MEDS12001 Lecture Notes - Lecture 7: Volumetric Flow Rate, Turbulence, Plug Flow
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CIRCULATORY SYSTEM
• Consists of the heart, arteries, arterioles,
capillaries, venules and veins
• Across the capillary walls, the exchange of
gases, nutrients, and waste products with
the cells takes place, sustaining their life
FLUIDS
• Matter generally is classified as follows:
o Gases
o Liquids
o Solids
• Gases and liquids are materials that flow
• Viscosity is the resistance to flow offered
by a fluid in motion
o Units: poise, kg/ms-1
PRESSURE
• Driving force behind fluid flow
• A pressure difference is required for flow
to occur
• The greater the pressure difference, the
greater will be the flow rate
VOLUMETRIC FLOW RATE (Q)
• The volume of blood passing a point per
unit of time
• Unit: millilitres (Ml/S)
• FORMULA:
POISEUILLE’S EQUATION
For steady flow in long, straight tubes
• If pressure difference or the diameter of
the tube increases, flow rate increases
• If viscosity or the length of the tube
increases, flow rate decreases
TYPES OF FLOW
• Plug
• Laminar
• Parabolic
• Disturbed
• Turbulent
PLUG FLOW
• The speed of the fluid is essentially
constant across the tube
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LAMINAR FLOW
• Streamlines are straight and parallel to
each other
• Flow speed is maximum at the centre of
the tube and minimum or zero at the
tubes walls
PARABOLIC FLOW
• A form of laminar flow
• The average flow speed across the vessel
is equal to one half the maximum flow
speed (centre)
DISTURBED FLOW
• A form of laminar flow
• Occurs when the parallel streamlines are
altered from their straight line form
• Occurs in the region of a stenosis or at a
bifurcation
TURBULENT FLOW
• Non-laminar flow with random and
chaotic speeds and directions
• Forward net flow is still maintained
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PULSATILE FLOW
• Non-steady flow, with acceleration and
deceleration over the cardiac cycle
• Arterial diastolic flow reveals much
concerning the state of the downstream
arterioles
CONTINUITY RULE
• Blood is neither created nor destroyed as
it flows through a vessel
• Volumetric flow rate must be constant
proximal within, and distal to a stenosis
• Q = mean spatial velocity x area (cross
sectional)
BERNOILLI EFFECT
• A drop in pressure associated with high
flow speed at a stenosis
• If flow speed increases, pressure decreases
DOPPLER EFFECT
• A change in frequency caused by the
motion of a sound source, receiver, or
reflector
DOPPLER EQUATION
• The Doppler equation can deal with any of
three situations:
1. Moving source
2. Moving receiver
3. Moving reflector
DOPPLER EFFECT APPLIED TO US
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Document Summary
The volume of blood passing a point per unit of time, unit: millilitres (ml/s, formula: (cid:1843) (cid:4666)(cid:1865)(cid:1864)(cid:4667) = (cid:1842)(cid:1870)(cid:1857)(cid:1871)(cid:1871)(cid:1873)(cid:1870)(cid:1857) (cid:1856)(cid:1858)(cid:1858)(cid:1857)(cid:1870)(cid:1857)(cid:1866)(cid:1855)(cid:1857) (cid:4666)(cid:1856)(cid:1866)(cid:1857)/(cid:1855)(cid:1865)2(cid:4667) (cid:1844)(cid:1857)(cid:1871)(cid:1871)(cid:1872)(cid:1866)(cid:1855)(cid:1857) (cid:1872)(cid:1867) (cid:1858)(cid:1864)(cid:1867) (cid:4666)(cid:1868)(cid:1867)(cid:1871)(cid:1857)(cid:4667) If pressure difference or the diameter of the tube increases, flow rate increases. If viscosity or the length of the tube increases, flow rate decreases. Circulatory system: consists of the heart, arteries, arterioles, capillaries, venules and veins, across the capillary walls, the exchange of gases, nutrients, and waste products with the cells takes place, sustaining their life. Fluids: matter generally is classified as follows, gases, liquids, solids, gases and liquids are materials that flow, viscosity is the resistance to flow offered by a fluid in motion, units: poise, kg/ms-1. Pressure: driving force behind fluid flow, a pressure difference is required for flow to occur, the greater the pressure difference, the greater will be the flow rate. Types of flow: plug, laminar, parabolic, disturbed, turbulent.
