File - Respiratory Therapy Files
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Transcript File - Respiratory Therapy Files
Physical Principles of Respiratory Care
I.
II.
III.
IV.
States of Matter
Change of State
Gas Behavior Under Changing Conditions
Fluid Dynamics
Fluid Dynamics
1.
2.
3.
4.
5.
6.
Pressure in Flowing Fluids
Patterns of Flow
Laminar Flow
Turbulent Flow
Transitional Flow
Flow,Velocity, and Cross-Sectional Area
Bernoulli Effect
Fluid Entrainment
Fluidics and the Coanda Effect
Fluid Dynamics
The study of fluids in motion is called
hydrodynamics.
The pressure exerted by a liquid in motion depends
on the nature of the flow itself.
A progressive decrease in fluid pressure occurs as the
fluid flows through a tube due to resistance.
3
Patterns of Flow
Patterns of flow
Laminar flowfluid moving in discrete cylindrical
layers or streamlines
Poiseuille’s lawpredicts pressure required to
produce given flow using
ΔP = 8nl V./ πr4
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Conditions that cause laminar flow to
become turbulent
1.
2.
3.
4.
High linear gas velocity
High gas density
Low gas viscosity
Large tube diameter
Patterns of flow
Turbulent flowloss of regular streamlines; fluid
molecules form irregular eddy currents in chaotic
pattern.
Predicted by using Reynold`s number (NR)
NR = v d2r / h
Patterns of Flow
Transitional Flow
7
Poiseuille’s Law
(only applies to laminar flow)
Flow of fluid through a tube:
Driving pressure
Resistance
Viscosity
Length of the tube
Radius of the tube
8
Poiseuille’s Law
1.
9
The more viscous the fluid the more pressure is
required to cause it to move through a given tube
Poiseuille’s Law
Resistance to flow is directly proportional to the
length of the tube
2.
10
If the length of a tube is increased four times, the
driving pressure to maintain a given flow must
be increased four times
Poiseuille’s Law
Resistance to flow is inversely proportional to the
fourth power of the radius of the tube
3.
11
If the inside diameter of the tube is decreased by
one half, the driving pressure must be increased
16 times to maintain original flow
Poiseuille’s Law
Respiratory
Application:
ETT
12
Care
Poiseuille’s Law
Asthma
13
Pressure in Flowing Fluids
14
Law of Continuity
The speed of flow in a closed system will be inversely
proportional to the area of the tubes through which it
flows
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Law of Continuity
2.54
If the area of flow is decreased, then the velocity must
increase
If the area of flow in increased, then the velocity must
decrease
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Law of Continuity
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The Bernoulli Effect
As the speed of the fluid increases, the
pressure in a fluid decreases
19
20
Venturi Principle of Fluid Entrainment
If the increase in velocity at a constriction is so great
that is causes the pressure of the fluid to fall below
atmospheric (becoming negative) it can pull another
fluid into the primary flow
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Fluid Entrainment
Respiratory
Application:
Air injector
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Care
Fluid Entrainment
Respiratory
Care
Application:
Entrainment mask
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Fluid Entrainment
Respiratory
Care
Application:
Small Volume
Nebulizer
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Fluid Entrainment
Respiratory
Care
Application:
Large volume jet
nebulizer
25
Fluid Dynamics
Fluidics and the Coanda effect
Fluidics is a branch of engineering that applies
hydrodynamics principles in flow circuits.
The Coanda effect (wall attachment) is observed
when fluid flows through a small orifice with properly
contoured downstream surfaces.
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Advantages
Operate
without moving parts, minimizing
maintenance expenses
Generally cost less than electronic
counterparts
Don’t break down as often as their
electronic counterparts
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Disadvantages
Not
easily interfaced with
microprocessors
Not as accurate as their electrical
counterparts
Difficult to measure tidal volume because
tidal volume exits with source gas
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