Haemodynamics Flashcards
Haemodynamics
Physical laws governing pressure/flow relationships in blood vessels
Why do they standard principles of fluid mechanics not technically apply to blood
Blood is a non newtonian fluid; red and white cells, platelets and lipids are suspended in a solution of proteins
Formula for flow of blood
Pressure gradient between arteries and veins (created by pumping) / Resistance of blood vessels against blood flow
What separates the vascular lumen from the media
Intima (endothelium)
In which layer of the vessel is smooth muscle contained
Tunica Media
Biggest artery
Aorta
Discuss elasticity of arteries as they get smaller (from aorta to arterioles/capillaries)
Elasticity decreases, with no elasticity at all at the capillaries
Compare elasticity & SM of capillaries, venules, veins and vena cava
No elasticity or smooth muscle in capillaries & venules, but there is some in veins and even more in the vena cava (not much still)
Biggest Vein
Vena Cava
Compare the individual vessel diameters
Aorta > Arteries > Arterioles > Capillaries
Compare total Cross Sectional Areas (CSA) of vessels
Aorta < Arteries < Arterioles < Capillaries
BECAUSE THERE ARE SO MANY CAPILLARIES
Velocity of blood formula
Look at this graaph
4 Determinants of Flow
Directly related to pressure difference
Inversely related to length of tube
Inversely related to viscosity of fluid
Directly related to radius of tube
(think of resistance)
Discuss importance of pressure difference in creating flow of blood vessels
Discuss importance of tube length in affecting flow of blood vessels
Longer vessels means less flow per unit time
Discuss importance of viscosity in affecting flow of blood vessels
Think of it like drinking water vs millkshake from a straw
Discuss importance of tube radius in affecting flow of blood vessels
The greater the diameter, the greater the flow
Think resistance
Flow related to r^4 (Remember) - exponential change
Which blood vessels have the greatest capacity to change radius - Resistance vessels
Small arteries & arterioles
When is the blood flow pulsatile and when is it steady
At capillaries it is steady but upstream of that it is more pulsatile
Role of small arteries and arterioles in terms of pressure
Dissipating the pressures and preventing the pressure form overwhelming the capillaries
Calculate total peripheral resistance and renal vascular resistance
Why must peripheral resistance be less than the parallel individual resistances
Think of parallel circuits
Issue of turbulent flow in terms of force and flow
More force is needed to acheive the same flow when flow is turbulent
Compliance (vessels) and how is it related to distensibility
Change in volume for a given change in pressure
Less compliant = Less distensible
Role of Arterial compliance
Provides ‘filtering’/smoothing of pressure for smaller vessels
Role of Venous compliance
Provides ‘capacity’ for storage
What happens to venous compliance as veins are constricted
Constriction of veins reduces venous capacity and increases return of blood to heart - increases effective circulating blood volume
Factors affecting venous return
Venomotor tone (constriction) Venous valve competence
Skeletal muscle pump
Respiration
