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CV physiology (from notes) > Control of MAP > Flashcards

Control of MAP Flashcards

1
Q

Velocity of blood entering aorta from LV

A

1.5-2m/s = 600ml/s

MEAN VELOCITY = o.2 m/s

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2
Q

How much of SV is ejected in the first 1/3rd of systole

A

2/3rds of SV

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3
Q

What does the aorta do to accommodate 80% of SV

A

stretches

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4
Q

Where does the remaining 20% of SV go

A

Peripheral vessels

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5
Q

What occurs first - peak in aortic pressure or peak in aortic blood flow and why

A

Peak in aortic blood flow due to elastic stretching of aorta

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6
Q

What happens following closure of aortic valve

A

Short backflow occurs

Incisura dicrotic notch

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7
Q

What is happening to the stretched aorta during diastole

A

Stretched aorta recoils elastically, propelling blood onto next segment of artery which in turn stretches as it fills

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8
Q

What does the elastic recoil convert

A

The intermittent flow from heart during ejection phase into a continuous pulsatile flow through the arterial system

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9
Q

What is peripheral pulse not equal to

A

Blood flow

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10
Q

What does the finger detect in pulse

A

Expansion of artery as pressure increases during systole

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11
Q

What is compliance

A

Change in volume/change in pressure

Arterial compliance in a young adult is 2 ml/mmHg

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12
Q

Is compliance higher or lower in arteriosclerosis

A

Lower

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13
Q

What is arteriosclerosis

A

Elasticity of ageing arteries is decreased by diffuse changes in elastic elements in the tunica media

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14
Q

What happens to the elastic lamellae

A

Become thin, broken and disordered and the arterial wall is weakened

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15
Q

What happens to arteries structurally as we age

A

They dilate - aorta is dilated by 50% 40 and 70 yrs

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16
Q

How does the artery become stiffer

A

More collagen laid down
Ca2+ salts are deposited
=> increase in systolic BP

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17
Q

Formula for pulse pressure

A

Systolic pressure - diastolic pressure

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18
Q

Velocity of pulse WAVE in young people

A

4 m/s

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19
Q

Velocity of pulse WAVE in older people

A

10 m/s

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20
Q

What does the pulse wave allow

A

Higher than average blood flow velocity in aorta (0.2 m/s)

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21
Q

Factors that increase the velocity of pressure pulse

A
  • more rigid vessel wall

- smaller lumen of artery

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22
Q

Systolic pressure and Korotkoff sounds

A

Pressure at which the sounds are first heard

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23
Q

Diastolic pressure and Korotkoff sounds

A

Pressure at which sounds are no longer heard

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24
Q

Formula for MAP

A

Diastolic pressure + 1/3(systolic - diastolic)
DP + 1/3(PP)
RECALL
Diastolic:systolic = 2/3:1/3

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25
Q

Normal diastolic pressure

A

70-89 mmHg

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26
Q

Normal systolic pressure

A

110-139 mmHg

27
Q

MAP

A

95-100 mmHg

28
Q

What happens to systolic P with age and why

A

Increases due to decreased compliance

29
Q

What happens to diastolic P with age

A

Diastolic pressure peaks @ 50 yrs and falls in old age - which may affect coronary blood flow (optimal in diastole)

30
Q

What happens to MAP with age and why

A

Increases moderately due to an increase in TPR

31
Q

What is diastolic pressure @ rest in HYPERTENSION

A

> 95 mmHg

32
Q

What is systolic pressure @ rest in HYPERTENSION

A

> 160 mmHg

33
Q

What does hypertension do

A

Increases risk of myocardial infarction, stroke, renal failure, death

34
Q

4 factors that affect diastolic pressure

A

***TPR
Heart rate
Systolic pressure
Aortic distensibility

35
Q

Effect of an increase in TPR on DP

A

Increase in diastolic pressure (increase in HR, increase in ejection volume)

36
Q

What does heart rate do to duration of diastole

A

shortens it => decreased blood outflow

37
Q

Effect of systolic pressure on arterial pressure and aortic distensibility

A

Arterial pressure starts from a higher volume

Decreases aortic distensibility

38
Q

Effect of a decrease in aortic distensibility on diastolic pressure

A

Decrease in aortic distensibility decreases DP

39
Q

3 factors that affect systolic pressure

A

***SV
Aortic distensibility
Diastolic pressure

40
Q

effect of an increase in SV on SP

A

Increases systolic P

41
Q

Effect of a decrease in aortic distensibility on SP

A

Increases systolic P

42
Q

Effect of an increase in diastolic P on SP

A

Increases systolic P

43
Q

What is the driving force for CV system

How is regulation achieved

A

MAP

By -ve feedback control (reflexes)

