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CV physiology (from notes) > Regional Blood Flow > Flashcards

Regional Blood Flow Flashcards

1
Q

What is responsible for phasic fluctuations in blood flow

A

Rhythmic pulsations in aortic pressure

Changing intramural myocardial pressure

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2
Q

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
A
  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
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3
Q

What are sub-endocardial regions of LV vulnerable to

A

Decreased blood flow

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4
Q

What is delivery of blood to endocardial regions influenced by

A

Intramyocardial pressure

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5
Q

How much of CO does cerebral circulation receive

A

13%

held constant at 50 ml/min/100g

CNS has no capacity for anaerobic metabolism

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6
Q

mean arterial pressure range of cerebral blood flow

A

50-150 mmHg

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7
Q

Mechanism of autoregulation of blood flow to the brain

A

Myogenic

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

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8
Q

What is local blood flow in cerebral tissue regulated by

A

Vasodilator metabolites

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9
Q

What is the regulation of CBF more sensitive to

A

CO2 than O2

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10
Q

What does an increase in PaCO2 cause

A

An increase in blood flow

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11
Q

What is the dizziness felt after excessive hyperventilation a result of

A

decreased CBF induced by a fall in PaCO2

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12
Q

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

A

When Pressure drops from 100 mmHg -> 50 mmHg

CBF x 2 if PaO2 is further decreased to 25 mmHg

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13
Q

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

A

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

syncope, faint, coma

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14
Q

What is the drainage function of the brain

A

Cerebrospinal fluid

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15
Q

Consequences of an increase in pressure exerted by CSF

A

Increase in cranial pressure

Compresses cerebral BVs

Decrease in CBF

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16
Q

2 ways we overcome a decrease in CBF

A

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
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17
Q

CBF and age

A

Cerebral blood flow decreases with age

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18
Q

Skin

  1. SA
  2. Weight
  3. Thickness

Where are the BVs found

A
  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

19
Q

What vitamin does skin help to produce

A

Vitamin D

20
Q

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

A

MIN

1 ml/min/100g

NORMAL

10-20 ml/min/100g

MAX

150-200 ml/min/100g

21
Q

Thermo-neutral environment temp

A

27-28

22
Q

Skin temp

A

33

23
Q

How is heat lost from skin (3)

A
  1. Radiation
  2. Conduction-convection
  3. evaporation of sweat
24
Q

What is radiation dependent on

A

Temp difference between skin and ambient temp

25
Q

How does conduction-convection get rid of heat

A

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

26
Q

Role of venous plexus in heat loss

A

Venous plexus can hold large quantities of blood

Heat from blood in venous plexus is transferred to surface for heat loss

27
Q

Density of AVAs in GLABROUS skin - smooth and hairless

(soles, palms, lips etc)

A

Many AVAs

=> involved in heat loss and heat retention

  • radiation
  • conduction/convection
28
Q

Density of AVAs in NON-GLABROUS skin - hairy

(trunk, limbs, scalp)

A

Some AVAs

Many sweat glands

HEAT LOSS - evaporation and conduction/convection

29
Q

Rate of delivery of sweat to skin

A

30g/min

MAX = 2-4 L/hr

30
Q

Sympathetic innervation of glabrous skin

A

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

31
Q

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

A

HIGH

AVAs are constricted

Little BF in venous plexus

32
Q

What happens if core temp rises above 37.5

A

AVAs dilate

hypothalamus activity decreases

Decreased R in venous plexus

Heat loss occurs

33
Q

What happens if core temp falls below 37

A

SNS drive is VERY HIGH

All AVAs are shut

heat is retained

34
Q

Sympathetic innervation of non-glabrous skin

A

Controlled by normal BP mechanism

  • MAP
  • Baroreceptors
  • CV centre in medulla
  • ANS
  • SNS
  • Basal tone
  • Increase in SNS - vasoconstriction
  • Decrease in SNS - vasodilation
35
Q

NON-GLABROUS

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

A

LOW

decreased temp => increased SNS drive and vasoconstriction

Increased temp => reduced SNS drive and vasodilation

36
Q

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

A

Flushed face

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

37
Q

Result of prolonged external cold and cold-induced vasoconstriction

A

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

38
Q

What can skin perfusion fall to

A

1 ml/min/100g

Subcutaneous fat exerts full insulation to protect core temp

39
Q

Skin BF during exercise

A

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

40
Q

What happens to non-glabrous skin BF during exercise

A

Vasodilation (sympathetic cholinergic - ACh and NO)

Linked with an increase in BF and sweating

41
Q

What happens to glabrous skin BF during exercise

A

decreased SNS stimulation to skin BVs occurs

Vasodilation and increased blood flow

42
Q

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

A
  • Decrease in TPR
  • Decrease plasma vol due to sweating
  • Decreased venous return
  • Decrease in CO
  • Low MAP

collapse

43
Q

What happens when we stand in heat

A

Cutaneous vasodilation

Large fall in TPR
Decrease in central venous pressure

Decrease in CO

Hypotension

Fainting

44
Q

Triple response

A
  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

CV physiology (from notes) (10 decks)

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