Intro to CVS

Question 1

What is mean arterial BP?

Answer 1

Diastolic pressure + 1/3 pulse pressure

Pulse pressure = systolic pressure - diastolic pressure

Question 2

What happens in post (orthostatic) hypotension?

Answer 2

Immediate effect from going supine to upright
Blood goes from upper body to legs
Decreased venous return therefore reduced CO and reduced BP

Reflex vasoconstirction in legs and lower abdomen (takes a few secs to kick in)

Question 3

Vascular compliance

Answer 3

Non-compliant - rigid tubes resist expansion when internal pressure rises (capillaries, arterioles, copper pipes)

Compliant - tubes with elastic walls swell when pressure inside rises (arteries, veins, rubber tyre)

Question 4

What is LaPlace’s Law and the clinical implications of it?

Answer 4

Distending pressure (P) - pressure during swelling - produces an opposing force or tension (T) in the vessel wall proportional to the radius of the vessel

T=PR

Practically…
1. Control of blood flow - low tension reuiqred to reduce blood flow in arterioles. Smooth muscle control of arteriole site of tissue blood flow regulation

2. Capillaries - can be extremely thin and still withstand the pressure - essential for exchange
3. Aneurysm

Question 5

What are the factors that affect blood flow through a vessel?

Answer 5

Directly proportional - radius of vessel and pressure gradient alogn the vessel

Inversely proportional - length of vessel and thickness of fluid

Question 6

What is relationship between flow, pressure and resistance?

Answer 6

Flow = change in presure / resistance

This is Poiseuille’s equation

Doesn’t hold true in turbulence however as this disrupts flow (Reynold’s number is used to indicate whether flow laminant or turbulent)

Also…
Art pressure = CO x TPR

Question 7

Regulation of arterolar radius

Answer 7

VASOCONSTRICT
Neural - Symp nerves
Hormonal - Adr, Ang II, Vasopressin
Local - myogenic response, Endothelin-1

VASODILATE
Neural - NO-releasing nerves
Hormonal - Adr, ANP
Local - potassium, CO2, hydrogen ions, NO, bradykinin, decreased oxygen,

Question 8

Reynold’s number - what is it and what does it increase with?

Answer 8

Likely to indicate whether flow is turbulent ot liminar

Velocity of flow x radius of vessel / viscosity

Turbulence more likely when Re no increases due to:

• High velocity flow
• Large diameter vessels
• Low blood viscosity
• Abnormal vessel wall