44
Q

Control of MAP is achieved by modulating

A
  1. CO - changing force and strength of cardiac contractions (HR and SV)
  2. TPR - vasoconstriction vs vasodilation of small systemic arteries and arterioles
45
Q

for short acting stabilisation of MAP, what is info required on

A
  1. Arterial BP (carotid and aortic baroreceptors)

2. Blood vol (veno-atrial stretch receptors in atria)

46
Q

Effect of an increase in EDV on SV

A

Increases SV (usually EDV is 130 ml and SV is 70 ml)

47
Q

Where are the veno-atrial stretch receptors

A

Located in endocardium @ junction of great veins and both atria
Encapsulated nerve-endings served // vagal afferents

48
Q

What does the receptor discharge (signals atrial vol)/B type pattern (provide info about blood vol) corespond with

A

V wave of atrial filling

49
Q

Stimulation of veno-atrial receptors (by increased atrial filling) induces what 2 reflex actions

A

Diuresis - loss of water // kidneys
Natriuresis - salt excretion // kidneys
ADH secretion will decrease, salt and water loss by kidneys will increase, thus decreasing plasma/blood volume and decreasing arterial BP

50
Q

What does gravity cause

A

Venous pooling of blood (500-600ml) in legs and lower abdomen

  • decrease in central venous P
  • decrease in SV
  • decrease in CO
  • decrease in MAP
  • baroreceptor reflex returns BP to normal
51
Q

How fast does the total blood volume circulate

A

circulates in 1 min

52
Q

Immediate response to haemorrhage

A

Baroreceptor reflex

53
Q

Intermediate response to haemorrhage

A

Movement of fluid into capillaries

54
Q

Long-term response to haemorrhage

A

Replacement of fluid and RBCs in blood

55
Q

What variables are NOT affected by haemorrhage

A

HR and TPR

HOWEVER due to reflex response they are elevated to values above pre-haemorrhage

56
Q

What variables are increased following haemorrhage, but do not reach pre-haemorrhage values

A

SV and CO

57
Q

How is MABP brought back close to pre-haemorrhage values

A

Increase in HR
Increase in TPR
- induced by SNS

58
Q

Where is blood flow maintained during haemorrhage

A

Brain

Heart

59
Q

Where is blood flow NOT maintained during haemorrhage

A

Skeletal muscle
Organs of GIT
Skin

60
Q

Pathway of response to fall in MABP following haemorrhage

A
  • MABP decreases because blood/plasma vol decreases
  • MABP is brought back to normal by baroreceptor reflex (Increase in SNS, decrease in PNS) SHORT TERM
  • Decrease in MABP causes a direct decrease in capillary hydrostatic pressure
  • arteriolar constriction and further decrease in capillary hydrostatic P
  • favours movement of fluid from interstitial -> vascular space
  • Plasma volume increases (12-24 hrs)
  • MABP restored toward normal (blood loss up to 1L - 20% of total blood volume)
61
Q

How is fluid replaced following haemorrhage

A

Reabsorption from interstitial compartment only re-distributes the EC fluid
Replacement of lost fluid involves kidney function and fluid ingestion

62
Q

Kidney’s role in replacing lost fluid

A

Aldosterone released from adrenal cortex
retention of Na+ and H2O by kidneys
thirst is stimulated - ingestion of fluid replaces what is lost
ALSO
renin -> angiotensinogen -> Ang I -> Ang II

63
Q

How are RBCs replaced following haemorrhage

A

RBC production occurs in bone marrow
Following haemorrhage, bone marrow is stimulated to produce RBCs
Replacement of RBCs lost will take 3-4 weeks

64
Q

Where is erythropoietin produced
Where does it act
What is it stimulated by

A

Produced by cells in kidney
Acts on bone marrow to stimulate production of erythrocytes
Main stimulus is decreased O2 delivery to kidney, which occurs in haemorrhage due to a fall in no. of erythrocytes

CV physiology (from notes) (10 decks)

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