Flow Flashcards
What is the equation of work out pressure gradient?
Pressure gradient = flow x resistance
What happens to flow and velocity if you change the diameter of a tube?
Flow stays the same but different velocity
What is the equation for BP?
BP = CO x systemic vascular resistance (TPR)
At a given flow, velocity is inversely proportional to….
Cross sectional area
What is the difference between laminar & turbulent flow?
Laminar - velocity is greatest in centre of tube. (4000)
- Increased resistance
- Flow is noisy - losing energy
When is turbulent flow more likely to happen?
- Velocity is too high
- Viscosity is low
- Blood vessel diameter is high
What is Reynold’s number?
Summarises conditions for turbulence – density, viscosity, diameter, mean velocity
What is Poiseuille’s law?
Resistance of vessel depends on its radius (r), length (l) & the viscosity (η) of the fluid.
• Resistance = 8ηl/πr4
What is the difference between resistance in series & in parallel?
In series – flow through each is the same (r= r1 + 22)
In parallel – overall resistance is reduced. Flow through each vessel is inversely proportional to its resistance (r = (r1.r2)/(r1 + r2))
What happens with a distensible tube when pressure increases?
Walls stretch –> lowering resistance
What happens if pressure falls towards zero?
Vessels collapse & flow ceases
What does distensibility enable?
Capacitance - more blood stored in vessel
Are arteries or veins more distensible?
Veins - hold 67% of circulating blood volume
