Factors affecting flow through tubes Flashcards
Define pressure.
Force exerted per unit area
Define pressure gradient.
The difference in forces exerted (per unit area) at either end / side of an object e.g. a tube or membrane
Define flow.
The volume of fluid passing a given level of the circulation / airways per unit time
Define velocity.
The rate of movement of fluid along a vessel / airway
Define resistance.
A force that tends to oppose the flow of a substance
What is flow generated by?
A pressure gradient
Describe Ohm’s law for fluid dynamics.
Flow = pressure gradient / resistance
What does Boyles Law state?
At a given temperature, the pressure and volume of an ideal gas are inversely proportional
How is pressure gradient calculated?
deltaP = Q x R
Apply the formula P = Q x R to the cardiovascular system.
Mean arterial pressure – central venous pressure = cardiac output x systemic vascular resistance
Where is velocity at the lowest and highest in laminar flow?
Lowest at edges. Highest at centre
Which 3 factors affect resistance?
Radius
Length
Viscosity
Give the equation for calculating resistance.
R = 8nl / pier4
Describe Poiseuille’s Law on affect on flow.
Q = deltaPpier4 / 8nl
Flow is directly proportional to which power of the radius of a tube?
Fourth
List 4 factors which make turbulent flow more likely.
Velocity is high (e.g. secondary to a narrowed tube)
Viscosity is low
Tube diameter is high
Tube branching or irregular surfaces
In which blood vessels is resistance highest and why?
Small arteries and arterioles, because they are arranged in series
The distensibility of blood vessels gives them which characteristic and what does it mean?
Capacitance – the ability to increase blood volume without significant increase in pressure
