Lecture 6 - cardiovascular response to stress

Question 1

What external factors affect CO?

Answer 1

ANS
noradrenaline / adrenaline 
drugs
electrolytes
excercise

Question 2

How is CO measured?

Answer 2

HR x SV

Question 3

What is SV?

Answer 3

EDV - ESV

Question 4

typical values for SV/EDV/ESV

Answer 4

SV = 70
EDV=140
ESV=70

Question 5

What factors affect HR?

Answer 5

• autonomic innervation
• hormones
• fitness levels
• age

Question 6

What factors affect SV?

Answer 6

• heart size
• fitness levels
• gender
• contractility
• duration of contraction
• Preload
• afterload

Question 7

How is heart rate maintained?

Answer 7

SAN intrinsic rate of 110bpm

PNS lowers the rate to 60-80

Question 8

what are factors that change the HR?

Answer 8

chronotropic agents?

Question 9

What are positive chronotrophic factors?

Answer 9

• SNS
• excercise
• increased body temperature
• hypercalaemia
• hypokalaemia
• hyponatraemia
• chemorceptors –> acidotic
• atropine/caffeine

Question 10

What factors are negative chronotrophic?

Answer 10

• PNS–> AcH
• hypocalaemia
• hyperkalaemia
• hypernataemia
• alkali state

Question 11

How does HR increase during excercise?

Answer 11

exercise stimulate proprioceptors in vessels and increases body temperature

Question 12

What is HR max

Answer 12

The maximum rate the heart can reach without affecting the filling of the ventricles

Question 13

why is there a limit to rapid filling time?

Answer 13

excessive increase in HR affects CO

Question 14

what is preload

Answer 14

Volume of blood entering the ventricles

-Preload= the degree of stretch on myocardium when filled with blood at end of diastole (EDV)

Question 15

What is afterload

Answer 15

resistance the ventricles have to overcome to pump blood out the ventricles

Question 16

What is contractility ?

Answer 16

contraction of the myocardium

Question 17

What is the preload increased in?

Answer 17

hypervolaemia
regurg of cardiac valves
heart failure

Question 18

What is afterload increased in?

Answer 18

HTN

vasoconstriction

Question 19

What happens when afterload increases?

Answer 19

CO increases

Question 20

What does a higher preload mean

Answer 20

Higher EDV

Question 21

What factors reduce preload

Answer 21

myocardium damage –> reduced stretch

Increased HR –> reduced filling time

Question 22

What factors ensure blood returns to the heart

Answer 22

• gravity when standing -ve
• skeletal muscle pump +ve
• A-T pump when breathing +ve

Question 23

Impact of IV fluids on blood volume?

Answer 23

Bainbridge reflex

• receptors in the right atrium detect distension
• sympathetic activity stimulate through SAN
• HR increases

Question 24

impact of IV fluids on BP in atrium?

Answer 24

Baroreceptor reflex

• pressure increase detected by baroreceptors in atria#
• signals to decrease HR
• increased urine output –> decreased vasopressin and increased ANP

Question 25

What does the overall effect of the baroreceptor and bainbridge reflex depend on?

Answer 25

the previous HR

Question 26

Explain how ANP works?

Answer 26

- secreted by the heart - in response to atrial stretch - causes glomerular arteriolar dilation - diuresis

Question 27

explain how RAAS works?

Answer 27

- regulates pressure + volume - decrease in GFR --> kidney releases renin - renin cleaves AT-1 into AT-2 - AT-2 is a potent vasoconstrictor --> increases BP

Question 28

What does an increase in afterload do to SV?

Answer 28

decreases SV

Question 29

what factors increase afterload?

Answer 29

- HTN - cartoid artery stenosis - atherosclerosis - carotid valve stenosis - pulmonary hypertension

Question 30

What does an increased afterload lead to?

Answer 30

LVH

Question 31

What is SCD?

Answer 31

- inherited heart condition - heart muscle thickens and becomes stiff - most common genetic heart condition 1 in 500 affected - AD

Question 32

How is contractility affected in pathology?

Answer 32

Acidoisis (poorly: diabetes, heart attack, sepsis) – reduced contractility H+ is the strongest –ve ionotrope Ionotropes for cardiogenic shock +ve: Digoxin, Ad, NorAd, Dopamine, Dobutamine -ve: β blockers, Diltiazem

Question 33

What is the frank-starling law?

Answer 33

The Frank–Starling law of the heart represents the relationship between stroke volume and end diastolic pressure. The law states that the stroke volume of the heart increases in response to an increase in the volume of blood in the ventricles, before contraction, when all other factors remain constant

Question 34

What does the frank-starling graph represent

Answer 34

relationship between cardiac output and EDV

Question 35

What does a steep curve on a frank-starling graph represent?

Answer 35

increased contractility | -

Question 36

What does a less steep frank-starling curve show?

Answer 36

reduced contractility