Hemodialysis: Chapter 1, Physiological Principles of Hemodialysis - Dr.Gawad
FLOW, physics, laminar, turbulant, physics
1. Basic Physics and Measurement
in Anaesthesia
Presented by:-DR.KALYAN REGMI
Moderator: DR. ANIL PRASAD NEUPANE
Assistant professor,Department of
anesthesiology,PAHS,Pokhara
3. • Flow is defined as the quantity of a fluid, i.e. a
gas or a liquid, passing a point in unit time
• where F = mean flow
• Q = quantity (mass or volume)
• t = time
FLOW
5. LAMINAR FLOW
• Fluid moves in a steady manner and there are no
eddies or turbulence.
• Laminar flow normally present in smooth tubes
at low rates of flow.
• The velocity of flow is highest in the centre.
6.
7. • Flow is directly proportional to pressure under
conditions of laminar flow
The ratio of pressure to flow is a constant
known as resistance R of the apparatus or tube
concerned
9. TURBULENT FLOW
• Flow in which fluid is no longer flows in a
smooth fashion but swirls in eddies.
• Laminar flow may change to turbulent flow if
a constriction is reached which results in the
increasing fluid velocity.
• In turbulent flow the resistance is higher for
the same laminar flow
10.
11. • For turbulent flow in tubes that are rough on the
inside it is found that the flow is approximately
proportional to the square root of the pressure
12. •The factors affecting turbulent flow are :-
1.Vicosity of fluid
2.Diameter of tube
3.Density of fluid and
4. Linear velocity of fluid
13. • These factors may all be combined to give an index
known as Reynolds number, which is calculated as
follows
14. •If Reynolds number exceeds about 2000, then
turbulent flow is likely to be present.
•If Reynolds number is below 2000, the flow is likely
to be laminar.
15. Clinical aspects of flow
•Changes between laminar and turbulent flow
depends on the velocity of gases,which in turn
depends on the volume flow and thus on the
diameter of tubing and airways.
•In patients airway,gases are humidified, warmed (34-
37ᵒ C) and contains carbondioxide. The overall effect
of these is reduction in density of gases and rises in
critical flow.
16. Critical flows for anesthetic gaseous
mixture of 60% nitrous oxide, oxygen
and air (20ᵒ C and patients airway)
17. •As breathing is cyclical, with peak flows over 50 lit
per min(turbulent flow during peak flow), laminar
flow at other times in respiratory cycles
•Bronchi and smaller air passages in lungs: slower
flow and laminar in lower respiratory tract.
18. Hegan- Poissuilles equation:
•Represents relationship between flow and
factors affecting flow.
• Applied for laminar flow.
Qᵒ = πPd4/128 ηl
Where, Qᵒ = flow
P = pressure across the tube
d = diameter of the tube
η = viscosity
l = length of the tube
π/128 = constant
23. SURFACE TENSION
• Surface tension is a result of the attraction
between molecules across the surface of a
liquid.
• In the surface water molecules are attracted
downwards and sidewise only.(air fluid
interface)
26. •surfactants are compounds that lower the surface
tension of a liquid.
•Surfactant molecules are synthesized by type II
pneumocytes (cuboidal cells lining alveoli) and kept in
clusters called lamilar bodies and secreted as tubular
myelin.
•The alveoli in the lungs are lined with fluid
which,comprising mainly water, has a significant
surface tension.
Surfactant
27. • Alveoli collapse
• Smaller sized alveoli collapses into large
sized alveoli causing ventillation perfusion
mismatch
• Tendency of edema formation in alveoli
• Surface area for gaseous exchange
decreases
Major problems with surface tension in
lungs
28.
29. VISCOCITY
•Viscosity is a measure of the frictional forces
acting between the layers of the fluid as it flows
along the tube.
•Flow and viscosity are inversely proportional.
31. BERNOULLI’S PRINCIPLE :
States that when a gas flowing through a tube,
encounters a constriction, at that point, the pressure
drops and velocity increases.
32. VENTURI EFFECT :
•consequence of the Bernoulli’s principle
•The entrainment of the air from the surroundings due
to fall in the pressure at the point of constriction is
called venturi effect.
33. •Suction: injectors working on this venturi effect may
be used to provide suction, either water or gases
being used as the driving fluid.
•Nebulisers
•Venturi masks
Uses of venturi effect
34. • A Venturi is a simple design of valve that provide control
oxygen supplied through a narrow port which allows room
air to be drawn in from atmosphere
• The rate of flow generated by this Venturi principle and
Venturi mask may be equal to peak inspiratory flow of
patient.
Venturi masks
38. COANDA EFFECT
:
•If a constriction occurs at a bifurcation, due to
increase in velocity and reduction of pressure, the
fluid/air tends to stick to the side of the branch
causing maldistribution.
39. APPLICATION:
• Mucus plug at the branching of tracheo-bronchial
tree may cause maldistribution of respiratory gases.
•Unequal flow may result because of atherosclerotic
plaques in the vascular tree
40. TAKE HOME MESSAGE
• Reynold number less than 2000 indicate laminar flow
• Fluid resuscitation is done via wide bored peripheral
catheter
• Surfactant helps to prevent alveoli collapses
• Gas/fluid flow from higher pressure to low pressure area
• Gas/ fluid following through tube when encounter
constriction at that point pressure drop and velocity
increases.
A known constant flow Qᵒ is passed through the apparatus concerned and differences in pressures P1-P2 between ends of the apparatus is measured.
If flow is laminar ,resistance can be measured by dividing the pressure differences by rate of flow.
Whenever there is narrowing or sharp bend in tubing, velocity of fluid increases leading to turbulent flow. Since density plays important role in turbulent flow, helium in oxygen can be used in patient with airway obstruction to reduce extent of turbulent flow (oxygen density— 1.3, helium density—0.16).
Critical flow is a flow in which specfic energy is minimum
Froude number =velocity /square root of gravity and depth (froude number =1 . Velocity of fluid = critical velocity)
Internal diameter = critical flow litre for min , increased temperture decrease density
The flow of anesthetic gases in 9mm internal diameter endotracheal tube becomes turbulent when flow exceeds about 9 liter per min.
Trachea which is approx 15 mm in internal diameter, flow becomes turbulent at flow 15 lit per min.
the flow is proportional to the fourth power of the diameter.
fluid flows rapidly through 16 G cannula compared to 22 G
small size ETT may cause a tremendous decrease in the flow of gases
-fluid flows slowly through central line compared to peripheral cannula
-
For Fluid resuscitation a wide bored pheripheral venous catheter is best
Components of surfactant molecules:
Di-palmitoyl-phosphatidyl choline,phophatidyl glycerol
surfactant-protein A, B, C,D hydrophobic-b and c
IgA, Albumin
Increased viscosity seen in incresed blood cell like thrombocytosis polycythemia leukemia , increases immnoglobin like multiple myeloma
Green 65% fio2 at 12-15l/min
Red 40% fio2 at 10-12l/min
Yellow 35% fio2 at 8-10l/min
White 28% fio2 at 4-6 l/min
Blue 24% fio2 at 2-4l/m
This phenomenon is also called as wall attachment there be unequal gas flow to the alveoli where there has been a slight narrowing of the bronchiole before it divides.It may also explain some cases of Myocardial Infraction, where there may be some narrowing, before the branching of the coronaries. Unequal flow may result because of atherosclerotic plaques in the vascular tree