Regional Blood Flow

Question 1

What is responsible for phasic fluctuations in blood flow

Answer 1

Rhythmic pulsations in aortic pressure

Changing intramural myocardial pressure

Question 2

What is happening during systole regarding

1. Intramural myocardial P
2. Blood flow in LV
3. IM P in RV
4. RCA blood flow
5. coronary sinus

Answer 2

1. IM myocardial pressure increases, compressing coronary BVs (mainly in SUB-ENDOCARDIUM)
2. Complete interruption of blood flow in LV during early systole due to high P development - thus its mainly in DIASTOLE
3. IM P is low in RV
4. RCA blood flow can occur during systole - follows fluctuations in aortic P
5. Surge of venous blood flow out of coronary sinus due to compression of muscular wall of heart

Question 3

What are sub-endocardial regions of LV vulnerable to

Answer 3

Decreased blood flow

Question 4

What is delivery of blood to endocardial regions influenced by

Answer 4

Intramyocardial pressure

Question 5

How much of CO does cerebral circulation receive

Answer 5

13%

held constant at 50 ml/min/100g

CNS has no capacity for anaerobic metabolism

Question 6

mean arterial pressure range of cerebral blood flow

Answer 6

50-150 mmHg

Question 7

Mechanism of autoregulation of blood flow to the brain

Answer 7

Myogenic

increase in perfusion pressure => vasoconstriction of cerebral arterioles and vice versa

Question 8

What is local blood flow in cerebral tissue regulated by

Answer 8

Vasodilator metabolites

Question 9

What is the regulation of CBF more sensitive to

Answer 9

CO2 than O2

Question 10

What does an increase in P_aCO2 cause

Answer 10

An increase in blood flow

Question 11

What is the dizziness felt after excessive hyperventilation a result of

Answer 11

decreased CBF induced by a fall in P_aCO2

Question 12

When is there an effect of a decrease in PO2 on CBF

Answer 12

When Pressure drops from 100 mmHg -> 50 mmHg

CBF x 2 if PaO2 is further decreased to 25 mmHg

Question 13

What happens if PaO2 decreases sufficiently or MAP falls below autoregulation range

Answer 13

CBF falls, O2 delivery to brain is impaired and a period of unconsciousness can follow

syncope, faint, coma

Question 14

What is the drainage function of the brain

Answer 14

Cerebrospinal fluid

Question 15

Consequences of an increase in pressure exerted by CSF

Answer 15

Increase in cranial pressure

Compresses cerebral BVs

Decrease in CBF

Question 16

2 ways we overcome a decrease in CBF

Answer 16

LOCAL VASODILATORS

• PCO2
• PO2

STIMULATION OF CV CENTRES

• Activates vasomotor sympathetic activity to the heart and systemic BVs
• Resultant increase in MAP will increase CBF

Question 17

CBF and age

Answer 17

Cerebral blood flow decreases with age

Question 18

Skin

1. SA
2. Weight
3. Thickness

Where are the BVs found

Answer 18

1. 1.8 m2
2. 2-3 kg
3. 1-2 mm

BVs in dermis

in epidermis, there is direct diffusion of atm O2 to epidermis

Question 19

What vitamin does skin help to produce

Answer 19

Vitamin D

Question 20

Different ranges of blood flow for temp regulation (in skin)

Answer 20

MIN

1 ml/min/100g

NORMAL

10-20 ml/min/100g

MAX

150-200 ml/min/100g

Question 21

Thermo-neutral environment temp

Answer 21

27-28

Question 22

Skin temp

Answer 22

33

Question 23

How is heat lost from skin (3)

Answer 23

1. Radiation
2. Conduction-convection
3. evaporation of sweat

Question 24

What is radiation dependent on

Answer 24

Temp difference between skin and ambient temp

Question 25

How does conduction-convection get rid of heat

Answer 25

Warm skin warms up adjacent air and is then moved away by convection

Question 26

Role of venous plexus in heat loss

Answer 26

Venous plexus can hold large quantities of blood Heat from blood in venous plexus is transferred to surface for heat loss

Question 27

Density of AVAs in GLABROUS skin - smooth and hairless (soles, palms, lips etc)

Answer 27

Many AVAs =\> involved in heat loss and heat retention - radiation - conduction/convection

Question 28

Density of AVAs in NON-GLABROUS skin - hairy (trunk, limbs, scalp)

Answer 28

Some AVAs Many sweat glands HEAT LOSS - evaporation and conduction/convection

Question 29

Rate of delivery of sweat to skin

Answer 29

30g/min MAX = 2-4 L/hr

Question 30

Sympathetic innervation of glabrous skin

Answer 30

AVAs are controlled exclusively by SNS fibres - hypothalamus temp regulating centres

Question 31

What is the SNS drive to glabrous skin like at thermo-neutrality

Answer 31

HIGH AVAs are constricted Little BF in venous plexus

Question 32

What happens if core temp rises above 37.5

Answer 32

AVAs dilate hypothalamus activity decreases Decreased R in venous plexus Heat loss occurs

Question 33

What happens if core temp falls below 37

Answer 33

SNS drive is VERY HIGH All AVAs are shut heat is retained

Question 34

Sympathetic innervation of non-glabrous skin

Answer 34

Controlled by normal BP mechanism * MAP * Baroreceptors * CV centre in medulla * ANS * SNS * Basal tone * Increase in SNS - vasoconstriction * Decrease in SNS - vasodilation

Question 35

NON-GLABROUS @ thermo-neutrality, what is the SNS drive to skin of limbs and trunks like

Answer 35

LOW decreased temp =\> increased SNS drive and vasoconstriction Increased temp =\> reduced SNS drive and vasodilation

Question 36

Whhat happens when there is a large volume of well O2 blood in glabrous skin

Answer 36

Flushed face External heat causes vasodilation of arterioles, venules and small veins and increased blood flow to skin

Question 37

Result of prolonged external cold and cold-induced vasoconstriction

Answer 37

Paradoxical vasodilation with flushing and pain relief and decreased bloodflow to skin, preventing skin injury during prolonged cold exposure

Question 38

What can skin perfusion fall to

Answer 38

1 ml/min/100g Subcutaneous fat exerts full insulation to protect core temp

Question 39

Skin BF during exercise

Answer 39

SNS-induced vasoconstriction initially As core temp increases, vasodilation occurs Increase in core temp is sensed by warmth receptors in hypothalamus - connected -\> CV centre for brainstem

Question 40

What happens to non-glabrous skin BF during exercise

Answer 40

Vasodilation (sympathetic cholinergic - ACh and NO) Linked with an increase in BF and sweating

Question 41

What happens to glabrous skin BF during exercise

Answer 41

decreased SNS stimulation to skin BVs occurs Vasodilation and increased blood flow

Question 42

how does cutaneous vasodilation contribute to fainting and heat exhaustion in hot weather

Answer 42

* Decrease in TPR * Decrease plasma vol due to sweating * Decreased venous return * Decrease in CO * Low MAP collapse

Question 43

What happens when we stand in heat

Answer 43

Cutaneous vasodilation Large fall in TPR Decrease in central venous pressure Decrease in CO Hypotension Fainting

Question 44

Triple response

Answer 44

1. RED LINE - histamine mediated vasodilation - mechanical 2. FLARE - vasodilation caused by substance P 3. WHEAL - Increased capillary permeability induced by trauma - histamine and substance P - fluid containing proteins leak out of capillaries and produce oedema