Generation/control Of Arterial Bp

Front 1

how is mean arterial BP calculated?

Back 1

BP = CO x TPR
(both heart & BV contribute equally to BP)

Front 2

how is arterial pressure generated
- 4 steps.

Back 2

Systole:
1. V. contracts: expel blood into arterioles (TPR), but blood can't quickly pass TPR
2. elastic arteries ↑ to accommodate blood: store potential energy in stretched wall

Diastole
3. elastic recoil maintain high art. pressure, driving blood through TPR
4. potential energy returned to the blood

Front 3

how is mean arterial BP estimated

Back 3

MABP = diastolic P + 1/3 pulse pressure
[Pulse pressure = Systolic P – Diastolic P]
[Pressure = Volume/Compliance]

Front 4

Factors affecting arterial pressure [3]

Back 4

Pressure in BV = (BV in vessel)/(vessel wall compliance)

1. vol. in arterial system = how much stretch to art. wall

2. Compliance = (vol change)/(unit change in pressure)
- how much tension produced per unit of stretch
- normal art. vol: elastin fibres stretched, wall is compliant
- larger vol: collagen fibres stretched, ↓compliance

3. AGE:
- elastin in art. wall broken into shorter lengths
- arteries ↑ where collagen fibres stretched
- ↓compliance, ↑pulse pressure in elderly

Front 5

cardiac output is calculated by?
what factors will increase CO?
what does systolic pressure and diastolic usually depend on?

Back 5

CO = HR x SV
↑ CO achieved by ↑HR or ↑SV

usually:
systolic pressure depends on CO,
diastolic pressure depends on TPR

Front 6

how is mean BP/arterial volume calculated?

Back 6

Mean BP = CO x TPR
- controlled by CO/stroke volume & TPR/HR
- depends on vol. added to artery by each heart beat and vol. flowing out of artery to periphery

CO: rate which blood added to arterial system
PR: rate which blood drains from arterial system

Front 7

how is mean BP/art volume changed? (2)
- which pressure is dependant on what?

Back 7

1. ↑CO
- either by ↑HR or ↑SV, or ↑both
- ↑SV produces larger ↑ in pulse pressure

2. ↑TPR
- ↑diastolic pressure, ↑mean pressure
- SV tends to ↓ if TPR is ↑. Systolic pressure ↑ is small.

- CO, TPR affect both systolic and diastolic pressure
- systolic strongly dependent on CO
- diastolic pressure strongly dependent on TPR

Front 8

baroreceptors: location (2), activation (3), function

Back 8

- in walls of [common carotid], and [aortic arch]

activation
- ↑BP will ↑transmural pressure, stretching arterial wall.
- Baroreceptor distorted within the wall.
- depolarisation, firing of nerve impulse

function: reflex correcting ACUTE changes in BP
(long term >> volume receptors)

Front 9

describe baroreceptor response
- location (2)
- components (2)

Back 9

- firing ↑ in proportion to BP

- carotid sinus baroreceptors: 50-180 mmHg
- aortic receptor: 80-200 mmHg

- dynamic: receptors fire in ANACROTIC (RISING) limb of arterial pressure wave
- static: no of impulses produced ∝ to mean pressure

Front 10

what is the baroreceptor response to increase in BP? (3)

- altogether what 4 things result?

Back 10

↑BP > ↑baroreceptor fire > CNS processing (CV centre)

1. ↓SNS tone, ↑PSNS (vagal) tone on heart
- ↓HR, ↓contractility, ↓CO

2. ↓SNS tone on arterioles
- ↓TPR (vasodilation)

3. ↓SNS tone on veins (↑compliance)
- ↓venous pressure, ↓venous return, ↓CO

altogether, ↓VR, ↓CO, ↓TPR so ↓BP!

Front 11

physiological changes in BP: give some examples (1)

Back 11

- CV centre integrates inputs from all CVS receptor & higher region of brain > control level of SNS tone
- can completely suppress normal reflex of CVS
- BP ↑in exercise

Front 12

vasovagal syncope? (3)

Back 12

- sudden withdrawal SNS noradrenergic tone on BV
- sudden ↑vagal tone on heart > bradycardia, ↓TPR, ↓BP
- when cerebral P ↓ below ~40mmHg, ↓cerebral flow