Exam 1 - Control Of Cardiac Output

Question 1

3 basic principles of blood flow

Answer 1

1 - Control of flow to local tissues depends on metabolic need
2 - VR is sum of flow from local tissues and CO is driven by VR
3 - BP is independent of control of flow through local tissue and CO

Question 2

Baroreceptors

Answer 2

• respond to moment to moment changes
• respond to increase or decrease in BP fro normal MAP
  ~ all others respond to drop in MAP

Question 3

Responds to changes in pressure over all ranges

Answer 3

• Baroreceptors
• Cap fluid shift
• Stress relaxation/constriction
• Renal BP control (long term)

Question 4

Responds to changes when MAP drops

Answer 4

• Chemoreceptors
• Renin-angiotensin / aldosterone
• CNS ischemic response

Question 5

CO

Answer 5

CO = HR x SV

HR: autonomic innervation (para) / drugs
SV: autonomic innervation (symp) / preload / afterload

Question 6

CO vs VR

Answer 6

• Over time…they must be equal
• May be different for a few beats
• CO affected by: metabolic activity / body mass / age
• VR determines CO

Question 7

Frank-Starling law

Answer 7

• SV changes based on VR

- Increased VR produces more stretch which increases SV/HR

Question 8

Q (sum of all VR) =

Answer 8

Q = P/SVR

• SVR changes based on metabolism…inversely proportional
  ~ only works if body maintains constant MAP

Question 9

ANS and maintaining MAP

Answer 9

• ANS keeps MAP constant (baroreceptors)
• Allows CO to change based on metabolic need / SVR changes
• Without ANS…MAP drops as SVR drops with minimal CO change

Question 10

Peak CI

Answer 10

• Age 8-10

- 4 to 4.5 L/min/m2

Question 11

Affect of age on CI

Answer 11

• metabolic activity determines CO
• CI drops as you age due to drop in muscle mass / activity
  ~2.4 @ 80 yo

Question 12

Average CO

Answer 12

• 5.0 L/min
• Male: 5.6
• Female: 4.9
• CI: 3.0

Question 13

Hypereffective

Answer 13

• Increased CO from changes in contractility and HR
• Curve shifts UP and LEFT
• Causes: sympathetic / hypertrophy

Question 14

Hypoeffective

Answer 14

• decreased CO
• curve shifts DOWN and RIGHT
• caused by: anything that makes the heart pump less effectively

Question 15

RAP

Answer 15

Resting Atrial Pressure aka CVP

Question 16

Normal ANS tone

Answer 16

Resting: RAP - 0 / CO - 5.0
Max: RAP > 4 / CO - 13.0

Question 17

Hypereffective heart values (nervous only)

Answer 17

Max: RAP > 4 / CO - 25

Question 18

Hypereffective heart values (hypertrophy and symp)

Answer 18

• Mass is 50 - 75% greater

- Max: RAP > 4 / CO - 30 to 40

Question 19

CO vs External Pressure

Answer 19

• Intrapleural pressure usually -4 mmHg
• Increase intrapleural pressure increases RAP
  ~ 1:1 ratio
• Hypereffective shifts cardiac function curve up (hypo is oppo)
• Increased intrapleural pressure shifts right (visa versa)

Question 20

Cardiac tamponade

Answer 20

• fluid build up around heart
• heart cannot fill properly
• hypoeffective
• drop in pre-load

Question 21

Factors that alter external pressure

Answer 21

• respiration cycle
• negative shifts left…positive shifts right
• open thoracic cage….move to 0 mmHg…. shift curve right 4
• cardiac tamponade

Question 22

To get VR….

Answer 22

Need pressure drop from caps to RA

Question 23

Central vs Peripheral venous compartment

Answer 23

Central: affected by intrathoracic pressure
Peripheral: not affected

VR = (peripheral venous p - CVP) / venous resistance
~ same equation as before

Question 24

Ventricle values

Answer 24

Volume: 30
Compliance: 24
Resistance: 0

Question 25

Artery values

Answer 25

Volume: 600 Compliance: 2 Resistance: 1

Question 26

Arterioles values

Answer 26

Volume: 100 Compliance: 0 Resistance: 13

Question 27

Capillary values

Answer 27

Volume: 250 Compliance: 0 Resistance: 5

Question 28

PVC values

Answer 28

Volume: 2500 Compliance: 110 Resistance: 1

Question 29

CVC values

Answer 29

Volume: 80 Compliance: 4 Resistance: 0

Question 30

Entire body values

Answer 30

Volume: 3560 Compliance: 140 Resistance: 20 R in Wood units

Question 31

Normal systemic volume

Answer 31

- 4500 mls - 4500-3560 = 1000 - 1000/140 = 7 mmHg pressure when full but no flow

Question 32

Mean systemic filling pressure

Answer 32

- Psf - similar to Pmf (Mean circulatory filling pressure) - Pmf includes pulmonary but it has minimal effect

Question 33

Arteries vs Venous compliance

Answer 33

- change in volume has bigger pressure change in arteries | ~ arteries have lower compliance (2 vs 110)

Question 34

CVC

Answer 34

- RA and central veins in thorax | - volume depends on VR (in) vs CO (out)

Question 35

Factors affecting VR

Answer 35

- Pressure in PVC (usually = Psf = 7 mmHg) - Venous resistance: 2/3 veins and 1/3 arterioles (1.4) - Pressure in CVC (usually 0 mmHg) - VR = Psf - RA / Resistance -> 7/1.4 = 5 L/min

Question 36

Venous function curve

Answer 36

- independent = RAP aka CVP - dependent = VR - RAP/CVP affect VR...not the other way around

Question 37

Changing Psf and venous curve

Answer 37

- Can change Psf by adding CBV - increase CBV....curve shifts right - increase resistance....curve SLOPE drops down ~ up resistance....down VR

Question 38

Intersection of Cardiac and Venous curves

Answer 38

- Shows CO / VR / CVP

Question 39

Increase in CVP on cardiac and venous curves

Answer 39

- increase CO - decrease VR - more volume leaving CVP than coming in -> CVP drops until back to equilibrium (CO and VR are equal)

Question 40

What has to happen to get a change in CO

Answer 40

- one or both curves have to shift - Cardiac shifts: Change in cardiac effectiveness (hyper/hypo) Change in external pressure - Venous shifts: Change in Psf aka CBV Change in venous resistance (slope)

Question 41

Effect of increasing CBV

Answer 41

- Increases Psf - Distends vessels so resistance drops - Venous curve shifts right and slope increases - Kidneys will take off extra volume over time (big player) ~ fluid also moves to 3rd space (edema) ~ autoregulation constricts ~ fluid stored in liver and spleen - all these try to bring Venous curve back to normal spot

Question 42

Response to hemorrhage

Answer 42

- Loss of volume shifts venous curve left - symp stimulation kicks in (cardiac curve up and left) ~baroreceptors / CNS ischemic / chemoreceptors / etc. - symp stimulation constricts veins (shifts venous curve back right a little)

Question 43

Inotropic drugs

Answer 43

- increase cardiac curve (increases contractility)

Question 44

Vasoactive drugs

Answer 44

Changes venous curve resistance (slope)

Question 45

Diuretic drugs

Answer 45

- shifts venous curve based on loss or gain of volume