeletal muscle vessels 2. TPR 3. venous return 4. stroke vol 5. HR 6. CO

Answer 26

1. vasodilated 2. decreases significantly 3. increases moderately 4. increases moderately 5. increases significantly 6. increases significantly

Question 27

effect of static exercise on 1. skeletal muscle vessels 2. TPR 3. venous return 4. stroke vol 5. HR 6. CO

Answer 27

1. compressed 2. increases moderately 3. decreases significantly 4. stays same or decreases slightly 5. increases slightly 6. stays the same or increases slightly

Question 28

how is HR increased to 90bpm

Answer 28

entirely by reducing PSNS

Question 29

how is HR increased above 90bpm

Answer 29

requires SNS input

Question 30

effect of adrenaline on heart muscle

Answer 30

increases contractility - therefore increases SV-therefore increases CO