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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
Normal diastolic pressure
70-89 mmHg
26
Normal systolic pressure
110-139 mmHg
27
MAP
95-100 mmHg
28
What happens to systolic P with age and why
Increases due to decreased compliance
29
What happens to diastolic P with age
Diastolic pressure peaks @ 50 yrs and falls in old age - which may affect coronary blood flow (optimal in diastole)
30
What happens to MAP with age and why
Increases moderately due to an increase in TPR
31
What is diastolic pressure @ rest in HYPERTENSION
> 95 mmHg
32
What is systolic pressure @ rest in HYPERTENSION
> 160 mmHg
33
What does hypertension do
Increases risk of myocardial infarction, stroke, renal failure, death
34
4 factors that affect diastolic pressure
***TPR Heart rate Systolic pressure Aortic distensibility
35
Effect of an increase in TPR on DP
Increase in diastolic pressure (increase in HR, increase in ejection volume)
36
What does heart rate do to duration of diastole
shortens it => decreased blood outflow
37
Effect of systolic pressure on arterial pressure and aortic distensibility
Arterial pressure starts from a higher volume | Decreases aortic distensibility
38
Effect of a decrease in aortic distensibility on diastolic pressure
Decrease in aortic distensibility decreases DP
39
3 factors that affect systolic pressure
***SV Aortic distensibility Diastolic pressure
40
effect of an increase in SV on SP
Increases systolic P
41
Effect of a decrease in aortic distensibility on SP
Increases systolic P
42
Effect of an increase in diastolic P on SP
Increases systolic P
43
What is the driving force for CV system | How is regulation achieved
MAP | By -ve feedback control (reflexes)
44
Control of MAP is achieved by modulating
1. CO - changing force and strength of cardiac contractions (HR and SV) 2. TPR - vasoconstriction vs vasodilation of small systemic arteries and arterioles
45
for short acting stabilisation of MAP, what is info required on
1. Arterial BP (carotid and aortic baroreceptors) | 2. Blood vol (veno-atrial stretch receptors in atria)
46
Effect of an increase in EDV on SV
Increases SV (usually EDV is 130 ml and SV is 70 ml)
47
Where are the veno-atrial stretch receptors
Located in endocardium @ junction of great veins and both atria Encapsulated nerve-endings served // vagal afferents
48
What does the receptor discharge (signals atrial vol)/B type pattern (provide info about blood vol) corespond with
V wave of atrial filling
49
Stimulation of veno-atrial receptors (by increased atrial filling) induces what 2 reflex actions
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
What does gravity cause
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
How fast does the total blood volume circulate
circulates in 1 min
52
Immediate response to haemorrhage
Baroreceptor reflex
53
Intermediate response to haemorrhage
Movement of fluid into capillaries
54
Long-term response to haemorrhage
Replacement of fluid and RBCs in blood
55
What variables are NOT affected by haemorrhage
HR and TPR | HOWEVER due to reflex response they are elevated to values above pre-haemorrhage
56
What variables are increased following haemorrhage, but do not reach pre-haemorrhage values
SV and CO
57
How is MABP brought back close to pre-haemorrhage values
Increase in HR Increase in TPR - induced by SNS
58
Where is blood flow maintained during haemorrhage
Brain | Heart
59
Where is blood flow NOT maintained during haemorrhage
Skeletal muscle Organs of GIT Skin
60
Pathway of response to fall in MABP following haemorrhage
- 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
How is fluid replaced following haemorrhage
Reabsorption from interstitial compartment only re-distributes the EC fluid Replacement of lost fluid involves kidney function and fluid ingestion
62
Kidney's role in replacing lost fluid
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
How are RBCs replaced following haemorrhage
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
Where is erythropoietin produced Where does it act What is it stimulated by
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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